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ASA NAT for SFTP Server Migration (maybe)

Hello, just wondering if anyone has done this and might have some tips, please ?

Due to an ftp (sftp) server migration a developer has asked me if:

For outgoing connections, the new server and the old server, say ip's = S1 and S2, can use the same existing public ip that S1 currently uses, say ip = P1. (He doesn't want the external suppliers to have change their firewall rules - he says there are only about 6 external suppliers)

For incoming unsolicited connections, the servers can also share this same ip P1 (using the same port = tcp 22).

The existing server has an existing simple static auto nat such that for both o/g and i/c connections, S1<=>P1.

e.g. (using S1 and P1 for the host ip addresses)

object network obj-S1

host S1
nat (dmz1,outside) static P1


My initial thought was 'no' but out of curiosity I'm wondering if the following would work:

a. Remove the existing nat

b. Add new twice nats so that each external supplier, say X1 to X6 can be migrated in turn such that we'd have as a first step

X1 is routed via P1 to S2

X2 to X6 are routed via P1 to S1 (as existing).


object network obj-S1

host S1

object network obj-S2

host S2

object network obj-P1

host P1

object network obj-X1

host X1 - (might be a range but using single hosts for simplicity)

object network obj-X2

host X2

object network obj-X3

host X3



nat (dmz1,outside) source static obj-S2 obj-P1 destination static obj-X1 obj-X1

nat (dmz1,outside) source static obj-S1 obj-P1 destination static obj-X2 obj-X2

nat (dmz1,outside) source static obj-S1 obj-P1 destination static obj-X3 obj-X3

nat (dmz1,outside) source static obj-S1 obj-P1 destination static obj-X4 obj-X4


Thanks in advance for any suggestions.

I wouldn't consider this if there weren't just a few external suppliers and even writing it out like this makes me think he should just tell the suppliers to add the new server.

Thanks again.




Managed to get hold of a spare small ASA (5506) and tried this - worked OK. Didn't need to remove the existing object auto NAT as the new manual twice NATs take precedence. We're not translating the external ip but need to match on it. So suppliers can be migrated one by one if needed.

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