01-24-2023 03:26 PM
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).
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01-27-2023 01:02 PM - last edited on 02-21-2023 01:20 AM by Translator
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
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
01-24-2023 03:36 PM
EEM + IP SLA for BGP
is OK for you ?
01-25-2023 06:09 AM
That's a good suggestion. I was thinking along the ways of changing BGP attributes such as bgp timers. Do you think that will help in this case?
01-25-2023 06:21 AM
Hi @paheeradan.nagulan ,
Reducing the bgp timers will certainly help. At the the end it all depends what convergence time you are expecting.
01-24-2023 04:28 PM
I cant remember (and cant test at the moment) But BFD echo mode might work. I am not sure if BFD needs to be enabled on the remote interface but echo mode is basically echo my BFD packet back to me (so I would assume only 1 side is needed). This is done to reduce the overhead of actually processing the packet bidirectionally. Maybe try configuring echo mode on your interface and see if it registers the protocol and can be used.
Hope that helps
01-24-2023 05:45 PM
Hi @David Ruess ,
BFD needs to be configured on both ends. Once it is configured on both end, you might then decide to configure the echo mode on one side only (asynchronous).
01-24-2023 05:47 PM
Yeah I tried to skim the documentation for it but couldn't find it. Thank you for the clarification.
01-25-2023 06:10 AM
Thanks for the suggestion!
01-25-2023 06:41 AM - edited 01-26-2023 07:24 AM
check my below Lab and comment
01-25-2023 07:12 AM
Hi @MHM Cisco World,
Thank you for the detailed lab. Highly appreciate it. Yes, it makes sense to use BFD echo. But in my case, the ISP mentioned that they won't support BFD. My understand is to run BFD echo on my side, I need to configure BFD neighborship on both ends which is not possible in my case. So I was trying to find other means of speeding up the BGP convergence? Also there will be a L2 in between us and the ISP.
01-25-2023 07:21 AM
I will share case2 after 1 hr.
01-25-2023 08:23 AM - edited 01-26-2023 07:24 AM
check my below lab and comments
01-26-2023 12:49 AM
Hi @MHM Cisco World ,
Thanks for the detailed analysis. Appreciate it. My case is similar to Case A(A- one side is run BFD echo and other DO NOT run bfd). So are you thinking that running bfd ONLY ON my side(ISP won't support BFD) will be sufficient to detect the peer reachability?
01-25-2023 07:25 AM
Hi @paheeradan.nagulan ,
> My understand is to run BFD echo on my side, I need to configure BFD neighborship on
> both ends
Your understanding is correct. If the other side is not configured for BFD, configuring BFD echo on you side will not work.
01-25-2023 07:26 AM
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