OSPF Graceful Restart

[ecitele10]

Hi all,

I would very appreciate if you can point me out to Cisco CLI command which begins OSPF Graceful Restart after all GR parameters are set.

Is there "some" Graceful" reset/reboot?

Thanks,

Dmitry Petrunin

[Reza Sharifi]

Hi Dmitry,

Have a look at this doc for OSPF GR commands:

http://www.cisco.com/en/US/docs/ios/ha/configuration/guide/ha-ospf_grrs.html

HTH

[Giuseppe Larosa]

Hello Dmitry,

you would need a device with two route processors to see graceful restart in action.

Indeed the graceful restart refers to a way to improve network convergence when a route processor switchover is performed, either by an operator command either because primary route processor has failed.

neighboring routers if capable of acting as helpers will hide the switchover from the rest of the network for X seconds after having received an LSA telling the node is performing switchover by using an opaque LSA with link local scope so that only adjacent routers receive it.

you could see the opaque LSA received on a neighbor device by using appropriate debug commands.

if after X seconds the local node is not come up completely or a topology change occurs in the OSPF domain the helpers will declare the local node down in OSPF.

A device with a single router processor can act as helper but it is not capable of GRES.

Recently devices like ASR 1000 have introduced a level of virtualisation that may change this rule, as they can run two IOS XE instances at the same time on a single route processor.

Hope to help

Giuseppe

[ecitele10]

Hi All,

Perhaps I asked not clear.

The question is not how configure GR , BUT WHAT is a cli command I have to call in order to begin the GRACEFUL RESTART process? Are there some "reset-command" extension which cause a Router sends Grace LSA and then restart itself.

Still hoping to get response )))),

Dmitry Petrunin

[Giuseppe Larosa]

Hello Dmitry,

as far as I know there isn't such a command, when I tested graceful restart I performed a route processor switchover manually on the device.

An hidden command may exist but I'm not aware of it.

What is the device you have configured for GR?

Does it have two route processors?

Example: c6500 with two sup 720 and SSO enabled, GSR router with two PRP2 and so on

the way to perform route processor switchover is platform dependent.

if you have a branch router for example you haven't two route processors so it can be just an helper

sorry for the basic note but if your device has a single route processor you cannot see advantages from GR

is it more clear now?

edit:

the device has to have two route processors and an indipendent/distributed forwarding plane so that is can foward traffic during switchover

Hope to help

Giuseppe

[Reza Sharifi]

Dmitry,

As Giuseppe noted, there is no such command.  If you meet the requirement Giuseppe noted above and configure GR, then the router will perform the task for you in case there is failure.  You do not need a command to provoke GR for you.

HTH

[Jon Marshall]

Guiseppe / Reza

I tried to answer this question for Dmitry before but ouldn't find the details and don't have a device with 2 router processors.

The RFC for OSPF graceful restart states -

1) if the RP is reloaded administratively ie. it is planned then an OSPF graceful restart LSA should be sent before the RP is reloaded.

2) it the RP crashes or switches over for some other reason not planned the OPSF graceful restart LSA can only be sent when the RP comes back up

I think from this Dmitry assumed, as did i, there might be a command to initiate the LSA before reloading.

Perhaps either -

1) the reload command does issue this LSA automatically because the device has been configured for OSPF graceful restart

or

2) Cisco have not implemented it exactly as the RFC says and they only issue the LSA on reboot not matter whether the reboot was planned or unplanned.

I guess only a packet capture would tell us for sure.

Jon

[Reza Sharifi]

Jon,

I went over this document

http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/gr_ospf.html#wp1054468

I still can't see any command beside the reload command that needs to be issued to provoke GR.

Reza

[ecitele10]

Jon,

You are right assuming that before reload a Router has to send "Grace LSA" in order to prepare its neighbors to Helper mode. Otherwise the Router has to manage sending "Grace LSA" (a.k.a Unplanned GR) in dead interval hopefully that neighbors will handle it before expairing their own "dead interval" , otherwise it would be considered "dead" )).

In general what Giuseppe has written does very make a sense. Probably it is platform dependant and implemented for multi - RP platform. I would rather expect that "pizza-box-router" to support GR , without RP switch over.

Very basic flow.

1. send Grace LSA and go sleep

2. do not touch Data Plane while reloading

3. wake up , set all FIb entries as "stale entries"

4. get adjacent/help from neighbors

5. remove "still-stale-entries" (if not-strict-LSA algorithm)

6. keep on advertizing )))

Thanks,

Dmitry