IBGP and EBGP peer relationships:

  • Timers
    • Hold time – 180 seconds
    • Keepalive – 60 seconds
    • Default min time between advertisement runs – 30 seconds
  • Peer Groups
    • R1(config)#router bgp 100
    • R1(config-router)#neighbor <PEER GROUP NAME> peer-group
    • R1(config-router)#neighbor <PEER GROUP NAME> remote-as 100
    • R1(config-router)#neighbor <PEER GROUP NAME> update-source lo0
    • R1(config-router)#neighbor <PEER GROUP NAME> next-hop-self
    • Now apply below:
    • R1(config-router)#neighbor 10.1.1.1 peer-group <PEER GROUP NAME>
    • R1(config-router)#neighbor 192.168.1.1 peer-group <PEER GROUP NAME>
      • Efficient for smaller configurations.
      • Efficient for grouping configuration settings.
  • Session Templates
    • Anything relevant to the session
      • timers, remote-as, update-source, ebgp-multihop
    • R1(config-router)#template peer-session <NAME>
    • R1(config-router)#inherit peer-session <NAME OF ALTERNATE PEERSESSION>
    • R1(config-router)#remote-as 100
    • R1(config-router)#update-source lo0
    • R1(config-router)#exit-peer-session
    • R1(config-router)#neighbor 10.12.12.2 inherit peer-session <NAME>
  • Policy Templates
    • Anything relevant to policy
      • next-hop-self, filter-list; route-map
    • Inheritance is more flexible – inherit from up to 7 templates directly.
    • R1(config-router)#template peer-policy <NAME>
    • R1(config-router)#inherit peer-policy <NAME OF ALTERNATE PEERPOLICY>
    • R1(config-router)#next-hop-self
    • R1(config-router)#route-map <MAP NAME> out/in
    • R1(config-router)#exit-peer-policy
    • R1(config-router)#neighbor 10.12.12.2 inherit peer-policy <NAME>
  • Dynamic Neighbors
    • Allows BGP peering to a group of remote neighbors that are defined by a range of IP addresses.
    • R1(config-router)#neighbor <NAME> peer-group
    • R1(config-router)#neighbor <NAME> remote-as 100
    • R1(config-router)#bgp listen range 10.10.10.0/24 peer-group <NAME>
    • R1(config-router)#neighbor <NAME> transport connection-mode passive
      • Allows routers falling in subnet 10.10.10.0/24 to initiate BGP session with R1.
  • Network Command
    • Classful
      • R1(config)#router bgp 65000
      • R1(config-router)#network 1.0.0.0 – (classful, no mask required)
    • Classless
      • R1(config)#router bgp 65000
      • R1(config-router)#network 11.11.11.0 mask 255.255.255.0
  • Private AS Numbers
    • 64512-65535 – 16 bit numbers
    • 4200000000 – 4294967294 – 32 bit numbers

Cisco Best PATH SELECTION:

  • Highest Weight
  • Highest Local Pref
  • Prefer locally originated
  • Shortest AS_Path
  • Lowest origin type
  • Lowest MED
  • Prefer eBGP over iBGP
  • Lowest IGP metric to the BGP NEXT_HOP
  • Oldest path
  • Lowest Router ID Source
  • Min cluster list length
  • Lowest neighbor address

Well-Known, Mandatory Attributes:

  • AS-Path
  • Origin Code
    • i – IGP
    • e – EGP
    • ? – Redistribution
  • Next Hop Value

Well-Known, Discretionary

  • Local Preference
    • Outbound traffic decisions
    • Default – 100
    • Higher is better
    • iBGP Transmitted, does not pass anywhere else.
  • Atomic Aggregate

Optional, Transitive

  • Aggregator
  • Community

Optional, non-transitive

  • Multi-Exit Discriminator
    • Advertising Metric on prefix information.
    • Lower Value preferred
  • Originator ID
  • Cluster List
  • Cluster ID
  • Weight

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s