Understanding CARP

freebsd at gorlani.net freebsd at gorlani.net
Sun Aug 27 17:38:09 UTC 2006


Hi
 I'm new to FreeBSD but I'm loving it very much! I'm experimenting with CARP
to create a redundant router/firewall.
I created a functioning two machine routing cluster and it works very well
while configured for failover. I'm going to test it with load balancing and
I'm wondering about some problems that could arise.
Suppose I enable load balancing features.
Situation: my cluster (made by CL1 and CL2) routes from Net A to Net B. I
have an A_client and a B_Server. A_Client initiates a connection to B_Server
and the packet is routed by the CL1 machine.
The response packet comes from the B network (it is from B_Server) and is
taken by CL2 to be routed (asymmetric routing problem, as documented in the
man page). If no packet filtering occurs, there is no problem. But what if I
use IPFilter? Is there a way to keep the state between CL1 and CL2 with
IPFilter? 

Also I would like to know in which way packets flow to all the members of
the cluster in a switched environment, since they share the same mac
address. Is CARP using a technique like Microsoft NLB to avoid switches from
learning mac addresses? Does this lead, like using NLB, to flooding?

Thanks



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