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Re: [lvs-users] lvs-tun MTU and fragmentation

To: "LinuxVirtualServer.org users mailing list." <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [lvs-users] lvs-tun MTU and fragmentation
From: "Sameer Garg" <sameer.garg@xxxxxxxxx>
Date: Thu, 6 Sep 2007 19:13:21 +0530
By trial and error I was able to find a work around this:

On the director I did the following

# ip route add REAL_SERVER_IP via DIRECTOR_GATEWAY dev eth0 advmss 1400

On the Real Server
# ip route change default via REAL_SERVER_GATEWAY dev eth0 advmss 1400

I am still not sure why I need to make the change on the director
because technically during the three way handshake the real server
should tell the client about MSS being 1400.I have tried it without
making the changes on the director but it doesn't work.

Sameer

On 9/3/07, Sameer Garg <sameer.garg@xxxxxxxxx> wrote:
> > So, for example, say VIP is 10.2.2.38
> > VIP_NETWORK is 10.2.2.0
> > VIP_NETWORK_GATEWAY is 10.2.2.1 (probably)
> >
> > ip route flush table 42
> > ip route add table 42 to 10.2.2.0/24 dev eth0 advmss 1440
> > ip route add table 42 to default via 10.2.2.1 advmss 1440
> > ip rule add from VIP table 42 priority 42
> > ip route flush cache
>
>
> Based on the instructions above and my interpretation I tried the
> following without success.
>
>
> tunl0/ VIP                   --- 10.2.2.38
> REAL_SERVER_NET --- 10.0.1.0/26
> REAL_SERVER_GW  --- 10.0.1.1
> REAL_SERVER_IP    --- 10.0.1.2
>
>
> This is the proposed setup.
> LVS                                                       Real Server
> ------------------------
> -----------------------------
> | LVS               |                                     | IP
> 10.0.0.2/26        |
> | VIP=10.2.2.38 |     ------------------------->     | tunl0 10.2.2.28/32  |
> ------------------------                                     | GW
> 10.0.1.1          |
>
> ------------------------------
> ip route flush table 42
> ip route add table 42 to REAL_SERVER_NET dev eth0 advmss 1420
> ip route add table 42 to default via REAL_SERVER_GW advmss 1420
> ip rule add from VIP table 42 priority 42
> ip route flush cache
>
>
> Also tried this on the Real Server without any luck.
>
> iptables -A OUTPUT -s VIP -p tcp -m tcp --tcp-flags SYN,RST,ACK
> SYN,ACK -j TCPMSS --set-mss 1440
>
>
> Thanks.
> Sameer
>


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