nanog mailing list archives
Re: Load balancing in routers
From: Iljitsch van Beijnum <iljitsch () muada com>
Date: Mon, 8 Apr 2002 10:50:29 +0200 (CEST)
On Sun, 7 Apr 2002, Richard A Steenbergen wrote:
Layer 3 devices usually do a form a load balancing called "equal cost" forwarding. If you have two routes to a single prefix (say you have two physical links), and both have the same routing "cost", packets may be load balanced across those links. Some mechanisms (for example Cisco CEF) can do this on a per-destination (flow-based) basis, to prevent packet reordering.
I seem to remember fast switching was per-destination, and CEF was round robin. But it seems CEF is now per-destination as well in IOS 12.2. Round robin is optional.
But some protocols can't support this, for example UDP or ICMP traceroutes usually don't get grouped into a "flow", so you can see this kind of load balancing in practice on the internet when you get back traceroute answers from different probes on the same hop.
Routers usually don't really take full flow information into account, but only look at the destination IP address or do a hash over some fields. So usually traceroute doesn't behave differently from regular traffic. This link answers the original question for another router vendor: http://www.juniper.net/techpubs/software/junos51/swconfig51-policy/html/policy-actions-config10.html#1015470
Current thread:
- Load balancing in routers abhijit bare (Apr 07)
- Re: Load balancing in routers Stephen J. Wilcox (Apr 07)
- Re: Load balancing in routers Richard A Steenbergen (Apr 07)
- Re: Load balancing in routers Steve Francis (Apr 07)
- Re: Load balancing in routers jeffrey arnold (Apr 07)
- Re: Load balancing in routers Eric Osborne (Apr 08)
- Re: Load balancing in routers Iljitsch van Beijnum (Apr 08)
- Re: Load balancing in routers Lincoln Dale (Apr 08)
- Re: Load balancing in routers Paul Vixie (Apr 08)
- Re: Load balancing in routers Iljitsch van Beijnum (Apr 08)
- Re: Load balancing in routers joe mcguckin (Apr 08)
- Re: Load balancing in routers Stephen Sprunk (Apr 08)
- Re: Load balancing in routers Alex Rubenstein (Apr 08)
- Re: Load balancing in routers Richard A Steenbergen (Apr 08)
- Re: Load balancing in routers Mark Kent (Apr 08)
- Re: Load balancing in routers Stephen J. Wilcox (Apr 08)
- Re: Load balancing in routers Mark Kent (Apr 08)
- Re: Load balancing in routers Steve Francis (Apr 07)