© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-1 Optimizing BGP Scalability Implementing BGP Peer Groups

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-2 Outline Overview Peer Group Requirements Peer Groups as a BGP Performance Tool BGP Peer Group Limitations BGP Peer Groups in Cisco IOS Software BGP Dynamic Update Peer-Groups Feature BGP Configuration Using Peer Templates Configuring Peer Groups Monitoring Peer Groups Summary

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-3 Peer Group Requirements BGP routers could have a large number of neighbors with similar requirements: –Provider edge router with many customer connections –BGP route reflector with many IBGP peers –Provider edge router at an exchange point Most of the parameters specified for the BGP neighbors are identical, with a few exceptions.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-4 Peer Group Requirements Example: Customer Connections

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-5 Peer Group Requirements Example: BGP Route Reflector

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-6 Peer Group Requirements Example: Edge Router at a Peering Point

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-7 Peer Groups as a BGP Performance Tool Cisco IOS software builds individual BGP updates for each BGP neighbor. –The CPU load imposed by the BGP process is proportional to the number of BGP neighbors. A single BGP update is built for all members of a BGP peer group. –The CPU load does not increase linearly with the increased number of neighbors. –Hint: Use peer groups wherever possible to reduce the CPU load of the BGP process.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-8 BGP Peer Group Limitations Peer groups have a number of limitations because of the way that they are used to build BGP updates. –Per-neighbor BGP parameters that affect outbound updates cannot be changed for peer group members. –IBGP and EBGP neighbors cannot be mixed in a peer group.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-9 BGP Peer Groups in Cisco IOS Software BGP peer group creates a neighbor parameter template. Configurable parameters include the following: –Community propagation –Source interface for TCP session –EBGP multihop sessions –MD5 password –Neighbor weight –Filter-lists and distribute-lists –Route-maps Individual parameters specified in a peer group can be overridden on a neighbor-by-neighbor basis.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-10 BGP Dynamic Update Peer Groups Feature Separates BGP update generation from peer-group configuration Introduces a new algorithm that dynamically calculates and optimizes update-groups of neighbors that share the same outbound policies Requires no configuration by the network operator ― optimal BGP update message generation occurs automatically and independently

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-11 BGP Configuration Using Peer Templates This feature introduces a new mechanism called the peer template. A peer template is a configuration pattern that can be applied to neighbors that share common policies. Peer templates are reusable and support inheritance, which allows the network operator to group and apply distinct neighbor configurations for BGP neighbors that share common policies. Peer templates also allow the network operator to define very complex configuration patterns through the ability of a peer template to inherit a configuration from another peer template.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-12 Peer session templates are used to group and apply the configuration of general session commands that are common to all address-family and NLRI configuration modes. Peer policy templates are used to group and apply the configuration of commands that are applied within specific address-family and NLRI configuration modes. Peer Templates

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-13 Configuring Peer Groups neighbor group-name peer-group router(config-router)# Creates a BGP peer group Peer group names are case-sensitive neighbor group-name any-BGP-parameter router(config-router)# Specifies any BGP parameter for the peer group

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-14 Configuring Peer Groups (Cont.) neighbor ip-address peer-group peer-group-name router(config-router)# Assigns a BGP neighbor to a peer group. The neighbor inherits all the BGP parameters specified for the peer group. neighbor ip-address any-BGP-parameter router(config-router)# Overrides a BGP parameter specified for the peer group with a neighbor-specific parameter.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-15 BGP Peer Group Example: Customer Connections

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-16 BGP Peer Group Example: BGP Route Reflector

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-17 BGP Peer Group Example: Edge Router at a Peering Point

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-18 Monitoring Peer Groups show ip bgp peer-group [peer-group-name] router> Displays the definition of the specified peer group or all peer groups show ip bgp peer-group [peer-group-name] summary router> Displays summary status of all neighbors in the peer group clear ip bgp [peer-group-name] [[soft] in|out] router# Clears BGP session with all peer group members

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-19 Monitoring Peer Groups (Cont.)

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-20 Monitoring Peer Groups (Cont.) The printout is identical to a show ip bgp summary printout but displays only neighbors that are members of the specified peer group.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-21 Monitoring Peer Groups (Cont.)

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-22 Summary Peer groups were introduced to ease the burden of configuring a large number of neighbors with identical or similar parameters. The use of peer groups can significantly reduce the increased router CPU load when there are more neighbors of a router. Peer groups have limitations because of the way that they are used to build BGP updates: Per-neighbor BGP parameters that affect outbound updates cannot be changed for peer group members, and IBGP and EBGP neighbors cannot be mixed in a peer group. Cisco IOS software optimizes the outgoing routes by running through the outgoing filters and route-maps only once and then replicating the results to each of the peer group members.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-23 Summary (Cont.) The BGP Dynamic Update Peer-Groups feature separates BGP update generation from peer-group configuration, using an algorithm that dynamically calculates and optimizes update-groups of neighbors that share the same outbound policies and can share the same update messages. Peer templates improve the flexibility and enhance the capability of neighbor configuration. Peer templates also provide an alternative to peer group configuration and overcome some limitations of peer groups. To configure BGP peer groups on Cisco IOS routers, create a BGP peer group, specify parameters for the BGP peer group, create a BGP neighbor, and then assign a neighbor to the peer group. You can use the show ip bgp peer-group command to monitor information about BGP peer groups and the clear ip bgp command to reset the BGP sessions with all the members of a peer group.

© 2005 Cisco Systems, Inc. All rights reserved. BGP v3.2—7-24