Date: Sun, 5 Dec 2021 21:53:33 +0100 From: Lutz Donnerhacke <lutz@donnerhacke.de> To: John Hay <jhay@meraka.org.za> Cc: "Bjoern A. Zeeb" <bz@freebsd.org>, Kurt Jaeger <pi@freebsd.org>, freebsd-net <freebsd-net@freebsd.org> Subject: Re: why multi-hop icmp redirects to 0.0.0.0 on 13.0 ? Message-ID: <20211205205333.GC8367@belenus.iks-jena.de> In-Reply-To: <CAGv8uarUvftonP9LBOPmVksqTz7pFuQoUP2OJFG4BKBTex6VAw@mail.gmail.com> References: <Yast8d1dRd7ZFWr3@fc.opsec.eu> <alpine.BSF.2.00.2112041609520.68830@ai.fobar.qr> <YauV138P1xyB53Ja@fc.opsec.eu> <alpine.BSF.2.00.2112041633090.68830@ai.fobar.qr> <YaufYWCM9YOUG5Op@fc.opsec.eu> <alpine.BSF.2.00.2112041905270.68830@ai.fobar.qr> <alpine.BSF.2.00.2112051718171.68830@ai.fobar.qr> <CAGv8uarUvftonP9LBOPmVksqTz7pFuQoUP2OJFG4BKBTex6VAw@mail.gmail.com>
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On Sun, Dec 05, 2021 at 08:20:08PM +0200, John Hay wrote: > Something I have observed is that if you use FreeBSD 13 as a router with 2 > subnets on the same interface, it will generate redirects when hosts send > packets to the other subnet via the FreeBSD router. I think it is wrong. No, it's correct. > The host does not have a more direct way to get to the other subnet. The other host can arp for an address in a non-connected network on the interface because it's the same L2 domain. Hence the ICMP redirect is send out to provide the shortcut (skipping the router). > RFC792 > on page 13 does not talk about interfaces, but networks, "If G2 and the > host identified by the internet source address of the datagram are on the > same network...". "network" == "layer 2 domain".
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