Optimizing BGP convergence with non-directly connected peers

Good day!

Much time has passed since my last blog entry. And now, i have some time to make some new notes in my blog.

First, yesterday i had a task to optimize BGP convergence between to ISP. There are a lot o ways to optimize convergence, e.g tune BGP timers, bfd, neighbor failover, eem and etc. I 've decided to implement an EEM (Embedded Event Manager), cause with it i can tweak a lot of events, parameters and etc.

In out topology we have one edge router and two ISP non directly connected routers.

Than let's begin with BGP conf. Here is standard configuration for BGP peering

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router bgp 199430

 no bgp fast-external-fallover

 bgp log-neighbor-changes

 neighbor 172.16.0.1 remote-as 65002

 neighbor 172.16.0.1 description ISP A

 neighbor 192.168.0.1 remote-as 65003

 neighbor 192.168.0.1 description ISP B

 !

 address-family ipv4

  network 10.0.0.0 mask 255.255.255.0

  neighbor 172.16.0.1 activate

  neighbor 172.16.0.1 soft-reconfiguration inbound

  neighbor 192.168.0.1 activate

  neighbor 192.168.0.1 soft-reconfiguration inbound

 exit-address-family

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Next, lets configure ip sla monitoring and tracking of BGP peers

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track 1 ip sla 1 reachability

track 2 ip sla 2 reachability

ip sla 1

 icmp-echo 172.16.0.1 source-interface GigabitEthernet0/0

 frequency 5

ip sla schedule 1 life forever start-time now

ip sla 2

 icmp-echo 192.168.0.1 source-interface FastEthernet0/0/0

 frequency 5

ip sla schedule 2 life forever start-time now

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And finally, let's configure our EEM for tracking

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event manager applet ISP_A _DOWN

 event track 1 state down

 action 2.0 cli command "enable"

 action 2.1 cli command "config t"

 action 2.2 cli command "router bgp 65001"

 action 2.3 cli command "neighbor 172.16.0.1 shutdown"

event manager applet ISP_A_UP

 event track 1 state up

 action 2.0 cli command "enable"

 action 2.1 cli command "config t"

 action 2.2 cli command "router bgp 65001"

 action 2.3 cli command "no neighbor 172.16.0.1 shutdown"

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event manager applet ISPB_DOWN

 event track 2 state down

 action 2.0 cli command "enable"

 action 2.1 cli command "config t"

 action 2.2 cli command "router bgp 65001"

 action 2.3 cli command "neighbor 192.168.0.1 shutdown"

event manager applet ISPB_UP

 event track 2 state up

 action 2.0 cli command "enable"

 action 2.1 cli command "config t"

 action 2.2 cli command "router bgp 65001"

 action 2.3 cli command "no neighbor 192.168.0.1  shutdown"

-------------------

 

So, when 1 imcp packet is dropped by IP SLA, track service generate down messages and then EEM aplet, which is listening that tracking generates neighbor shutdown command, and when neighbor returns no UP states, EEM generates "no" command.

As I previously mentioned we can tweak lots of different parameters with such a bunch of tehnologies: ip sla, tracking and EEM.