From: Adam Crisp (adam.crisp@totalise.co.uk)
Date: Fri Nov 29 2002 - 12:45:57 GMT-3
Hi David,
It's perfectly OK to have a split area 4. This is because each ABR will
forward type 1,2,& 3 LSA's without interfering.
The Backbone will therefore know which ABR to use to get to each subnet.
You run into problems however when you start summarising!!!!
If your summarising blocks the type 1&2 LSA's then you wont have a valid
routing table in the backbone and you'll loose half the packets or worse
depending on your configuration.
Yes, you can improve things by making the R3/R4 link area 4, however then
you run into the same problem but in reverse if you loose the link between
(R4 and R6) or (R3 and R5)
Summarising routes in OSPF is actually even more complicated when you
consider what area the loopback address should reside in ;-)
For maximum stability in big network you'll see extra links for redundanc
cheers
Adam
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
David Bader
Sent: 29 November 2002 14:33
To: CCIE Lab (E-mail)
Subject: OSPF Split nonzero area
Hi all
As we all know a split area zero in OSPF is a bad thing. My problem is i
have a split area 4, this is my scenario:
R1-----------R2
| |
| 4 |
| |
R3-----------R4
| |
| 0 |
| |
R5-----------R6
R3, R4, R5 and R6 are in area 0. R1, R2 and the two interfaces from R3 and
R4 are in area 4.
My problem is. If i shut down the link between R1 and R2 i have two area 4!
Is this a problem?
If R4 and R3 are summarising, they will advertise the same supernet!!!
Is there a workaround or a general design recommandation to this scenario?
Is it possible to include the link between R3 and R4 into area 4 and area 0
and would this be ok?
thanks for your help!!
regards dave
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