nanog mailing list archives
Re: PMTUD for IPv4 Multicast - How?
From: Chris Marget <chris () marget com>
Date: Mon, 31 Aug 2015 17:34:27 -0400
It's not as obvious to me as it is to you. I mean, v6 *requires* exactly this behavior, so it can't be all that bad, can it?ICMP replies to multicast packets can cause ICMP "implosion". This is not a new discussion - see for instance http://mailman.nanog.org/pipermail/nanog/2012-June/048685.html
Thanks very much for the pointer to that discussion. "ICMP implosion" has been a helpful search term. The position taken there appears to boil down to: - The IPv6 requirement to generate "too big" messages *really is a problem* - RFC2463 should not have made the exception which allows sending these messages - Multicast PMTUD should not be a thing - Multicast speakers should send un-fragmentable minimum-sized packets I remain fuzzy on exactly the nature of the implosion problem. Is the concern that I might DDoS myself by sending un-fragmentable traffic? It's hard for me to recognize this as a problem, but I'm working on it. It seems to me that as a multicast speaker, the influx of ICMP errors is both desirable (I set DF because I intend to react) and under my control. It certainly beats sending minimum-sized packets, which appears to be the recommendation in the linked discussion. If somebody would be so kind as to detail the disastrous nature of the implosion, that would be helpful.
Current thread:
- PMTUD for IPv4 Multicast - How? Chris Marget (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Valdis . Kletnieks (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Chris Marget (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? sthaug (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? William Herrin (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Masataka Ohta (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Chris Marget (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Chris Marget (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Masataka Ohta (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Chris Marget (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Masataka Ohta (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Chris Marget (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Valdis . Kletnieks (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? William Herrin (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Masataka Ohta (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Mark Andrews (Aug 31)
- Re: PMTUD for IPv4 Multicast - How? Masataka Ohta (Aug 31)