We are using a MikroTik CRS312-4C+8XG-RM as a switch and noticed we need to run dhclient on the Ubuntu clients connected to the switch every time there is a reboot.
Is this a known issue or what would you recommend to troubleshoot the issue?
Thank you!
Networking skills.
Anyone else? It doesn't happen with other switches, for example Netgear...
That just proves that I was right ¯\_(ツ)_/¯
My first instinct is to check that the switchport is spanning-tree-forwarding when the ubuntu machines tries to get an ip. Try forcing a port in "edge" and see if it changes something.
@vingjfg is on the right track. The giveaway is that dhclient by hand always works: by the time you are logged in, the port finished its STP transition long ago. During boot the DISCOVER goes out while the bridge port is still in learning and those frames simply die. Fits the Netgear test too, unmanaged switches have no STP and forward from link-up.
Easy to confirm, reboot one Ubuntu box while watching its port:
/interface bridge port monitor [find where interface=etherX] once
If forwarding says no while the client is asking, that is the whole story. Fix:
/interface bridge port set [find where interface=etherX] edge=yes
Only on ports facing hosts, keep auto towards other switches. Mind that edge=auto is not enough here: the port still goes through learning until discovery decides it is edge, and those first seconds after link-up are exactly when the client asks. Explicit yes skips the transition entirely, straight to forwarding.