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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: Joseph Mack NA3T <jmack@xxxxxxxx>
Date: Fri, 31 Aug 2007 12:47:45 -0700 (PDT)
On Fri, 31 Aug 2007, Casey Zacek wrote:

> But, for some reason that I cannot remember,

Ratz (quoted somewhere in the HOWTO) said that the MTU 
should be set for the route and not for the device, since 
not all routes/packet types to/from a device need an altered 
MTU.

> I have switched off of
> this iptables method in favor of using some advanced routing to take
> care of the MSS setting.  I wish I would have shared with the group
> when I started it, because I can't remember why I'm doing it this way now.
> Still on the real servers, I use routing like so:
>
> This assumes the VIP is in a class C network
>
> ip route flush table 42
> ip route add table 42 to VIP_NETWORK/24 dev eth0 advmss 1440

I've never had a good grasp on the /32 network size for the 
VIP. Do you know why you need /24 (other than you need to 
get the packet to the router)? What happens if you use /32?

> ip route add table 42 to default via VIP_NETWORK_GATEWAY advmss 1440
> ip rule add from VIP table 42 priority 42
> ip route flush cache
>
> 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
>
> The number 42 is just a number I chose when I started this.

It's the answer to everything :-)

Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!


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