CLI Book 1: Cisco ASA Series General Operations CLI Configuration Guide, 9.1
Configuring Multiple Context Mode
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Table of Contents

Configuring Multiple Context Mode

Information About Security Contexts

Common Uses for Security Contexts

Context Configuration Files

Context Configurations

System Configuration

Admin Context Configuration

How the ASA Classifies Packets

Valid Classifier Criteria

Classification Examples

Cascading Security Contexts

Management Access to Security Contexts

System Administrator Access

Context Administrator Access

Information About Resource Management

Resource Classes

Resource Limits

Default Class

Using Oversubscribed Resources

Using Unlimited Resources

Information About MAC Addresses

Default MAC Address

Interaction with Manual MAC Addresses

Failover MAC Addresses

MAC Address Format

Licensing Requirements for Multiple Context Mode

Prerequisites

Guidelines and Limitations

Default Settings

Configuring Multiple Contexts

Task Flow for Configuring Multiple Context Mode

Enabling or Disabling Multiple Context Mode

Enabling Multiple Context Mode

Restoring Single Context Mode

Configuring a Class for Resource Management

Configuring a Security Context

Automatically Assigning MAC Addresses to Context Interfaces

Changing Between Contexts and the System Execution Space

Managing Security Contexts

Removing a Security Context

Changing the Admin Context

Changing the Security Context URL

Reloading a Security Context

Reloading by Clearing the Configuration

Reloading by Removing and Re-adding the Context

Monitoring Security Contexts

Viewing Context Information

Viewing Resource Allocation

Viewing Resource Usage

Monitoring SYN Attacks in Contexts

Viewing Assigned MAC Addresses

Viewing MAC Addresses in the System Configuration

Viewing MAC Addresses Within a Context

Configuration Examples for Multiple Context Mode

Feature History for Multiple Context Mode

Information About Security Contexts

You can partition a single ASA into multiple virtual devices, known as security contexts. Each context acts as an independent device, with its own security policy, interfaces, and administrators. Multiple contexts are similar to having multiple standalone devices. For unsupported features in multiple context mode, see the “Guidelines and Limitations” section.

This section provides an overview of security contexts and includes the following topics:

Common Uses for Security Contexts

You might want to use multiple security contexts in the following situations:

  • You are a service provider and want to sell security services to many customers. By enabling multiple security contexts on the ASA, you can implement a cost-effective, space-saving solution that keeps all customer traffic separate and secure, and also eases configuration.
  • You are a large enterprise or a college campus and want to keep departments completely separate.
  • You are an enterprise that wants to provide distinct security policies to different departments.
  • You have any network that requires more than one ASA.

Context Configuration Files

This section describes how the ASA implements multiple context mode configurations and includes the following topics:

Context Configurations

For each context, the ASA includes a configuration that identifies the security policy, interfaces, and all the options you can configure on a standalone device. You can store context configurations in flash memory, or you can download them from a TFTP, FTP, or HTTP(S) server.

System Configuration

The system administrator adds and manages contexts by configuring each context configuration location, allocated interfaces, and other context operating parameters in the system configuration, which, like a single mode configuration, is the startup configuration. The system configuration identifies basic settings for the ASA. The system configuration does not include any network interfaces or network settings for itself; rather, when the system needs to access network resources (such as downloading the contexts from the server), it uses one of the contexts that is designated as the admin context . The system configuration does include a specialized failover interface for failover traffic only.

Admin Context Configuration

The admin context is just like any other context, except that when a user logs in to the admin context, then that user has system administrator rights and can access the system and all other contexts. The admin context is not restricted in any way, and can be used as a regular context. However, because logging into the admin context grants you administrator privileges over all contexts, you might need to restrict access to the admin context to appropriate users. The admin context must reside on flash memory, and not remotely.

If your system is already in multiple context mode, or if you convert from single mode, the admin context is created automatically as a file on the internal flash memory called admin.cfg. This context is named “admin.” If you do not want to use admin.cfg as the admin context, you can change the admin context.

How the ASA Classifies Packets

Each packet that enters the ASA must be classified, so that the ASA can determine to which context to send a packet. This section includes the following topics:


NoteIf the destination MAC address is a multicast or broadcast MAC address, the packet is duplicated and delivered to each context.


Valid Classifier Criteria

This section describes the criteria used by the classifier and includes the following topics:


NoteFor management traffic destined for an interface, the interface IP address is used for classification.

The routing table is not used for packet classification.


Unique Interfaces

If only one context is associated with the ingress interface, the ASA classifies the packet into that context. In transparent firewall mode, unique interfaces for contexts are required, so this method is used to classify packets at all times.

Unique MAC Addresses

If multiple contexts share an interface, then the classifier uses unique MAC addresses assigned to the interface in each context. An upstream router cannot route directly to a context without unique MAC addresses. By default, auto-generation of MAC addresses is enabled. You can also set the MAC addresses manually when you configure each interface.

NAT Configuration

If you disable use of unique MAC addresses, then the ASA uses the mapped addresses in your NAT configuration to classify packets. We recommend using MAC addresses instead of NAT, so that traffic classification can occur regardless of the completeness of the NAT configuration.

Classification Examples

Figure 6-1 shows multiple contexts sharing an outside interface. The classifier assigns the packet to Context B because Context B includes the MAC address to which the router sends the packet.

Figure 6-1 Packet Classification with a Shared Interface Using MAC Addresses

 

Note that all new incoming traffic must be classified, even from inside networks. Figure 6-2 shows a host on the Context B inside network accessing the Internet. The classifier assigns the packet to Context B because the ingress interface is Gigabit Ethernet 0/1.3, which is assigned to Context B.

Figure 6-2 Incoming Traffic from Inside Networks

 

For transparent firewalls, you must use unique interfaces. Figure 6-3 shows a packet destined to a host on the Context B inside network from the Internet. The classifier assigns the packet to Context B because the ingress interface is Gigabit Ethernet 1/0.3, which is assigned to Context B.

Figure 6-3 Transparent Firewall Contexts

 

Cascading Security Contexts

Placing a context directly in front of another context is called cascading contexts ; the outside interface of one context is the same interface as the inside interface of another context. You might want to cascade contexts if you want to simplify the configuration of some contexts by configuring shared parameters in the top context.


NoteCascading contexts requires unique MAC addresses for each context interface (the default setting). Because of the limitations of classifying packets on shared interfaces without MAC addresses, we do not recommend using cascading contexts without unique MAC addresses.


Figure 6-4 shows a gateway context with two contexts behind the gateway.

Figure 6-4 Cascading Contexts

 

Management Access to Security Contexts

The ASA provides system administrator access in multiple context mode as well as access for individual context administrators. The following sections describe logging in as a system administrator or as a context administrator:

System Administrator Access

You can access the ASA as a system administrator in two ways:

  • Access the ASA console.

From the console, you access the system execution space , which means that any commands you enter affect only the system configuration or the running of the system (for run-time commands).

  • Access the admin context using Telnet, SSH, or ASDM.

See “Configuring Management Access,” to enable Telnet, SSH, and ASDM access.

As the system administrator, you can access all contexts.

When you change to a context from admin or the system, your username changes to the default “enable_15” username. If you configured command authorization in that context, you need to either configure authorization privileges for the “enable_15” user, or you can log in as a different name for which you provide sufficient privileges. To log in with a new username, enter the login command. For example, you log in to the admin context with the username “admin.” The admin context does not have any command authorization configuration, but all other contexts include command authorization. For convenience, each context configuration includes a user “admin” with maximum privileges. When you change from the admin context to context A, your username is altered to enable_15, so you must log in again as “admin” by entering the login command. When you change to context B, you must again enter the login command to log in as “admin.”

The system execution space does not support any AAA commands, but you can configure its own enable password, as well as usernames in the local database to provide individual logins.

Context Administrator Access

You can access a context using Telnet, SSH, or ASDM. If you log in to a non-admin context, you can only access the configuration for that context. You can provide individual logins to the context. See “Configuring Management Access,” to enable Telnet, SSH, and ASDM access and to configure management authentication.

Information About Resource Management

By default, all security contexts have unlimited access to the resources of the ASA, except where maximum limits per context are enforced; the only exception is VPN resources, which are disabled by default. If you find that one or more contexts use too many resources, and they cause other contexts to be denied connections, for example, then you can configure resource management to limit the use of resources per context. For VPN resources, you must configure resource management to allow any VPN tunnels.

