Subject: OSPF Adjacencies

From: Kerpal Abdar <[email-masked]>
Date: Thu, 17 Oct 2002 13:09:32 -0700

Hi All,

  I am looking to understand what are the reason in which an OSPF adjacency
may be torn down (aside from physical layer issues and RouterDeadInterval).

More specific, would not receiving an acknowledgement for a LSU result in an
adjacency to be torn down?

thanks

Kerpal

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From: Sina Mirtorabi <[email-masked]>
Date: Thu, 17 Oct 2002 15:24:59 -0700

Kerpal,

> may be torn down (aside from physical layer issues and

those are actually the main one, receiving a 1 one way Hello also tear down
an adj

> adjacency to be torn down?

some implementation tear down the adj after N number of retransmission for
update or DBD packet
RFC actually states that if ack is not received, retransmission will
re-occur until adj is destroyed by Hello. mostly this condition would be
enough for non-DC link but might not be in some very rare cases for example
if Hello packet make it through and not the update ( say because of the
packet size the packet gets corrupted on lower layer etc ) ....

Sina

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From: "Kerpal.Abdar" <[email-masked]>
Date: Thu, 17 Oct 2002 21:17:52 -0400

Gotcha.  After I had sent the question, I found the section in the RFC that
speaks about this (page 88).  However, I was unable to find where it states
that if ack is not received, retransmission will re-occur until adj is
destroyed by Hello.  Could you point me to this?

In addition, does the "lack of not receiving an ack and retransmitting the
update until adj is destroy by hello"  then tell me that the adjacency is
not actually brought down by the lack off acks but by the lack of a hello.
Is this correct?

Is it mandatory for ALL updates to be ack?

Is it that common to see implementations of OSPF tear down the adj after N
number of retransmission for update or DBD packet? Do you know which vendors
actually do this?

Thank you!

Kerpal

-----Original Message-----
From: Mailing List [mailto:[email-masked]]On Behalf Of Sina
Mirtorabi
Sent: Thursday, October 17, 2002 6:25 PM
To: [email-masked]
Subject: Re: OSPF Adjacencies

Kerpal,

Sina

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From: Sina Mirtorabi <[email-masked]>
Date: Fri, 18 Oct 2002 09:03:56 -0700

Kerpal

> destroyed by Hello.  Could you point me to this?

see end of section 13.6

> not actually brought down by the lack off acks but by the lack of a hello.

Padma already answered this

> Is it mandatory for ALL updates to be ack?

yes unless it is received less than MinLSArrival

> number of retransmission for update or DBD packet? Do you know

Cisco does it and we do for both DC and non-DC link, further setting N is
configurable and can also be disabled through configuration

Sina