nanog mailing list archives
Re: PMTU-D: remember, your load balancer is broken
From: Ryan O`Connell <nemesis () eh org>
Date: Wed, 14 Jun 2000 10:57:35 +0100 (BST)
On 14-Jun-2000 Valdis.Kletnieks () vt edu wrote:
b) If you're a webserver or something else providing service Out There to random users, just nail the MTU at 1500, which will work for any Ethernet/PPP/SLIP out there. And if you're load balancing to geographically disparate servers, then your users are probably Out There, with an MTU almost guaranteed to be 1500. I assert that the chances of PMTU-D helping are in direct ratio to the number of end users who have connections with MTU>1500 - it's almost a sure thing that you probably won't have users with an MTU on their last-hop that's bigger than their campus backbone and/or Internet connection's MTU.
www.bt.com drops (Or at least used to) all ICMP silently, and this can cause problems - one of our ISPs (U-Net) runs a Frame Relay network internally from some customers that had an MTU of 1496, (The default MTU for FR on some equipment, including (earlier?) Cisco IOSes, apparently) Symptom - web site unreachable. Complained to bt.com, go the usual "everything is fine here" response. :-( Similar symptoms accessing other sites, although it was intermittent. Apparently, the problem is more often seen on NT servers (No surprise there, then) as they set the DF bit on outbound packets. Managed to persuade U-Net to change their Frame Relay network to have an MTU of 1500, which was quite nice of them as it wasn't really their system that was broken! Improved performance noticably however. -- Ryan O'Connell - http://www.complicity.co.uk/ - <nemesis () eh org> You are the Dancing Queen, young and sweet, only seventeen Dancing Queen, feel the beat from the tambourine You can dance, you can jive, having the time of your life See that girl, watch that scene, dig in the Dancing Queen
Current thread:
- Re: PMTU-D: remember, your load balancer is broken, (continued)
- Re: PMTU-D: remember, your load balancer is broken Valdis . Kletnieks (Jun 13)
- Re: PMTU-D: remember, your load balancer is broken Marc Slemko (Jun 13)
- Re: PMTU-D: remember, your load balancer is broken Valdis . Kletnieks (Jun 14)
- RE: PMTU-D: remember, your load balancer is broken Roeland Meyer (E-mail) (Jun 14)
- RE: PMTU-D: remember, your load balancer is broken John Fraizer (Jun 14)
- Re: PMTU-D: remember, your load balancer is broken Paul Vixie (Jun 17)
- Re: PMTU-D: remember, your load balancer is broken Valdis . Kletnieks (Jun 17)
- Re: PMTU-D: remember, your load balancer is broken Bora Akyol (Jun 18)
- Re: PMTU-D: remember, your load balancer is broken Paul Vixie (Jun 19)
- Re: PMTU-D: remember, your load balancer is broken Marc Slemko (Jun 13)
- Re: PMTU-D: remember, your load balancer is broken Valdis . Kletnieks (Jun 13)
- Re: PMTU-D: remember, your load balancer is broken Bennett Todd (Jun 14)
- Re: PMTU-D: remember, your load balancer is broken Valdis . Kletnieks (Jun 13)
- Re: PMTU-D: remember, your load balancer is broken Brett Frankenberger (Jun 14)
- Re: PMTU-D: remember, your load balancer is broken Greg A. Woods (Jun 15)
- Re: PMTU-D: remember, your load balancer is broken Greg A. Woods (Jun 15)
- Re: PMTU-D: remember, your load balancer is broken Marc Slemko (Jun 15)
- Re: PMTU-D: remember, your load balancer is broken Greg A. Woods (Jun 15)