From nobody Mon Dec 06 18:00:19 2021 X-Original-To: freebsd-net@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 8468318CC273 for ; Mon, 6 Dec 2021 18:00:34 +0000 (UTC) (envelope-from freebsd-rwg@gndrsh.dnsmgr.net) Received: from gndrsh.dnsmgr.net (br1.CN84in.dnsmgr.net [69.59.192.140]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4J7B6p09g9z3rdd; Mon, 6 Dec 2021 18:00:33 +0000 (UTC) (envelope-from freebsd-rwg@gndrsh.dnsmgr.net) Received: from gndrsh.dnsmgr.net (localhost [127.0.0.1]) by gndrsh.dnsmgr.net (8.13.3/8.13.3) with ESMTP id 1B6I0KtC065663; Mon, 6 Dec 2021 10:00:20 -0800 (PST) (envelope-from freebsd-rwg@gndrsh.dnsmgr.net) Received: (from freebsd-rwg@localhost) by gndrsh.dnsmgr.net (8.13.3/8.13.3/Submit) id 1B6I0JuR065662; Mon, 6 Dec 2021 10:00:19 -0800 (PST) (envelope-from freebsd-rwg) From: "Rodney W. Grimes" Message-Id: <202112061800.1B6I0JuR065662@gndrsh.dnsmgr.net> Subject: Re: why multi-hop icmp redirects to 0.0.0.0 on 13.0 ? In-Reply-To: To: "Bjoern A. Zeeb" Date: Mon, 6 Dec 2021 10:00:19 -0800 (PST) CC: Lutz Donnerhacke , John Hay , Kurt Jaeger , freebsd-net X-Mailer: ELM [version 2.4ME+ PL121h (25)] List-Id: Networking and TCP/IP with FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-net List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-net@freebsd.org MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 4J7B6p09g9z3rdd X-Spamd-Bar: ---- Authentication-Results: mx1.freebsd.org; none X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[] X-ThisMailContainsUnwantedMimeParts: N > 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