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BGP Optimization, Peer Groups, Peer Templates, Route Dampening and Route Refresh - part4

This is part 4 of 4. My shortish summarized version of Cisco BGP Optimization, Peer Groups, Peer Templates, Route Dampening and Route Refresh.




Optimizations:

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ip tcp path-mtu-discovery (default is 536 bytes)
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interface Gi0/0
hold-queue 1000 in (default is 75 packets)

The BGP process scans the BGP table for changes for triggered updates.

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router bgp 100
  bgp scan-time <SECONDS> (default is 60 seconds)
  neighbor x.x.x.x advertisement-interval <SECONDS> (default is 30 seconds eBGP and 5 seconds iBGP)

Setting a maximum prefix limit:

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neighbor x.x.x.x maximum-prefix <NUM>

show ip bgp summary (State/PfxRcd)

Peer Groups:

  • Can be used to make neighbor configurations more effecient by using templates.
  • CANNOT combine iBGP and eBGP peer-groups

Example:

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router bgp 100
  neighbor MY_PEERGROUP peer-group
  neighbor MY_PEERGROUP update-source loopback0
  neighbor ...............
  neighbor x.x.x.x peer-group MY_PEERGROUP

show ip bgp peer-group

Peer Templates:

  • Generates single outbound update for all peers.
  • Individual configurations supported for inbound updates.

Example: (peer-session)

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router bgp 100
  template peer-session MYTEMPLATE1
    timers 30 300
  exit-peer-session
  
  template peer-session MYTEMPLATE2
    remote-as 200
    inherit peer-session MYTEMPLATE1
  exit-peer-session

  neighbor x.x.x.x inherit peer-session MYTEMPLATE1

show ip bgp template peer-session

Example: (peer-policy)

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router bgp 100
  template peer-policy MYTEMPLATE1
    prefix-list MYPREFIXLIST in
  exit-peer-policy

  neighbor x.x.x.x inherit peer-policy MYTEMPLATE1

show ip bgp template peer-policy

Route Dampening:

  • Controls flapping routes
  • Default 5 seconds WAIT for iBGP and 30 seconds WAIT for eBGP
  • Flapping route will be dampened after 3 successive flaps and for 30 minutes default.
  • Every route will receive the following by default:
    • Penalty = 1000
    • Suppress Limit = 750
    • Reuse limit = 750
  • Decay algorithm = 15 minutes (Half-life)
  • Maximum penalty = 4x decay algorithm = 60 minutes

Example:

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router bgp 100
  bgp dampening 10 1000 4000 255

clear ip bgp dampening x.x.x.x x.x.x.x (resets dampening)
clear ip bgp x.x.x.x flap-statistics (resets dampening)

Refreshing neighbor changes without tearing down the BGP session:

  • Outbound soft reconfigure = clear ip bgp x.x.x.x soft-out (NO extra configuration needed)
  • Inbound soft reconfigure = clear ip bgp x.x.x.x soft-in (MUST be pre-configured: neighbor x.x.x.x soft-reconfiguration inbound)
  • Route refresh ONLY = clear ip bgp x.x.x.x soft-in (WITHOUT neighbor config as above)

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