“The shifts of fortune tests the reliability of friends.”
Marcus T. Cicero.
In yesterday’s blog we discussed the concept of multi-homing.
For some of the reasons discussed, you may not want duplication of data links. However, you may have one or more of your systems in cold-standby mode and want to be able to cut live data feeds across to it quickly in the event of a failure. For example, in primary state Device#1 may publish traps to EMS#1 but you explicitly do not want to multi-home the same feed to the cold standby EMS#2.
However, in the event that EMS#1 fails, you will want to divert Device#1’s traps to EMS#2. This is usually a fairly quick and easy task to do via reconfiguration of Device#1 to point traps to the address of EMS#2 instead of EMS#1.
Unfortunately, one of the often overlooked tasks in this failover situation is that the network path (ie routes, ACL’s, firewall rules) between Device#1 and EMS#2 haven’t been established before the failure occurred.
So the moral of the story is that if you’re establishing multi-homing or are likely to divert to a different node in the event of a failure, always establish and test all paths before going live.