From: OhioHondo (ohiohondo@columbus.rr.com)
Date: Thu Feb 27 2003 - 14:45:31 GMT-3
As Brian mentions there are other methods but as always the best method fits
a particular situation -- as in most things there are trade-offs. Depending
on your needs you may want to choose using the 'area 0 range' command,
making a new area or doing a redistribute connected.
If you are concerned about too many routes in the OSPF area 0, the "area 0
range" command may not be your option.
If your area 0 router has an ASBR connection to an AS running RIP and the
link to the AS uses a classful network that you need to summarize you may
not want to use "area 0 range"
If one of the above is not true then I would use "area 0 range" on all of
the ABR's in the network simply because the same commands can be applied to
every router. This makes it easy to support.
If there are many area 0 routers and you have many of these summaries to do,
you're either creating LSA type 5's (summary address) or a new area at each
router. The design policy is the same but the config at each router is
different. I would think this is harder to support. Additionally, you
probably do not want to create a lot of OSPF areas for this reason unless
it's absolutely necessary. (In the small environment of a test lab or CCIE
test lab it's OK.)
I tested this in my lab and adding 'area 0 range x.x.x.x y.y.y.y" at all
ABR's does work OK. If a network is designed for area 0 to have a specific
block of IP address space, this can be only one (rea range" entry on each
ABR.
As Brian noted, the summary resulting from an "area range" command will not
propagate through the area from which it is configured. So, when "area 7
range x.x.x.x y.y.y.y" is configured on an ABR, that summary does not
propagate to any of the routers in area 7. If you had a need to summarize
routes that originated in area 7 for an ASBR attached to area 7, you would
have the same problems as you encounter with an ASBR connection to area 0.
Also if Area 7 was very large, you would have the same - too large of an IP
routing table -- problem in area 7 as you would in area 0.
The method you use should probably meet the requirements of your situation.
Your comments are solicited...
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Brian Dennis
Sent: Wednesday, February 26, 2003 11:28 PM
To: 'pita40'; ccielab@groupstudy.com
Subject: RE: summary for area 0
If you use the "network" statement to advertise these loopbacks and then
use the "area range" command to summarize them, one of the problems you
can run into is that you can not summarize within the same area. This
means that all routers in the same area as the loopbacks will always see
the specifics. You need to either put these loopbacks into their own
area and then use the "area range" command or redistribute them in
(redistribute connected subnets) and use the "summary-address" command.
Remember to use a route-map if you redistribute connected routes into
OSPF and only allow the loopbacks in.
Here is the exact task from one of my mock labs:
Create four loopback interfaces on R2. Use the 161.X.2.16/28,
161.X.2.32/29, 161.X.2.48/28 and 161.X.2.64/27 subnets from the
161.X.0.0/16 network. Advertise them with OSPF and use only one network
statement for all four loopbacks. Summarize the second and third
loopbacks and ensure that the summary appears as a one network to all
other OSPF routers.
Brian Dennis, CCIE #2210 (R&S/ISP Dial/Security)
brian@labforge.com
http://www.labforge.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
pita40
Sent: Wednesday, February 26, 2003 4:26 PM
To: ccielab@groupstudy.com
Subject: summary for area 0
I have the following lo in area 0
You are told to configure ospf to send one route for the above lo
networks
lo 7.7.1.1/24
lo1 7.7.2.1/24
lo2 7.7.3.1/24
lo3 7.7.3.1/24
How do I make this work. I am aware you cannot summarize area 0.
Peter
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