nanog mailing list archives
Re: NANOG 40 agenda posted
From: Joe Abley <jabley () ca afilias info>
Date: Mon, 4 Jun 2007 16:36:28 -0400
On 4-Jun-2007, at 02:03, Colm MacCarthaigh wrote:
On Mon, Jun 04, 2007 at 02:53:52AM +0000, Paul Vixie wrote:ipv6 load balancers exist, one's current load balancer is/may probablynot be up to the task.my favourite load balancer is OSPF ECMP, since there are no extra boxes,just the routers and switches and hosts i'd have to have anyway.quagga ospf6d works great, and currently lacks only a health check API.If you're load-balancing N nodes, and 1 node dies, the distribution hashis re-calced and TCP sessions to all N are terminated simultaneously.
Yep. This is a disadvantage that was mentioned in both <http:// www.nanog.org/mtg-0505/abley.cluster.html> and <http://www.isc.org/ pubs/tn/isc-tn-2004-1.txt>. I seem to think there's general text about this in RFC 4786, too. From the ISC tech note:
CEF's route selection algorithm is stateless and deterministic for a stable set of ECMP routes. In general, however, a change in thenumber or ordering of those routes may cause the route selected for a
particular (source, destination) hash to change. This fragility should be considered when gauging whether this load distribution approach is appropriate to particular protocols.I have used dedicated load-balancing appliances for this kind of application. They have the disadvantages that (a) they are not cheap, and (b) sometimes the non-cheapness encourages people to use them in a fashion which exposes a single point of failure. They have many advantages, too, including (often) a sufficiently-capable state engine that the issue you mention does not arise.
As with all things, the trick is to weigh the risk of disaster against the probability of benefit and do whatever makes sense within your own particular constraints.
Joe
Current thread:
- Re: IPv6 transition work was RE: NANOG 40 agenda posted, (continued)
- Re: IPv6 transition work was RE: NANOG 40 agenda posted JORDI PALET MARTINEZ (Jun 04)
- Re: NANOG 40 agenda posted Donald Stahl (Jun 03)
- Re: NANOG 40 agenda posted Valdis . Kletnieks (Jun 03)
- Re: NANOG 40 agenda posted Joel Jaeggli (Jun 03)
- Re: NANOG 40 agenda posted Paul Vixie (Jun 03)
- Re: NANOG 40 agenda posted Donald Stahl (Jun 03)
- Re: NANOG 40 agenda posted Paul Vixie (Jun 04)
- Re: NANOG 40 agenda posted Colm MacCarthaigh (Jun 04)
- Re: NANOG 40 agenda posted Paul Vixie (Jun 04)
- Re: NANOG 40 agenda posted Colm MacCarthaigh (Jun 03)
- Re: NANOG 40 agenda posted Joe Abley (Jun 04)
- Re: NANOG 40 agenda posted Paul Vixie (Jun 04)
- Re: NANOG 40 agenda posted Matt Peterson (Jun 05)
- Re: NANOG 40 agenda posted Donald Stahl (Jun 03)
- Re: NANOG 40 agenda posted Nathan Ward (Jun 03)
- Re: NANOG 40 agenda posted Bernhard Schmidt (Jun 04)