Table Of Contents

Interface POS Configuration Application

General Tab

IPv4 Configuration Subtab

Dampening Subtab

POS Tab

PPP Common Subtab

PAP Subtab

CHAP Subtab

Operation Tab

Interface POS Configuration Application

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The Interface POS Configuration application contains the following tabs and subtabs:

•General Tab

–IPv4 Configuration Subtab

–Dampening Subtab

•POS Tab

–PPP Common Subtab

–PAP Subtab

–CHAP Subtab

•Operation Tab

The Interface POS Configuration application allows you to configure interface attributes that are specific to packet-over-SONET/SDH (POS) interfaces. With the exception of the attributes in the POS tab, when an attribute is configured in the Interface POS Configuration application, the changes can be displayed and edited in the Common application. See Chapter 4 "Interface Common Attributes Configuration Application," for information on the Common application.

POS provides a method for efficiently carrying data packets in SONET or Synchronous Digital Hierarchy (SDH) frames. High-bandwidth capacity and efficient link utilization are characteristics that make POS largely preferred for building the core of data networks. POS uses PPP in High-Level Data Link Control (HDLC)-like framing for data encapsulation at Layer 2 (data link) of the Open System Interconnection (OSI) stack. This method provides efficient packet delineation and error control.

In addition to high-bandwidth efficiency, POS offers secure and reliable transmission for data. Reliable data transfer depends on timing integrity.

The real-time POS functionality is performed in hardware, according to the hardware configuration offline setup. Configured hardware events are detected by the framer application-specific integrated circuits (ASICs) and the control is passed to the software. The generic POS driver is responsible for providing a mechanism to configure the hardware on a per-interface basis, handle interface state transitions, and collect POS-related statistics.

See Figure 6-1 for an example of the Interface POS Configuration application.

See Cisco Craft Works Interface User Interface Guide for information on the common window elements and common activities procedures in the Interface POS Configuration application.

Figure 6-1 Interface POS Application

General Tab

The General tab contains two subtabs: IPv4 Configuration and Dampening. The IPv4 Configuration subtab is displayed by default when the General tab is clicked.

The General tab allows you to perform the following tasks:

•Provide a description of the interface.

•Specify the maximum transmission unit (MTU) Layer 2 value.

•Choose to enable or disable the Cisco Discovery Protocol (CDP).

See Figure 6-1 for an example of the General tab. Table 6-1 describes the General tab fields.

Table 6-1 General Tab Description 

Field	Description
Description field	Allows you to enter a description of the interface.
MTU Layer 2 (bytes) field	Allows you to enter an MTU1 Layer 2 value in bytes for the POS2 interface. This value is the maximum packet size or MTU size. Each interface has a default maximum packet size or MTU size. This number generally defaults to the largest size possible for that interface type.
CDP list	Allows you to enable or disable CDP3 on the POS interface. CDP is disabled by default at the global level. CDP is supported on all interfaces except SRP4 interfaces. To start sending and receiving CDP information on the interface, choose enable. Choose disable to stop sending and receiving CDP information on the interface. CDP allows Cisco routers to discover each other in a protocol- and media-independent way. It allows a device to advertise its existence to other devices and also to detect all other devices on the same LAN (or on the other side of a WAN). CDP is a hello-based protocol, and all devices running CDP periodically advertise their attributes to their neighbors.

1 MTU= maximum transmission unit 2 POS = Packet over SONET/SDH 3 CDP = Cisco Discovery Protocol 4 SRP = Spatial Reuse Protocol

IPv4 Configuration Subtab

The IPv4 Configuration subtab allows you to perform the following tasks:

•Specify the IPv4 address and mask.

•Specify secondary addresses for the interface.

•Specify the IPv4 MTU for the interface.

•Configure the software response to Internet Control Message Protocol (ICMP) mask requests.

•Specify helper addresses for the interface.

See Figure 6-1 for an example of the IPv4 Configuration subtab. Table 6-2 describes the IPv4 Configuration subtab fields.

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Note If any networking device on a network segment uses a secondary address, all other devices on that same segment must also use a secondary address from the same network or subnet. Inconsistent use of secondary addresses on a network segment can quickly cause routing loops.

