You Are Here: Home » Router » -Router Cisco » BGP Update Generation – Part 2

BGP Update Generation – Part 2

BGP Update Generation – Part 2

Traditional peer-groups  were introduced to improve CPU utilization, and make configuration less redundant and easy to read. However, the way peer-groups work, the common attributes must be replicated across peer-groups. Hence, redundant configuration is not completely avoided and the ability to have session-specific configuration is limited.

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-

  1. Peer session templates
  2. 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.

About The Author

harrychanputra.web.id

Number of Entries : 295

Leave a Comment

© 2011 Powered By Wordpress, Goodnews Theme By Geeks Docuementation

Scroll to top