Firewall Wizards mailing list archives
Re: Firewall routing thought...
From: Gwendolynn ferch Elydyr <gwen () reptiles org>
Date: Thu, 8 Jul 2004 19:17:27 -0400 (EDT)
On Thu, 8 Jul 2004, Dana Nowell wrote:
Aaahhhh, if they are on the same subnet, why is the gateway involved at all? Last time I checked, 10.1.1.1 (assume mask 255.255.255.0) talked directly to 10.1.1.2, no gateway in the middle. There is an automagic 'static route' that says 10.1.1.x is local to the segment.
To quote myself: "... as soon as you make a change in broadcast domains, the router is going to be involved" I'm quite sure that your machine, at 10.1.1.1/24 somewhere in New Hampshire isn't talking directly to my machine, at 10.1.1.2/24 somewhere in Ontario ;> If instead, both of our machines were sitting at a conference together, connected to the [ethernet] switch in front of us, then yes - you'd expect that they'd be able to communicate directly - although not quite as you describe. -For ethernet- it's accurate to say that "all hosts in the same broadcast domain are able to use ARP to translate IP addresses to link layer addresses (MAC addresses) and vice versa, to allow direct communication within that broadcast domain". It's disingenious to describe it as an "automagic static route". It's also not true for all networking technologies. At any rate, this really boils down to "without knowing what the network of the original poster looks like, it's dangerous to make presumptions". Speaking of making presumptions, I've just realized, reading back over the OP's email, still more closely, that his concern is routing the networks that the firewalls are protecting, not between the firewalls per se, which makes most of this email a tangent. What he's really asking is whether it makes more sense to establish and maintain [static] routing tables on his firewalls, rather than set a default route, and let the router sort out what networks are where. In terms of performance, almost all firewalls handle routing decisions in software. The router handles the same decisions in hardware. The router is going to be faster[0]. It's the difference between taking the freeway or the back roads to a given location, presuming traffic conditions are clear. cheers! [0] This is the general case - I'm sure the list members can come up with ways to speed up software, and slow down hardware.
On Tue, 6 Jul 2004 13:50:18 -0400 (EDT) Gwendolynn ferch Elydyr penned:On Fri, 2 Jul 2004, Eric Appelboom wrote:If one has firewall A with external ip on the same subnet as firewall B. How common is the practice of adding static routes on firewall A for The networks protected by firewall B and the other way round. Would this technique not lower the latency or overheads of not having the packets en route from firewall A to firewall B being sent to its default gateway to then be processed by the router and sent to firewall B. Thus the traffic would be direct A<-->BI think you're a bit confused about how routing/routers work, and what the relative "costs" are. Your network layout isn't really clear from your email, but as soon as you make a change in broadcast domains, the router is going to be involved.Besides being a tad messy would it be considered and at what traffic rate?Well - I generally wouldn't consider it at any traffic rate. First of all, it's not likely to improve your latency or overhead. The packets are still going to be seen by the router. Secondly, you've now added complexity to your network in the form of a bunch of static routes in different places, all of which need to be maintained - and almost certainly won't be, until some changes breaks things. "a tad messy" is almost always a signal to run away screaming. That's code for "unmaintainable" and "all-nighters". Ranting briefly, a good design should be clear and easy to understand and explain. If you find yourself handwaving, or muttering quickly to get past some point in your design [or adding in "here be dragons"], you should stop and figure out why.-- Dana Nowell Cornerstone Software Inc. Voice: 603-595-7480 Fax: 603-882-7313 email: DanaNowell_at_CornerstoneSoftware.com
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Current thread:
- Firewall routing thought... Eric Appelboom (Jul 06)
- Re: Firewall routing thought... Gwendolynn ferch Elydyr (Jul 08)
- RE: Firewall routing thought... Ben Nagy (Jul 08)
- Re: Firewall routing thought... Ng Pheng Siong (Jul 09)
- Re: Firewall routing thought... Ng Pheng Siong (Jul 08)
- Re: Firewall routing thought... Devdas Bhagat (Jul 08)
- Re: Firewall routing thought... Ng Pheng Siong (Jul 13)
- Multiple separate Ethernet switches in a single chassis? Brent Chapman (Jul 08)
- RE: Firewall routing thought... Ben Nagy (Jul 08)
- <Possible follow-ups>
- Re: Firewall routing thought... Dana Nowell (Jul 08)
- Re: Firewall routing thought... Gwendolynn ferch Elydyr (Jul 08)
- Re: Firewall routing thought... Mark (Jul 09)
- Re: Firewall routing thought... Gwendolynn ferch Elydyr (Jul 08)
- Re: Firewall routing thought... Gwendolynn ferch Elydyr (Jul 08)