RE: OSPF Adj in case of different subnet masks of neighbours

From: Scott Morris (smorris@internetworkexpert.com)
Date: Sun Oct 26 2008 - 19:57:14 ARST

With point-to-point links, from back in the old dialer days, the subnet mask
doesn't need to match up (spelled out in the RFC).

For other network types, it does indeed need to match and is part of the
adjacency requirements.

Scott Morris, CCIE4 #4713, JNCIE-M #153, JNCIS-ER, CISSP, et al.
CCSI/JNCI-M/JNCI-ER
Senior CCIE Instructor

smorris@internetworkexpert.com

 

Knowledge is power.
Power corrupts.
Study hard and be Eeeeviiiil......
 

-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Fahad Khan
Sent: Sunday, October 26, 2008 4:25 PM
To: Cisco certification
Subject: OSPF Adj in case of different subnet masks of neighbours

Dear All,

Have a look to the scenario,

R1(s1/0-10.0.0.1/*16*)------------------(10.0.0.2/*8*-s1/0)R2

*OSPF adj forms* in case if i set the network type "point-to-point" on both
serial interfaces

But if I set network type as "Broadcast", *adj is not formed*

and the "debug ip ospf adj+events+packets" looks like (on R1);

*Mar 1 00:08:58.783: OSPF: Send with youngest Key 0 *Mar 1 00:08:58.783:
OSPF: Send hello to 224.0.0.5 area 0 on Serial1/0 from 10.
0.0.1
*Mar 1 00:09:06.431: OSPF: rcv. v:2 t:1 l:44 rid:2.2.2.2
      aid:0.0.0.0 chk:0 aut:2 keyid:0 seq:0x3C7EC691 from Serial1/0 *Mar 1
00:09:06.435: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial1/0 10.0.0.
2
*Mar 1 00:09:06.439: OSPF: Mismatched hello parameters from 10.0.0.2 *Mar
1 00:09:06.443: OSPF: Dead R 40 C 40, Hello R 10 C 10 Mask R 255.0.0.0 C
255.255.0.0

Can any body shed light on the reason behind all this?
Thanks in advance

best regards, 

--
Fahad Khan

Blogs and organic groups at http://www.ccie.net

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