BGP

This section describes the following functionality:

For general information about BGP support, see the following topics in the 7450 ESS, 7750 SR, 7950 XRS, and VSR Unicast Routing Protocols Guide, "BGP" :

  • BGP overview

  • BGP sessions

    • BGP session state

    • Detecting BGP session failures

      • Peer tracking

      • Bidirectional Forwarding Detection

    • High availability BGP sessions (BGP graceful restart only)

    • BGP session security

    • BGP address family support for different session types

    • BGP groups

  • BGP design concepts

  • BGP messages

  • BGP path attributes

    • Origins

    • AS path

    • Next-hop

      • Unlabeled IPv4 unicast routes

      • Unlabeled IPv6 unicast routes

      • VPN-IPv4 routes

      • VPN-IPv6 routes

      • Next-hop resolution

      • Next-hop tracking

    • Local preference

    • Route aggregation path attributes

    • Community attributes

    • Route reflection attributes

    • 4-Octet AS attributes

    • AIGP metric

  • BGP routing information base (RIB)

  • BGP applications

    • BGP prefix origin validation

    • BGP route leaking

    • BGP optimal route reflection

  • BGP configuration process overview

  • Configuration notes

  • Configuring BGP with CLI

  • BGP configuration management tasks

For descriptions of BGP commands, see the 7450 ESS, 7750 SR, 7950 XRS, and VSR Classic CLI Command Reference Guide and the 7450 ESS, 7750 SR, 7950 XRS, and VSR Clear, Monitor, Show, and Tools CLI Command Reference Guide.

Using a router interface address as the BGP local address

In cellular and WLAN networks, the router interface IP address can be assigned statically or dynamically. A cellular port supports different modes of operation depending on whether the IP address must be assigned statically or dynamically. See PDN router interfaces for information about the supported modes of operation on the PDN router interface.

When the PDN router interface is operating in dynamic cellular interface IP mode, the dynamically changing interface IP address must be reflected in BGP advertisements. Neighbor peers that are originating services that rely on BGP routing information to reach the local node must use the IP address of the PDN router interface on the local node in order to reach it. The local address for BGP sessions from the local node to neighbor peers must therefore match the IP address of the PDN router interface at all times, even after the IP address changes.

To facilitate a dynamically changing router interface IP address, the BGP local-address command must be configured with the name of the loopback interface used by the unnumbered interface under the PDN router interface instead of a fixed IP address. Using the loopback interface name, the SR OS will automatically assign the current IP address of the PDN router interface as the BGP local-address when the PDN router interface comes up (for example, when the cellular PDN interface learns the IP address during the cellular attachment procedure). This means that the BGP local address will inherit the loopback interface's dynamic address information and when routes are being advertised to peers, those peers will be able to route traffic toward this router's PDN router interface.

Configuring the loopback interface name used by the PDN router interface as the local address is available in both the config>router>bgp>group context and the config>router>bgp>group>neighbor context. For complete command syntax, description, and parameter information, see the 7450 ESS, 7750 SR, 7950 XRS, and VSR Classic CLI Command Reference Guide, "configure router bgp commands".

When BGP sessions are using the loopback interface name that is used PDN router interface as the local address, the remote neighbor peer must use the dynamic-neighbor command in order to accept BGP sessions from 7705 SAR-Hm nodes that have dynamically changing router interface IP addresses.

When dual SIM operation is required, there are two PDN interfaces, one per cellular port associated with each SIM. At a minimum, two BGP sessions are required, one for each PDN interface. Each BGP session must be configured with the local-address using the loopback interface associated with each PDN router interface.