This section includes the following topics:

Resource Classes

The ASA manages resources by assigning contexts to resource classes. Each context uses the resource limits set by the class. To use the settings of a class, assign the context to the class when you define the context. All contexts belong to the default class if they are not assigned to another class; you do not have to actively assign a context to default. You can only assign a context to one resource class. The exception to this rule is that limits that are undefined in the member class are inherited from the default class; so in effect, a context could be a member of default plus another class.

Resource Limits

You can set the limit for individual resources as a percentage (if there is a hard system limit) or as an absolute value.

For most resources, the ASA does not set aside a portion of the resources for each context assigned to the class; rather, the ASA sets the maximum limit for a context. If you oversubscribe resources, or allow some resources to be unlimited, a few contexts can “use up” those resources, potentially affecting service to other contexts. The exception is VPN resource types, which you cannot oversubscribe, so the resources assigned to each context are guaranteed. To accommodate temporary bursts of VPN sessions beyond the amount assigned, the ASA supports a “burst” VPN resource type, which is equal to the remaining unassigned VPN sessions. The burst sessions can be oversubscribed, and are available to contexts on a first-come, first-served basis.

Default Class

All contexts belong to the default class if they are not assigned to another class; you do not have to actively assign a context to the default class.

If a context belongs to a class other than the default class, those class settings always override the default class settings. However, if the other class has any settings that are not defined, then the member context uses the default class for those limits. For example, if you create a class with a 2 percent limit for all concurrent connections, but no other limits, then all other limits are inherited from the default class. Conversely, if you create a class with a limit for all resources, the class uses no settings from the default class.

For most resources, the default class provides unlimited access to resources for all contexts, except for the following limits:

  • Telnet sessions—5 sessions. (The maximum per context.)
  • SSH sessions—5 sessions. (The maximum per context.)
  • IPsec sessions—5 sessions. (The maximum per context.)
  • MAC addresses—65,535 entries. (The maximum per context.)
  • VPN site-to-site tunnels—0 sessions. (You must manually configure the class to allow any VPN sessions.)

Figure 6-5 shows the relationship between the default class and other classes. Contexts A and C belong to classes with some limits set; other limits are inherited from the default class. Context B inherits no limits from default because all limits are set in its class, the Gold class. Context D was not assigned to a class, and is by default a member of the default class.

Figure 6-5 Resource Classes

 

Using Oversubscribed Resources

You can oversubscribe the ASA by assigning more than 100 percent of a resource across all contexts (with the exception of non-burst VPN resources). For example, you can set the Bronze class to limit connections to 20 percent per context, and then assign 10 contexts to the class for a total of 200 percent. If contexts concurrently use more than the system limit, then each context gets less than the 20 percent you intended. (See Figure 6-6.)

Figure 6-6 Resource Oversubscription

 

Using Unlimited Resources

The ASA lets you assign unlimited access to one or more resources in a class, instead of a percentage or absolute number. When a resource is unlimited, contexts can use as much of the resource as the system has available. For example, Context A, B, and C are in the Silver Class, which limits each class member to 1 percent of the connections, for a total of 3 percent; but the three contexts are currently only using 2 percent combined. Gold Class has unlimited access to connections. The contexts in the Gold Class can use more than the 97 percent of “unassigned” connections; they can also use the 1 percent of connections not currently in use by Context A, B, and C, even if that means that Context A, B, and C are unable to reach their 3 percent combined limit. (See Figure 6-7.) Setting unlimited access is similar to oversubscribing the ASA, except that you have less control over how much you oversubscribe the system.

Figure 6-7 Unlimited Resources

 

Information About MAC Addresses

To allow contexts to share interfaces, the ASA assigns virtual MAC addresses to each shared context interface by default. To customize or disable auto-generation, see the “Automatically Assigning MAC Addresses to Context Interfaces” section.

The MAC address is used to classify packets within a context. If you share an interface, but do not have unique MAC addresses for the interface in each context, then other classification methods are attempted that might not provide full coverage. See the “How the ASA Classifies Packets” section for information about classifying packets.

In the rare circumstance that the generated MAC address conflicts with another private MAC address in your network, you can manually set the MAC address for the interface within the context. See the “Configuring the MAC Address, MTU, and TCP MSS” section to manually set the MAC address.

This section includes the following topics:

Default MAC Address

Automatic MAC address generation is enabled by default. The ASA autogenerates the prefix based on the last two bytes of the interface (ASA 5500) or backplane (ASASM) MAC address. You can customize the prefix if desired.

If you disable MAC address generation, see the following default MAC addresses:

  • For the ASA 5500 series appliances—The physical interface uses the burned-in MAC address, and all subinterfaces of a physical interface use the same burned-in MAC address.
  • For the ASASM—All VLAN interfaces use the same MAC address, derived from the backplane MAC address.

See also the “MAC Address Format” section.


Note(8.5(1.6) and earlier) To maintain hitless upgrade for failover pairs, the ASA does not convert an existing legacy auto-generation configuration upon a reload if failover is enabled. However, we strongly recommend that you manually change to the prefix method of generation when using failover, especially for the ASASM. Without the prefix method, ASASMs installed in different slot numbers experience a MAC address change upon failover, and can experience traffic interruption. After upgrading, to use the prefix method of MAC address generation, reenable MAC address autogeneration to use a prefix. For more information about the legacy method, see themac-address auto command in the command reference.


Interaction with Manual MAC Addresses

If you manually assign a MAC address and also enable auto-generation, then the manually assigned MAC address is used. If you later remove the manual MAC address, the auto-generated address is used.

Because auto-generated addresses (when using a prefix) start with A2, you cannot start manual MAC addresses with A2 if you also want to use auto-generation.

Failover MAC Addresses

For use with failover, the ASA generates both an active and standby MAC address for each interface. If the active unit fails over and the standby unit becomes active, the new active unit starts using the active MAC addresses to minimize network disruption. See the “MAC Address Format” section section for more information.

MAC Address Format

The ASA generates the MAC address using the following format:

A2 xx.yyzz.zzzz

Where xx.yy is a user-defined prefix or an autogenerated prefix based on the last two bytes of the interface (ASA 5500) or backplane (ASASM) MAC address, and zz.zzzz is an internal counter generated by the ASA. For the standby MAC address, the address is identical except that the internal counter is increased by 1.

For an example of how the prefix is used, if you set a prefix of 77, then the ASA converts 77 into the hexadecimal value 004D ( yyxx ). When used in the MAC address, the prefix is reversed ( xxyy ) to match the ASA native form:

A2 4D.00 zz.zzzz

For a prefix of 1009 (03F1), the MAC address is:

A2 F1.03 zz.zzzz


NoteThe MAC address format without a prefix is a legacy version not supported on newer ASA versions. See themac-address auto command in the command reference for more information about the legacy format.


Licensing Requirements for Multiple Context Mode

 

Model
License Requirement

ASA 5505

No support.

ASA 5510

  • Base License: No support.
  • Security Plus License: 2 contexts.

Optional license: 5 contexts.

ASA 5520

Base License: 2 contexts.

Optional licenses: 5, 10, or 20 contexts.

ASA 5540

Base License: 2 contexts.

Optional licenses: 5, 10, 20, or 50 contexts.

ASA 5550

Base License: 2 contexts.

Optional licenses: 5, 10, 20, 50, or 100 contexts.

ASA 5580

Base License: 2 contexts.

Optional licenses: 5, 10, 20, 50, 100, or 250 contexts.

ASA 5512-X

  • Base License: No support.
  • Security Plus License: 2 contexts.

Optional license: 5 contexts.

ASA 5515-X

Base License: 2 contexts.

Optional license: 5 contexts.

ASA 5525-X

Base License: 2 contexts.

Optional licenses: 5, 10, or 20 contexts.

ASA 5545-X

Base License: 2 contexts.

Optional licenses: 5, 10, 20, or 50 contexts.

ASA 5555-X

Base License: 2 contexts.

Optional licenses: 5, 10, 20, 50, or 100 contexts.

ASA 5585-X with SSP-10

Base License: 2 contexts.

Optional licenses: 5, 10, 20, 50, or 100 contexts.

ASA 5585-X with SSP-20, -40, and -60

Base License: 2 contexts.

Optional licenses: 5, 10, 20, 50, 100, or 250 contexts.

ASASM

Base License: 2 contexts.

Optional licenses: 5, 10, 20, 50, 100, or 250 contexts.

