Date: Tue, 13 Nov 2012 10:54:53 -0800 From: Sean Chittenden <sean@chittenden.org> To: Andre Oppermann <oppermann@networx.ch> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, gnn@freebsd.org Subject: Re: 0.0.0.0/8 oddities... Message-ID: <7C614093-6408-49C6-8515-F6C09183453B@chittenden.org> In-Reply-To: <50A20359.9080906@networx.ch> References: <DC8A0D79-8DF3-472F-9B1A-76BF8577A03C@chittenden.org> <50A20359.9080906@networx.ch>
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>> Hello. I ran in to an interesting situation in what appears to be an exotic situation. Specifically, after reviewing RFC5735 again and searching for a datacenter-local or rack-local IP range (i.e trying to provide services that are guaranteed to be provided in the same rack as the server), I settled on the 0.0.0.0/8 network. Per §3 of RFC5735, it would appear that this network is valid: >> >> https://tools.ietf.org/html/rfc5735#section-3 >> >>> 0.0.0.0/8 - Addresses in this block refer to source hosts on "this" >>> network. Address 0.0.0.0/32 may be used as a source address for this >>> host on this network; other addresses within 0.0.0.0/8 may be used to >>> refer to specified hosts on this network ([RFC1122], Section 3.2.1.3). >> >> And this works as expected, with regards to TCP services. But ICMP? Not so much. Is there a reason that ICMP would fail, but TCP (e.g. ssh) works? For example, I pulled 0.42.123.10 and 0.42.123.20 as IP addresses to use for NTP servers, but much to my surprise, I could ssh between the hosts, but I couldn't ping. Is this intentional? I understand that 0.0.0.0/32 == INADDR_ANY for source addresses, but it doesn't appear that there should be a restriction of inbound echoreq packets. According to tcpdump(1), the host is receiving echoreq packets, however no echorep packets are generated. As a work around, I threw things in to a more traditional RFC1918 network and things immediately worked for both SSH and ICMP. > > The check to drop ICMP replies to a source of 0.0.0.0/8 was added > in r120958 as part of a fix for link local addresses. It was only > applied to ICMP which is inconsistent as you've found out. > >> ?? Any thoughts as to why? It doesn't appear that the current behavior abides by RFC5735. > > Reading this section and RFC1122 it is not entirely clear to me > what the allowed scope of 0.0.0.0/8 is. I do agree though that > blocking it only in ICMP is not useful if it is allowed in the > normal IP input path. > > Can you please check how other OS's (Linux, Windows) deal with it? I... err.. I don't have any Linux or windows boxes that I can play with for a few weeks, but I can stand one up later this month sometime. ELINUXFREE ? > You may also want to search for this question on NANOG, and if not > found raise it there. I looked around to see if this was changed recently, but I couldn't find any reference as such. The thought was to pluck an easy mnemonic for remembering and correlating network services that are guaranteed and required to be site-local and not available through an MPLS or VPN network (10/8, 192.168/16 and 172.16/12 are managed by BGP or some other IGP, I wanted something explicitly that would not match). 0.42.123.10 & 0.42.123.20 = site-local NTP server. ^ | ^^ | | ^^^ | | | ^ | | | | | | | +------ primary, .20 = secondary | | +--------- "port 123 services" | +------------ "the answer to" +--------------- site/data center local There were a host of convenience things that came for free with this, including easy to identify what traffic should be on the segment, etc. DNS would be at 0.42.53.{10,20}, etc. Answering questions like "this data center's DNS server is at 172.29.167.4" is a PITA, and it doesn't need to be. I saw you just made a commit to enable this a few minutes ago, thank you. Any plans to MFC r242956? Thanks Andre. -sc -- Sean Chittenden seanc@FreeBSD.org
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