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Mobile IP - Generic Routing Encapsulation for Mobile Networks

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Mobile IP - Generic Routing Encapsulation for Cisco Mobile Networks

Contents

Prerequisites for GRE for Cisco Mobile Networks

Restrictions for GRE for Cisco Mobile Networks

Information About GRE for Cisco Mobile Networks

Generic Routing Encapsulation

GRE for Cisco Mobile Networks Feature Design

GRE Keepalive Messages

Benefits of GRE for Cisco Mobile Networks

How to Configure GRE for Cisco Mobile Networks

Configuring GRE on the Mobile Router

Configuring GRE Globally on the Mobile Router

Configuring GRE per Interface on the Mobile Router

Configuring GRE Keepalive Messages

Configuration Examples for GRE for Cisco Mobile Networks

Configuring GRE for Cisco Mobile Networks Globally: Example

Configuring GRE for Cisco Mobile Networks on an Interface: Example

Verifying GRE for Cisco Mobile Networks: Examples

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

ip mobile router-service tunnel mode

show ip mobile router

show ip mobile router interface

tunnel mode gre

Glossary


Mobile IP - Generic Routing Encapsulation for Cisco Mobile Networks

Prior to the introduction of the Generic Routing Encapsulation for Cisco Mobile Networks feature, Cisco Mobile Networks supported only IP-in-IP encapsulation. This feature adds generic routing encapsulation (GRE) support for mobile networks. Benefits of the Generic Routing Encapsulation for Cisco Mobile Networks feature include the following:

•GRE supports multiprotocol tunneling.

•GRE provides explicit protection against recursive encapsulation.

•Hardware support of GRE tunneling increases the performance of the router.

•GRE keepalive messages allow the status of the end-to-end tunnel to be monitored.

Feature History for the Mobile IP - GRE for Cisco Mobile Networks Feature

Release
Modification

12.3(7)T

This feature was introduced.


Finding Support Information for Platforms and Cisco IOS Software Images

Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.

Contents

•Prerequisites for GRE for Cisco Mobile Networks

•Restrictions for GRE for Cisco Mobile Networks

•Information About GRE for Cisco Mobile Networks

•How to Configure GRE for Cisco Mobile Networks

•Configuration Examples for GRE for Cisco Mobile Networks

•Additional References

•Command Reference

•Glossary

Prerequisites for GRE for Cisco Mobile Networks

Roaming must be enabled on an interface before GRE encapsulation can be enabled on the interface.

Restrictions for GRE for Cisco Mobile Networks

The foreign agent (FA) and home agent (HA) must support GRE encapsulation in order for the mobile router to register with GRE encapsulation enabled. If the mobile router is attempting to register using collocated care-of address (CCoA) with GRE encapsulation, the HA must support GRE encapsulation.

GRE keepalives do not support Network Address Translation (NAT). If there is NAT in the path between a mobile router and its HA, GRE keepalive messages will not work properly. To work around the problem, consider using the Mobile IP NAT Traversal feature, which offers UDP encapsulation. The Mobile IP NAT Traversal feature documentation can be found at the following URL:

•http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123newft/123t/123t_8/gtnatmip.htm

Information About GRE for Cisco Mobile Networks

To configure the GRE for Cisco Mobile Networks feature, you should understand the following concepts:

•Generic Routing Encapsulation

•GRE for Cisco Mobile Networks Feature Design

•GRE Keepalive Messages

•Benefits of GRE for Cisco Mobile Networks

Generic Routing Encapsulation

Generic routing encapsulation (GRE) is a tunneling protocol used by Mobile IP. The GRE tunnel interface creates a virtual point-to-point link between two routers at remote points over an IP internetwork. GRE tunnels can transport a passenger protocol or encapsulated protocol.

Unlike IP-in-IP encapsulation, GRE provides the following:

•Explicit protection against recursive encapsulation, a condition in which tunneled packets reenter the same tunnel before exiting.

•Configurable keepalive messages to monitor the end-to-end status of the tunnel.

GRE is beneficial for certain applications because of its support for multiprotocol tunneling and explicit prevention of recursive encapsulation.

GRE for Cisco Mobile Networks Feature Design

To understand the components of the Cisco Mobile Networks solution, refer to the Cisco Mobile Networks feature documentation.

