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Thank you!
I make the message lenth to be smaller than 1452, then the problem is fixed.
I think if make the MTU larger can alse resolve the problem.
I studied the kernel code for lvs. In the kernel,I find that if the message
is larger than MTU-20 and DON'T FRAGMENT flag is 1,it will return an ICMP
message. This will coordinate the Path MTU,but in my system it didn't do
this.
Maybe the firewall drop the ICMP message, just a guess.
2010/9/11 Simon Horman <horms@xxxxxxxxxxxx>
> On Thu, Sep 02, 2010 at 04:55:32PM +0800, eric li wrote:
> > Hi,all
> >
> > I have a problem when use LVS:
> >
> > director use Tunnel Mode
> > a UDP server running on the realserver
> >
> > when client send UDP requests to lvs, it can not receive the
> realserver's
> > response.
> >
> >
> > I capture packets on the director using ethereal, the packet shows
> that:
> >
> > director receives the requests , but dose not transmit then to
> > realserver
> > the requests size is 1464(not include the UDP and IP header)
> > the IP header set the DON'T FRAGMENT to 1
> >
> >
> > i guess the reason is like that:
> >
> > requests size is 1464 and plus UDP and IP header will become
> 1492.
> > when director add a IP header on it,its size will be 1512, which exceeds
> the
> > MTU(1500). Because the IP header set the DON'T FRAGMENT to 1, director
> only
> > have to drop the packets.
> >
> >
> > Can anynoe tell me why ?
> >
> > Why the the IP header's DON'T FRAGMENT flag is 1?
>
> Hi Eric,
>
> off-hand I don't have an answer for that.
> But could you try manually reducing the MTU on the client
> to see if that helps?
>
>
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