---------- Forwarded message ---------- Date: Wed, 23 Jul 2003 07:53:26 -1000 From: DOUGS@oceanic.com To: oberman@es.net Cc: dave@ordinaryworld.com Subject: RE: rfc1918 ignorant There's a common misconception reflected here that I wanted to correct. I don't have nanog-post, so I apologize if its not appropriate to reply directly. You may repost my comments if you'd like. [Kevin Oberman <mailto:oberman@es.net> wrote on Wednesday, July 23, 2003 7:07 AM:]
Comcast and many others seem to blithely ignore this for convenience sake. (It's not like they need a huge amount of space to give private addresses to these links.)
ARIN required cable operators to use RFC 1918 space for the management agents of the bridge cable modems that have been rolled out to the millions of residential cable modem customers. Doing so obviously requires a 1918 address on the cable router, but Cisco's implementation requires that address to be the primary interface address. There is also a publicly routable secondary which in fact is the gateway address to the customer, but isn't the address returned in a traceroute. Cisco has by far the lead in market share of the first gen Docsis cable modem router market so any trace to a cable modem customer is going to show this. In fact, Comcast and others _do_ need a huge amount of private IP space because of this. We didn't "blithely ignore" the RFC, but didn't have a choice in implementation. Perhaps Cisco will improve their implementation for the next round of CMTS development... Filtering of RFC 1918 space by cable ISPs is of course another topic. -Doug- [Kevin Oberman <mailto:oberman@es.net> wrote on Wednesday, July 23, 2003 7:07 AM:]
Date: Wed, 23 Jul 2003 08:59:18 -0400 (EDT) From: Dave Temkin <dave@ordinaryworld.com> Sender: owner-nanog@merit.edu
Is this really an issue? So long as they're not advertising the space I see no issue with routing traffic through a 10. network as transit. If you have no reason to reach their router directly (and after Cisco's last exploit, I'd think no one would want anyone to reach their router directly :-) ), what's the harm done?
RFC1918 merely states that it shouldn't be routed on the global internet, not that it can't be used for transit space.
That's not what is in my copy of 1918.
"In order to use private address space, an enterprise needs to determine which hosts do not need to have network layer connectivity outside the enterprise in the foreseeable future and thus could be classified as private. Such hosts will use the private address space defined above. Private hosts can communicate with all other hosts inside the enterprise, both public and private. However, they cannot have IP connectivity to any host outside of the enterprise. While not having external (outside of the enterprise) IP connectivity private hosts can still have access to external services via mediating gateways (e.g., application layer gateways)."
As I read this, packets with a source address in 19298 space should NEVER appear outside the enterprise. Comcast and many others seem to blithely ignore this for convenience sake. (It's not like they need a huge amount of space to give private addresses to these links.)