Prerequisites

After you are in multiple context mode, connect to the system or the admin context to access the system configuration. You cannot configure the system from a non-admin context. By default, after you enable multiple context mode, you can connect to the admin context by using the default management IP address. See “Getting Started,” for more information about connecting to the ASA.

Guidelines and Limitations

This section includes the guidelines and limitations for this feature.

Firewall Mode Guidelines

Supported in routed and transparent firewall mode; set the firewall mode per context.

Failover Guidelines

Active/Active mode failover is only supported in multiple context mode.

IPv6 Guidelines

Supports IPv6.


NoteCross context IPv6 routing is not supported.


Model Guidelines

Does not support the ASA 5505.

Unsupported Features

Multiple context mode does not support the following features:

  • RIP
  • OSPFv3. (OSPFv2 is supported.)
  • Multicast routing
  • Threat Detection
  • Unified Communications
  • QoS
  • Remote access VPN. (Site-to-site VPN is supported.)

Additional Guidelines

  • The context mode (single or multiple) is not stored in the configuration file, even though it does endure reboots. If you need to copy your configuration to another device, set the mode on the new device to match.
  • If you store context configurations in the root directory of flash memory, on some models you might run out of room in that directory, even though there is available memory. In this case, create a subdirectory for your configuration files. Background: some models, such as the ASA 5585-X, use the FAT 16 file system for internal flash memory, and if you do not use 8.3-compliant short names, or use uppercase characters, then fewer than 512 files and folders can be stored because the file system uses up slots to store long file names (see http://support.microsoft.com/kb/120138/en-us ).

Default Settings

Configuring Multiple Contexts

This section describes how to configure multiple context mode and includes the following topics:

Task Flow for Configuring Multiple Context Mode

To configure multiple context mode, perform the following steps:


Step 1 Enable multiple context mode. See the “Enabling or Disabling Multiple Context Mode” section.

Step 2 (Optional) Configure classes for resource management. See the “Configuring a Class for Resource Management” section. Note : For VPN support, you must configure VPN resources in a resource class; the default class does not allow VPN.

Step 3 Configure interfaces in the system execution space.

Step 4 Configure security contexts. See the “Configuring a Security Context” section.

Step 5 (Optional) Customize MAC address assignments. See the “Automatically Assigning MAC Addresses to Context Interfaces” section.

Step 6 Complete interface configuration in the context. See “Completing Interface Configuration (Routed Mode),” or Chapter12, “Completing Interface Configuration (Transparent Mode)”


 

Enabling or Disabling Multiple Context Mode

Your ASA might already be configured for multiple security contexts depending on how you ordered it from Cisco. If you need to convert from single mode to multiple mode, follow the procedures in this section.

This section includes the following topics:

Enabling Multiple Context Mode

When you convert from single mode to multiple mode, the ASA converts the running configuration into two files: a new startup configuration that comprises the system configuration, and admin.cfg that comprises the admin context (in the root directory of the internal flash memory). The original running configuration is saved as old_running.cfg (in the root directory of the internal flash memory). The original startup configuration is not saved. The ASA automatically adds an entry for the admin context to the system configuration with the name “admin.”

Prerequisites

Back up your startup configuration. When you convert from single mode to multiple mode, the ASA converts the running configuration into two files. The original startup configuration is not saved. See the “Backing Up Configurations or Other Files” section.

Detailed Steps

 

Command
Purpose

mode multiple

 

ciscoasa(config)# mode multiple

Changes to multiple context mode. You are prompted to reboot the ASA.

Restoring Single Context Mode

To copy the old running configuration to the startup configuration and to change the mode to single mode, perform the following steps.

Prerequisites

Perform this procedure in the system execution space.

Detailed Steps

 

Command
Purpose

Step 1

copy disk0:old_running.cfg startup-config

 

ciscoasa(config)# copy disk0:old_running.cfg startup-config

Copies the backup version of your original running configuration to the current startup configuration.

Step 2

mode single

 

ciscoasa(config)# mode single

Sets the mode to single mode. You are prompted to reboot the ASA.

Configuring a Class for Resource Management

To configure a class in the system configuration, perform the following steps. You can change the value of a particular resource limit by reentering the command with a new value.

Prerequisites

Perform this procedure in the system execution space.

Guidelines

Table 6-1 lists the resource types and the limits. See also the show resource types command.

 

Table 6-1 Resource Names and Limits

Resource Name
Rate or Concurrent
Minimum and Maximum Number per Context
System Limit 1
Description

asdm

Concurrent

1 minimum

5 maximum

32

ASDM management sessions.

Note ASDM sessions use two HTTPS connections: one for monitoring that is always present, and one for making configuration changes that is present only when you make changes. For example, the system limit of 32 ASDM sessions represents a limit of 64 HTTPS sessions.

conns2

Concurrent or Rate

N/A

Concurrent connections: See the “Supported Feature Licenses Per Model” section for the connection limit available for your model.

Rate: N/A

TCP or UDP connections between any two hosts, including connections between one host and multiple other hosts.

hosts

Concurrent

N/A

N/A

Hosts that can connect through the ASA.

inspects

Rate

N/A

N/A

Application inspections per second.

mac-addresses

Concurrent

N/A

65,535

For transparent firewall mode, the number of MAC addresses allowed in the MAC address table.

routes

Concurrent

N/A

N/A

Dynamic routes.

vpn burst other

Concurrent

N/A

The Other VPN session amount for your model minus the sum of the sessions assigned to all contexts for vpn other .

The number of site-to-site VPN sessions allowed beyond the amount assigned to a context with vpn other . For example, if your model supports 5000 sessions, and you assign 4000 sessions across all contexts with vpn other , then the remaining 1000 sessions are available for vpn burst other . Unlike vpn other , which guarantees the sessions to the context, vpn burst other can be oversubscribed; the burst pool is available to all contexts on a first-come, first-served basis.

vpn other

Concurrent

N/A

See the “Supported Feature Licenses Per Model” section for the Other VPN sessions available for your model.

Site-to-site VPN sessions. You cannot oversubscribe this resource; all context assignments combined cannot exceed the model limit. The sessions you assign for this resource are guaranteed to the context.

ssh

Concurrent

1 minimum

5 maximum

100

SSH sessions.

syslogs

Rate

N/A

N/A

Syslog messages per second.

telnet

Concurrent

1 minimum

5 maximum

100

Telnet sessions.

xlates 2

Concurrent

N/A

N/A

Network address translations.

1.If this column value is N/A, then you cannot set a percentage of the resource because there is no hard system limit for the resource.

2.Syslog messages are generated for whichever limit is lower xlates or conns. For example, if you set the xlates limit to 7 and the conns to 9, then the ASA only generates syslog message 321001 (“Resource 'xlates' limit of 7 reached for context 'ctx1'”) and not 321002 (“Resource 'conn rate' limit of 5 reached for context 'ctx1'”).

Detailed Steps

 

Command
Purpose

Step 1

class name

 

ciscoasa(config)# class gold

Specifies the class name and enters the class configuration mode. The name is a string up to 20 characters long. To set the limits for the default class, enter default for the name.

Step 2

limit-resource [ rate ] resource_name number [ % ]

 

ciscoasa(config-class)# limit-resource rate inspects 10

Sets the resource limit for a resource type. See Table 6-1 for a list of resource types. If you specify all , then all resources are configured with the same value. If you also specify a value for a particular resource, the limit overrides the limit set for all .

Enter the rate argument to s et the rate per second for certain resources.

For most resources, specify 0 for the number to set the resource to be unlimited or to be the system limit, if available. For VPN resources, 0 sets the limit to none.

For resources that do not have a system limit, you cannot set the percentage ( % ); you can only set an absolute value.

Examples

For example, to set the default class limit for conns to 10 percent instead of unlimited, and to allow 5 site-to-site VPN tunnels with 2 tunnels allowed for VPN burst, enter the following commands:

ciscoasa(config)# class default
ciscoasa(config-class)# limit-resource conns 10%
ciscoasa(config-class)# limit-resource vpn other 5
ciscoasa(config-class)# limit-resource vpn burst other 2
 

All other resources remain at unlimited.

