Date: Mon, 6 Dec 2021 10:00:19 -0800 (PST) From: "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net> To: "Bjoern A. Zeeb" <bz@FreeBSD.org> Cc: Lutz Donnerhacke <lutz@donnerhacke.de>, John Hay <jhay@meraka.org.za>, 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: <202112061800.1B6I0JuR065662@gndrsh.dnsmgr.net> In-Reply-To: <alpine.BSF.2.00.2112052148170.68830@ai.fobar.qr>
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> On Sun, 5 Dec 2021, Lutz Donnerhacke wrote: > > > 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). > > That has always be a very Linux-y approach; FreeBSD should not ARP > for any subnet it is not connected to (at least it didn't use to). > > I think you could add a host route in the past and then it would but > with the current IPv4 I couldn't even say from quickly looking what it > would do. route add foo -direct > > > >> 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". > > No, no in this context; it talks about about the "internet source > address of a datagram" and hence network == Layer 3 as that is where > internet addresses belong. No one would phrase it anymore like this > these days but in those days ... Concur, in RFC's "network" almost always refers to a layer 2 domain, the word "link" is use refers to a layer 2 domain. > Bjoern A. Zeeb r15:7 -- Rod Grimes rgrimes@freebsd.org
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