During agent discovery, HAs and FAs advertise their presence on their attached links by periodically multicasting or broadcasting messages called agent advertisements. The agent advertisements are ICMP Router Discovery Protocol (IRDP) messages with one or more extensions specific to Mobile IP. The agent advertisement extension consists of several fields including the following field that is relevant to this feature:

•G: This agent can receive tunneled IP datagrams that use GRE (referred to as the G bit)

If the GRE for Cisco Mobile Networks feature is enabled, the mobile router will request GRE encapsulation in the registration request only if the FA advertises that it is capable of GRE encapsulation (the G bit is set in the advertisement). If the registration request is successful, packets will be tunneled using GRE encapsulation.

If the GRE for Cisco Mobile Networks feature is enabled and the mobile router is using collocated care-of address (CCoA), the mobile router will attempt to register with the HA using GRE encapsulation. If the registration request is successful, packets will be tunneled using GRE encapsulation.

If the mobile router receives a denied registration reply with error code 72 (foreign agent required encapsulation unavailable) or error code 139 (home agent unsupported encapsulation), the mobile router will send another registration request with the G bit unset and the default IP-in-IP encapsulation will be used.

GRE Keepalive Messages

GRE tunnels support keepalive messages, which are messages sent periodically to the HA that allow the detection of an interruption in the end-to-end tunnel. Tunnels that use IP-in-IP encapsulation do not use keepalive messages. If a tunnel that is using IP-in-IP encapsulation loses its connection to the HA, the mobile router will not be aware of the disruption until it tries to register with the HA again. This can take up to one half of the mobile router's registration lifetime. GRE keepalive messages allow the status of the end-to-end tunnel to be checked at a configurable interval. If the mobile router detects an interruption in the connection to the HA, it will tear down the existing tunnel and attempt to reregister using the best interface. Typically this is the same interface on which the connection was previously established. If the registration attempt is unsuccessful, the mobile router will then try to register on the next best interface if one exists.

Benefits of GRE for Cisco Mobile Networks

The GRE for Cisco Mobile Networks feature introduces the ability for a mobile router to use GRE tunneling in addition to the default encapsulation method of IP-in-IP. GRE is a widely supported tunneling protocol, and some platforms support GRE tunnels in hardware. Hardware support of GRE tunneling offloads software operations, such as Cisco Express Forwarding (CEF) switching, from the CPU and increases the performance of the router. In addition, GRE supports multiprotocol tunneling and provides explicit protection against recursive encapsulation. Finally, the ability to configure keepalive messages with GRE allows the status of the end-to-end tunnel to be checked at a configurable interval, and reregistration can be attempted as soon as an interruption is detected.

How to Configure GRE for Cisco Mobile Networks

This section contains the following tasks:

•Configuring GRE on the Mobile Router (required)

•Configuring GRE Keepalive Messages (optional)

Configuring GRE on the Mobile Router

GRE encapsulation can be configured per interface or globally. Configuring GRE encapsulation on an interface allows only that interface to attempt to register with GRE encapsulation enabled. Configuring GRE encapsulation globally allows all roaming interfaces to attempt to register with GRE encapsulation enabled, unless the interface is configured for IP-in-IP encapsulation. The interface-level configuration overrides the global configuration.

Perform one of the following tasks to configure GRE on the mobile router:

•Configuring GRE Globally on the Mobile Router

•Configuring GRE per Interface on the Mobile Router

Configuring GRE Globally on the Mobile Router

Perform this task to configure GRE globally on the mobile router.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip mobile router

4. tunnel mode gre

5. end

6. show ip mobile router registration

7. show ip mobile router

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

ip mobile router

Example:

Router(config)# ip mobile router

Enables the mobile router and enters mobile router configuration mode.

Step 4 

tunnel mode gre

Example:

Router(mobile-router)# tunnel mode gre

Sets the global encapsulation mode on all roaming interfaces of a mobile router to GRE.

Note Configuring an encapsulation protocol on an interface overrides the globally configured encapsulation protocol.

Step 5 

end

Example:

Router(mobile-router)# end

Ends the current configuration session and returns to privileged EXEC mode.

Step 6 

show ip mobile router registration

Example:

Router# show ip mobile router registration

Displays the pending and accepted registrations of the mobile router.

Step 7 

show ip mobile router

Example:

Router# show ip mobile router

Displays configuration information and monitoring statistics about the mobile router.

