Re: [babel] Investigating ICMP behaviour of the Linux kernel in IPv6-only mode
Toke Høiland-Jørgensen <toke@toke.dk> Tue, 15 June 2021 12:59 UTC
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From: Toke Høiland-Jørgensen <toke@toke.dk>
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To: Juliusz Chroboczek <jch@irif.fr>
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Date: Tue, 15 Jun 2021 14:59:18 +0200
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Subject: Re: [babel] Investigating ICMP behaviour of the Linux kernel in IPv6-only mode
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Juliusz Chroboczek <jch@irif.fr> writes: >> I've submitted a patch[0] to make the kernel fall back to the dummy >> address specified in RFC7600. > >> [0] https://lore.kernel.org/netdev/20210615110709.541499-1-toke@redhat.com/ > > Thanks a lot, Toke. After spending a few hours going through the maze > that is the Linux ICMP code, I decided I needed help from somebody > competent. You're welcome! And yeah, that code does offer all the best in kernel-style indirection :) >> What I found was that the kernel is perfectly happy to send out ICMP >> messages with an all-zero source address if no real address is >> configured on any interface. > > The question is -- what is the behaviour of PMTUd implementations when > they receive such an ICMP packet? Do they reduce the PMTU, or do they > drop the ICMP as obviously incorrect? As far as I can tell by poking around in the code, the kernel will generally drop packets with an all-zero source; see for instance this check: https://elixir.bootlin.com/linux/latest/source/net/ipv4/route.c#L2139 I'll leave actually testing this as an exercise for the reader ;) > I'm going to merge the v4via6 code (I've reviewed it, and I think it > needs a few fixes), and going to enable it automatically if there's at > least one IPv4 address somewhere, including the loopback interface. > Thanks a lot for the information above, that's very helpful. Cool! You're welcome :) -Toke
- [babel] Investigating ICMP behaviour of the Linux… Toke Høiland-Jørgensen
- Re: [babel] Investigating ICMP behaviour of the L… Juliusz Chroboczek
- Re: [babel] Investigating ICMP behaviour of the L… Toke Høiland-Jørgensen