To add a class called gold, enter the following commands:

ciscoasa(config)# class gold
ciscoasa(config-class)# limit-resource mac-addresses 10000
ciscoasa(config-class)# limit-resource conns 15%
ciscoasa(config-class)# limit-resource rate conns 1000
ciscoasa(config-class)# limit-resource rate inspects 500
ciscoasa(config-class)# limit-resource hosts 9000
ciscoasa(config-class)# limit-resource asdm 5
ciscoasa(config-class)# limit-resource ssh 5
ciscoasa(config-class)# limit-resource rate syslogs 5000
ciscoasa(config-class)# limit-resource telnet 5
ciscoasa(config-class)# limit-resource xlates 36000
ciscoasa(config-class)# limit-resource routes 5000
ciscoasa(config-class)# limit-resource vpn other 10
ciscoasa(config-class)# limit-resource vpn burst other 5
 

Configuring a Security Context

The security context definition in the system configuration identifies the context name, configuration file URL, interfaces that a context can use, and other settings.

Prerequisites

  • Perform this procedure in the system execution space.
  • For the ASASM, assign VLANs to the ASASM on the switch according to Chapter2, “Configuring the Switch for Use with the ASA Services Module”
  • For the ASA 5500, configure physical interface parameters, VLAN subinterfaces, EtherChannels, and redundant interfaces according to Chapter9, “Starting Interface Configuration (ASA 5510 and Higher)”
  • If you do not have an admin context (for example, if you clear the configuration) then you must first specify the admin context name by entering the following command:

    ciscoasa(config)# admin-context name

    Although this context does not exist yet in your configuration, you can subsequently enter the context name command to continue the admin context configuration.

Detailed Steps

 

Command
Purpose

Step 1

context name

 

ciscoasa(config)# context administrator

Adds or modifies a context. The name is a string up to 32 characters long. This name is case sensitive, so you can have two contexts named “customerA” and “CustomerA,” for example. You can use letters, digits, or hyphens, but you cannot start or end the name with a hyphen.

“System” or “Null” (in upper or lower case letters) are reserved names, and cannot be used.

Step 2

(Optional)

description text

 

ciscoasa(config-ctx)# description Administrator Context

Adds a description for this context.

Step 3

To allocate an interface:

allocate-interface interface_id [ mapped_name ] [ visible | invisible ]

 

To allocate one or more subinterfaces:

allocate-interface interface_id . subinterface [ - interface_id . subinterface ] [ mapped_name [ - mapped_name ]] [ visible | invisible ]

 
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.100 int1
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.200 int2
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/2.300-gigabitethernet0/2.305 int3-int8

Specifies the interfaces you can use in the context. Do not include a space between the interface type and the port number.

Enter these commands multiple times to specify different ranges. If you remove an allocation with the no form of this command, then any context commands that include this interface are removed from the running configuration.

Transparent firewall mode allows a limited number of interfaces to pass through traffic; however, you can use a dedicated management interface, Management slot / port (physical, subinterface, redundant, or EtherChannel), as an additional interface for management traffic. A separate management interface is not available for the ASASM.

You can assign the same interfaces to multiple contexts in routed mode, if desired. Transparent mode does not allow shared interfaces.

The mapped_name is an alphanumeric alias for the interface that can be used within the context instead of the interface ID. If you do not specify a mapped name, the interface ID is used within the context. For security purposes, you might not want the context administrator to know which interfaces the context is using. A mapped name must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, or an underscore. For example, you can use the following names:

int0 , inta , int_0
 

If you specify a range of subinterfaces, you can specify a matching range of mapped names. Follow these guidelines for ranges:

  • The mapped name must consist of an alphabetic portion followed by a numeric portion. The alphabetic portion of the mapped name must match for both ends of the range. For example, enter the following range:
int0-int10
 

If you enter gig0/1.1-gig0/1.5 happy 1- sad 5 , for example, the command fails.

  • The numeric portion of the mapped name must include the same quantity of numbers as the subinterface range. For example, both ranges include 100 interfaces:
gigabitethernet0/0.100-gigabitethernet0/0.199 int1-int100
 

If you enter gig0/0. 100 -gig0/0. 199 int 1 -int 15 , for example, the command fails.

Specify visible to see the real interface ID in the show interface command if you set a mapped name. The default invisible keyword shows only the mapped name.

Step 4

config-url url

 
ciscoasa(config-ctx)# config-url ftp://user1:passw0rd@10.1.1.1/configlets/test.cfg

Identifies the URL from which the system downloads the context configuration. When you add a context URL, the system immediately loads the context so that it is running, if the configuration is available.

Note Enter the allocate-interface command(s) before you enter the config-url command. If you enter the config-url command first, the ASA loads the context configuration immediately. If the context contains any commands that refer to (not yet configured) interfaces, those commands fail.

The filename does not require a file extension, although we recommend using “.cfg”. The server must be accessible from the admin context. If the configuration file is not available, you see the following message:

WARNING: Could not fetch the URL url
INFO: Creating context with default config
 

For non-HTTP(S) URL locations, after you specify the URL, you can then change to the context, configure it at the CLI, and enter the write memory command to write the file to the URL location. (HTTP(S) is read only).

Note The admin context file must be stored on the internal flash memory.

Available URL types include: disk number (for flash memory), ftp , http , https , or tftp .

To change the URL, reenter the config-url command with a new URL. See the “Changing the Security Context URL” section for more information about changing the URL.

Step 5

(Optional)

member class_name

 
ciscoasa(config-ctx)# member gold

Assigns the context to a resource class. If you do not specify a class, the context belongs to the default class. You can only assign a context to one resource class.

Step 6

(Optional)

allocate-ips sensor_name [ mapped_name ] [ default ]

 
ciscoasa(config-ctx)# allocate-ips sensor1 highsec

Assigns an IPS virtual sensor to this context if you have the IPS module installed.

See the “Assigning Virtual Sensors to a Security Context (ASA 5510 and Higher)” section in the firewall configuration guide for detailed information about virtual sensors.

Step 7

(Optional)

join-failover-group { 1 | 2 )

 

ciscoasa(config-ctx)# join-failover-group 2

Assigns a context to a failover group in Active/Active failover. By default, contexts are in group 1. The admin context must always be in group 1.

See the “Configuring Optional Failover Parameters” section for detailed information about failover groups.

Step 8

(Optional)

scansafe [ license key ]

 

ciscoasa(config-ctx)# scansafe

Enables Cloud Web Security for this context.

If you do not specify a license , the context uses the license configured in the system configuration. The ASA sends the authentication key to the Cloud Web Security proxy servers to indicate from which organization the request comes. The authentication key is a 16-byte hexidecimal number.

See “Configuring the ASA for Cisco Cloud Web Security” section in the firewall configuration guide for detailed information about ScanSafe.

Examples

The following example sets the admin context to be “administrator,” creates a context called “administrator” on the internal flash memory, and then adds two contexts from an FTP server:

ciscoasa(config)# admin-context administrator
ciscoasa(config)# context administrator
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/0.1
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.1
ciscoasa(config-ctx)# config-url disk0:/admin.cfg
 
ciscoasa(config-ctx)# context test
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/0.100 int1
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/0.102 int2
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/0.110-gigabitethernet0/0.115 int3-int8
ciscoasa(config-ctx)# config-url ftp://user1:passw0rd@10.1.1.1/configlets/test.cfg
ciscoasa(config-ctx)# member gold
 
 
ciscoasa(config-ctx)# context sample
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.200 int1
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.212 int2
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.230-gigabitethernet0/1.235 int3-int8
ciscoasa(config-ctx)# config-url ftp://user1:passw0rd@10.1.1.1/configlets/sample.cfg
ciscoasa(config-ctx)# member silver
 

Automatically Assigning MAC Addresses to Context Interfaces

This section describes how to configure auto-generation of MAC addresses.

The MAC address is used to classify packets within a context. See the “Information About MAC Addresses” section for more information, especially if you are upgrading from an earlier ASA version. See also the “Viewing Assigned MAC Addresses” section.

Guidelines

  • When you configure a nameif command for the interface in a context, the new MAC address is generated immediately. If you enable this feature after you configure context interfaces, then MAC addresses are generated for all interfaces immediately after you enable it. If you disable this feature, the MAC address for each interface reverts to the default MAC address. For example, subinterfaces of GigabitEthernet 0/1 revert to using the MAC address of GigabitEthernet 0/1.
  • In the rare circumstance that the generated MAC address conflicts with another private MAC address in your network, you can manually set the MAC address for the interface within the context. See the “Configuring the MAC Address, MTU, and TCP MSS” section to manually set the MAC address.

