As someone who has used IPMP extensively in Sun's internal datacenters and seen some interesting failure modes, I would like to throw out one big suggestion:
Please give sysadmins the ability to specify probe targets explicitly in /etc/default/mpathd (or some other appropriate config file). We have run into cases where allowing lots of servers' in.mpathd to bang away at the default router constantly is a bad idea. Some routers/firewalls de-prioritize responding to ICMP when their CPU load is above some threshold. This results in every server on the subnet suddenly thinking that both IPMP interfaces have failed simultaneously. If you have other interfaces (like some sort of back-end network for NAS or management purposes) that you want to run IPMP on (other than the one on which the default route resides), IPMP sends multicast pings to find other hosts to probe. This is also problematic, particularly in hardened environments where ip_respond_to_echo_multicast has been disabled (JASS does this). In both cases, we would like to be able explicitly control who in.mpathd pings. The method of inserting static host routes in the route table seems like a kludge at best, and if you list less than 5 per subnet in.mpathd still falls back to its other methods anyway. Therefore, ability to explicitly list probe targets in /etc/default/mpathd would be really nice. -- Chuck Cox Sun Microsystems Global Internet Services (303)223-6099 or x69526 Chuck.Cox at Sun.COM
