OSPF GR Helper with Cisco 3825

[trudeau02]

Hi,

I would like to enable OSPF Gracefull Restart on my Cisco 3825 router, however, it's unclear to me if this is possible. "The router undergoing OSPF graceful restart must be capable of performing a stateful switchover (SSO) operation". My understanding is that you need dual processors to perform SSO, such as a hitless software upgrade, or if one RP crashes, the backup RP will take over.

Do I require dual processors for OSPF Gracefull Restart/NSF or is dual processors only required for NSR (Non Stop Routing)?

How is SSO achieved/triggered on the 3825, to ensure OSPF Gracefull Restart is supported? Juniper has the "restart routing gracefully" command. Is there something similar on Cisco, or is it only achieved by hitless software upgrade or RP failure?

I'm currently running Version 12.4(19)MR, and there does not appear to be an option to configure SSO. Is this because it's not supported on the Cisco 3825? If it is supported, why is the configuration option not available?

SYS22-Cis(config)#redundancy
SYS22-Cis(config-r)#?
Redundancy configuration commands:
  exit  Exit from redundancy configuration mode
  mode  Redundancy mode
  no    Negate a command or set its defaults

SYS22-Cis(config-r)#mode ?
  y-cable  Y Cable Redundancy Mode

SYS22-Cis(config-r)#mode y-c
SYS22-Cis(config-r)#mode y-cable ?
  <cr>

SYS22-Cis(config-r)#mode sso    
                         ^
% Invalid input detected at '^' marker.

SYS22-Cis(config-r)#

From RFC 3623 Graceful OSPF Restart
Today many Internet routers implement a separation of control and forwarding functions.  Certain processors are dedicated to control and management tasks such as OSPF routing, while other processors perform the data forwarding tasks.  This separation creates the possibility of maintaining a router's data forwarding capability while the router's control software is restarted/reloaded.  We call such a possibility "graceful restart" or "non-stop forwarding"

Thank you for your support

[Atif Awan · Accepted solution]

Your understanding of SSO is correct in that it requires dual RPs. SSO is used with NSF along with graceful restart protocol support to minimize service interruption in case of failure of the Active RP. While all Cisco devices now support graceful restart as a feature, you can only configure it on devices that have dual RPs. Other devices (like the 3800, 7200) that do not have dual RPs act in what we call a graceful restart helper mode. In this mode these devices understand the graceful restart implementation for various protocols (OSPF, BGP, LDP) and if their graceful restart neighbor undergoes an RP failure these devices help it to gracefully recover from this situation by not bringing down their adjacency with the neighbor. NSR is a relatively recent feature which removes any dependency on neighbors for such failure cases. Again NSR will be applicable to dual RP devices only.

Atif