Detailed Steps

 

Command
Purpose

mac-address auto [ prefix prefix ]

 

ciscoasa(config)# mac-address auto prefix 19

Automatically assigns private MAC addresses to each context interface.

If you do not enter a prefix, then the ASA autogenerates the prefix based on the last two bytes of the interface (ASA 5500) or backplane (ASASM) MAC address.

If you manually enter a prefix, then the prefix is a decimal value between 0 and 65535. This prefix is converted to a four-digit hexadecimal number, and used as part of the MAC address. See the “MAC Address Format” section section for more information about how the prefix is used.

Changing Between Contexts and the System Execution Space

If you log in to the system execution space (or the admin context), you can change between contexts and perform configuration and monitoring tasks within each context. The running configuration that you edit in a configuration mode, or that is used in the copy or write commands, depends on your location. When you are in the system execution space, the running configuration consists only of the system configuration; when you are in a context, the running configuration consists only of that context. For example, you cannot view all running configurations (system plus all contexts) by entering the show running-config command. Only the current configuration displays.

Detailed Steps

 

Command
Purpose

changeto context name

Changes to a context. The prompt changes to the following:

ciscoasa/ name #
 

changeto system

Changes to the system execution space. The prompt changes to the following:

ciscoasa#
 

Managing Security Contexts

This section describes how to manage security contexts and includes the following topics:

Removing a Security Context

You cannot remove the current admin context, unless you remove all contexts using the clear context command.


NoteIf you use failover, there is a delay between when you remove the context on the active unit and when the context is removed on the standby unit. You might see an error message indicating that the number of interfaces on the active and standby units are not consistent; this error is temporary and can be ignored.


Prerequisites

Perform this procedure in the system execution space.

Detailed Steps

 

Command
Purpose

no context name

Removes a single context. All context commands are also removed. The context configuration file is not removed from the config URL location.

clear context

Removes all contexts (including the admin context). The context configuration files are not removed from the config URL locations.

Changing the Admin Context

The system configuration does not include any network interfaces or network settings for itself; rather, when the system needs to access network resources (such as downloading the contexts from the server), it uses one of the contexts that is designated as the admin context.

The admin context is just like any other context, except that when a user logs in to the admin context, then that user has system administrator rights and can access the system and all other contexts. The admin context is not restricted in any way, and can be used as a regular context. However, because logging into the admin context grants you administrator privileges over all contexts, you might need to restrict access to the admin context to appropriate users.

Guidelines

You can set any context to be the admin context, as long as the configuration file is stored in the internal flash memory.

Prerequisites

Perform this procedure in the system execution space.

Detailed Steps

 

Command
Purpose

admin-context context_name

 

ciscoasa(config)# admin-context administrator

Sets the admin context. Any remote management sessions, such as Telnet, SSH, or HTTPS, that are connected to the admin context are terminated. You must reconnect to the new admin context.

Note A few system configuration commands, including ntp server, identify an interface name that belongs to the admin context. If you change the admin context, and that interface name does not exist in the new admin context, be sure to update any system commands that refer to the interface.

Changing the Security Context URL

This section describes how to change the context URL.

Guidelines

  • You cannot change the security context URL without reloading the configuration from the new URL. The ASA merges the new configuration with the current running configuration.
  • Reentering the same URL also merges the saved configuration with the running configuration.
  • A merge adds any new commands from the new configuration to the running configuration.

If the configurations are the same, no changes occur.

If commands conflict or if commands affect the running of the context, then the effect of the merge depends on the command. You might get errors, or you might have unexpected results. If the running configuration is blank (for example, if the server was unavailable and the configuration was never downloaded), then the new configuration is used.

  • If you do not want to merge the configurations, you can clear the running configuration, which disrupts any communications through the context, and then reload the configuration from the new URL.

Prerequisites

Perform this procedure in the system execution space.

Detailed Steps

 

Command
Purpose

Step 1

(Optional, if you do not want to perform a merge)

changeto context name
clear configure all
 

ciscoasa(config)# changeto context ctx1

ciscoasa/ctx1(config)# clear configure all

Changes to the context and clears its configuration. If you want to perform a merge, skip to Step 2.

Step 2

changeto system

 

ciscoasa/ctx1(config)# changeto system

ciscoasa(config)#

Changes to the system execution space.

Step 3

context name

 

ciscoasa(config)# context ctx1

Enters the context configuration mode for the context you want to change.

Step 4

config-url new_url

 

ciscoasa(config)# config-url ftp://user1:passw0rd@10.1.1.1/configlets/ctx1.cfg

Enters the new URL. The system immediately loads the context so that it is running.

Reloading a Security Context

You can reload the context in two ways:

  • Clear the running configuration and then import the startup configuration.

This action clears most attributes associated with the context, such as connections and NAT tables.

  • Remove the context from the system configuration.

This action clears additional attributes, such as memory allocation, which might be useful for troubleshooting. However, to add the context back to the system requires you to respecify the URL and interfaces.

This section includes the following topics:

Reloading by Clearing the Configuration

To reload the context by clearing the context configuration and reloading the configuration from the URL, perform the following steps.

Detailed Steps

 

Command
Purpose

Step 1

changeto context name

 

ciscoasa(config)# changeto context ctx1

ciscoasa/ctx1(comfig)#

Changes to the context that you want to reload.

Step 2

clear configure all

 

ciscoasa/ctx1(config)# clear configure all

Clears the running configuration. This command clears all connections.

Step 3

copy startup-config running-config

 

ciscoasa/ctx1(config)# copy startup-config running-config

Reloads the configuration. The ASA copies the configuration from the URL specified in the system configuration. You cannot change the URL from within a context.

Reloading by Removing and Re-adding the Context

To reload the context by removing the context and then re-adding it, perform the steps in the following sections:

1. “Removing a Security Context” section.

2. “Configuring a Security Context” section

Monitoring Security Contexts

This section describes how to view and monitor context information and includes the following topics:

Viewing Context Information

From the system execution space, you can view a list of contexts including the name, allocated interfaces, and configuration file URL.

From the system execution space, view all contexts by entering the following command:

 

Command
Purpose

show context [ name | detail | count ]

Shows all contexts.

If you want to show information for a particular context, specify the name .

The detail option shows additional information. See the following sample outputs below for more information.

The count option shows the total number of contexts.

The following is sample output from the show context command. The following sample output shows three contexts:

ciscoasa# show context
 
Context Name Interfaces URL
*admin GigabitEthernet0/1.100 disk0:/admin.cfg
GigabitEthernet0/1.101
contexta GigabitEthernet0/1.200 disk0:/contexta.cfg
GigabitEthernet0/1.201
contextb GigabitEthernet0/1.300 disk0:/contextb.cfg
GigabitEthernet0/1.301
Total active Security Contexts: 3
 

Table 6-2 shows each field description.

 

Table 6-2 show context Fields

Field
Description

Context Name

Lists all context names. The context name with the asterisk (*) is the admin context.

Interfaces

The interfaces assigned to the context.

URL

The URL from which the ASA loads the context configuration.

The following is sample output from the show context detail command:

ciscoasa# show context detail
 
Context "admin", has been created, but initial ACL rules not complete
Config URL: disk0:/admin.cfg
Real Interfaces: Management0/0
Mapped Interfaces: Management0/0
Flags: 0x00000013, ID: 1
 
Context "ctx", has been created, but initial ACL rules not complete
Config URL: ctx.cfg
Real Interfaces: GigabitEthernet0/0.10, GigabitEthernet0/1.20,
GigabitEthernet0/2.30
Mapped Interfaces: int1, int2, int3
Flags: 0x00000011, ID: 2
 
Context "system", is a system resource
Config URL: startup-config
Real Interfaces:
Mapped Interfaces: Control0/0, GigabitEthernet0/0,
GigabitEthernet0/0.10, GigabitEthernet0/1, GigabitEthernet0/1.10,
GigabitEthernet0/1.20, GigabitEthernet0/2, GigabitEthernet0/2.30,
GigabitEthernet0/3, Management0/0, Management0/0.1
Flags: 0x00000019, ID: 257
 
Context "null", is a system resource
Config URL: ... null ...
Real Interfaces:
Mapped Interfaces:
Flags: 0x00000009, ID: 258
 

See the command reference for more information about the detail output.

The following is sample output from the show context count command:

ciscoasa# show context count
Total active contexts: 2
 

Viewing Resource Allocation

From the system execution space, you can view the allocation for each resource across all classes and class members.

