The BGP dynamic peer-group feature identifies peers that have same outbound policy and optimizes update generation and replication across those peers. Dynamic peer-groups separate the peer-group configuration from update-replication through two features-
Peer Templates
Update groups
Peer Templates
The configuration feature of peer templates allows a set of configuration options to be applied to a set of neighbors. Peer templates are reusable and support inheritance. There are two types of peer templates-
Peer session templates
Peer policy templates
Peer session templates are used to build a template of general session configuration. It does not include any policy-type attributes. It can be configured as below and supports these commands-
Peer session template
Edge-1(config)# router bgp 100
Edge-1(config-router)# template ?
peer-policy Template configuration for policy parameters
peer-session Template configuration for session parameters
Edge-1(config-router)# template peer-session ?
WORD Name of peer-session template
Edge-1(config-router)# template peer-session GENERAL_SESSION
Edge-1(config-router-stmp)#?
BGP peer-policy configuration commands:
allowas-in Accept as-path with my AS present in it
default Set a command to its defaults
description Neighbor specific description
disable-connected-check One-hop away EBGP peer using loopback address
ebgp-multihop Allow EBGP neighbors not on directly connected
networks
exit-peer-session Exit from template configuration mode
fall-over session fall on peer route lost
inherit Inherit a template
local-as Specify a local-as number
no Negate a command or set its defaults
password Set a password
remote-as Specify a BGP neighbor
shutdown Administratively shut down this neighbor
timers BGP per neighbor timers
translate-update Translate Update to MBGP format
transport Transport options
ttl-security BGP ttl security check
update-source Source of routing updates
version Set the BGP version to match a neighbor
Peer policy templates are used to build a template of policy information. This includes manipulating actual BGP prefix information, such as filtering, capabilities and route-reflection. Peer policy template is configured as follows and support these commands-
Peer policy template
Edge-1(config)# router bgp 100
Edge-1(config-router)# template peer-policy GENERAL_POLICY
Edge-1(config-router-ptmp)#?
BGP peer-policy configuration commands:
advertisement-interval Minimum interval between sending BGP routing updates
allowas-in Accept as-path with my AS present in it
as-override Override matching AS-number while sending update
capability Advertise capability to the peer
default Set a command to its defaults
default-originate Originate default route to this neighbor
distribute-list Filter updates to/from this neighbor
dmzlink-bw Propagate the DMZ link bandwidth
exit-peer-policy Exit from template configuration mode
filter-list Establish BGP filters
inherit Inherit a template
maximum-prefix Maximum number of prefixes accepted from this peer
next-hop-self Disable the next hop calculation for this neighbor
next-hop-unchanged Propagate the iBGP paths's next hop unchanged for
this neighbor
no Negate a command or set its defaults
prefix-list Filter updates to/from this neighbor
remove-private-as Remove private AS number from outbound updates
route-map Apply route map to neighbor
route-reflector-client Configure a neighbor as Route Reflector client
send-community Send Community attribute to this neighbor
soft-reconfiguration Per neighbor soft reconfiguration
unsuppress-map Route-map to selectively unsuppress suppressed routes
weight Set default weight for routes from this neighbor
Update groups:
Update groups handle update replication. The router builds update groups dynamically based on examining the outbound policy of the configured BGP sessions. BGP peers with same outbound policies are assigned to same update group. No configuration is required for this feature.
Network topology:
This example will demonstrate peer session and peer policy templates on Edge-1 router. Edge-1 router creates a GENERAL_SESSION peer-session template which includes password and version. Edge-1 router also creates an INTERNAL_SESSION peer-session template for iBGP peers which includes iBGP specific configuration and also inherit GENERAL_SESSION settings. And lastly, it creates an EXTERNAL_SESSION template for eBGP peers and inherit GENERAL_SESSION settings too.
