Security Basics mailing list archives
RE: 2 NIC's on same network, possible?
From: "David Gillett" <gillettdavid () fhda edu>
Date: Tue, 29 Jul 2003 18:00:06 -0700
The *effect* of the default route is to match any networks for which you do not have any other route, but it does this by matching ALL destinations. It only fails to match networks you have another route because it does not get checked for a match until all other routes have been considered. Routing decisions are made by examining one possibility at a time; once a match has been found, the rest of the routes need not be examined. So the presence of multiple candidate matches doesn't interfere with the process at all. Someone else has indicated that some implementations may complain about multiple routes to a specific (non-default) destination network UNLESS they have different weights, but (a) you weren't that specific, and (b) this simply ensures that the route table entries always get *ordered* the same way. (In fact, some dynamic route-selection algorithms act by modifying the weights of redundant routes to reflect load distribution -- and that *requires* two or more routes to exactly the same network. OSPF, I believe, allows four.) The example of the default route is only the most common counter-example which contradicts your assertion. You most certainly CAN have multiple routes "pointing towards the same network". David Gillett
-----Original Message----- From: Ansgar Wiechers [mailto:bugtraq () planetcobalt net] Sent: July 29, 2003 12:33 To: security-basics () securityfocus com Subject: Re: 2 NIC's on same network, possible? David, On 2003-07-29 David Gillett wrote:Correct. Your machine can't have two routes pointingtowards the samenetwork.If you have a default route, you HAVE two routes pointing towards every network for which you have an explicit route. This cannot be a correct statement without some further qualifiers!The default route is a fallback which applies to every address/network you do *not* have an explicit route for. I do not see how this would qualify as "two routes towards the same network". Regards Ansgar Wiechers
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Current thread:
- 2 NIC's on same network, possible? Vineet Mehta (Jul 28)
- Re: 2 NIC's on same network, possible? Ansgar Wiechers (Jul 29)
- RE: 2 NIC's on same network, possible? David Gillett (Jul 29)
- Re: 2 NIC's on same network, possible? Ansgar Wiechers (Jul 29)
- RE: 2 NIC's on same network, possible? David Gillett (Jul 30)
- Re: 2 NIC's on same network, possible? Ansgar Wiechers (Jul 31)
- RE: 2 NIC's on same network, possible? David Gillett (Jul 29)
- Re: 2 NIC's on same network, possible? Ansgar Wiechers (Jul 29)
- Re: 2 NIC's on same network, possible? thedistance (Jul 30)
- <Possible follow-ups>
- RE: 2 NIC's on same network, possible? Nick Russell (Jul 29)
- RE: 2 NIC's on same network, possible? Ghaith Nasrawi (Jul 29)
- RE: 2 NIC's on same network, possible? Burton M. Strauss III (Jul 29)
- RE: 2 NIC's on same network, possible? Max Harvey (Jul 30)
- RE: 2 NIC's on same network, possible? Shane Lahey (Jul 29)
- RE: 2 NIC's on same network, possible? Burton M. Strauss III (Jul 29)
- RE: 2 NIC's on same network, possible? Jane Han (Jul 29)
- RE: 2 NIC's on same network, possible? David Gillett (Jul 30)