AW: [DRBD-user] OSPF config and bind problem (was Using DRBD between hosts with dual redundant network interfaces)

Martin Bene martin.bene at
Sat Jul 9 11:43:33 CEST 2005

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

> Today i tried to use DRBD on loopback interfaces with OSPF routing.
> It turns out, DRBD is not yet ready for such a setup (see below).
> First of all, please really think about wether you need and want this 
> added complexity of ospf. It is a tradeoff: You add ospf as a new 
> possible error source. You get some extra protection against network 
> failures.

Thanks for the detailed information on this setup!

I'm just trying to decide wether this is actually worth the added

What I actually want to get from my HA setup is protection from SPOFs;
additional protection from multiple failures is nice to have but I
wouldn't add much complexity to get it.

Failure scenario with a standard setup (without lo/ospf):
 * one of the network cards (or the cable) for the internal drbd network
 * System is still up and running, but no longer tolerant to a 2nd
fault. Failover is no longer possible. 

The interesting question is: what does the admin have to do to recover
from the situation? Most other failures in a ha system leave you with a
bad system that can be shut off and repaired; here that's only the case
if you've got an active/passive system and the failure happens on the
passive/standby node. If you're running active/active (multiple drbd
devices with primaries on both nodes) or if the failed card is on the
primary it starts getting tricky.

Solution: change drbd config to use addresses from the other network,
reconnect using these new addresses, figure out which card is bad, fail
over to the other host. Now shutdown bad node and repair, reboot. Repeat
config change to get back onto the original drbd connection.

Not trivial and needs an admin that really knows his way around drbd.

Compare to recovery WITH lo/ospf setup: 
Failover to good node, shut down /repair node with bad NIC, reboot. MUCH
easier und less fiddling required.

Conclusion for me: Just for the ease of recovery from a failure
situation I'll give this a try.

Bye, Martin

More information about the drbd-user mailing list