Subject: Re: Message Flow after Link Failure

From: Christian Glomb <[email-masked]>
Date: Tue, 10 Sep 2002 08:00:22 -0400

Acee, Vishwas,

thank you for your comments. I will try to summarize what
I've learned now:

1.
At Router A the state (in the neighbor conversation state
machine) for Router B goes to state "Down".

The following operations are then performed:
- Clear the LS Retransmission List, Database Summary List
  and the LS Request list for this neighbor.
- Cancel any pending timers.
- Destroy any pending retransmission messages.

In the interface state machine the state for the interface
connecting to Router B also goes to state "Down". Is this
true?

Refering to section 12.4 of RFC 2328 a LINK_STATE_UPDATE
containing a Router-LSA is then originated since
"
 (2) An interface's state changes (see Section 9.1).  This may
     mean that it is necessary to produce a new instance of the
     router-LSA.
"
and
"
 (4) One of the neighboring routers changes to/from the FULL
     state.  This may mean that it is necessary to produce a new
     instance of the router-LSA.  ...
"

2.
At the receipt of the LINK_STATE_UPDATE message at the remaining
neighbor routers of Router A, the flooding procedure as described
in section 13 of RFC 2328 starts at these remaining neighbors.

3.
Vishwas said: "The neighbor list in a hello consists of neighbor on
that particular interface not all neighbors on all interfaces."

Assuming that we have no networks within an area, there is always
one neighbor router connected to one interface and thus there is
only one NEIGHBOR ID per HELLO message. Is this true?
What happens if we have networks within an area? Are there HELLOs
from all routers of these networks sent to the DR of each network
which in turn includes all NEIGHBOR IDs in the HELLO message sent
to the neighbor in the area? Or does the area neighbor of the DR
only see the NEIGHBOR ID from itself?

For clarification:

            AS
       ´     |   `
    ´        |      `
  ´          |         `
Area_1     Area_2    Area_n
         ´   |   `
       ´     |     `
     NW_1   NW_2   NW_n

Thanks again a lot!

Christian.

---

From: Acee Lindem <[email-masked]>
Date: Tue, 10 Sep 2002 09:34:53 -0400

Hello Christian,

I'm assuming the event triggering this is a neighbor
inactivity timeout between routers A and B on a single
OSPF interface.

> connecting to Router B also goes to state "Down". Is this

No. OSPF neighbor FSM changes will not bring the OSPF
interface FSM down.

> only see the NEIGHBOR ID from itself?

I think there is some confusion here. Neighbors are maintained on
an OSPF interface level. The only neighbors IDs included in HELLO
messages are those for neighbor on that interface (of course, the
areas also need to match or the hello will be rejected).

--
Acee