Unanswered Question
Feb 9th, 2007

Welcome to the Cisco Networking Professionals Ask the Expert conversation. This is an opportunity to discuss with Cisco expert Aamer Akhter about Bidirectional Forwarding Detection (BFD) and how it is used to quickly detect IP forwarding failures. Aamer is currently working as a technical marketing engineer in the areas of Network Virtualization, Wan-Optimization and router instrumentation. He is CCIE certified (# 4543). Aamer is also the vice-chair of the Certification Work Group of the MFA Forum.

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devang_etcom Fri, 02/09/2007 - 14:36


which protocols supprot BFD and perticular on which platform i can enable BFD?

is it good idea for enabling on the WAN connectivity? and what is the minimum bandwidth requirement for it?

and i also want to know the benifites of the BFD feature in the Transport Network like SONET SDH...?

aakhter Mon, 02/12/2007 - 14:41

BFD for WAN is an ideal placement. Keep in mind that for IOS today only Ethernet interfaces are supported. The bandwidth per packet is extremely small (less 100B), but will depend on your rate of packet transmission.

Protocols currently supported in IOS: OSPF, ISIS, BGP (single hop)

For IOS-XR, both POS and Ethernet interfaces are supported.

Protocols currently supported in IOS-XR: OSPF, ISIS, BGP (single hop), statics, MPLS-FRR

BFD is not only important in cases where there is a L2 switch in between your L3 routers, but is useful for other cases also (as in SONET/SDH that already provide Loss of Signal indication) where a check of the forwarding plane can be useful.

devang_etcom Mon, 02/12/2007 - 14:48

hi akhter,

thank you very much for your reply...

now one more thing is: BFD works at which layer?

and will you please provide some link where i can find some confugiration or some explanation with SONET/SDH/ATM... as right now i am working for the same topology and would like to test it...

and also want to understand the BFD between two devices if they are running the HSRP... like will BFD helpfull to detect the fast failover when you have HSRP in your network?

thanks and regards


sabuz_banik Mon, 02/12/2007 - 02:03


can u provide information about e-guide book to study for Cisco 642-381 exam? Plz i am in big problem for this exam, help me out from this problem.

with thanks


b.henshaw Tue, 02/13/2007 - 05:18

Are there plans to support BFD in the 3750 Metro switches? BFD would be ideal in these switches as the only option we have for improved failure detection at this point in time is fast OSPF timers, where OSPF is in use.

BFD seems to be supported in a limited range of hardware at the moment.

aakhter Tue, 02/13/2007 - 07:26


BFD is on the current year (2nd half) roadmap for the 3750.

Please be advised that roadmaps are subject to change and it is highly recommended to notify your cisco representative about this need so that it can be correctly prioritized.

prakashj Sun, 02/18/2007 - 22:59

Hi Aamer,

I want to run BFP for OSPF over an EoMPLS tunnel, ie over SP network. Can I still get subsecond convergence? Service provider is doing policing at their end.



jiangu Tue, 02/20/2007 - 21:38

There could be a problem with your application, BFD hello packet is UDP packet with TTL set to 255, if MPLS changes TTL, the BFD won't form neighbor relationship.

BFD is intended to work over directly connected L3 link.

aakhter Wed, 02/21/2007 - 05:24


Technically, there is no reason why BFD would not work over EoMPLS. The TTL problem pointed out earlier does not apply as EoMPLS is at layer 2 and the IP TTL of the customer traffic is not decremented.

Couple of things that I would be wary of:

* delay characteristics of the path (lets say the path in the SP changes all of a sudden and the packets your were expecting start arriving later than expected)

* policing on SP side. You'll need to make sure that you have a shaping policy implemented that prevents the SP from dropping your traffic (or get agreement from SP not to drop prec 6 traffic first, as that is what BFD will be under). Your shaping policy should make sure that BFD has a clear policy that will allow it to send packets without worry of dropping.


prakashj Thu, 02/22/2007 - 00:57

Thanks Amer...We tested it and it is working fine...(just one drop..:) :)


aakhter Thu, 02/22/2007 - 06:29


Please make sure that the detect time you are using takes into account a minor reconvergence within the SP cloud. Such a reconvergence (could be a couple of seconds or sub-seconds depending on what the SP has done) would be be a indication of a major failure at your level and you may not want to take corrective action in these cases.

saeedalam Fri, 02/23/2007 - 01:34

hi , i m looking additional infomation of the following poduct , CVPN3000-UKITA-K9.




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