09-06-2006 12:07 AM - edited 03-03-2019 01:53 PM
i am trying to summarise following networks on the ABR but its giving an error.
Networks :
192.168.1.16 /28
192.168.1.32 /28
192.168.1.48 /28
192.168.1.64 /28
p1r1(config-router)#area 1 range 192.168.1.16 255.255.255.192
% OSPF: Inconsistent address/mask 192.168.1.16/26 for area range <<<<<<<<<
p1r1(config-router)#
Please suggest !
09-06-2006 12:23 AM
hi,
if you want exclusive summarization (only these networks), than you could summarize ony to these:
192.168.1.16/28
192.168.1.32/27
192.168.1.64/28
with inclusive summary (less summaries, but other networks will as well be included):
192.168.1.0/25
or
192.168.1.0/26, 192.168.1.64/28
hope this helps
anton
09-06-2006 12:27 AM
Hi,
I think in this case the correct summarisation mask would be /25 not /26 becouse the 192.168.1.64 network is not a
part of the /26 summary.
x.x.x.00010000
x.x.x.00100000
x.x.x.00110000
x.x.x.01000000
Hope this helps!
09-06-2006 01:10 AM
Dear Friends,
Fine ! i got what you wanna explain but again there is a doubt.
By norms, if i have 4 contiguous networks to be summarized, its 4 = 2 raise to power 2.
Hence, 2 bits needs to be reduced from the network part of the mask. And the subnet being defined in the configuration is the least among all. Am i right ? Please clarify.
192.168.1.16 /28
192.168.1.32 /28
192.168.1.48 /28
192.168.1.64 /28
p1r1(config-router)#area 1 range 192.168.1.16 255.255.255.192
% OSPF: Inconsistent address/mask 192.168.1.16/26 for area range <<<<<<<<<
p1r1(config-router)#
Thanks.
09-06-2006 01:50 AM
Hi,
You understanding regarding subnets and summarisation is not correct.
Probably you might want to have a look at this document to clarify the concepts.
In your example,
192.168.1.16 /28
192.168.1.32 /28
192.168.1.48 /28
192.168.1.64 /28
You cannot summarise this in to a 192.168.1.16/26.
A /26 means, the first 2 bit in the last octet is reserved for the network.
Last octet bit wise & their decimal value
*****************************************
128 64 32 16 8 4 2 1
Only the following values are possible in the last octet, if you reserve the first 2 bits( in the last octet).
1 => 0
2 => 64
3 => 128
4 => 192
So it can only be
192.168.1.0/26
192.168.1.64/26
192.168.1.128/26
192.168.1.192/26
You can clearly see that the /28 networks that you mentioned are spanning across the first 2 /26 subnets.
Kindly spend some time reading the document that i have highlighted in the above URL. It will be very good to understand the concepts involved in IP addressing.
Hope this helps. Rate the post if you find it useful.
-VJ
09-06-2006 07:31 AM
Dear VJ,
Thanks for the detailed reply.
Let me go through the detailed document once.
Will definately revert back to you with an update.
Cheers !
Hemant.
09-11-2006 04:32 AM
Hi Hemant,
You can try ..
1.
p1r1(config-router)#area 1 range 192.168.1.0 255.255.255.192
Above line covers 1.0 to 1.63
Let this be 192.168.1.64 /28 propogated individually outside the area.
ELSE
2. you can use 192.168.1.0 /25 sunbet in area range.
In both the solutions you cover more IPs than what u have . You have no absolute best solution as the subnets u mentioned cannot be summerized in one line.
Thx,
G
09-11-2006 09:13 PM
After reading the web document that the other poster sent you, you might also want to download the Boson utility called IP Subnet Calculator from http://www.boson.com/FreeUtilities.html. It'll make your life much easier when you're trying to break up or aggregate/summarise subnets.
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