2 networks on Cisco ASA 5510 (out of ip addresses).  Slow migration to new Network

Posted on 2010-01-12
Medium Priority
Last Modified: 2012-05-08
I have a Cisco ASA 5510 on a Class C (/24) network thats running out of IP addresses.  Id like to slowly migrate over to a new network.  The current network has several site to site VPN connections that I dont want to disturb.  I was thinking of establishing another network on a second spare port to create a larger Class C (/22 1022 addresses) or B network and slowly migrating servers over.  I have a spare Domain Controller for the new network but, as I move users over, I want to make sure they will be able to reach the mail and file servers on the original Class C (/24) network.  In addition, the site to site VPN connections in the first class C need to be connected to the new network, with continuous traffic until I can retire the old Class C.
A few questions -
1. If my new network is Class C /24, on port 1 of the ASA, will it be able to transfer traffic to my new network (either Class C /22, or Class B) on port 3 of ASA?  Can a Class C talk to a Class B?
2. Looking for recommendation on best practices for 500 nodes.  Advantages/ Disadvantages for supernetting on Class C (/22, 1022 addresses) or installing Class B.
Question by:checkonetwo
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1 Comment
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Accepted Solution

GuruChiu earned 1600 total points
ID: 26297243
The simple answer to #1 - yes. #2 - no differences.

These are other things that you need to consider:

You need to make sure the ports that connect your two internal networks have same security level, and trun on the ASA feature to allow traffic between same security. The default is not forward.

ASA is not the perfect platform to route between two high speed LAN. If you have a L3 switch, it is better to use a switch for this purpose.

Of course you have to deal with all the issues with changing IP addresses. Another thought for you is why don't you keep two network permanantly. One subnet for servers only, and the other for end users. This way you do not have to change the servers IP addresses. Most end users just get their IP addresses from DHCP and much easier to manage change.

Personally, I will perfer you use a subnet of /22 instead of a full class B /16. Modern network really have no advanage to follow the class boundaries. On the other hand, it uses up address spaces unnecessary. Your company may grow exponentially. You may merge with others. It is more responsible to plan the addressing space wisely than just use a unrealistic large subnet. Anyway a subnet with more than 4,000 machines we need to break it up to limit the bandwidth wasted for boardcast traffic.


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