Linux 2.4 as a router, when is it appropriate?

Could someone please tell me (or refer me to docs) on when using the Linux on PC hardware as a router is an appropriate solution and when one should consider a "real" router (e.g., Cisco)?

I have heard that performance wise, if you have a fast CPU, much memory and good NICs that Linux can be as good all but the high end routers. Are there important missing features or realiability issues that make using Linux not suitable for "enterprise" use?

Thanks.

Russ

CPU and RAM isnt that important. Your normal limit is the PCI bus bandwidth. At gigabit speeds that becomes a bottleneck, followed by RAM bandwidth.

I have a Linux-based router and it can handle about as much as a cisco 7206vxr with GE interfaces. I think both of them reaches the bandwidth limit of the PCI bus. The PC can be much better with 64bit/66MHz PCI buses or you can even buy motherboards with 100 or 133MHz PCI-X slots. I guess those can drive 3 or 4 GE interfaces at gigabit speed.

You need a cisco when you care about interface density, you have interfaces you can't buy for a PC or you need to route protocols other than IP or proprietary to cisco.

endre

I have used Linux/Zebra in production as a route reflector. That machine was simply a BGP peer of the others and not directly in the traffic path. That configuration had several commercial border routers (actually L2/3 switches) collecting full Internet routes from their upstream peers. These border routers fed their routing table via BGP to the Linux route reflector. The Linux/Zebra box aggregated the table, applied various policy to the routes received, and sent the resulting table on to the core routers.

The reason for using Linux in this case was the large amount of memory required for handling all the peers. Zebra handled it just fine and you can just keep adding RAM to a PC. To get the same capability in a commercial unit you have to get some very expensive iron. This allowed the border units to be relatively inexpensive with only enough RAM to handle 1 Internet peer with full routes and kept the core router CPU free to handle traffic rather than process routes so it could also be a lower cost unit than would otherwise be required.

The unit was in production for over a year without a single reboot.

From: Russell Leighton <[email protected]>
Date: Fri, 03 May 2002 09:25:12 -0400

Could someone please tell me (or refer me to docs) on when using the Linux on PC hardware as a router is an appropriate solution and when one should consider a "real" router (e.g., Cisco)?

The most heavily accessed ftp site in europe uses Linux machines exclusively as it's routers.

And what kind of traffic are you speaking of (I mean how much megs/teras per day)?

Mathieu Chouquet-Stringer              E-Mail : [email protected]
    It is exactly because a man cannot do a thing that he is a
                      proper judge of it.
                      -- Oscar Wilde

From: Mathieu Chouquet-Stringer <[email protected]>
Date: 05 May 2002 22:27:52 -0400

And what kind of traffic are you speaking of (I mean how much megs/teras per day)?

We're talking about several hundred kilo packet per second routing over gigabit.

What kind of hardware are those routers?

endre

Impressive (thanks for this quick reply).

Mathieu Chouquet-Stringer              E-Mail : [email protected]
    It is exactly because a man cannot do a thing that he is a
                      proper judge of it.
                      -- Oscar Wilde

Professional routers may support non-IP protocols which Linux doesn't,
and the non-IP protocols which are in Linux are far less less used than IP. That does not mean they don't work, but somewhat untrodden ground.

For IP, particularly for tricky, messy, nasty stuff, I do prefer
Linux/iptables. I'm looking forward to having time to see how well UML and iptables play, so I can have a whole DMZ full of "machines" to test some challenging setups.

Throughput and latency are pretty competitive with any commercial
router, given good hardware. I believe preempt does improve latency, but I really haven't had a case where I needed to worry about it, Linux is fast as-is.

bill davidsen <[email protected]>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.