If it were me and had the requirement of having both NICs in the same L2 segment, but unique IP addresses, I'd assign a secondary IP address to the Layer3 SVI on the upstream device, and give the 2nd NIC on the server an IP on that secondary IP block. Ken Matlock Network Analyst Exempla Healthcare (303) 467-4671 matlockk@exempla.org -----Original Message----- From: Chris Meidinger [mailto:cmeidinger@sendmail.com] Sent: Monday, May 11, 2009 3:39 PM To: Dan White Cc: nanog@nanog.org Subject: Re: two interfaces one subnet On 11.05.2009, at 23:31, Dan White wrote:
Chris Meidinger wrote:
Hi,
This is a pretty moronic question, but I've been searching RFC's on- and-off for a couple of weeks and can't find an answer. So I'm hoping someone here will know it offhand. I've been looking through RFC's trying to find a clear statement that having two interfaces in the same subnet does not work, but can't find it that statement anywhere. The OS in this case is Linux. I know it can be done with clever routing and prioritization and such, but this has to do with vanilla config, just setting up two interfaces in one network. I would be grateful for a pointer to such an RFC statement, assuming it exists.
If your goal is to achieve redundancy or to increase bandwidth, you can bond the interfaces together - assuming that you have a switch / switch stack that supports 802.3ad.
Then you could assign multiple IPs to the bonded interface without any layer 3 messyness.
I should have been clearer. The case in point is having two physical interfaces, each with a unique IP, in the same subnet. For example, eth0 is 10.0.0.1/24 and eth1 is 10.0.0.2/24, nothing like bonding going on. The customers usually have the idea of running one interface for administration and another for production (which is a _good_ idea) but they want to do it in the same subnet (not such a good idea...) Chris