Fred,
The following are failure modes for a GRE tunnel that includes ECMP/LAG:
- one ECMP/LAG member is dropping 100% of traffic, regardless of packet size
- one ECMP/LAG member is dropping all packets with MTU > N
Why is a probing mechanism OK to detect the first and not the second?
Ron
> -----Original Message-----
> From: Templin, Fred L [mailto:[email protected]]
> Sent: Thursday, April 23, 2015 11:59 AM
> To: Ronald Bonica; [email protected]
> Subject: RE: [Int-area] I-D Action: draft-ietf-intarea-gre-ipv6-07.txt
>
> Hi Ron,
>
> > -----Original Message-----
> > From: Ronald Bonica [mailto:[email protected]]
> > Sent: Thursday, April 23, 2015 8:18 AM
> > To: Templin, Fred L; [email protected]
> > Subject: RE: [Int-area] I-D Action: draft-ietf-intarea-gre-ipv6-07.txt
> >
> > Fred,
> >
> > If we can't probe a tunnel, we can't do GRE at all. Ever. Not with IPv4, not
> with IPv6, not with anything.
> >
> > MTU issues aside, before activating a tunnel, we must be certain that the
> tunnel can carry a 1-byte packet from GRE ingress to egress.
> > If we don't do that, we risk black-holing traffic. This is why nearly
> > all GRE implementations have some type of proprietary probing
> mechanism.
>
> I said earlier that I am fine with going ahead and probe with a small packet
> (I
> said 100 bytes, but 1 byte would be fine too) to see if the GRE ingress is
> alive.
> But, that probe does nothing to test for a particular MTU.
>
> > Beyond suggesting that the probing mechanism use a 1280-byte payload,
> > we have put the details of that probing mechanism out of scope for this
> document.
>
> If a 1280 byte probe (which becomes 1280+ENCAPS bytes following
> encapsulation) succeeds along one path of a multipath, but would have failed
> along another path, then there is possibility for black holing. And, there is
> no
> way for the ingress to know that there may be ECMP or LAG on the path to
> the egress. Hence, having the ingress probe for the purpose of minimum
> MTU detection is problematic if there may be some kind of multipath.
>
> Thanks - Fred
> [email protected]
>
> >
> >
> > Ron
> >
> > > -----Original Message-----
> > > From: Templin, Fred L [mailto:[email protected]]
> > > Sent: Wednesday, April 22, 2015 6:32 PM
> > > To: Ronald Bonica; [email protected]
> > > Subject: RE: [Int-area] I-D Action:
> > > draft-ietf-intarea-gre-ipv6-07.txt
> > >
> > > Hi Ron,
> > >
> > > So, this gives way to the following, which may be the best we can do
> > > if we can't probe:
> > >
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