With older version of Lustre I was used to have IB as default network, but also to have a ethernet connection as fallback, so each NID specified for failover.node or mgs.node contained both networks, e.g.:

failover.node=10.3.0.228@o2ib,192.168.50.128@tcp

When I try this with 2.4.0 it appears the parser does not understand this syntax anymore. I get an error in syslog:

LDISKFS-fs (dm-7): Unrecognized mount option "192.168.50.128@tcp" or missing value