Configuring GRE per Interface on the Mobile Router

Perform this task to configure GRE on an interface of the mobile router.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. ip mobile router-service tunnel mode {gre | ipip}

5. end

6. show ip mobile router registration

7. show ip mobile router interface

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface type number

Example:

Router(config)# interface serial 2

Configures an interface type and enters interface configuration mode.

Step 4 

ip mobile router-service tunnel mode {gre | ipip}

Example:

Router(config-if)# ip mobile router-service tunnel mode gre

Sets the encapsulation mode for a mobile router interface.

•gre—Specifies that the mobile router will attempt to register with GRE encapsulation on the interface.

•ipip—Specifies that IP-in-IP encapsulation will be used on the interface.

Note Configuring an encapsulation protocol on an interface overrides the globally configured encapsulation protocol on that interface.

Step 5 

end

Example:

Router(config-if)# end

Ends the current configuration session and returns to privileged EXEC mode.

Step 6 

show ip mobile router registration

Example:

Router# show ip mobile router registration

Displays the pending and accepted registrations of the mobile router.

Step 7 

show ip mobile router interface

Example:

Router# show ip mobile router interface

Displays information about the interface that the mobile router is using for roaming.

Configuring GRE Keepalive Messages

Perform this task on the mobile router to enable GRE keepalive messages. No configuration is required on the HA to respond to GRE keepalive messages from the mobile router.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface tunnel interface-number

4. exit

5. keepalive [period [retries]]

6. ip mobile router

7. template tunnel interface-number

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface tunnel interface-number

Example:

Router(config)# interface tunnel 121

Enters interface configuration mode for the specified interface.

Step 4 

keepalive [period [retries]]

Example:

Router(config-if)# keepalive 5 3

Enables keepalive packets and specifies the number of times that the Cisco IOS software tries to send keepalive packets without a response before bringing down the interface or before bringing the tunnel protocol down for a specific interface.

Step 5 

exit

Example:

Router(config-if)# exit

Returns to global configuration mode.

Step 6 

ip mobile router

Example:

Router(config)# ip mobile router

Enables the mobile router and enters mobile router configuration mode.

Step 7 

template tunnel interface-number

Example:

Router(mobile-router)# template tunnel 121

Applies a tunnel template to tunnels brought up at the mobile router.

Configuration Examples for GRE for Cisco Mobile Networks

The following sections contain configuration examples for the GRE for Cisco Mobile Networks feature:

•Configuring GRE for Cisco Mobile Networks Globally: Example

•Configuring GRE for Cisco Mobile Networks on an Interface: Example

•Verifying GRE for Cisco Mobile Networks: Examples

Configuring GRE for Cisco Mobile Networks Globally: Example

The following example globally configures GRE encapsulation on a mobile router and enables GRE keepalive messages: 

router mobile

!

ip mobile secure home-agent 10.40.40.1 spi 101 key hex 12345678123456781234567812345678 
     algorithm md5 mode prefix-suffix

ip mobile router

 address 10.80.80.1 255.255.255.0

 home-agent 10.40.40.1

 mobile-network Ethernet1/3

 mobile-network FastEthernet0/0

 template Tunnel 121

 tunnel mode gre

!

interface tunnel 121

 keepalive 5 3

Configuring GRE for Cisco Mobile Networks on an Interface: Example

The following example configures GRE encapsulation on an interface of a mobile router and enables GRE keepalive messages: 

interface FastEthernet0/0

 ip address 10.52.52.2 255.255.255.0

 ip mobile router-service roam

 ip mobile router-service tunnel mode gre

!

interface tunnel 121

 keepalive 5 3

!

ip mobile router

 template tunnel 121

Verifying GRE for Cisco Mobile Networks: Examples

The following example shows display output from the show ip mobile router registration command when GRE encapsulation is configured on the mobile router. The Flags field shows that GRE encapsulation is enabled by displaying a capital "G." If GRE encapsulation were not enabled, a lowercase "g" would be displayed. 

