3.7.a Describe implement and troubleshoot peer relationships

3.7.a [i] Peer-group, template

In older versions of Cisco IOS software, BGP update messages were grouped based on peer group configurations. This method of grouping neighbors for BGP update message generation reduced the amount of system processing resources needed to scan the routing table. This method, however, had the following limitations:

● All neighbors that shared the same peer group configuration also had to share the same outbound routing policies.

● All neighbors had to belong to the same peer group and address family. Neighbors configured in different address-families could not belong to different peer groups.

These limitations existed to balance optimal update generation and replication against peer group configuration. These limitations also caused the network operator to configure smaller peer groups, which reduced the efficiency of update message generation and limited the scalability of neighbor configuration.

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 capability of a peer template to inherit a configuration from another peer template.

There are two types of peer templates:

● Peer session templates are used to group and apply the configuration of general session commands that are common to all address family and Network Layer Reachability Information (NLRI) configuration modes.

● Peer policy templates are used to group and apply the configuration of commands that are applied within specific address-families and NLRI configuration modes.

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. With the configuration of the BGP Configuration Using Peer Templates feature and the support of the BGP Dynamic Update Peer-Groups feature, the network operator no longer needs to configure peer groups in BGP and can benefit from improved configuration flexibility and convergence.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Location 3747).  . Kindle Edition.