NSR, NSF and graceful restart

[Hariharasudhan Natarajan]

Hello all,

I have understand the difference between NSF and NSR. NSF supports forwarding without traffic loss during a brief outage of the control plane. Whereas NSR allows for the forwarding of data packets to continue along known routes while the routing protocol information is being refreshed following a processor switchover.

Would like to know

1. Working principle of Graceful restart.

2. Do we need to enable gracefule restart along with NSF abd NSR?

3. What is the advantage of enabling Graceful restart with NSR?

4. If possible, please explain what is checkpointing and mirroring?

Thanks

Hari

[xthuijs]

Hi Hari,

Ah I think I provided a lot of that detail in your other discussion you started.

To sume up:

1) GR assists in not declaring a peering down (grace period) while the control plane is converging.

while this is happening the FIB maintains its forwarding table as it knew it was before the convergence. this is also called "headless routing"

2) NSF is by default in XR/A9K because of its distributed architecture. It mainly is composed of the SSO functionality, and yes GR will definitely help but not mandated.

NSR is a separate option to maintain a routing peering by syncing state and seq numbers between active and standby control plane.

4) checkpointing is the concept of making snapshots of data and synchronizing or saving that to a particular location. Mirroring, yeah that is something you look at when you shave in the morning, or it is just the same as checkpointing really. Checkpoints are usually done in batches, at least that is what the concept refers to.

regards

xander

[eric.follos]

Xander,

So if I follow, NSR on a 9001 serves no purpose (say with process restarts) unless you have clustering enabled?

Thanks,

Eric

[xthuijs]

hey eric, correct,NSR/NSF is useful for dual RP systems, the 9001 is a single RP system hence serves little (=no?:) purpose...!

cheers!

xander

[Matt A]

If you have a process-restart SMU, GR on the device will be useful as it will prevent traffic routing around the device when peering drops due to SMU initiated restart.

[adorins]

So it turns out that there is a reason to enable nsr/nsf/gr even on a single-rsp box like asr9001? Or in case of some service restart (by SMU or manually) IOS XR by default uses nsr to leave packet forwarding in place during a process restart, without any explicit configuration for routing protocols?

[xthuijs]

nsr state sync between active/standby is not applicable on the 9001 obviously.

nsf, the forwarding is by nature of a distributed system.

cheers!

xander

[KATTUBAVA E.S]

Check this article by Jeff Doyle

http://www.networkworld.com/article/2347847/cisco-subnet/nsf--nsr--and-gr.html

HTH

bava

[mythology]

Better explained in the below link

http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/high-availability/solution_overview_c22-487228.html

Graceful Restart (GR) (also known as Non Stop Forwarding (NSF)) and Non Stop Routing (NSR) are two different mechanisms to prevent routing protocol re-convergence during a processor switchover.

When Graceful Restart (NSF) is used, peer networking devices are informed, via protocol extensions prior to the event (so peers should also be NSF (GR) capable). The peer routers are aware of a failure and so  will give the switching over router a "grace" period to re-establish the neighbor relationship, while continuing to forward to the routes from that peer.
When NSR is used, peer networking devices have no knowledge of any event on the switching over router. All information needed to continue the routing protocol peering state is transferred to the standby processor so it can "pick up" immediately upon a switchover. NSR is desirable in cases where the routing protocol peer doesn't support the RFCs necessary to support Graceful Restart.

[Vahid Tavajjohi]

Hari,

I think we can describe difference between NSR and NSF as below:

NSR is for control plane and NSF is for data plane. wherever you need forwarding you should choose NSF and wherever you need Routing convergence , you should choose NSR.