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Table 6-2 IPv4 Configuration Subtab Description 

Field	Description
IPv4 Configuration Area
Enable IPv4 Processing check box	Enables IPv4 processing, which allows you to either set primary and secondary IP Version 4 addresses for an interface or set an unnumbered interface to make this interface use the unnumbered interface IP address. An interface can have one primary IP address and multiple secondary IP addresses. Packets generated by the software always use the primary IP address. Therefore, all networking devices on a segment should share the same primary network number.
Unnumbered	Allows you to enable IPv4 processing without an explicit address.
Unnumbered radio button	Allows you to enable IPv4 processing.
Unnumbered field	Allows you to enter a valid interface name. The Unnumbered radio button must be chosen to enable the Unnumbered field. (See Unnumbered radio button.)
Unnumbered button	Allows you to choose an interface from the Select Interfaces dialog box. The Unnumbered radio button must be chosen to enable the Unnumbered field. (See Unnumbered radio button.)
IP Address	Allows you to enter a valid IPv4 address for the interface.
IP Address radio button	Allows you to configure the IPv4 address.
IP Address field	Allows you to enter a valid IP address. The IP Address radio button must be chosen to enable the IP Address field. (See IP Address radio button.)
Mask field	Allows you to enter a valid mask for the IP address of the interface.
Secondary Addresses table	Allows you to specify secondary IP addresses for the interface. Click the Add button to add a secondary address. Choose an address in the table and click Remove to delete a secondary address from the interface. Double-click a cell in the IP Address column to activate it and enter the IP address for the secondary address. Double-click a cell in the Mask column to activate it and enter the mask for the secondary address. There can be more than one secondary address specified. Secondary addresses are treated like primary addresses, except that the system never generates datagrams other than routing updates with secondary source addresses. IP broadcasts and ARP requests are handled properly, as are interface routes in the IP routing table. Secondary IP addresses can be used in a variety of situations. The following are the most common applications: •There may not be enough host addresses for a particular network segment. For example, your subnetting allows up to 254 hosts for each logical subnet, but on one physical subnet you need to have 300 host addresses. Using secondary IP addresses on the networking devices allows you to have two logical subnets using one physical subnet. •Many older networks were built using Level 2 bridges. The judicious use of secondary addresses can aid in the transition to a subnetted, router-based network. Routers on an older, bridged segment can be easily made aware that there are many subnets on that segment. •Two subnets of a single network might otherwise be separated by another network. This situation is not permitted when subnets are in use. In these instances, the first network is extended, or layered on top of the second network using secondary addresses.
General Area
MTU Layer 3 (bytes) field	Allows you to enter a valid MTU1 Layer 3 size in bytes. The MTU Layer 3 field contains the maximum MTU available for IP traffic.
ICMP Mask Reply check box	Allows you to configure the software response to ICMP2 mask requests by sending ICMP mask reply messages to the interface. Hosts can determine subnet masks using the ICMP mask request message. Networking devices respond to this request with an ICMP mask reply message.
Helper Addresses table	Allows you to specify helper addresses for the interface. Helper addresses are the addresses to which the software forwards UDP3 broadcasts/packets, including BOOTP, received on an interface. Click the Add button to add a helper address. Choose an address in the table and click Remove to delete a helper address from the interface. There can be more than one helper address for an interface. Double-click a cell in the Helper IP Address column to activate it and enter the IP address for the helper address. One common application that requires helper addresses is DHCP, which is defined in RFC 1531. DHCP4 protocol information is carried inside of BOOTP packets. To enable BOOTP broadcast forwarding for a set of clients, configure a helper address on the networking device interface closest to the client. The helper address should specify the address of the DHCP server. If you have multiple servers, you can configure one helper address for each server. Because BOOTP packets are forwarded by default, DHCP information can now be forwarded by the networking device. The DHCP server now receives broadcasts from the DHCP clients.

