Well, yes, you can run backup interfaces with OSPF. However, because OSPF
doesn't do unequal-cost load balancing, you have a problem.
If you set the bandwidth on each interface to be the real bandwidth (and don't
fiddle with the OSPF costs directly), then your backup link S3 will be activated
by the load, but OSPF will not send any traffic down it because S3 will have a
higher cost than S1.
Your other option is to 'fudge' the OSPF costs, either by setting the bandwidth
on the two links the same or by using the 'ip ospf cost' command. However if
you do this, OSPF will send equal amounts of traffic down each link (give or
take a bit depending on whether you're doing per-destination or per-packet
balancing). This is likely to actually REDUCE your throughput, because S3 will
be flooded while S1 will be just ticking over at 128Kbps instead of 512Kbps
(been a while since I've seen this in practice but from memory S1 in this
situation will NOT run at 512 Kbps).
I think you'd need to run EIGRP to be able to do this effectively with
different-speed links. Any other thoughts, anyone?
JMcL
---------------------- Forwarded by Jenny Mcleod/NSO/CSDA on 16/11/2000 11:33 am
---------------------------
"ZAPP, JULIAN F (PB)" <[EMAIL PROTECTED]> on 16/11/2000 09:31:15 am
Please respond to "ZAPP, JULIAN F (PB)" <[EMAIL PROTECTED]>
To: "'[EMAIL PROTECTED]'" <[EMAIL PROTECTED]>
[EMAIL PROTECTED]
cc: (bcc: JENNY MCLEOD/NSO/CSDA)
Subject: RE: backup interface on ospf router
Unless you are using the second circuit for something special like Voice
over IP, you should set the bandwidth under each interface and let OSPF do
the rest.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Friday, November 10, 2000 12:51 AM
To: [EMAIL PROTECTED]
Subject: backup interface on ospf router
Hi all,
Can we have a backup interface on an ospf enabled
router.
for example.
Router ospf 100
network x.x.x.x
...
interface s1
ip address x.x.x.x ...
backup interface serial 3
backup load 60 5
....
Is it possible with ospf enabled router.
Both the interface S1 and S3 are going to same
destination with different speed.
S1= 512 KBPS
S3= 128 KBPS
thanks in advance
pratik
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