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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: PMTU-D: remember, your load balancer is broken
On 14-Jun-2000 [email protected] 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/ - <[email protected]> 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
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