From: Lord, Chris (chris.lord@lorien.co.uk)
Date: Mon May 24 2004 - 08:56:49 GMT-3
Emil,
Here goes......
OSPF network types Broadcast and non-Broadcast elect a DR/BDR
OSPF network types p-t-p, p-t-m and p-t-m non-broadcast do not elect a DR/BDR
Now, the hello packets being sent between neighbors have a DR and BD Router-ID field (ref Doyle Vol1 p498). The question is if you are using a network type where there is no DR/BDR on the network what information is the sending router going to put in to these fields. Ans 0.0.0.0 The point is not what the actual router ID is but what the DR/BDR ID is - I think?
Check it out. Build a simple hub & spoke FR network: R2--R1--R4 where R1 is the hub. Use "ip ospf net point-to-m" then on R1 do a "sh ip ospf neigh detail" and look at the DR/BDR router IDs on the 4th line down:
R1#sh ip ospf neigh det
Neighbor 151.10.100.4, interface address 151.10.124.4
In the area 0 via interface Serial0/0
Neighbor priority is 0, State is FULL, 6 state changes
DR is 0.0.0.0 BDR is 0.0.0.0
Options is 0x52
Dead timer due in 00:01:59
Neighbor is up for 00:02:00
Index 2/2, retransmission queue length 0, number of retransmission 1
First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
Last retransmission scan length is 1, maximum is 1
Last retransmission scan time is 0 msec, maximum is 0 msec
Neighbor 151.10.124.2, interface address 151.10.124.2
In the area 0 via interface Serial0/0
Neighbor priority is 1, State is FULL, 6 state changes
DR is 0.0.0.0 BDR is 0.0.0.0
Options is 0x52
Dead timer due in 00:01:44
Neighbor is up for 00:02:13
Index 1/1, retransmission queue length 0, number of retransmission 1
First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
Last retransmission scan length is 1, maximum is 1
Last retransmission scan time is 0 msec, maximum is 0 msec
R1#
Best regards,
Chris.
-----Original Message-----
From: Fernando, Emil [mailto:emil.fernando@atosorigin.com]
Sent: 24 May 2004 08:29
To: Lord, Chris
Subject: RE: can 0.0.0.0 be used as a router ID in ospf ?
Chris,
Thanks for your reply. Could you explain this bit more. I am still confused
as the router refuse to accept this in ospf.
Are you saying that when a router has broadcast interfaces under ospf, it is
not possible to make router-id 0.0.0.0 on it.
please correct me if I misunderstand..
Is there a way that I can make a neighbour router-id appears as 0.0.0.0 from
sh ip ospf nei
Thanks
Emil
-----Original Message-----
From: Lord, Chris [mailto:chris.lord@lorien.co.uk]
Sent: Monday, 24 May 2004 4:43 PM
To: Fernando, Emil
Subject: RE: can 0.0.0.0 be used as a router ID in ospf ?
Hi,
Not explicitly. However, if you are faced with a frame-relay scenario where
the OSPF DR/BDR needs to have a router ID of 0.0.0.0 it is instructing you
to use "ip ospf net point-to-multipoint" command. Under these circumstances
no DR/BDR is elected so none exist. The OSPF routers register this by
setting their DR/BDR flags to 0.0.0.0
Hope this helps.
Regards,
Chris.
-----Original Message-----
From: Fernando, Emil [mailto:emil.fernando@atosorigin.com]
Sent: 24 May 2004 02:53
To: ccielab@groupstudy.com
Subject: can 0.0.0.0 be used as a router ID in ospf ?
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