Subject: [OSPF] graceful restart doubt

From: "Santosh P K" <[email-masked]>
Date: Thu, 7 Jun 2007 16:36:07 +0530

Hi all,
     I have couple of doubt in graceful restart for ospf.

1.      Router X receives an LSA that is inconsistent with its pre-
         restart router-LSA.  For example, X receives a router-LSA
         originated by router Y that does not contain a link to X, even
         though X's pre-start router-LSA did contain a link to Y.  This
         indicates that either a) Y does not support graceful restart,
         b) Y never received the grace-LSA or c) Y has terminated its
         helper mode for some reason (Section 3.2).

Why is it really required to validate the router LSA?
In all the above three cases mentioned the restarting router can come
to know about inconsistency in hello packet itself, as the hello
received by that restarting router from its previously adjacent
neighbor would contain a one-way.

2    Seciont 2 point 2
        The restarting router runs its OSPF routing calculations, as
         specified in Section 16 of [1].  This is necessary to return
         any OSPF virtual links to operation.  However, the restarting
         router does *not* install OSPF routes into the system's
         forwarding table(s) and relies on the forwarding entries that
         it installed prior to the restart.

At wht point of time I need to run SPF when the router comes up?
Because after adjacency is formaed the restarting router exits
graceful restart and anyways at this point it calculates SPF and
update forwarding table.

Thanks and regards
Santosh P K

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From: Erblichs <[email-masked]>
Date: Thu, 07 Jun 2007 12:36:54 -0700

Santosh,

        Just an an answer to 1.

        Thus, I read "an LSA" as a Grace LSA as an
        example..

        Within "Router X recieves an LSA"...  

        Grace LSAs are Opaque LSAs and Opaque capability
         is first required for GR. Secondly, then the
         understanding of what a Grace-LSA is, and then
         third the willingness to respond to a recieved
         Grace-LSA.

        Mitchell Erblich
        -----------------

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From: "Sundaresan Rajangam - TLS , Chennai" <[email-masked]>
Date: Fri, 8 Jun 2007 09:48:44 +0530

Santhosh

> graceful restart and anyways at this point it calculates SPF and

	SPF will be scheduled or invoked as specified in the RFC 2328.
So, there is   no need to schedule SPF at any other point of time
[specially in graceful-restart mode]. The only thing that needs to be
handled is that, no route should be installed when the router is running
in the graceful-restart mode.

Regards
Sundar

-----Original Message-----
From: Erblichs [mailto:[email-masked]] 
Sent: Friday, June 08, 2007 1:07 AM
To: Santosh P K
Cc: [email-masked]
Subject: Re: [OSPF] graceful restart doubt

Santosh,

        Just an an answer to 1.

        Mitchell Erblich
        -----------------

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From: "Sundaresan Rajangam - TLS , Chennai" <[email-masked]>
Date: Fri, 8 Jun 2007 10:12:46 +0530

Santhosh

Santosh P K wrote:

a) Y does not support graceful restart,
b) Y never received the grace-LSA
 	Router X [running in graceful-restart mode] may send Hello prior
to receiving Hello from Router Y. In this case, inconsistency can be
detected from Y's router LSA. 

c) Y has terminated its helper mode for some reason
	Router Y, on terminating helper mode, need not send Hello with
one-way. Instead, it can reset the adjacency with Router X. 

Regards
Sundar

-----Original Message-----
From: Santosh P K [mailto:[email-masked]] 
Sent: Thursday, June 07, 2007 4:36 PM
To: [email-masked]
Subject: [OSPF] graceful restart doubt

Hi all,

2    Seciont 2 point 2

Thanks and regards
Santosh P K

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