Router# show ip mobile router registration


Mobile Router Registrations:


Foreign agent 10.52.52.1:

    Registration accepted 01/11/00 07:01:24, On FastEthernet0/0

    Care-of addr 10.52.52.1, HA addr 10.40.40.1, Home addr 10.80.80.1 

    Lifetime requested 10:00:00 (36000), Granted 01:00:00 (3600) 

    Remaining 00:59:47 

    Flags sbdmG-t-, Identification B68B7673.81565B8

    Register next time 00:59:27 

    Extensions:

        Mobile Network 172.16.153.0/24 

        Mobile Network 172.16.143.0/24 

        MN-HA Authentication SPI 101

The following example shows display output from the show ip mobile router command when GRE encapsulation is globally configured on the mobile router. When GRE encapsulation is enabled, the line "Request GRE tunnel" is displayed in the output and the tunnel mode is shown as "GRE/IP". 

Router# show ip mobile router


Mobile Router 

    Enabled 01/11/00 06:59:19 

    Last redundancy state transition NEVER 


Configuration:

    Home Address 10.80.80.1 Mask 255.255.255.0 

    Home Agent 10.40.40.1 Priority 100 (best) (current) 

    Registration lifetime 65534 sec 

    Retransmit Init 1000, Max 5000 msec, Limit 3 

    Extend Expire 20, Retry 10, Interval 1 

    Request GRE tunnel

    Mobile Networks:Ethernet1/3 (172.16.143.0/255.255.255.0) 

                     FastEthernet0/0 (172.16.153.0/255.255.255.0) 


Monitor:

    Status -Registered- 

    Active foreign agent 10.52.52.1, Care-of 10.52.52.1 

    On interface FastEthernet0/0

    Tunnel0 mode GRE/IP

The following example shows display output from the show ip mobile router interface command when GRE encapsulation is configured on an interface of the mobile router. When GRE encapsulation is enabled on the interface, the line "Request GRE tunnel" is displayed in the output. 

Router# show ip mobile router interface


FastEthernet0/0:

    Priority 110, Bandwidth 100000, Address 10.52.52.2 

    Periodic solicitation disabled, Interval 600 sec 

    Retransmit Init 1000, Max 5000 msec, Limit 3 

    Current 2000, Remaining 0 msec, Count 2 

    Hold down 0 sec 

    Routing disallowed 

    Collocated CoA disabled 

    Request GRE tunnel

Additional References

The following sections provide references related to the GRE for Mobile Networks feature.

Related Documents

Related Topic
Document Title

Mobile IP commands: complete command syntax, command mode, defaults, usage guidelines, and examples

Cisco IOS IP Command Reference, Volume 4 of 4: IP Mobility, Release 12.3 T

Mobile IP commands and configuration tasks related to mobile networks

Cisco Mobile Networks feature document, Release 12.2(4)T and 12.2(13)T

Additional information about GRE keepalives

Generic Routing Encapsulation (GRE) Tunnel Keepalive feature document, Release 12.2(8)T

Information on configuring quality of service (QoS) with GRE

Quality of Service Options on GRE Tunnel Interfaces


Standards

Standards
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

—


MIBs

MIBs
MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFCs
Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

—


Technical Assistance

Description
Link

Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/public/support/tac/home.shtml


Command Reference

This section documents new and modified commands only.

•ip mobile router-service tunnel mode

•show ip mobile router

•show ip mobile router interface

•tunnel mode gre

ip mobile router-service tunnel mode

To set the encapsulation mode for a mobile router interface, use the ip mobile router-service tunnel mode command in interface configuration mode. To restore the default encapsultion mode on an interface, use the no form of this command.

ip mobile router-service tunnel mode {gre | ipip}

no ip mobile router-service tunnel mode

Syntax Description

gre

Specifies that the mobile router will attempt to register with Generic Routing Encapsulation (GRE) on the interface.

ipip

Specifies that IP-in-IP encapsulation will be used on the interface.


Defaults

The default encapsulation mode for Mobile IP is IP-in-IP encapsulation.

Command Modes

Interface configuration

Command History

Release
Modification

12.3(7)T

This command was introduced.


Usage Guidelines

If the ip mobile router-service tunnel mode gre command is configured, the mobile router will request GRE encapsulation in the registration request only if the foreign agent (FA) advertises that it is capable of GRE encapsulation (the G bit is set in the advertisement). If the registration request is successful, packets will be tunneled using GRE.

If the ip mobile router-service tunnel mode gre command is enabled and collocated care-of address (CCoA) is configured, the mobile router will attempt to register with the home agent (HA) using GRE encapsulation. If the registration request is successful, packets will be tunneled using GRE.

