nanog mailing list archives
Re: two interfaces one subnet
From: Brielle Bruns <bruns () 2mbit com>
Date: Mon, 11 May 2009 15:52:19 -0600
On 5/11/09 3:23 PM, Chris Meidinger wrote:
On 11.05.2009, at 23:19, Alex H. Ryu wrote:Unless you configure Layer 2 for two interfaces, it's not going to work. It is invalid from networking principle. If you have to send the traffic for host in same subnet you configured, which interface it should send out ? Basically it may create broadcast storm loop by putting two ip addresses in same subnet in different interface. It may be allowed from host-level, but from router equipment, I don't think it was allowed at all.Alex, I _personally_ know that it's a problem. I was hoping for an RFC-reference, or similar standards document, to show to customers to convince them to stop trying to hack things to make it work. Chris
In Linux, I ran into the exact situation talked about in the link: http://lwn.net/Articles/45373/Basically, recent versions of Linux will respond to arp requests for IPs on another interface on the receiving interface. Basically, you end up with traffic going in/out of unexpected interfaces. I discovered my iptables rules weren't quite working right and I couldn't get into one of my boxen because the allow was set to eth0, and the packets were coming in/out of eth1 even though the IP was bound to eth0.
One of the more interesting gotchas that had me stumped for hours before I found out what was really going on.
-- Brielle Bruns The Summit Open Source Development Group http://www.sosdg.org / http://www.ahbl.org
Current thread:
- Re: two interfaces one subnet, (continued)
- Re: two interfaces one subnet Chris Meidinger (May 11)
- Re: two interfaces one subnet Patrick W. Gilmore (May 11)
- Re: two interfaces one subnet Chris Meidinger (May 11)
- Re: two interfaces one subnet Mikael Abrahamsson (May 11)
- Re: two interfaces one subnet Duane Waddle (May 11)
- Re: two interfaces one subnet Daryl G. Jurbala (May 12)
- Re: two interfaces one subnet Charles Wyble (May 11)
- Re: two interfaces one subnet Chris Meidinger (May 11)
- Re: two interfaces one subnet Nathan Ward (May 11)
- Re: two interfaces one subnet Duane Waddle (May 11)
- Re: two interfaces one subnet Alex H. Ryu (May 11)
- Re: two interfaces one subnet Chris Meidinger (May 11)
- Re: two interfaces one subnet Brielle Bruns (May 11)
- Re: two interfaces one subnet Kevin Oberman (May 11)
- Re: two interfaces one subnet Chris Meidinger (May 11)
- Re: two interfaces one subnet Patrick W. Gilmore (May 11)
- Re: two interfaces one subnet Arnold Nipper (May 11)
- Re: two interfaces one subnet Patrick W. Gilmore (May 11)
- Re: two interfaces one subnet Arnold Nipper (May 11)
- Re: two interfaces one subnet Patrick W. Gilmore (May 11)
- Re: two interfaces one subnet Chris Meidinger (May 11)
- Re: two interfaces one subnet Hector Herrera (May 11)
- Re: two interfaces one subnet Ben Scott (May 11)