To view the resource allocation, enter the following command:

 

Command
Purpose

show resource allocation [ detail ]

Shows the resource allocation. This command shows the resource allocation, but does not show the actual resources being used. See the “Viewing Resource Usage” section for more information about actual resource usage.

The detail argument shows additional information. See the following sample outputs for more information.

The following sample output shows the total allocation of each resource as an absolute value and as a percentage of the available system resources:

ciscoasa# show resource allocation
Resource Total % of Avail
Conns [rate] 35000 N/A
Inspects [rate] 35000 N/A
Syslogs [rate] 10500 N/A
Conns 305000 30.50%
Hosts 78842 N/A
SSH 35 35.00%
Routes 5000 N/A
Telnet 35 35.00%
Xlates 91749 N/A
Other VPN Sessions 20 2.66%
Other VPN Burst 20 2.66%
All unlimited
 

Table 6-3 shows each field description.

 

Table 6-3 show resource allocation Fields

Field
Description

Resource

The name of the resource that you can limit.

Total

The total amount of the resource that is allocated across all contexts. The amount is an absolute number of concurrent instances or instances per second. If you specified a percentage in the class definition, the ASA converts the percentage to an absolute number for this display.

% of Avail

The percentage of the total system resources that is allocated across all contexts, if the resource has a hard system limit. If a resource does not have a system limit, this column shows N/A.

The following is sample output from the show resource allocation detail command:

ciscoasa# show resource allocation detail
Resource Origin:
A Value was derived from the resource 'all'
C Value set in the definition of this class
D Value set in default class
Resource Class Mmbrs Origin Limit Total Total %
Conns [rate] default all CA unlimited
gold 1 C 34000 34000 N/A
silver 1 CA 17000 17000 N/A
bronze 0 CA 8500
All Contexts: 3 51000 N/A
 
Inspects [rate] default all CA unlimited
gold 1 DA unlimited
silver 1 CA 10000 10000 N/A
bronze 0 CA 5000
All Contexts: 3 10000 N/A
 
Syslogs [rate] default all CA unlimited
gold 1 C 6000 6000 N/A
silver 1 CA 3000 3000 N/A
bronze 0 CA 1500
All Contexts: 3 9000 N/A
 
Conns default all CA unlimited
gold 1 C 200000 200000 20.00%
silver 1 CA 100000 100000 10.00%
bronze 0 CA 50000
All Contexts: 3 300000 30.00%
 
Hosts default all CA unlimited
gold 1 DA unlimited
silver 1 CA 26214 26214 N/A
bronze 0 CA 13107
All Contexts: 3 26214 N/A
 
SSH default all C 5
gold 1 D 5 5 5.00%
silver 1 CA 10 10 10.00%
bronze 0 CA 5
All Contexts: 3 20 20.00%
 
Telnet default all C 5
gold 1 D 5 5 5.00%
silver 1 CA 10 10 10.00%
bronze 0 CA 5
All Contexts: 3 20 20.00%
 
Routes default all C unlimited N/A
gold 1 D unlimited 5 N/A
silver 1 CA 10 10 N/A
bronze 0 CA 5 N/A
All Contexts: 3 20 N/A
 
Xlates default all CA unlimited
gold 1 DA unlimited
silver 1 CA 23040 23040 N/A
bronze 0 CA 11520
All Contexts: 3 23040 N/A
 
mac-addresses default all C 65535
gold 1 D 65535 65535 100.00%
silver 1 CA 6553 6553 9.99%
bronze 0 CA 3276
All Contexts: 3 137623 209.99%
 

Table 6-4 shows each field description.

 

Table 6-4 show resource allocation detail Fields

Field
Description

Resource

The name of the resource that you can limit.

Class

The name of each class, including the default class.

The All contexts field shows the total values across all classes.

Mmbrs

The number of contexts assigned to each class.

Origin

The origin of the resource limit, as follows:

  • A—You set this limit with the all option, instead of as an individual resource.
  • C—This limit is derived from the member class.
  • D—This limit was not defined in the member class, but was derived from the default class. For a context assigned to the default class, the value will be “C” instead of “D.”

The ASA can combine “A” with “C” or “D.”

Limit

The limit of the resource per context, as an absolute number. If you specified a percentage in the class definition, the ASA converts the percentage to an absolute number for this display.

Total

The total amount of the resource that is allocated across all contexts in the class. The amount is an absolute number of concurrent instances or instances per second. If the resource is unlimited, this display is blank.

% of Avail

The percentage of the total system resources that is allocated across all contexts in the class. If the resource is unlimited, this display is blank. If the resource does not have a system limit, then this column shows N/A.

Viewing Resource Usage

From the system execution space, you can view the resource usage for each context and display the system resource usage.

 

Command
Purpose

show resource usage [ context context_name | top n | all | summary | system ] [ resource { resource_name | all } | detail ] [ counter counter_name [ count_threshold ]]

By default, all context usage is displayed; each context is listed separately.

Enter the top n keyword to show the contexts that are the top n users of the specified resource. You must specify a single resource type, and not resource all , with this option.

The summary option shows all context usage combined.

The system option shows all context usage combined, but shows the system limits for resources instead of the combined context limits.

For the resource resource_name , see Table 6-1 for available resource names. See also the show resource type command. Specify all (the default) for all types.

The detail option shows the resource usage of all resources, including those you cannot manage. For example, you can view the number of TCP intercepts.

The counter counter_name is one of the following keywords:

  • current —Shows the active concurrent instances or the current rate of the resource.
  • denied —Shows the number of instances that were denied because they exceeded the resource limit shown in the Limit column.
  • peak —Shows the peak concurrent instances, or the peak rate of the resource since the statistics were last cleared, either using the clear resource usage command or because the device rebooted.
  • all —(Default) Shows all statistics.

The count_threshold sets the number above which resources are shown. The default is 1. If the usage of the resource is below the number you set, then the resource is not shown. If you specify all for the counter name, then the count_threshold applies to the current usage.

Note To show all resources, set the count_threshold to 0.

The following is sample output from the show resource usage context command, which shows the resource usage for the admin context:

ciscoasa# show resource usage context admin
 
Resource Current Peak Limit Denied Context
Telnet 1 1 5 0 admin
Conns 44 55 N/A 0 admin
Hosts 45 56 N/A 0 admin
 

The following is sample output from the show resource usage summary command, which shows the resource usage for all contexts and all resources. This sample shows the limits for six contexts.

ciscoasa# show resource usage summary
 
Resource Current Peak Limit Denied Context
Syslogs [rate] 1743 2132 N/A 0 Summary
Conns 584 763 280000(S) 0 Summary
Xlates 8526 8966 N/A 0 Summary
Hosts 254 254 N/A 0 Summary
Conns [rate] 270 535 N/A 1704 Summary
Inspects [rate] 270 535 N/A 0 Summary
Other VPN Sessions 0 10 10 740 Summary
Other VPN Burst 0 10 10 730 Summary
 
S = System: Combined context limits exceed the system limit; the system limit is shown.
 

The following is sample output from the show resource usage summary command, which shows the limits for 25 contexts. Because the context limit for Telnet and SSH connections is 5 per context, then the combined limit is 125. The system limit is only 100, so the system limit is shown.

ciscoasa# show resource usage summary
 
Resource Current Peak Limit Denied Context
Telnet 1 1 100[S] 0 Summary
SSH 2 2 100[S] 0 Summary
Conns 56 90 130000(S) 0 Summary
Hosts 89 102 N/A 0 Summary
S = System: Combined context limits exceed the system limit; the system limit is shown.
 

The following is sample output from the show resource usage system command, which shows the resource usage for all contexts, but it shows the system limit instead of the combined context limits. The counter all 0 option is used to show resources that are not currently in use. The Denied statistics indicate how many times the resource was denied due to the system limit, if available.

ciscoasa# show resource usage system counter all 0
 
Resource Current Peak Limit Denied Context
Telnet 0 0 100 0 System
SSH 0 0 100 0 System
ASDM 0 0 32 0 System
Routes 0 0 N/A 0 System
IPSec 0 0 5 0 System
Syslogs [rate] 1 18 N/A 0 System
Conns 0 1 280000 0 System
Xlates 0 0 N/A 0 System
Hosts 0 2 N/A 0 System
Conns [rate] 1 1 N/A 0 System
Inspects [rate] 0 0 N/A 0 System
Other VPN Sessions 0 10 750 740 System
Other VPN Burst 0 10 750 730 System
 
 

Monitoring SYN Attacks in Contexts

The ASA prevents SYN attacks using TCP Intercept. TCP Intercept uses the SYN cookies algorithm to prevent TCP SYN-flooding attacks. A SYN-flooding attack consists of a series of SYN packets usually originating from spoofed IP addresses. The constant flood of SYN packets keeps the server SYN queue full, which prevents it from servicing connection requests. When the embryonic connection threshold of a connection is crossed, the ASA acts as a proxy for the server and generates a SYN-ACK response to the client SYN request. When the ASA receives an ACK back from the client, it can then authenticate the client and allow the connection to the server.

