Hi Joe,
In my understanding, RFC4821 does not adequately address scenarios where the
probe packets may (for legitimate reasons) take a different path than the data
packets, e.g., when Equal-Cost Multi Path (ECMP) is present. This is not only a
consideration for tunnels, but also for path MTU sharing between transport layer
sessions where an MTU learned by a first session is shared with a second session
bound for the same destination. In that case, the probes of the first session
may
take a different path than the data packets of the second session, and a black
hole is possible.
Thanks - Fred
fred(_dot_)l(_dot_)templin(_at_)boeing(_dot_)com
-----Original Message-----
From: tsv-area [mailto:tsv-area-bounces(_at_)ietf(_dot_)org] On Behalf Of Joe
Touch
Sent: Tuesday, February 07, 2017 10:26 AM
To: otroan(_at_)employees(_dot_)org; Eggert, Lars <lars(_at_)netapp(_dot_)com>
Cc: tsv-area(_at_)ietf(_dot_)org; 6man-chairs(_at_)ietf(_dot_)org; 6man WG
<ipv6(_at_)ietf(_dot_)org>; ietf(_at_)ietf(_dot_)org;
draft-ietf-6man-rfc1981bis(_at_)ietf(_dot_)org
Subject: Re: Last Call: <draft-ietf-6man-rfc1981bis-04.txt> (Path MTU
Discovery for IP version 6) to Internet Standard
On 2/4/2017 10:40 AM, otroan(_at_)employees(_dot_)org wrote:
Lars,
My apologies: my comments were probably misleading. Certainly, this
document is simply RFC1981 to Std, and hence recommending RFC4821 would
be kind of ou of scope, here.
That say, one might wonder to what extent, and for the general Internet,
RFC1981 can be considered succesful (given the filtering of ICMP
messages). -- i.e., at this point in time you wouldn't rely on RFC1981
(icmp-based pmtud) for path-mtu discovery.
What Fernando said: I'm certainly not opposed to lifting this to Standard,
but it is painting an incorrect picture - PLPMTUD is de facto
mandatory these days, and has been for years.
While I'm all in favour of PLMTUD. It doesn't seem like a complete solution.
PMTUD on the other hand supports all protocols on top of IP.
If by "supports" you mean "doesn't work", then yes. That's why we now
have PLPMTUD.
Looking just at our specifications, we cannot state that PLMTUD can replace
PMTUD. Take RFC2473 (IPv6 tunnelling) for example.
See draft-ietf-intarea-tunnels, esp. v03 Section 5.5.2
(yes, that doc has expired while we're preparing the 04 update, which
should be issued shortly)
Joe