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[lvs-users] Recursive SYN packets sent from Director to RealServer

To: <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: [lvs-users] Recursive SYN packets sent from Director to RealServer
From: "Calcote, Lee" <lcalcote@xxxxxxxxx>
Date: Mon, 11 Aug 2008 13:26:38 -0700
Hi,

We¹re having intermittent luck using LVS/TUN and LS/DR while trying to
load-balance web services running on high port numbers: 10000, 60000, and
60001. To handle the ARP issue, we¹re using the hidden interface approach
with the following sysctl settings on the real servers:

> net.ipv4.conf.eth0.arp_ignore = 1
> net.ipv4.conf.eth0.arp_announce = 2
> net.ipv4.conf.all.arp_ignore = 1
> net.ipv4.conf.all.arp_announce = 2
> net.ipv4.conf.tunl0.arp_ignore = 1
> net.ipv4.conf.tunl0.arp_announce = 2

We find that client making HTTP requests at <VIP>:10000 (Webmin),
<VIP>:60000 and <VIP>:60001 (both in-house web services) are able to
successfully connect to real servers only intermittently. During failed
requests, we find the Director is generating SYN after SYN request to the
real server. The real server receives these (many thousand) SYN requests but
sends no reply (SYN, ACK). One of the mysteries here is that at other times
the same client will make a request and successfully connect to the web
service. We¹ve test the load-balancing of SSH and had a 100% success rate.

Does anyone know if this is a bug with LVS or have suggestions on what
further troubleshooting may be done to identify the issue? Any help would be
appreciated.

Thanks, 
Lee 

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