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BGP peer-group vs peer-session

Can some body explain the difference between peer-group and template peer-session/peer-policy commands of BGP?
1 Solution
Cisco's configuration guides provide the details:

Templates offer more flexibility.  Grouping was an earlier feature, and some attributes cannot be bound to a BGP peer group that can be used with templates.

A peer can directly inherit from one session template.  A session template can inherent from another session template  in a hierarchical arrangement.
For example:   You can have a template A,  and a template B that is based on template A through inheretence (nesting).    Then a peer that template B is applied to,  will include properties defined in both template A and template B, with properties added in template B  overriding  defaults provided by template A.

This notion of  inheretence is unique to templates.   When you use peer groups, a peer is a member of one group, and there is no inheretence  or basing groups off one another.

The BGP update policy is different.   Updates for members of a peer group are grouped together  (at least on routers that do not support Dynamic update peer groups).

This reduces CPU usage on the router, due to BGP scan, but results in restrictions, including:
* All neighbors in the same peer group have to share the same outbound routing policies
* All neighbors in the same peer group must have the same address family.
You cannot have an IPv4 peer and an IPv6 peer in the same peer group.
But if using peer templates,  they could use the same template.

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