NOTE: Any configuration at the neighbor level takes precedence over template settings.
peer session templates on Edge-1
router bgp 100
template peer-session GENERAL_SESSION
password cisco
version 4
exit-peer-session
!
template peer-session INTERNAL_SESSION
inherit peer-session GENERAL_SESSION
remote-as 100
update-source Loopback 0
timers 30 90
exit-peer-session
!
template peer-session EXTERNAL_SESSION
inherit peer-session GENERAL_SESSION
remote-as 200
exit-peer-session
!
neighbor 2.2.2.2 inherit peer-session INTERNAL_SESSION
neighbor 3.3.3.3 inherit peer-session INTERNAL_SESSION
neighbor 10.2.2.2 inherit peer-session EXTERNAL_SESSION
!
The show ip bgp replication command displays update replication statistics for update-groups. Core-1 and Core-2 routers are part of the same update-group.
show ip bgp replication
Edge-1# show ip bgp replication
Current Next
Index Members Leader MsgFmt MsgRepl Csize Version Version
1 2 2.2.2.2 2 2 0/1000 6/0
2 1 10.2.2.2 1 0 0/100 6/0
The show ip bgp update-group command displays update-group statistics.
show ip bgp update-group
Edge-1# show ip bgp update-group
BGP version 4 update-group 1, internal, Address Family: IPv4 Unicast
BGP Update version : 6/0, messages 0
Update messages formatted 2, replicated 2
Number of NLRIs in the update sent: max 3, min 2
Minimum time between advertisement runs is 0 seconds
Has 2 members (* indicates the members currently being sent updates):
2.2.2.2 3.3.3.3
BGP version 4 update-group 2, external, Address Family: IPv4 Unicast
BGP Update version : 6/0, messages 0
Update messages formatted 1, replicated 0
Number of NLRIs in the update sent: max 3, min 3
Minimum time between advertisement runs is 30 seconds
Has 1 member (* indicates the members currently being sent updates):
10.2.2.2
Advertise only Default-route to Core-1:
Now, a condition arises that only default-route be advertised to Core-1 router while full BGP table be advertised to Core-2 router. Admittedly, this can be achieved through various ways, however, peer policy template is also one of the options.
peer policy template on Edge-1
router bgp 100
template peer-policy DEFAULT_ONLY
filter-list 20 out
default-originate
exit-peer-policy
neighbor 2.2.2.2 inherit peer-policy DEFAULT_ONLY
!
ip prefix-list 20 seq 5 deny 0.0.0.0/0 le 32
!
The show ip bgp replication command shows that Core-1 router is dynamically assigned to another update-group since its outbound policy changed.
show ip bgp replication
Edge-1# show ip bgp replication
Current Next
Index Members Leader MsgFmt MsgRepl Csize Version Version
1 1 10.2.2.2 1 0 0/100 6/0
2 1 3.3.3.3 2 0 0/100 6/0
3 1 2.2.2.2 0 0 0/100 6/0
The show ip bgp update-group command also shows Core-1 router in a different update-group.
show ip bgp update-group
Edge-1# show ip bgp update-group
BGP version 4 update-group 1, external, Address Family: IPv4 Unicast
BGP Update version : 6/0, messages 0
Update messages formatted 1, replicated 0
Number of NLRIs in the update sent: max 3, min 3
Minimum time between advertisement runs is 30 seconds
Has 1 member (* indicates the members currently being sent updates):
10.2.2.2
BGP version 4 update-group 2, internal, Address Family: IPv4 Unicast
BGP Update version : 6/0, messages 0
Update messages formatted 2, replicated 0
Number of NLRIs in the update sent: max 3, min 2
Minimum time between advertisement runs is 0 seconds
Has 1 member (* indicates the members currently being sent updates):
3.3.3.3
BGP version 4 update-group 3, internal, Address Family: IPv4 Unicast
BGP Update version : 6/0, messages 0
Outgoing update AS path filter list is 20
Unconditional default-originate
Update messages formatted 0, replicated 0
Number of NLRIs in the update sent: max 0, min 0
Minimum time between advertisement runs is 0 seconds
Has 1 member (* indicates the members currently being sent updates):
2.2.2.2
The template settings can be viewed using show ip bgp template {peer-session | peer-policy} command.
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