Cisco IOS NAT automatic aliasing

[snakayama]

Hi everyone,

I have a question about

I understand automatic aliasing is used when inside global addresses in static entries

allocated from unused addresses from an attached subnet.

So the router can answer ARP requests for those addresses and packets destined for the global addresses are accepted by the router and translated.

Above information described in

http://www.cisco.com/en/US/customer/tech/tk648/tk361/technologies_white_paper09186a0080091cb9.shtml

And when disable this automatic aliasing, configure "no-alias" keyword.

My question is;

- What purpose of automatic aliasing ?

Is the purpose of automatic aliasing to answer ARP request for inside global addresses in static entries

allocated from unused addresses from an attached subnet ?

Are there other purpose ?

- What situation need to configure "no-alias" keyword ?

I understand the router does not answer ARP request when "no-alias" configured.

So I confuse when I should configure "no-alias" keyword.

Your information would be greatly appreciated.

Best Regards,

[thomas.chen]

When a NAT pool used as an inside global or outside local pool consists of addresses on an attached subnet, the software will generate an alias for that address so that the router will answer ARPs for those addresses. This automatic aliasing also occurs for inside global or outside local addresses in static entries. It is sometimes useful to disable this for static entries by using the "no-alias" keyword.