RE: Ability to detect swapped/merged LSPs

[[e-mail]]

Jeff,

Yes I agree, if BFD packets are being sent to the wrong place then we'll get a detection timeout and LSP ping can then be used to locate and diagnose the problem.

Regards,
Richard

> -----Original Message-----
> From: Jeffrey Haas [mailto:[e-mail]]
> Sent: 01 March 2005 17:56
> To: Spencer,R,Richard,XDE73 R
> Cc: [e-mail]
> Subject: Re: Ability to detect swapped/merged LSPs
> 
> 
> Richard,
> 
> I wont claim to be a MPLS expert, but I'm struck by the following:
> 
> On Tue, Mar 01, 2005 at 05:09:26PM -0000, 
> [e-mail] wrote:
> > If we get a swapped LSP (e.g. due to a corrupted forwarding 
> table or configuration error) then all BFD packets received 
> for the corresponding session will be dropped and the session 
> will be declared down as a detection timeout will occur. 
> However, if we get a merging defect where a node receives 
> both valid BFD packets in addition to invalid BFD packets 
> then this defect will not be detected.
> > 
> > In both cases, traffic is being forwarded onto the wrong 
> destination and therefore these defects need to be detected 
> and appropriate actions taken, e.g. raise an alarm and inform 
> the LSP source (using the appropriate BFD status code) that a 
> defect has occurred so that the source can stop forwarding 
> packets or switch over to an alternative path if one exists.
> 
> If we are receiving some other node's traffic due to forwarding
> corruption in the network, then wouldn't:
> a. The intended target of the session time out the session after the
>    appropriate interval?
> b. The node that is accidentally receiving the traffic may be 
> potentially
>    unable to respond due to the inherent unidirectionality of an LSP?
>    (In other words, the case where we do not have an LSP that would
>    permit us to respond.)
> 
> > By adding new processing rules and status codes, both of 
> these defects could be detected using BFD. An alternative 
> would be to use LSP ping but it would not provide the same 
> defect detection speed, i.e. an LSP might only get tested 
> using LSP pings every 30mins or maybe every hour in a large 
> network with hundreds of thousands of PWs/LSPs, as opposed to 
> BFD packets that can be sent every second.
> 
> It's probably worth reminding people that a session for BFD for
> MPLS LSPs must be bootstrapped using LSP-Ping.
> 
> Upon failure of a BFD session, it's very reasonable to use 
> LSP-Ping not
> only to reinitialize (or attempt to reinitialize) the BFD session, but
> also do further troubleshooting.
> 
> > Richard
> 
> -- 
> Jeff Haas 
> NextHop Technologies
>