DNAT, LVS and MTU

Julian Anastasov ja at ssi.bg
Fri May 31 17:51:02 BST 2002


	Hello,

On 31 May 2002, Chris Beauchamp wrote:

> We have a problem.
>
> We're setting up LVS and squid in front of our webserver as an

	LVS version?

> Further investigation (after quickly removing the DNAT rule ;-) has
> revealed that it is the size of the outgoing packets which is causing
> it to fail - some are getting lost, due to being too big, and
> something isn't negociating the MTU properly. Analysis with Ethereal
> reveal a large packet missing, and TCP desparately trying to get the
> other end to resend it!

	Can you provide tcpdump output ... and some settings,
of course?

> The strange thing is, that it works fine going directly to the VIP
> (just Masquerading outwards), and, perhaps more interestingly, if
> there is a DNAT rule direct to Squid, it works also! Which implies
> that its an interaction between LVS and DNAT. (we've got to DSL lines
> here, admittedly from roughly the same supplier, but with different
> hardware, and symptoms persist whichever one we use)
>
> Does anyone have any ideas on this, and whether there's anything we
> can do about it?
>
> Thanks
>
> Chris Beauchamp
> Internet Systems Admin
> digitalbrain PLC

Regards

--
Julian Anastasov <ja at ssi.bg>





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