If the mobile router receives a denied registration reply with error code 72 (foreign agent required encapsulation unavailable) or error code 139 (home agent unsupported encapsulation), the mobile router will send another registration request with the G bit unset and IP-in-IP encapsulation will be used.

The no ip mobile router-service tunnel mode command instructs the mobile router to revert to the default encapsulation mode and register with IP-in-IP encapsulation.

Note If an encapsulation type is configured on an interface using the ip mobile router-service tunnel mode command, that encapsulation type takes precedence over the global encapsulation type configured with the tunnel mode gre command.

Once GRE encapsulation is enabled, GRE keepalives can be configured on an interface using the keepalive command. GRE keepalives check for a failure in the end-to-end tunnel at a configurable interval. If the connection to the HA is lost, the mobile router will attempt to reregister. GRE keepalives must be configured on the mobile router only—no configuration is required on the HA.

Note If the GRE keepalive messages time out, indicating an interruption in the end-to-end tunnel, only the mobile router will tear down the GRE tunnel. The HA will not tear down its side of the tunnel.

Examples

The following example configures GRE encapsulation and GRE keepalive messages on an interface of a mobile router: 

interface FastEthernet0/0

 ip address 10.52.52.2 255.255.255.0

 ip mobile router-service roam

 ip mobile router-service tunnel mode gre

!

interface tunnel 121

 keepalive 5 3

!

ip mobile router

 template tunnel 121

Related Commands

Command
Description

keepalive

Enables keepalive packets and specifies the number of times that the Cisco IOS software tries to send keepalive packets without a response before bringing down the interface or before bringing the tunnel protocol down for a specific interface.

tunnel mode gre

Sets the global encapsulation mode on all roaming interfaces of a mobile router to GRE.


show ip mobile router

To display configuration information and monitoring statistics about the mobile router, use the show ip mobile router command in privileged EXEC mode.

show ip mobile router

Syntax Description

This command has no arguments or keywords.

Command Modes

Privileged EXEC

Command History

Release
Modification

12.2(4)T

This command was introduced.

12.2(13)T

This command was enhanced to display information about the mobile network interfaces.

12.2(15)T

This command was enhanced to display information about collocated care-of addresses (CCoAs).

12.3(7)T

This command was enhanced to display information about requests for generic routing encapsulation (GRE).


Usage Guidelines

The display includes the mobile router configuration information such as the home address and network mask, home agent, and registration settings, and operational information such as status, tunnel interface, active foreign agent, and care-of address.

Examples

The following is sample output from the show ip mobile router command: 

Router# show ip mobile router


Mobile Router

  Enabled 05/30/02 11:16:03

  Last redundancy state transition 05/30/02 11:15:01


Configuration:

  Home Address 10.0.4.1 Mask 255.255.255.0

  Home Agent 10.0.0.3 Priority 100 (best) (current)

  Registration lifetime 120 sec

  Retransmit Init 1000, Max 5000 msec, Limit 3

  Extend Expire 120, Retry 3, Interval 10

  Redundancy group AlwaysUp (active)

  Mobile Networks:Ethernet5 (10.0.0.0/255.255.255.248) 

    Ethernet2 (10.0.0.0/255.0.0.0) 

    Ethernet3 (10.1.0.0/255.255.255.0)


Monitor:

  Status -Registered-

  Active foreign agent 10.0.1.2, Care-of 10.0.1.2

  On interface Serial0

  Tunnel0 mode IP/IP

The following is sample output from the show ip mobile router command when a mobile router is registered using a CCoA: 

Router# show ip mobile router


Mobile Router

  Enabled 02/12/02 18:29:13

  Last redundancy state transition NEVER

Configuration:

  Home Address 10.0.4.1 Mask 255.255.255.0

  Home Agent 10.0.0.3 Priority 100 (best)

  Registration lifetime 120 sec

  Retransmit Init 1000, Max 5000 msec, Limit 3

  Extend Expire 120, Retry 3, Interval 10

Monitor:

  Status -Registered-

  Using Collocated Care-of Address 10.0.0.1 

  On interface Ethernet1

  Tunnel0 mode IP/IP

The following is sample output from the show ip mobile router command when GRE encapsulation is globally configured on the mobile router. When GRE encapsulation is enabled, the line "Request GRE tunnel" is displayed in the output and the tunnel mode is shown as "GRE/IP". 

