[CentOS] Monitoring IP masquerading on LVS load-balancing

Wed Mar 25 21:50:46 UTC 2009
David Dyer-Bennet <dd-b at dd-b.net>

I've got small numbers of connections moving through a load balancer
configured in NAT mode.  So I've got an iptables table called "nat", which
has in it a line "-A POSTROUTING -o eth0 -j MASQUERADE" (lan connect is
eth0, private lan inside the cluster is eth1).

The load balancer is working; connections made to the virtual ip on that
host do get routed to one of the real servers behind this load load

But I want to observe the connections on the load balancer.

My first attempt was to use netstat with the --masquerade switch.  This
produced the result "netstat: no support for `ip_masquerade' on this
system."  Consistent with this, there is no /proc/net/ip_masquerade.

On the other hand, the load balancer *IS* working; those connections *are*
getting NATted and routed.

Also, lsmod shows varous relevant modules loaded:
iptable_nat            40773  1
ip_nat                 53101  2 ipt_MASQUERADE,iptable_nat
ip_conntrack           91237  5
nfnetlink              40457  2 ip_nat,ip_conntrack
ip_tables              55329  2 iptable_filter,iptable_nat
x_tables               50377  7

So, netstat just isn't somehow the right monitoring tool, right?  So what
is the right monitoring tool?  I need to know the source IP and
real-server IP of connections being handled by the load balancer.  I don't
need a lot showing exactly how each one was handled, but I'd like to be
able to determine the state of any connection currently active.  How can I
do this?

David Dyer-Bennet, dd-b at dd-b.net; http://dd-b.net/
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