Re: Multiple BFD sessions over one path

[Dave Katz <dkatz at juniper.net>]

The point of the text in 1hop is that there isn't any use in having  
more than one session over a "path", and in any case it can't be done  
because there would be no way to demultiplex the initial packet of  
multiple sessions on the same "path" (because the first packet carries  
discriminator 0).

But diffserv is essentially a tunnel of sorts;  each service level has  
potentially different forwarding characteristics, so it may be useful  
to run BFD over more than one level (and the sessions can be  
demultiplexed because they are contextualized by the diffserv level).

Essentially, each diffserv service level is considered to be a  
separate path, not unlike GRE or IPsec or what have you.

Implementors are free to do as they please;  the point of the text is  
to not preclude creative use of BFD where it can be useful.

--Dave



On Sep 18, 2009, at 9:27 PM, Mach Chen wrote:

> Hi,
>
> After reading the two drafts (draft-ietf-bfd-generic-05 and draft- 
> ietf-bfd-v4v6-1hop-09), I have some confusion about the session  
> limitation over a specific network-layer path.
>
> Section 2 of draft-ietf-bfd-v4v6-1hop-09 says:
> "Each BFD session between a pair of systems MUST traverse a separate  
> network-layer path in both directions..."
>
> But section 6 of draft-ietf-bfd-generic-05 says:
> "...if multiple differentiated services [DIFFSERV] are being  
> operated over IPv4, an independent BFD session may be run for each  
> service level...", this implicates that there may be mulitiple BFD  
> sessions over one network-layer(ipv4) path, but it seems that this  
> is not allowed in draft-ietf-bfd-v4v6-1hop-09. How to understand  
> this conflict?  or do I miss something?
>
> Best regards,
> Mach Chen