no BFD support for the BGP peering with ISP. Any suggestions?

[paheeradan.nagulan]

We have a DIA(Internet) circuit with our ISP at the Nexus 9k EDGE switch. We are doing BGP(Learning default route and advertising our public network to the internet) with them. The ISP mentioned that they don't support BFD(I was planning to use it with BGP. So the router will bring down the BGP process in case there is a link failure).  What are the recommendations that we can deploy to reduce the network convergence(Changing the BGP hold-down timer to a lower value etc).

[Georg Pauwen]

Hello,

I have not followed the entire thread, but if BFD is out of the question, what about BGP fast failover (bgp fast-external-failover) ?

What are you failing over to, by the way ?

[paheeradan.nagulan]

Hi @Georg Pauwen , that's a good recommendation. Yes, I'll be using BGP fast failover. Since we never know whether there will a layer 2 device in between our edge switch and the ISP device(We are doing BGP), do you think we should also change the BGP hold down timer to a lower value(just in case if something happens on the ISP side)? To give more context about our network setup, we are dual homed( 2  Nexus 9k switches, each has a DIA circuit with a different ISP. Also those 2 nexus 9k switches are doing BGP in between. So for some reason, if one switch loses it's connection to the ISP, IT WILL learn the default route through the other switch). 

[MHM Cisco World · Accepted solution]

I want to clear this topic for all Engineer want to apply BFD.



Note:- the BFD echo is enable by default and you can disable it by

NO bfd echo 

under interface 

Case1:- both router run BFD and as I mention above BFD echo is also run by default if we enable BFD under interface.

the BFD echo if not receive from neighbour it will down the BGP.

Case2:- both router run BFD and only one router disable bfd echo
to capture the traffic of BFD echo, do 
udp.port==3785 <<-filter in wireshark

capture BFD by using bfd <<- in filter of wireshark 

you can see that BFD control is exchange between two router but the bfd echo no exchange.

you can also see that fall-over is use in this case bfd control not bfd echo, when the neighbour not receive bfd control it down the BGP

Case3:- both router run BFD and both router disable bfd echo
you can see bfd echo not exchange why? we only disable bfd echo in one router, other must use bfd echo!!
answer is in cisco IOS XE

""The steps in this procedure show how to disable BFD echo mode without asymmetry—no echo packets will be sent by the router, and the router will not forward BFD echo packets that are received from any neighbor routers.""

and we can see that both router exchange the bfd control and depend on this packet,
if the packet not receive bfd control it will down the BGP

AFTER these three case, the Q come can I use BFD in one router? NO you can not

I run lab this time one router config with BFD and w/wo disable bfd echo and other router not run bfd at all
the result as you can see the bfd is down (not work) and to test is 
I shut down the interface in L2SW and router with BFD still remain the BGP up, i.e. bfd not work at all

[paheeradan.nagulan]

Hi @MHM Cisco World ,

Sorry for the delayed response. Thanks a lot for the detailed response. That answers my question.

[MHM Cisco World]

what can I use if BFD can not use ?
you can use EEM+IP SLA as I suggest before