1 MTU = maximum transmission unit 2 ICMP = Internet Control Message Protocol 3 UDP = User Datagram Protocol 4 DHCP = Dynamic Host Configuration Protocol

Dampening Subtab

Currently, a router with an unstable data link (also known as link flap) may remove itself from service and return to service several times in a matter of seconds, requiring all other routers to rebuild their routing tables with each event. Dampening enables a router experiencing link flap to remove itself from network routing tables until return to data-link stability is ensured. After the link is stable, an up event is sent and the route is added back to the routing table.

With interface state dampening, the interface immediately removes itself from the routing table on the down event (link flap). If there are multiple link flaps in a short period of time, the interface ignores the next up event. The interface remains down until the data link has stabilized based on the dampening configuration parameters. Dampening can ignore up events based but cannot ignore down events unless the interface is already down.

Dampening delivers resiliency improvements that include the following issues:

•Faster convergence. Routers that are not experiencing link flap reach convergence sooner because routing tables are not rebuilt each time the offending router leaves and enters service. Faster convergence provides a more stable network because a router remains out of service until it is ready to enter service, ensuring fewer transitions.

•Increased network stability. A router with data-link problems removes itself from service until the data link is consistently stable, so other routers simply redirect traffic around the affected router until data-link issues are resolved, thus ensuring that the router loses no data packets.

The Dampening subtab allows you to perform the following tasks:

•Enable dampening for the interface.

•Configure the half-life, suppress, resuse, and maximum suppress values.

See Figure 6-2 for an example of the Dampening subtab. Table 6-3 describes the Dampening subtab fields.

Figure 6-2 Dampening Subtab

Table 6-3 Dampening Subtab Description 

Field	Description
Dampening check box	Allows you to enable state dampening for the interface.
HalfLife (min) field	Allows you to enter a time after which a penalty is decreased (decay half-life). After the interface has been assigned a penalty, the penalty is decreased by half after the half-life period.
Suppress field	Allows you to set a suppress threshold. An interface state is suppressed when its penalty (increased by state flaps) exceeds the suppress threshold.
Reuse field	Allows you to set the reuse threshold. An interface state is unsuppressed if the penalty for an interface decreases enough to fall below the reuse threshold.
Max Suppress (min) field	Allows you to set the maximum time (in minutes) that an interface state can be suppressed. A reasonable rule is to configure the maximum suppress to approximately four times the half-life value.

POS Tab

The POS tab contains three subtabs: PPP Common, PAP, and CHAP. The PPP Common subtab is displayed by default when the tab is clicked.

The POS tab allows you to perform the following tasks:

•Configure encapsulation.

•Configure PPP parameters.

•Configure Password Authentication Protocol (PAP) parameters.

•Configure Challenge Handshake Authentication Protocol (CHAP) parameters.

See Figure 6-3 for an example of the POS tab. Table 6-4 describes the POS tab fields.

Figure 6-3 POS Tab

Table 6-4 POS Tab Description 

Field	Description
Encapsulation list	Allows you to choose the encapsulation type for the interface. The following options are listed: •ppp1 —Standard protocol for sending data over synchronous serial links •hdlc2 —ISO communications protocol used in X.25 packet switching networks.

1 PPP = Point-to-Point Protocol 2 HDLC = High-Level Data Link Controller

PPP Common Subtab

The PPP Common subtab allows you to perform the following tasks:

•Configure the number of authentication retries, unacknowledged confirmation requests, consecutive negative acknowledgments, and unacknowledged terminate requests.

•Enable authentication types.

•Configure the timeout parameters.

See Figure 6-3 for an example of the PPP Common subtab. Table 6-5 describes the PPP Common subtab fields.

