[j-nsp] BFD Distributed Mode for IPv6

[Gert Doering]

Hi,

On Wed, Oct 03, 2018 at 10:51:08AM +0100, James Bensley wrote:
> On Wed, 3 Oct 2018 at 10:13, Mark Tinka <mark.tinka at seacom.mu> wrote:
> > On 3/Oct/18 11:09, adamv0025 at netconsultings.com wrote:
> >
> > If you'd have separate ISIS process for v6 would it be possible to spin up a
> > separate/dedicated BFD process for that ISIS?
> 
> Unless I'm mistaken BFD isn't "multi-tenant", so only one set of BFD
> packet exchanges can exist per-interface, there is no support for
> multiple BFD session on the same interface (by which I mean layer 2
> broadcast domain in the case of sub-interfaces). 

If you run different IGPs for IPv4 and IPv6, you'll have independent
BFD sessions for IPv4 and IPv6.  Just the "dual-stack ISIS hooking into
BFD" won't give you "dual BFD" - since there is a common ISIS adjacency
for all transported routing information (ISIS is signalled neither over
IPv4 nor IPv6...) there is no other way than "if BFD breaks, assume
the interface is down and tear down the ISIS adjacency".

> This kind of makes
> sense as BFD is supposed to test for unidirectional communication
> failure of the physical link (the fact that it runs in both directions
> gives bidirectional failure detection). So we can run BFDv4 and/or
> BFDv6 on an interface but only one instance per-interface otherwise
> you'd need to negotiate different port numbers for the different
> instances on the same interface?

A listening socket can listen on "just IPv4, port <x>" just fine, while
a second socket can take "just IPv6, port <x>".

gert

-- 
"If was one thing all people took for granted, was conviction that if you 
 feed honest figures into a computer, honest figures come out. Never doubted 
 it myself till I met a computer with a sense of humor."
                             Robert A. Heinlein, The Moon is a Harsh Mistress

Gert Doering - Munich, Germany                             gert at greenie.muc.de
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