Router# show ip mobile router


Mobile Router 

    Enabled 01/11/00 06:59:19 

    Last redundancy state transition NEVER 


Configuration:

    Home Address 10.80.80.1 Mask 255.255.255.0 

    Home Agent 10.40.40.1 Priority 100 (best) (current) 

    Registration lifetime 65534 sec 

    Retransmit Init 1000, Max 5000 msec, Limit 3 

    Extend Expire 20, Retry 10, Interval 1 

    Request GRE tunnel

    Mobile Networks:Ethernet1/3 (172.16.143.0/255.255.255.0) 

                     TokenRing4/3 (172.16.153.0/255.255.255.0) 


Monitor:

    Status -Registered- 

    Active foreign agent 10.52.52.1, Care-of 10.52.52.1 

    On interface TokenRing4/2 

    Tunnel0 mode GRE/IP

Table 1 describes the significant fields shown in the display.

Table 1 show ip mobile router Field Descriptions 

Field
Description

Enabled

Date and time (in hh:mm:ss) when the mobile router was enabled.

Last redundancy state transition

Date and time (in hh:mm:ss) when the redundancy state of the mobile router changed.

Home Address/Mask

Home IP address of the mobile router, including the network mask.

Home Agent

Home agent that the mobile router registers with. The mobile router registers only to the home agent with the highest priority when multiple addresses are configured.

Registration lifetime

Registration lifetime (in seconds) granted by the home agent for the mobile router.

Retransmit Init/Max/Limit

Registration request retransmission settings. When registration requests are not responded to, the mobile router will resend. Displays the initial and maximum transmission timers and the limit on the number of retries allowed.

Extend Expire/ Retry/Interval

Extend registration lifetime. After the mobile router has registered, reregister before the lifetime expires. Retry is the number of attempts to reregister between intervals.

Request GRE tunnel

The mobile router requests GRE encapsulation when it registers.

Redundancy group

Name of redundancy group used to provide mobile router redundancy. Mobile router is either "active" or "passive." If redundancy is enabled or disabled, this information is displayed or absent, respectively. Active means that the mobile router is functioning fully, and passive means that the mobile router is idle.

Mobile Networks

Mobile networks associated to the mobile router.

Reverse tunnel required

If reverse tunnel is enabled or disabled, this information is displayed or absent, respectively.

Status

Indication of the state of the mobile router. Options are as follows:

•Home—Connected to home network.

•Registered—Registered on foreign network.

•Pending—Sent registration and waiting for reply.

•Isolated—Mobile router has heard an agent advertisement but is isolated from the network.

•Unknown—Cannot determine status.

Active foreign agent/Care-of

Foreign agent and care-of address used by the registered mobile router.

Using Collocated Care-of Address

Displayed if a mobile router is registered using a CCoA.

On interface

Mobile router registered on this interface.

Tunnel

Tunnel number between mobile router and home agent.

mode

The type of encapsulation being used. The encapsulation type can be one of the following:

•GRE/IP—GRE encapsulation is being used.

•IP/IP—IP-in-IP encapsulation is being used.


Related Commands

Command
Description

ip mobile router

Enables the mobile router and enters mobile router configuration mode.


show ip mobile router interface

To display information about the interfaces configured for roaming, use the show ip mobile router interface command in privileged EXEC mode.

show ip mobile router interface

Syntax Description

This command has no arguments or keywords.

Command Modes

Privileged EXEC

Command History

Release
Modification

12.2(4)T

This command was introduced.

12.2(15)T

This command was enhanced to display information about static collocated care-of addresses (CCoAs).

12.3(4)T

This command was enhanced to display information about dynamic CCoAs.

12.3(7)T

This command was enhanced to display information about a request for a generic routing encapsulation (GRE) tunnel.


Usage Guidelines

The mobile router uses the interfaces for roaming, discovering foreign agents, and registering its location on the foreign network.

Use this command to display information about roaming interfaces. If the interface is configured for a collocated care-of address (CCoA), the CCoA IP address is displayed. If it is not configured for a CCoA, "disabled" is displayed. The interface can be up or down.

Examples

The following is sample output from the show ip mobile router interface command. Fast Ethernet interface 0/0 and Fast Ethernet interface 2/0 have no CCoA configuration, serial interface 1/0 has a static CCoA configuration, and serial interface 1/1 has a dynamic CCoA address with CCoA only. GRE encapsulation is configured on Fast Ethernet interface 2/0. 

