From: Jonathan V Hays (jhays@jtan.com)
Date: Fri Oct 17 2003 - 20:00:27 GMT-3
There is one situation where using the host versus network address
changes the behavior of OSPF, namely the OSPF forwarding address for
Type 5 LSAs.
Let us say we have 3 routers, R10, R11, and R12 connected via an
Ethernet segment, 192.168.1.0/24, with IP addresses 192.168.1.10,
192.168.1.11, and 192.168.1.12, respectively. Below is the ASCII
physical topology.
OSPF+RIP
R11
|
+-----+----+-192.168.1.0/24
| |
R10 R12 RIP-only
OSPF |
only 200.12.12.12/24 (RIP)
From a routing protocol perspective, the logical flow is
R10--OSPF--R11--RIP--R12 with R11 being the ASBR.
Routers R10 and R11 are running OSPF in area 8, R11 is running OSPF and
RIP, and R12 is running RIP only. The RIP route 200.12.12.0/24 is being
redistributed into OSPF on R11. This route will show up in the routing
table of R10 (OSPF-only) as a Type 5 (O E2) with a next hop of ... well,
it depends.
If the ASBR (R11) OSPF config is "network 192.168.1.0 0.0.0.255 area 8"
then the Type 5 forwarding address for 200.12.12.0/24 will be
192.168.1.12 and packets will go directly from R10 to R12. This is a
good thing.
But if R11's OSPF config is "network 192.168.1.0 0.0.0.0 area 8" then
the Type 5 LSA forwarding address advertised by R11 is set to null or
0.0.0.0 and packets going from R10 to R12 will be forwarded through the
ASBR, R11. This is an unnecessary hop.
It is the use of 0.0.0.0 as the wildcard mask in the OSPF network
statement that negates this useful feature.
HTH,
Jonathan
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Mac
Sent: Thursday, October 16, 2003 11:31 PM
To: ccielab@groupstudy.com
Subject: OSPf Network command
Dear all,
Just wonder what is the difference of configuring ospf using host
addreess and
network address under router configuration, example as below:
Using host address:
router ospf 1
network 192.168.1.1 0.0.0.0 area 0
Using network address:
router ospf 1
network 192.168.1.0 0.0.0.255 area 0
Thanks a lot,
++++
MAC
++++
This archive was generated by hypermail 2.1.4 : Mon Nov 24 2003 - 07:53:04 GMT-3