Monitor SYN attacks using the following commands:

 

Command
Purpose

show perfmon

Monitors the rate of attacks for individual contexts.

show resource usage detail

Monitors the amount of resources being used by TCP intercept for individual contexts.

show resource usage summary detail

Monitors the resources being used by TCP intercept for the entire system.

The following is sample output from the show perfmon command that shows the rate of TCP intercepts for a context called admin.

ciscoasa/admin# show perfmon
 
Context:admin
PERFMON STATS: Current Average
Xlates 0/s 0/s
Connections 0/s 0/s
TCP Conns 0/s 0/s
UDP Conns 0/s 0/s
URL Access 0/s 0/s
URL Server Req 0/s 0/s
WebSns Req 0/s 0/s
TCP Fixup 0/s 0/s
HTTP Fixup 0/s 0/s
FTP Fixup 0/s 0/s
AAA Authen 0/s 0/s
AAA Author 0/s 0/s
AAA Account 0/s 0/s
TCP Intercept 322779/s 322779/s
 

The following is sample output from the show resource usage detail command that shows the amount of resources being used by TCP Intercept for individual contexts. (Sample text in bold shows the TCP intercept information.)

ciscoasa(config)# show resource usage detail
Resource Current Peak Limit Denied Context
memory 843732 847288 unlimited 0 admin
chunk:channels 14 15 unlimited 0 admin
chunk:fixup 15 15 unlimited 0 admin
chunk:hole 1 1 unlimited 0 admin
chunk:ip-users 10 10 unlimited 0 admin
chunk:list-elem 21 21 unlimited 0 admin
chunk:list-hdr 3 4 unlimited 0 admin
chunk:route 2 2 unlimited 0 admin
chunk:static 1 1 unlimited 0 admin
tcp-intercepts 328787 803610 unlimited 0 admin
np-statics 3 3 unlimited 0 admin
statics 1 1 unlimited 0 admin
ace-rules 1 1 unlimited 0 admin
console-access-rul 2 2 unlimited 0 admin
fixup-rules 14 15 unlimited 0 admin
memory 959872 960000 unlimited 0 c1
chunk:channels 15 16 unlimited 0 c1
chunk:dbgtrace 1 1 unlimited 0 c1
chunk:fixup 15 15 unlimited 0 c1
chunk:global 1 1 unlimited 0 c1
chunk:hole 2 2 unlimited 0 c1
chunk:ip-users 10 10 unlimited 0 c1
chunk:udp-ctrl-blk 1 1 unlimited 0 c1
chunk:list-elem 24 24 unlimited 0 c1
chunk:list-hdr 5 6 unlimited 0 c1
chunk:nat 1 1 unlimited 0 c1
chunk:route 2 2 unlimited 0 c1
chunk:static 1 1 unlimited 0 c1
tcp-intercept-rate 16056 16254 unlimited 0 c1
globals 1 1 unlimited 0 c1
np-statics 3 3 unlimited 0 c1
statics 1 1 unlimited 0 c1
nats 1 1 unlimited 0 c1
ace-rules 2 2 unlimited 0 c1
console-access-rul 2 2 unlimited 0 c1
fixup-rules 14 15 unlimited 0 c1
memory 232695716 232020648 unlimited 0 system
chunk:channels 17 20 unlimited 0 system
chunk:dbgtrace 3 3 unlimited 0 system
chunk:fixup 15 15 unlimited 0 system
chunk:ip-users 4 4 unlimited 0 system
chunk:list-elem 1014 1014 unlimited 0 system
chunk:list-hdr 1 1 unlimited 0 system
chunk:route 1 1 unlimited 0 system
block:16384 510 885 unlimited 0 system
block:2048 32 34 unlimited 0 system
 

The following sample output shows the resources being used by TCP intercept for the entire system. (Sample text in bold shows the TCP intercept information.)

ciscoasa(config)# show resource usage summary detail
Resource Current Peak Limit Denied Context
memory 238421312 238434336 unlimited 0 Summary
chunk:channels 46 48 unlimited 0 Summary
chunk:dbgtrace 4 4 unlimited 0 Summary
chunk:fixup 45 45 unlimited 0 Summary
chunk:global 1 1 unlimited 0 Summary
chunk:hole 3 3 unlimited 0 Summary
chunk:ip-users 24 24 unlimited 0 Summary
chunk:udp-ctrl-blk 1 1 unlimited 0 Summary
chunk:list-elem 1059 1059 unlimited 0 Summary
chunk:list-hdr 10 11 unlimited 0 Summary
chunk:nat 1 1 unlimited 0 Summary
chunk:route 5 5 unlimited 0 Summary
chunk:static 2 2 unlimited 0 Summary
block:16384 510 885 unlimited 0 Summary
block:2048 32 35 unlimited 0 Summary
tcp-intercept-rate 341306 811579 unlimited 0 Summary
globals 1 1 unlimited 0 Summary
np-statics 6 6 unlimited 0 Summary
statics 2 2 N/A 0 Summary
nats 1 1 N/A 0 Summary
ace-rules 3 3 N/A 0 Summary
console-access-rul 4 4 N/A 0 Summary
fixup-rules 43 44 N/A 0 Summary

Viewing Assigned MAC Addresses

You can view auto-generated MAC addresses within the system configuration or within the context. This section includes the following topics:

Viewing MAC Addresses in the System Configuration

This section describes how to view MAC addresses in the system configuration.

Guidelines

If you manually assign a MAC address to an interface, but also have auto-generation enabled, the auto-generated address continues to show in the configuration even though the manual MAC address is the one that is in use. If you later remove the manual MAC address, the auto-generated one shown will be used.

Detailed Steps

 

Command
Purpose

show running-config all context [ name ]

Shows the assigned MAC addresses from the system execution space.

The all option is required to view the assigned MAC addresses. Although the mac-address auto command is user-configurable in global configuration mode only, the command appears as a read-only entry in context configuration mode along with the assigned MAC address. Only allocated interfaces that are configured with a nameif command within the context have a MAC address assigned.

Examples

The following output from the show running-config all context admin command shows the primary and standby MAC address assigned to the Management0/0 interface:

ciscoasa# show running-config all context admin
 
context admin
allocate-interface Management0/0
mac-address auto Management0/0 a24d.0000.1440 a24d.0000.1441
config-url disk0:/admin.cfg
 

The following output from the show running-config all context command shows all the MAC addresses (primary and standby) for all context interfaces. Note that because the GigabitEthernet0/0 and GigabitEthernet0/1 main interfaces are not configured with a nameif command inside the contexts, no MAC addresses have been generated for them.

 
ciscoasa# show running-config all context
 
admin-context admin
context admin
allocate-interface Management0/0
mac-address auto Management0/0 a2d2.0400.125a a2d2.0400.125b
config-url disk0:/admin.cfg
!
 
context CTX1
allocate-interface GigabitEthernet0/0
allocate-interface GigabitEthernet0/0.1-GigabitEthernet0/0.5
mac-address auto GigabitEthernet0/0.1 a2d2.0400.11bc a2d2.0400.11bd
mac-address auto GigabitEthernet0/0.2 a2d2.0400.11c0 a2d2.0400.11c1
mac-address auto GigabitEthernet0/0.3 a2d2.0400.11c4 a2d2.0400.11c5
mac-address auto GigabitEthernet0/0.4 a2d2.0400.11c8 a2d2.0400.11c9
mac-address auto GigabitEthernet0/0.5 a2d2.0400.11cc a2d2.0400.11cd
allocate-interface GigabitEthernet0/1
allocate-interface GigabitEthernet0/1.1-GigabitEthernet0/1.3
mac-address auto GigabitEthernet0/1.1 a2d2.0400.120c a2d2.0400.120d
mac-address auto GigabitEthernet0/1.2 a2d2.0400.1210 a2d2.0400.1211
mac-address auto GigabitEthernet0/1.3 a2d2.0400.1214 a2d2.0400.1215
config-url disk0:/CTX1.cfg
!
 
