3.7.a Describe implement and troubleshoot peer relationships

3.7.a [i] Peer-group, template


R3#sh run | b router bg
router bgp 123
bgp log-neighbor-changes
neighbor my-as peer-group
 neighbor my-as remote-as 123
 neighbor my-as update-source Loopback1
neighbor peer-group my-as
 neighbor password cisco
neighbor peer-group my-as

the peer group is called my-as (or my ass)

the point of the peer group is to limit configuration keystrokes by grouping like values together…

in the case above the similar features are ibgp AS and update-source, then the neighbors are assigned to the peer group…

note the individual statement for neighbor as r3 is using md5 authentication only with r1…

R1(config)#router bgp 123
R1(config-router)#neighb pass chicso
*Mar  8 10:32:45.243: %TCP-6-BADAUTH: Invalid MD5 digest from to tableid – 0
*Mar  8 10:32:46.643: %TCP-6-BADAUTH: Invalid MD5 digest from to tableid – 0
R1(config-router)#neighb pass cisco
R1(config-router)#do sh ip bgp summ
BGP router identifier, local AS number 123
BGP table version is 1, main routing table version 1

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd         4          123       4       5        1    0    0 00:02:15                                    0         4          123       4       5        1    0    0 00:02:17                                    0     4          678       0       0        1    0    0 never                            Idle

according to wendell:

BGP peer groups do not allow any new BGP configuration settings; they
simply allow you to group BGP neighbor configuration settings into a group, and then apply that set of settings to a neighbor using the neighbor peer-group command. Additionally, BGP builds one set of Update messages for the peer group, applying routing policies for the entire group—rather than one router at a time—thereby reducing some BGP processing and memory overhead.