From owner-freebsd-hackers@freebsd.org Mon Apr 26 14:56:38 2021 Return-Path: Delivered-To: freebsd-hackers@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 2D7495E3360 for ; Mon, 26 Apr 2021 14:56:38 +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 4FTSdw4Jcxz3jQR for ; Mon, 26 Apr 2021 14:56:36 +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 13QEuXhD098220; Mon, 26 Apr 2021 07:56:33 -0700 (PDT) (envelope-from freebsd-rwg@gndrsh.dnsmgr.net) Received: (from freebsd-rwg@localhost) by gndrsh.dnsmgr.net (8.13.3/8.13.3/Submit) id 13QEuXEa098219; Mon, 26 Apr 2021 07:56:33 -0700 (PDT) (envelope-from freebsd-rwg) From: "Rodney W. Grimes" Message-Id: <202104261456.13QEuXEa098219@gndrsh.dnsmgr.net> Subject: Re: Are there any RFCs for address selection for IPv4 In-Reply-To: <76578.1619447095@critter.freebsd.dk> To: Poul-Henning Kamp Date: Mon, 26 Apr 2021 07:56:33 -0700 (PDT) CC: "Rodney W. Grimes" , freebsd-hackers@freebsd.org X-Mailer: ELM [version 2.4ME+ PL121h (25)] MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 4FTSdw4Jcxz3jQR X-Spamd-Bar: / Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=none (mx1.freebsd.org: domain of freebsd-rwg@gndrsh.dnsmgr.net has no SPF policy when checking 69.59.192.140) smtp.mailfrom=freebsd-rwg@gndrsh.dnsmgr.net X-Spamd-Result: default: False [-1.00 / 15.00]; RCVD_TLS_LAST(0.00)[]; ARC_NA(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; TO_DN_SOME(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; DMARC_NA(0.00)[dnsmgr.net]; RBL_DBL_DONT_QUERY_IPS(0.00)[69.59.192.140:from]; AUTH_NA(1.00)[]; NEURAL_SPAM_SHORT(0.10)[0.104]; SPAMHAUS_ZRD(0.00)[69.59.192.140:from:127.0.2.255]; TO_MATCH_ENVRCPT_SOME(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; R_SPF_NA(0.00)[no SPF record]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:13868, ipnet:69.59.192.0/19, country:US]; RCVD_COUNT_TWO(0.00)[2]; MAILMAN_DEST(0.00)[freebsd-hackers] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Technical discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 26 Apr 2021 14:56:38 -0000 > -------- > Rodney W. Grimes writes: > > > > Does anybody know why we put a (ipv6)LL on loopback interfaces ? > > > > I believe someplace in the bowls of all the IPv6 specs this > > is a requirement. I could not find it quickly though. > > I'm not seeing Linux doing it for instance ? I'll investigate further and see if I can discover why we do this, if it is or isnt in spec, etc. > > > Question: Should we allow a route to have a next hop of a LL(ipv4)? > > Reason: RFC3927 2.6.2: > > The host MUST NOT send a packet with an IPv4 Link-Local destination > > address to any router for forwarding. > > > > So, arguably, it is a violation to allow the default route to have > > a LL next hop for ipv4. For that matter, it is a violation to allow > > ANY ipv4 LL address to be the next hop in the routing table(s). > > You are reading that wrong. Yep > > It is OK to have a LL as next-hop. > > It is not OK to send a packet with dst=LL to any next-hop. No, that is explicity forbidden: RFC 3927 at 2.7 paragraph 2: An IPv4 packet whose source and/or destination address is in the 169.254/16 prefix MUST NOT be sent to any router for forwarding, and any network device receiving such a packet MUST NOT forward it, regardless of the TTL in the IPv4 header. If dst=LL you must ARP for the destination is also in the spec some place, no routing allowed. Now if you had said dst != LL to any next-hop, that would be true. > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" > -- Rod Grimes rgrimes@freebsd.org