Table 6-5 PPP Common Subtab Description 

Field	Description
Max Authentication Failures field	Allows you to enter a specified number of authentication retries. After the number of specified retries is reached, the interface is reset.
Max Conf Requests field	Allows you to enter the number of unacknowledged confirmation requests.
Max Consecutive Conf Naks field	Allows you to enter the number of consecutive negative acknowledgments.
Max Terminate Requests field	Allows you to enter the number of unacknowledged terminate requests.
Authentication Area
PAP check box	Allows you to choose PAP1 authentication.
CHAP check box	Allows you to choose CHAP2 authentication.
MS-CHAP check box	Allows you to choose MS-CHAP3 authentication.
Authentication List field	Allows you to specify an authentication to be used with the interface. Type default to use the default list. This list is enabled when at least one of PAP, CHAP, or MS-CHAP is selected.
Timeout Parameters Area
Authentication Timeout (sec) field	Allows you to specify the maximum time to wait for a response to an authentication packet.
NCP Timeout (sec) field	Allows you to set a time limit for the successful negotiation of at least one network layer protocol after a PPP connection is established. If no network protocol is negotiated in the given time, the connection is disconnected. The NCP4 timeout protects against the establishment of links that are physically up and carrying traffic at the link level, but are unusable for carrying data traffic due to failure to negotiate the capability to transport any network level data. Timeout is particularly useful for dialed connections, in which it is usually undesirable to leave a telephone circuit active when it cannot carry network traffic.
Retry Timeout (sec) field	Allows you to set a time limit for the maximum amount of time PPP5 should wait for a response to any control packet it sends.

1 PAP = Password Authentication Protocol 2 CHAP = Challenge Handshake Authentication Protocol 3 MS-CHAP = Microsoft CHAP 4 NCP = Network Control Protocol 5 PPP = Point-to-Point Protocol

PAP Subtab

The PAP subtab allows you to perform the following tasks:

•Refuse PAP authentication from peers.

•Specify the PAP username and password.

See Figure 6-4 for an example of the PAP subtab. Table 6-6 describes the PAP subtab fields.

Figure 6-4 PAP Subtab

Table 6-6 PAP Subtab Description 

Field	Description
Refuse PAP list	Allows you to refuse PAP1 authentication from peers requesting it. Authentication is disabled for all calls, meaning that all attempts by the peer to force the user to authenticate using PAP are refused. If outbound PAP has been enabled, PAP is suggested as the authentication method in the refusal packet.
PAP Username field	Allows you to enter a username to reenable remote PAP support for an interface and include the sent username and password in the PAP authentication request packet to the peer. This field allows you to replace username configurations on any dialer interface or asynchronous group interface.
PAP Password field	Allows you to enter a password to reenable remote PAP support for an interface and include the sent username and password in the PAP authentication request packet to the peer. This field allows you to replace password configurations on any dialer interface or asynchronous group interface.
PAP Encryption check box	Allows you to enable PAP encryption.

1 PAP = Password Authentication Protocol

CHAP Subtab

The CHAP subtab allows you to perform the following tasks:

•Refuse CHAP authentication from peers.

•Specify the CHAP username and password.

See Figure 6-5 for an example of the CHAP subtab. Table 6-7 describes the CHAP subtab fields.

Figure 6-5 CHAP Subtab

Table 6-7 CHAP Subtab Description 

Field	Description
Refuse CHAP list	Allows you to refuse CHAP1 authentication from peers requesting it. Authentication is disabled for all calls, meaning that all attempts by the peer to force the user to authenticate using CHAP are refused. If outbound CHAP has been enabled, CHAP is suggested as the authentication method in the refusal packet.
CHAP Host Name field	Allows you to enter a username to enable a router calling a collection of routers that do not support this command to configure a common CHAP secret password to use in response to challenges from an unknown peer. The CHAP hostname is used for remote CHAP authentication only (when routers authenticate to the peer) and does not affect local CHAP authentication.
CHAP Password field	Allows you to enter a password to enable a router calling a collection of routers that do not support this command to configure a common CHAP secret password to use in response to challenges from an unknown peer. The CHAP password is used for remote CHAP authentication only (when routers authenticate to the peer) and does not affect local CHAP authentication.
CHAP Encryption check box	Allows you to enable CHAP encryption.

1 CHAP = Challenge Handshake Authentication Protocol

Operation Tab

The Operation tab allows you to manually shut down the interface.

See Figure 6-6 for an example of the Operation tab. Table 6-8 describes the Operation tab fields.

Figure 6-6 Operation Tab

Table 6-8 Operation Tab Description 

Field	Description
Shutdown check box	Allows you to shut down the POS1 interface. Shutdown administratively brings down an interface.

1 POS = Packet over SONET/SDH