Hi! Thank you all for your reply Jeff, Gilles and rhc.
Thank you Jeff and rhc for clarifying to me some of the openmpi's internals. >> FWIW: we never send interface names to other hosts - just dot addresses > Should have clarified - when you specify an interface name for the MCA param, then it is the interface name that is transferred as that is the value of the MCA param. However, once we determine our address, we only transfer dot addresses between ourselves If only dot addresses are sent to the hosts then why doesn't openmpi use the default route like `ip route get <other host IP>` instead of choosing a random one? Is it an expected behaviour? Can it be changed? Sorry. As Gilles pointed out I forgot to mention which openmpi version I was using. I'm using openmpi 3.0.0 gcc 7.3.0 from openhpc. Centos 7.5. > mpirun—mca oob_tcp_if_exclude 192.168.100.0/24 ... I cannot just exclude that interface cause after that I want to add another computer that's on a different network. And this is where things get messy :( I cannot just include and exclude networks cause I have different machines on different networks. This is what I want to achieve: compute01 compute02 compute03 ens3 192.168.100.104/24 10.0.0.227/24 192.168.100.105/24 ens8 10.0.0.228/24 172.21.1.128/24 --- ens9 172.21.1.155/24 --- --- So I'm in compute01 MPI_spawning another process on compute02 and compute03. With both MPI_Spawn and `mpirun -n 3 -host compute01,compute02,compute03 hostname` Then when I include the mca parameters I get this: `mpirun --oversubscribe --allow-run-as-root -n 3 --mca oob_tcp_if_include 10.0.0.0/24,192.168.100.0/24 -host compute01,compute02,compute03 hostname` WARNING: An invalid value was given for oob_tcp_if_include. This value will be ignored. ... Message: Did not find interface matching this subnet This would all work if it were to use the system's internals like `ip route`. Best regards, Carlos.
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