- The extendable keyword allows the user to configure several ambiguous static translations, where an ambiguous translations are translations with the same local or global address.
The software does not allow two static translations with the same local address, though, because it is ambiguous from the inside. The router will accept these static translations and resolve the ambiguity by creating full translations (all addresses and ports) if the static translations are marked as "extendable".
- Regarding "no-alias": Many customers want to configure the NAT software to translate their local addresses to global addresses allocated from unused addresses from an attached subnet. This requires that the router answer ARP requests for those addresses so that packets destined for the global addresses are accepted by the router and translated. (Routing takes care of this packet delivery when the global addresses are allocated from a virtual network which isn't connected to anything.) 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 can be disabled for static entries by using the "no-alias" keyword
Hope this helps