Router# show ip mobile router interface


Mobile Router Interfaces:


Listed in order of preference.


FastEthernet0/0:

  Priority 102, Bandwidth 10000, Address 10.0.0.9

  Periodic solicitation disabled, Interval 600 sec

  Retransmit Init 1000, Max 5000 msec, Limit 3

  Current 0, Remaining 0 msec, Count 0

  Hold down 0 sec

  Routing disallowed

  Collocated CoA disabled


Serial1/0:

  Priority 100, Bandwidth 1544, Address 10.0.0.7

  Periodic solicitation disabled, Interval 600 sec

  Retransmit Init 1000, Max 5000 msec, Limit 3

  Current 1000, Remaining 0 msec, Count 1

  Hold down 0 sec

  Routing disallowed

  Collocated CoA 10.0.0.7 (static)


Serial1/1

  Priority 100, Bandwidth 1544, Address 10.0.0.5

  Periodic solicitation disabled, Interval 600 sec

  Retransmit Init 1000, Max 5000 msec, Limit 3

  Current 0, Remaining 0 msec, Count 0

  Hold down 0 sec

  Routing disallowed

  Collocated CoA 10.0.0.5 - Solicit FA first


FastEthernet2/0

  Priority 110, Bandwidth 16000, Address 10.52.52.2 

  Periodic solicitation disabled, Interval 600 sec 

  Retransmit Init 1000, Max 5000 msec, Limit 3 

  Current 2000, Remaining 0 msec, Count 2 

  Hold down 0 sec 

  Routing disallowed 

  Collocated CoA disabled 

  Request GRE tunnel

Table 2 describes the significant fields shown in the display.

Table 2 show ip mobile router interface Field Descriptions 

Field
Description

Priority

Interface priority. Comparison to decide the preferred interface to register by the mobile router. The interface with the highest priority is used to send registrations.

Bandwidth

Interface bandwidth. When multiple interfaces have the highest priority, the highest bandwidth is the preferred choice.

Address

Interface IP address. If priority and bandwidth are the same among roaming interfaces, the highest address is preferred by the mobile router.

Periodic solicitation

Send solicitations periodically (enabled) or wait for periodic advertisements (disabled).

Interval

Period of time (in seconds) to wait before sending the next periodic solicitation.

Retransmit Init/Max/Limit

Solicitation retry settings. Displays the initial and maximum transmission timers and the limit on the number of retries allowed.

Current/ Remaining

Current retransmission interval and remaining time (in milliseconds) before it expires.

Count

Retransmission count.

Hold down

Period of time (in seconds) to wait before registering to a learned agent.

Routing

Routing is disallowed when the mobile router is roaming and allowed when the mobile router is home.

Collocated CoA

IP address is displayed if the interface is configured for CCoA; otherwise "disabled" is displayed. The CCoA is displayed if configured, even if the interface is down. The type of CCoA (static or dynamic) is given in parentheses.

Solicit FA first

Interface will solicit foreign agents first. If none are heard, CCoA processing is enabled on the interface.

Request GRE tunnel

Interface will request GRE encapsulation when it registers with an agent.


Related Commands

Command
Description

ip mobile router-service

Enables mobile router service on an interface.

ip mobile router-service collocated

Enables static or dynamic CCoA processing on a mobile router interface.

keepalive

Enables keepalive packets and specifies the number of times that the Cisco IOS software tries to send keepalive packets without response before bringing the tunnel protocol down for a specific interface.


tunnel mode gre

To set the global encapsulation mode on all roaming interfaces of a mobile router to generic routing encapsulation (GRE), use the tunnel  mode gre command in mobile router configuration mode. To restore the global default encapsulation mode, use the no form of this command.

tunnel mode gre

no tunnel mode gre

Syntax Description

This command has no arguments or keywords.

Defaults

The default encapsulation mode for Mobile IP is IP-in-IP encapsulation.

Command Modes

Mobile router configuration

Command History

Release
Modification

12.3(7)T

This command was introduced.


Usage Guidelines

If the tunnel mode gre command is configured, the mobile router will try to register with the foreign agent (FA) with the G bit set if the FA advertises GRE. If the registration request is successful, packets will be routed using GRE.

If the tunnel mode gre command is enabled and collocated care-of address (CCoA) is configured, the mobile router will try to register with the home agent (HA) with the G bit set. If the registration request is successful, packets will be routed using GRE.

