IP NAT Pool

COG

Hi All,

When configuring ip nat pool, what determines the netmask to be used? I have seen different instances of this.

Please in answering this question, I will appreciate an example to accompany the answer to the question.

Thanks.
COG

EdTheLad

COG wrote:

Hi All,

When configuring ip nat pool, what determines the netmask to be used? I have seen different instances of this.

Please in answering this question, I will appreciate an example to accompany the answer to the question.

Thanks.
COG

The netmask depends on how many public IP addresses you want to use in your pool.For example
ip nat pool test 171.68.1.1 171.68.1.10 netmask 255.255.255.240

In this example with this mask it will allow
a range 171.68.1.1 -> 171.68.1.15

If you dont understand this go back and study subnet masks!

p.s A nice little edit to fix the post!

COG

Thanks ed, but I think your answer is a bit muddled up.

You have specified a range for your inside global address which is 171.68.1.1 171.68.1.10 and then you give a netmask that is supposed to widen your range (AFTER SPECIFYING A RANGE ALREADY):"171.68.1.1 -> 171.16.15.254" (now there is also a typo here, since the address range cannot go from 171.68.1.1 to 171.16.15.254). Netmasks are supposed to help you specify sub-network and host ranges.

I do not buy this: "The netmask depends on how many public IP addresses you want to use in your pool.",.... but you already have specified the range??

It does not sound right. I would rather consider a statement that says it depends on the number of "inside local addresses" that you desire to be mapped.

Please can someone clear the air here?

COG

EdTheLad

COG wrote:

I do not buy this: "The netmask depends on how many public IP addresses you want to use in your pool."

I does not sound right. I would rather consider a statement that says it depends on the number of "inside local address" that I want to map.

This all depends on which way you look at it! What i was saying is it depends on how many inside global addresses you have and want to use!

Yep, typo's everywhere , i just did a copy and paste which didnt work out as planned.

The subnet mask is used to check the addresses allocated from the pool (so you don't allocate the subnet broadcast address, for example). The subnet mask must match the size of the subnet into which you are translating.