29 Apr

Virtual IP, MgmtEth interfaces and switchover on ASR9k

On ASR9000 router you have two RSP’s, both with MgmtEth0 interfaces. Interfaces on both of RSP’s have to be in the same subnet, what more a Virtual IP address, that is in the same subnet as MgmtEth0’s interfaces have to be configured. So technically you may think that you have three out-of-band management entry points to the router. This is unfortunately false.

Virtual IP inherits MAC address of active RSP, so you always connect to active RSP. Connecting to standby RSP is not possible, console port will display message informing you that you have to connect to active RSP, something similar like on standby switch supervisor on 6500 VSS. So what happens if we try to connect to standby RSP IP address? Internal mechanisms will switch us to active RSP. So we will always use a CLI from active RSP.
So what happens during switchover? Unfortunately you will be disconnected, or while you are using consoles you have to switch to new active RSP console line. Are you get disconnected if you are connected to virtual IP address too? Answer is yes, because telnetd process is not a critical one and during switchover it have to be respawned on new active RSP. Therefor all information about open sessions are lost.

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