Subject: Re: OSPF Adjacencies

From: Maneesh Sharma <[email-masked]>
Date: Fri, 18 Oct 2002 13:40:31 +0530

Padma,

Hello is instrumental in making up and breaking of OSPF adjaciencies.
ACK transmission or  reception is dependent upon adjacency being formed,
which in turn relies on Hello. Hello is like a lower layer protocol
which signals to upper layers whether or not updates can be sent or
acked. In the event of no acks being received for sent updates, the dead
interval timer has to fire before a neighbor can be pronounced dead.

Regards

Maneesh
-----Original Message-----
From: padma [mailto:[email-masked]]
Sent: Friday, October 18, 2002 5:39 AM
To: OSPF
Cc: padma
Subject: Re: OSPF Adjacencies

Kerpal

<Snip>

> >
> > 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?
> >

Yes - according to spec.

> > 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?
> >

It is not common, AFAIK the only implementation that does this is
Cisco's
for over DC. Derek Yeung and I came up with this to solve problem of the
detection of neighbors that died over a DC circuit after being FULL.
This was later documented in a draft.

Padma

> > 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,
> >
> > > 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).
> > >
> >
> > those are actually the main one, receiving a 1 one way Hello also
tear
> > down
> > an adj
> >
> >
> > > More specific, would not receiving an acknowledgement for a LSU
> > > result in an
> > > 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
> >
> >
> > >
> > >
> > > thanks
> > >
> > > Kerpal
> >
>
> _______________________________________________
> Join Excite! - http://www.excite.com
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>

---

From: Padma Pillay-Esnault <[email-masked]>
Date: Fri, 18 Oct 2002 06:30:32 -0700

> interval timer has to fire before a neighbor can be pronounced dead.

We are talking about DC -Demand Circuit here and the hellos are suppressed
so precisely you do not have a Dead timer Interval in Demand Circuit

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>