DNS Loadbalancing problem

[James Wilson <james.wilson77@xxxxxxxxx>]

Hi All,

We are running Red Hat Enterprise 3 AS with:

ipvsadm-1.21-9.ipvs108
piranha-0.7.6-1

And 

Kernel 2.4.21-27.0.2.ELsmp

We have a basic requirement to utilise 2 DNS server behind a pair of
LVS boxes.  We noticed that our 8 Squid servers (also behind a pair of
LVS servers) display huge delays retrieving web pages when a DNS
server from /etc/resolv.conf fails.  To aliviate this, we decided to
stick the DNS servers behind the LVS boxes.

The problem I find is that I can resolve from the DNS server directly,
however through the LVS box they fail.  The following also reports in
/var/log/messages:

Aug 25 19:55:41 xxx nanny[27167]: READ to 172.18.0.121:53 timed out
Aug 25 19:55:41 xxx nanny[27168]: READ to 172.18.0.122:53 timed out


lvs.conf extract (TCP is there not for zone transfers but requests
that are > 512bytes):

virtual DNS-UDP {
     active = 1
     address = 172.18.0.120 sw0:3
     vip_nmask = 255.255.255.0
     fwmark = 53
     port = 53
     load_monitor = none
     scheduler = wlc
     service = none
     protocol = udp
     timeout = 6
     reentry = 15
     quiesce_server = 0
     server DNS3 {
         address = 172.18.0.121
         active = 1
         weight = 5
     }
     server DNS4 {
         address = 172.18.0.122
         active = 1
         weight = 5
     }
}

virtual DNS-TCP {
     active = 1
     address = 172.18.0.120 sw0:3
     vip_nmask = 255.255.255.0
     fwmark = 153
     port = 53
     load_monitor = none
     scheduler = wlc
     protocol = tcp
     timeout = 6
     reentry = 15
     quiesce_server = 0
     server DNS3 {
         address = 172.18.0.121
         active = 1
         weight = 5
     }
     server DNS4 {
         address = 172.18.0.122
         active = 1
         weight = 5
     }
}


IPTables mangle rules:

-A PREROUTING -d 172.18.0.120 -p udp -m udp --dport 53 -j MARK --set-mark 0x35 
-A PREROUTING -d 172.18.0.120 -p tcp -m tcp --dport 53 -j MARK --set-mark 0x99


Can anyone help, or point to some useful documentation - 

http://www.austintek.com/LVS/LVS-HOWTO/HOWTO/LVS-HOWTO.services.single-port.html#DNS

Stumped me even more :)


Cheers,

James

-- 
Senior Systems Engineer
MCP+I, MCSE, RHCE, CCA
CSM Technology Adelaide
ph: 08 8418 7804
fax: 08 8418 7820
email: james.wilson@xxxxxxxxxx
internet: http://www.csm.com.au