HA configuration in Cisco ISR Router

[ushanshrestha]

Can we do HA (not HSRP, VRRP) configuration in cisco routers like we do in firewalls. I want to configure Routers in Active/Passive and configuration done in one router to be synced in another router like in firewalls.

[Kasun Bandara · Accepted solution]

yes. read complete document to understand limitations before proceed.

https://www.cisco.com/c/en/us/td/docs/routers/access/4400/software/configuration/xe-16-8/isr4400swcfg-xe-16-8-book/configuring_high_availability.pdf

[MHM Cisco World]

depend on if you HA is for L2 or L3.

[ushanshrestha]

For L3

[MHM Cisco World]

to be more specific can you draw topology.

[Richard Burts]

My initial reaction was that I did not think that configuring HA was possible on routers. But the link provided by @Kasun Bandara does seem to indicate that for at least one model of Cisco router it may be possible to implement HA. So +5 for finding this. I will point out one important caveat about this type of HA "• When the configuration is replicated to the standby router, it is not committed to the startup configuration; it is in the running configuration. A user must run the

write memory

command to commit the changes that have been synchronized from the active router, on the standby router."

Perhaps it might be helpful to think about several aspects of the implementation of HA and the differences between firewall implementation and router implementation:

- each device has an interface in a common subnet/vlan. An IP address on one of the devices is designated as primary and the device with the primary address does the forwarding of traffic received from that subnet. In the event that there is a failure on the device with the primary IP address then the primary IP address switches over and is used by the second device. This functionality is implemented on both firewall and router HSRP.

- Sync the configuration - this function is implemented on firewalls. With the quite limited implementation on the 4400 routers I do not believe that this is implemented on routers.

- If a failure is detected on any interface of the primary device there is a failover of al processing to the standby device. This is implemented on firewalls and with the exception of 4400 routers I do not believe that it is implemented on Cisco routers.