If the mobile router receives a denied registration reply with error code 72 (foreign agent required encapsulation unavailable) or error code 139 (home agent unsupported encapsulation), the mobile router will send another registration request with the G bit unset and IP-in-IP encapsulation will be used.

The no tunnel mode gre command instructs the mobile router to revert to the default and register with IP-in-IP encapsulation.

Note If an encapsulation type is configured on an interface using the ip mobile router-service tunnel mode command, that encapsulation type takes precedence over the global encapsulation type configured with the tunnel mode gre command.

Once GRE encapsulation is enabled, GRE keepalives can be configured using the keepalive command. GRE keepalives check for a failure in the end-to-end tunnel at a configurable interval. If the connection to the HA is lost, reregistration will be attempted.

Examples

The following example globally configures GRE encapsulation on a mobile router and enables GRE keepalive messages: 

router mobile

!

ip mobile secure home-agent 10.40.40.1 spi 101 key hex 12345678123456781234567812345678 
     algorithm md5 mode prefix-suffix

ip mobile router

 address 10.80.80.1 255.255.255.0

 home-agent 10.40.40.1

 mobile-network Ethernet1/3

 mobile-network FastEthernet0/0

 template Tunnel 121

 tunnel mode gre

!

interface tunnel 121

 keepalive 5 3

Related Commands

Command
Description

ip mobile router-service tunnel mode gre

Sets the encapsulation mode to GRE for a mobile router interface.

keepalive

Enables keepalive packets and specifies the number of times that the Cisco IOS software tries to send keepalive packets without a response before bringing down the interface or before bringing the tunnel protocol down for a specific interface.


Glossary

agent advertisement—An advertisement message constructed by an attachment of a special extension to an ICMP Router Discovery Protocol (IRDP) to advertise mobility services to potential users.

agent discovery—The method by which a mobile node or mobile router determines whether it is currently connected to its home network or a foreign network and detects whether it has moved and the way it has moved. It is the mechanism by which mobile nodes or mobile routers query and discover mobility agents. Agent discovery is an extension to ICMP Router Discovery Protocol (IRDP) (RFC 1256), which includes a mechanism to advertise mobility services to potential users.

care-of address—The termination point of the tunnel to a mobile node or mobile router. This can be a collocated care-of address, by which the mobile node or mobile router acquires a local address and detunnels its own packets, or a foreign agent care-of address, by which a foreign agent detunnels packets and forwards them to the mobile node or mobile router.

FA—Foreign agent. A router on the visited network of a foreign network that provides routing services to the mobile node while registered. The foreign agent detunnels and delivers packets to the mobile node or mobile router that were tunneled by the home agent of the mobile node. For packets sent by a mobile node, the foreign agent may serve as a default router for registered mobile nodes.

GRE—generic routing encapsulation. Tunneling protocol that can encapsulate a wide variety of protocol packet types inside IP tunnels, creating a virtual point-to-point link to routers at remote points over an IP internetwork. By connecting multiprotocol subnetworks in a single-protocol backbone environment, IP tunneling using GRE allows network expansion across a single-protocol backbone environment.

HA—Home agent. A router on a home network of the mobile node that tunnels packets to the mobile node or mobile router while the mobile node or router is away from home. It keeps current location information for registered mobile nodes called a mobility binding.

mobile network—A network that moves with the mobile router. A mobile network is a collection of hosts and routes that are fixed with respect to each other but are mobile, as a unit, with respect to the rest of the Internet.

mobile router—A mobile node that is a router. It provides for the mobility of one or more entire networks moving together, perhaps on an airplane, a ship, a train, an automobile, a bicycle, or a kayak. The nodes connected to a network served by the mobile router may themselves be fixed nodes or mobile nodes or routers.

registration—The process by which the mobile node is associated with a care-of address on the home agent while it is away from home. Registration may happen directly from the mobile node to the home agent or through a foreign agent.

tunnel—The path followed by a packet while it is encapsulated from the home agent to the mobile node. The model is that, while the packet is encapsulated, it is routed to a knowledgeable decapsulating agent, which decapsulates the datagram and then correctly delivers it to its ultimate destination.

Note Refer to Internetworking Terms and Acronyms for terms not included in this glossary.

Copyright © 2004 Cisco Systems, Inc. All rights reserved.