NAT with PAT: single address pool or interface overload ?

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Hello,

If I understand correctly, on Cisco routers you can configure NAT with
PAT using a single public IP address in two ways:

1) Define a pool of just one IP address. Then overload the pool with
the following command:

#ip nat inside source list 1 pool poolname overload

2) Do not use pools but just overload the interface with a public IP,
like:

#ip nat inside source list 1 interface serial 0 overload

Am I correct ? I ask because in the additional chapter on NAT
(ftp://ftp.sybex.com/4391/4391CCNA_NAT.pdf ) Todd Lammle doesn't mention
case 2) at all and I wonder if there is a technical reason to prefer
option 1) vs option 2).

Also, in the event a question like this pops up in the CCNA
certification sim, would both answers be considered correct ?

Finally, one last question: Does the network mask in the pool
declaration need to be precise or not ? The same Lammle changes each
time in his own chapter like this:

ip nat pool poolname 198.18.131.65 198.18.131.70 255.255.255.0

and

ip nat pool poolname 198.18.131.65 198.18.131.70 255.255.255.248

If it's the same, the once again how area those two going to be
evaluated by the sim software ? is it smart enough to contemplate such
cases ?

Thank you.



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