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Ask the Expert- SD-WAN

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Resubnetting IP Address

Hello All

I am facing an issue in my production environment.

Right now one one of our office using an IP Pool, For example-  SITE_A- (192.168.38.0/24)

but I have been asked for subnet this pool (first 32 address) and use this on another site.

For Example- 192.168.38.0/27 for SITE_B

This is ok !! but problem is that they asked me to not to subnet more for remaining IP and all remaining address will be used as a single

subnet for SITE_A.....

CONCLUSION IS... I have 192.168.38.0/24 network.

I want to use 192.168.38.0/27 for SITE_B --- 192.168.38.0 to 192.168.38.31

and remaining address 192.168.38.32 to 192.168.38.255  for SITE_A (one subnet)

Is this possible??? 

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VIP Collaborator

No, since you assigned the

No, since you assigned the /27 to the other site, you cannot allocate 192.168.38.32 - 255 in a single network.

The largest single subnet you can assign would be 192.168.38.128 - 255, or a /25. After that you have the following networks available: 192.168.38.64 - 127, or a /26, and 192.168.38.32 - 63 or a /27.

Hall of Fame Master

I would suggest that there is

I would suggest that there is more than one way to look at this question and its answer. The answer that you can not have the /27 at a different site is the easy answer and in some aspects would be the correct answer. But there is another way to look at this issue. If you have the ability to assure that site A will not use any of the addresses between 192.168.38.0 and 192.168.38.31 then it could work ok for site B to use those addresses. The result would be that both sites would have a route for 192.168.38.0/24 pointing to site A and another route for 192.168.38.0/27 which points to site B. Both routes are valid and could be present in the routing table at the same time. A basic principle of IP routing is that longest match wins. So all sites would route 192.168.38.1 through 192.168.38.31 to site B while routing the rest of the subnet to site A.

HTH

Rick

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