Re: Multiple BFD sessions over one path

[Mach Chen <mach at huawei.com>]

Hi Dave,

Thanks for your response!

Based on your explanation, the point is whether there is a way to 
demultiplex the initial patcket, if there is, means no need to limit the BFD 
sesion. So, IMHO, it's better to clarify this in 1hop(since the draft is 
still in IESG review state, seems not too late to do it:-).

Have a good weekend!

Best regards,
Mach


--------------------------------------------------
From: "Dave Katz" <dkatz at juniper.net>
Sent: Saturday, September 19, 2009 2:39 PM
To: "Mach Chen" <mach at huawei.com>
Cc: <rtg-bfd at ietf.org>
Subject: Re: Multiple BFD sessions over one path

> 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