From: Huizinga, Rene (rhuizinga@upcbroadband.com)
Date: Thu Mar 29 2007 - 18:49:37 ART
Hi Premkumar,
The network-command under OSPF simply stated is there to define an IP-range
within which the router is scanning all of it's local interfaces that fall
within it. For all interfaces it finds within that range, it'll ensure it's
taken up into OSPF, within the area configured at the end of the
network-command.
One can e.g. define an address with a '0.0.0.0' wildcard-mask to
specifically identify a single interface instead of using the real subnet.
But also, as you can see now, if one would use e.g. 'network 0.0.0.0
255.255.255.255 area 0', the router would take all of it's interfaces
configured with IP and place all of them into OSPF, using area 0 for this
example here.
Can be easy, but at the same time also backfire practically in case your
network was setup initially like this and you later add e.g. a small
management-subnet which you didn't actually want into OSPF.
A sample:
Interface fa0/0 has as ip-address 192.168.1.1 , subnet-mask 255.255.255.0.
Now all 4 variants stated below will put it into ospf, area 0:
1. network 192.168.1.1 0.0.0.0 area 0
2. network 192.168.1.0 0.0.0.3 area 0
3. network 192.168.1.0 0.0.0.255 area 0
4. network 0.0.0.0 255.255.255.255 area 0
The best option/best practice would normally be to use option 3. It uses the
real subnet configured for that interface. Also it gives you a better
overview within the router ospf config on which subnets are included.
Option 1,2 and 4 will do the same but identifies it specifically (1),
identifies a small range in which the router will also find this interface
(2) or identifies the whole IPv4 range, risking that other unwanted
interfaces are taken into OSPF as well.
When wanting to use an aggregate to include OSPF-interface, use at least as
best-practice the 'passive-interface default' command with it and 'activate'
interfaces individually with the 'no passive-interface' command to identify
which ones you'd want to be active and form an adjacency. That won't solve
the issue of e.g. having the same network being advertised multiple times
into OSPF in case of local management-links for example, but would at least
be an additional safe-guard.
In favor of using aggregates is the case where one has a nice and tidy
IP-addressing scheme.
eg. One would always use the '192.168.0.0/16' ONLY for internal core-links
within your network which should always be active. In that case one can
include the 'network 192.168.0.0 0.0.255.255 area 0' for all core-link
carrying routers into your config-baseline !!!
Cya
Rene.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
premkumar somasundaram
Sent: Thursday, March 29, 2007 11:24 PM
To: ccielab@groupstudy.com
Subject: Network 0.0.0.0
Team,
Could any one tell me what is the purpose of the command network
0.0.0.0under Eigrp or OSPF??...
Prem
This archive was generated by hypermail 2.1.4 : Sun Apr 01 2007 - 06:35:53 ART