context CTX2
allocate-interface GigabitEthernet0/0
allocate-interface GigabitEthernet0/0.1-GigabitEthernet0/0.5
mac-address auto GigabitEthernet0/0.1 a2d2.0400.11ba a2d2.0400.11bb
mac-address auto GigabitEthernet0/0.2 a2d2.0400.11be a2d2.0400.11bf
mac-address auto GigabitEthernet0/0.3 a2d2.0400.11c2 a2d2.0400.11c3
mac-address auto GigabitEthernet0/0.4 a2d2.0400.11c6 a2d2.0400.11c7
mac-address auto GigabitEthernet0/0.5 a2d2.0400.11ca a2d2.0400.11cb
allocate-interface GigabitEthernet0/1
allocate-interface GigabitEthernet0/1.1-GigabitEthernet0/1.3
mac-address auto GigabitEthernet0/1.1 a2d2.0400.120a a2d2.0400.120b
mac-address auto GigabitEthernet0/1.2 a2d2.0400.120e a2d2.0400.120f
mac-address auto GigabitEthernet0/1.3 a2d2.0400.1212 a2d2.0400.1213
config-url disk0:/CTX2.cfg
!

Viewing MAC Addresses Within a Context

This section describes how to view MAC addresses within a context.

Detailed Steps

 

Command
Purpose

show interface | include (Interface)|(MAC)

Shows the MAC address in use by each interface within the context.

Examples

For example:

ciscoasa/context# show interface | include (Interface)|(MAC)
 
Interface GigabitEthernet1/1.1 "g1/1.1", is down, line protocol is down
MAC address a201.0101.0600, MTU 1500
Interface GigabitEthernet1/1.2 "g1/1.2", is down, line protocol is down
MAC address a201.0102.0600, MTU 1500
Interface GigabitEthernet1/1.3 "g1/1.3", is down, line protocol is down
MAC address a201.0103.0600, MTU 1500
...
 

NoteTheshow interface command shows the MAC address in use; if you manually assign a MAC address and also have auto-generation enabled, then you can only view the unused auto-generated address from within the system configuration.


Configuration Examples for Multiple Context Mode

The following example:

  • Automatically sets the MAC addresses in contexts with a custom prefix.
  • Sets the default class limit for conns to 10 percent instead of unlimited, and sets the VPN other sessions to 10, with a burst of 5.
  • Creates a gold resource class.
  • Sets the admin context to be “administrator.”
  • Creates a context called “administrator” on the internal flash memory to be part of the default resource class.
  • Adds two contexts from an FTP server as part of the gold resource class.

ciscoasa(config)# mac-address auto prefix 19

 

ciscoasa(config)# class default
ciscoasa(config-class)# limit-resource conns 10%
ciscoasa(config-class)# limit-resource vpn other 10
ciscoasa(config-class)# limit-resource vpn burst other 5
 
ciscoasa(config)# class gold
ciscoasa(config-class)# limit-resource mac-addresses 10000
ciscoasa(config-class)# limit-resource conns 15%
ciscoasa(config-class)# limit-resource rate conns 1000
ciscoasa(config-class)# limit-resource rate inspects 500
ciscoasa(config-class)# limit-resource hosts 9000
ciscoasa(config-class)# limit-resource asdm 5
ciscoasa(config-class)# limit-resource ssh 5
ciscoasa(config-class)# limit-resource rate syslogs 5000
ciscoasa(config-class)# limit-resource telnet 5
ciscoasa(config-class)# limit-resource xlates 36000
ciscoasa(config-class)# limit-resource routes 700
ciscoasa(config-class)# limit-resource vpn other 100
ciscoasa(config-class)# limit-resource vpn burst other 50
 
ciscoasa(config)# admin-context administrator
ciscoasa(config)# context administrator
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/0.1
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.1
ciscoasa(config-ctx)# config-url disk0:/admin.cfg
 
ciscoasa(config-ctx)# context test
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/0.100 int1
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/0.102 int2
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/0.110-gigabitethernet0/0.115 int3-int8
ciscoasa(config-ctx)# config-url ftp://user1:passw0rd@10.1.1.1/configlets/test.cfg
ciscoasa(config-ctx)# member gold
 
ciscoasa(config-ctx)# context sample
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.200 int1
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.212 int2
ciscoasa(config-ctx)# allocate-interface gigabitethernet0/1.230-gigabitethernet0/1.235 int3-int8
ciscoasa(config-ctx)# config-url ftp://user1:passw0rd@10.1.1.1/configlets/sample.cfg
ciscoasa(config-ctx)# member gold
 

Feature History for Multiple Context Mode

Table 6-5 lists each feature change and the platform release in which it was implemented.

 

Table 6-5 Feature History for Multiple Context Mode

Feature Name
Platform Releases
Feature Information

Multiple security contexts

7.0(1)

Multiple context mode was introduced.

We introduced the following commands: context , mode , and class .

Automatic MAC address assignment

7.2(1)

Automatic assignment of MAC address to context interfaces was introduced.

We introduced the following command: mac-address auto .

Resource management

7.2(1)

Resource management was introduced.

We introduced the following commands: class , limit-resource , and member .

Virtual sensors for IPS

8.0(2)

The AIP SSM running IPS software Version 6.0 and above can run multiple virtual sensors, which means you can configure multiple security policies on the AIP SSM. You can assign each context or single mode ASA to one or more virtual sensors, or you can assign multiple security contexts to the same virtual sensor.

We introduced the following command: allocate-ips .

Automatic MAC address assignment enhancements

8.0(5)/8.2(2)

The MAC address format was changed to use a prefix, to use a fixed starting value (A2), and to use a different scheme for the primary and secondary unit MAC addresses in a failover pair. The MAC addresses are also now persistent across reloads. The command parser now checks if auto-generation is enabled; if you want to also manually assign a MAC address, you cannot start the manual MAC address with A2.

We modified the following command: mac-address auto prefix .

Maximum contexts increased for the ASA 5550 and 5580

8.4(1)

The maximum security contexts for the ASA 5550 was increased from 50 to 100. The maximum for the ASA 5580 was increased from 50 to 250.

Automatic MAC address assignment enabled by default

8.5(1)

Automatic MAC address assignment is now enabled by default.

We modified the following command: mac-address auto .

Automatic generation of a MAC address prefix

8.6(1)

In multiple context mode, the ASA now converts the automatic MAC address generation configuration to use a default prefix. The ASA auto-generates the prefix based on the last two bytes of the interface (ASA 5500) or backplane (ASASM) MAC address. This conversion happens automatically when you reload, or if you reenable MAC address generation. The prefix method of generation provides many benefits, including a better guarantee of unique MAC addresses on a segment. You can view the auto-generated prefix by entering the show running-config mac-address command. If you want to change the prefix, you can reconfigure the feature with a custom prefix. The legacy method of MAC address generation is no longer available.

Note To maintain hitless upgrade for failover pairs, the ASA does not convert the MAC address method in an existing configuration upon a reload if failover is enabled. However, we strongly recommend that you manually change to the prefix method of generation when using failover, especially for the ASASM. Without the prefix method, ASASMs installed in different slot numbers experience a MAC address change upon failover, and can experience traffic interruption. After upgrading, to use the prefix method of MAC address generation, reenable MAC address generation to use the default prefix.

We modified the following command: mac-address auto .

Dynamic routing in Security Contexts

9.0(1)

EIGRP and OSPFv2 dynamic routing protocols are now supported in multiple context mode. OSPFv3, RIP, and multicast routing are not supported.

New resource type for routing table entries

9.0(1)

A new resource type, routes, was created to set the maximum number of routing table entries in each context.

We modified the following commands: limit-resource, show resource types, show resource usage, show resource allocation .

Site-to-Site VPN in multiple context mode

9.0(1)

Site-to-site VPN tunnels are now supported in multiple context mode.

New resource type for site-to-site VPN tunnels

9.0(1)

New resource types, vpn other and vpn burst other, were created to set the maximum number of site-to-site VPN tunnels in each context.

We modified the following commands: limit-resource, show resource types, show resource usage, show resource allocation .