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Re: [2.4 PATCH] bugfix: ARP respond on all devices

To: Carlos Velasco <carlosev@xxxxxxxxxxxx>
Subject: Re: [2.4 PATCH] bugfix: ARP respond on all devices
From: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Date: 17 Aug 2003 18:24:06 +0100
Cc: Lamont Granquist <lamont@xxxxxxxxxxxxxxxx>, Bill Davidsen <davidsen@xxxxxxx>, "David S. Miller" <davem@xxxxxxxxxx>, bloemsaa@xxxxxxxxx, Marcelo Tosatti <marcelo@xxxxxxxxxxxxxxxx>, netdev@xxxxxxxxxxx, linux-net@xxxxxxxxxxxxxxx, layes@xxxxxxxxx, torvalds@xxxxxxxx, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
In-reply-to: <200308171827130739.00C3905F@xxxxxxxxxxxxxx>
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On Sul, 2003-08-17 at 17:27, Carlos Velasco wrote:
> Really, I don't know if you don't uderstand or you don't want to
> understand...
> 
> There is _NOT_ any problem of duplicated IPs or so.
> It's a Load Balancing scenary, similar to linuxvirtualserver and ARP
> problem that rise _ONLY_ when using Linux as real server:
> http://www.linuxvirtualserver.org/docs/arp.html

Which says

| In the LVS/TUN and LVS/DR clusters, the Virtual IP (VIP) addresses are
| shared by both the load balancer and real servers, because they all 
| configure the VIP address on one of their interfaces.

Which is not legal IP, and is why you are having problems.

> If you send a packet through dev eth0 to dev lo IP address or other
> interface, when Linux try to map the MAC address with the IP address of
> the default gateway (or the gateway to reach the packet Source IP
> address), it uses the lo IP address (or other dev) in the ARP Request.

So stick the address on eth0 not on lo since its not a loopback but an eth0
address, then use arpfilter so you don't arp for the invalid magic shared IP
address, or NAT it, or it may work to do

         ip route add nexthop-addr src my-virtual-addr dev eth0 scope local 
onlink
         ip route add default src my-virtual-addr via nexthop-addr dev eth0 
scope global

if you have no other routes getting in the way, especially old style ifconfig 
ones



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