I have a query in one fundamental concept
In NAT, I am seeing the optional keyword "reversible". Cisco Literature says as below:
"(Optional) Enables outside-to-inside initiated sessions to use route maps for destination-based NAT."
I tried hard to understand and googled enough to know the use of this command. But I am not able to get any clues.
I tried this in a Lab environment also. The setup is as below:
R1 ---> R4-----> R5
R4 NAT CONFIG:
ip nat pool 1 220.127.116.11 18.104.22.168 prefix-length 24
ip nat pool 2 22.214.171.124 126.96.36.199 prefix-length 24
ip nat inside source route-map SAIRAM-1 pool 1
ip nat inside source route-map SAIRAM-2 pool 2
It is working fine If I initated icmp traffic from R1 to R5 Loopback (188.8.131.52). Once the NAT translation entry is created in R4 I am able to ping R1 NATed IP (184.108.40.206 defined in pool) from R5
But after clearing NAT translation, I am not able to ping 220.127.116.11.
I expected that that from R5 i will be able to ping R1 NATed IP 18.104.22.168 even before the traffic is initiated from R1. It failed to work!!!!!
Can you give your valuable time to tell me with an example the purpose of this command
Thanks in advance
I haven't used the "no-alias" personally but I believe that it can be attributed mostly to conserving system resources.
You can imagine that if you are using a large NAT pool that contains hundreds of addresses, maintaining all those aliases can be quite memory and CPU consuming. In that case, you can use the "no-alias" keyword and instead advertise the address range of the NAT pool in a routing protocol, for example:
ip nat pool MyPool 192.0.2.0 192.0.2.255 netmask 255.255.255.0
ip route 192.0.2.0 255.255.255.0 Null0
redistribute static ...
ip nat inside source list YYY pool MyPool no-alias