[j-nsp] helper-only mode for graceful-restart

[Gary Tate]

Dual RE systems are not required to do graceful-restart.  Dual RE 
systems are only required when using graceful-switchover. 

A single RE system can do graceful-restart as this feature keeps 
forwarding information in tact while the RPD or Protocol recovers i.e 
the forwarding plane still functions while the control plane restarts.  
After restarting the helping routers (who have not declared the router 
down) initiate neighbors/adjacencies and retransmit routing information 
and the restarting router synchronises.

A dual RE system can do graceful-switchover whereby the control state is 
duplicated between RE kernels.  If one RE fails the other takes over and 
forwarding is not interupted.  In conjuction with graceful-restart this 
can provice hitless failover.   The forwarding plane is again 
undisturbed as the backup RE takes over masteraship and then protocols 
recover  using graceful-restart/

Let me know if you need any more information

Gary

Pekka Savola wrote:

>Hi,
>
>AFAICS, JunOS allows either:
>  1) no graceful-restart, no GR helper mode (default)
>  2) enabling graceful-restart (and helper mode)
>
>What JunOS does _not_ (AFAICS) support is enabling just the helper 
>mode, but not graceful restart.
>
>This would be extremely useful in the single-RE adjacent routers which 
>should never do graceful restart themselves (because that could result 
>in blackholing traffic), but could still assist the dual-RE routers in 
>their graceful restart.
>
>Have I understood the current features correctly?  Is this a feature 
>others would like to see as well?
>_______________________________________________
>juniper-nsp mailing list juniper-nsp at puck.nether.net
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>
>  
>