nanog mailing list archives
RE: Charter ARP Leak
From: Phil Bedard <bedard.phil () gmail com>
Date: Mon, 29 Dec 2014 13:22:38 -0500
The CM is just a bridge for that traffic. It has a management IP assigned to it by the provider but that's a different network so to speak. Phil -----Original Message----- From: "Jay Ashworth" <jra () baylink com> Sent: 12/29/2014 12:52 PM To: "NANOG" <nanog () nanog org> Subject: Re: Charter ARP Leak ----- Original Message -----
From: "Brett Frankenberger" <rbf () rbfnet com>
On Mon, Dec 29, 2014 at 12:27:04PM -0500, Jay Ashworth wrote:Valdis, you are correct. What your seeing is caused by multiple IP blocks being assigned to the same CMTS interface.Am I incorrect, though, in believing that ARP packets should only be visible within a broadcast domain,broadcast domain != subnet
Yeah; I didn't use the right term. That's why my networks are small. :-)
and that because of that, they should not be being passed through a cablemodem attached to such a CMTS interface unless they're within the IP network in which that interface lives (which is probably not 0/0)? This sounds like a firmware bug in either the CMTS or the cablemodem.int ethernet 0/0 ip address 10.0.0.1 255.255.0.0 ip address 11.0.0.1 255.255.0.0 secondary ip address 12.0.0.1 255.255.0.0 secondary The broadcast domain will have ARP broadcasts for all three subnets. Doing it over a CMTS doesn't change that.
Ok. But the interface to which the cablemodem is attached, in the general single-DHCP-IP case, is a /24, is it not? The example Valdis posted had 5 or 6 different /24s from all over the v4 address space; that seems exceptionally sloppy routing... I have seen ARP-traffic-not-for-me come through a cablemodem in the past as well, but it was *uniformly* for the /24 in which my modem's address lived that day. Cheers, -- jra -- Jay R. Ashworth Baylink jra () baylink com Designer The Things I Think RFC 2100 Ashworth & Associates http://www.bcp38.info 2000 Land Rover DII St Petersburg FL USA BCP38: Ask For It By Name! +1 727 647 1274
Current thread:
- Re: Charter ARP Leak, (continued)
- Re: Charter ARP Leak Jay Ashworth (Dec 29)
- Re: Charter ARP Leak Brett Frankenberger (Dec 29)
- Re: Charter ARP Leak Jay Ashworth (Dec 29)
- Re: Charter ARP Leak David Coulson (Dec 29)
- Re: Charter ARP Leak Jay Ashworth (Dec 29)
- RE: Charter ARP Leak Corey Touchet (Dec 29)
- Re: Charter ARP Leak Ricky Beam (Dec 29)
- RE: Charter ARP Leak Phil Bedard (Dec 29)
- Message not available
- Re: Charter ARP Leak Larry Sheldon (Dec 29)
- Re: Charter ARP Leak Chris Boyd (Dec 29)
- RE: Charter ARP Leak Phil Bedard (Dec 29)
- Message not available
- Re: Charter ARP Leak Larry Sheldon (Dec 29)
- Re: Charter ARP Leak Jason Hellenthal (Dec 29)
- Re: Charter ARP Leak Jared Mauch (Dec 29)