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

paheeradan.nagulan · ‎01-24-2023

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).

MHM Cisco World · ‎01-27-2023

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

View solution in original post

MHM Cisco World · ‎01-24-2023

are
EEM + IP SLA for BGP
is OK for you ?

paheeradan.nagulan · ‎01-25-2023

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?

Harold Ritter · ‎01-25-2023

Hi @paheeradan.nagulan ,

Reducing the bgp timers will certainly help. At the the end it all depends what convergence time you are expecting.

Regards,

Regards,
Harold Ritter, CCIE #4168 (EI, SP)

David Ruess · ‎01-24-2023

Hello,

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.

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus9000/sw/6-x/interfaces/configuration/guide/b_Cisco_Nexus_9000_Series_NX-OS_Interfaces_Configuration_Guide/b_Cisco_Nexus_9000_Series_NX-OS_Interfaces_Configuration_Guide_chapter_0101.html#...

Hope that helps

-David

Harold Ritter · ‎01-24-2023

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).

Regards,

Regards,
Harold Ritter, CCIE #4168 (EI, SP)

David Ruess · ‎01-24-2023

Yeah I tried to skim the documentation for it but couldn't find it. Thank you for the clarification.

paheeradan.nagulan · ‎01-25-2023

Thanks for the suggestion!

MHM Cisco World · ‎01-25-2023

check my below Lab and comment

paheeradan.nagulan · ‎01-25-2023

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.

MHM Cisco World · ‎01-25-2023

I will share case2 after 1 hr.

MHM Cisco World · ‎01-25-2023

check my below lab and comments

paheeradan.nagulan · ‎01-26-2023

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?

Harold Ritter · ‎01-25-2023

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.

Regards,

Regards,
Harold Ritter, CCIE #4168 (EI, SP)

paheeradan.nagulan · ‎01-25-2023

Thanks @Harold Ritter for confirming it.