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I have a working configuration on two Juniper Netscreen devices that I'm trying to replicate on an ASA 5505. Here's the scenario:

+-----+   77.77.77.77   +-----+ 10.20.0.0/24 *******
| WAN | =============== | ASA | ------------ * DMZ *
+-----+                 +-----+    VLAN 20   *******
                           |
                           |  10.30.0.0/24   ***********
                           +---------------- * Clients *
                                VLAN 30      ***********

I'm trying to perform PAT on both internal subnets (i.e. so all internal clients can access the internet). However, when I try to configure the NAT rules using ASDM, it says that there's a PAT range overlap. There must be some way to configure the NAT rules such that both zones/subnets can share an external PAT IP (just like in ScreenOS), but I haven't found it yet.

Unfortunately, ordering extra external IPs isn't an option at the moment, so I hope there's a way to do this without purchasing any more gear.

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  • PAT is really made up. The RFCs use NAPT for what some people call PAT. See RFC 2663, IP Network Address Translator (NAT) Terminology and Considerations, Section 4.1.2 Network Address Port Translation (NAPT): "NAPT extends the notion of translation one step further by also translating transport identifier (e.g., TCP and UDP port numbers, ICMP query identifiers). This allows the transport identifiers of a number of private hosts to be multiplexed into the transport identifiers of a single external address." There is more in the RFC.
    – Ron Maupin
    Jan 30 '17 at 15:56
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 12 '17 at 3:58
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I think that should do it:

  object-group FOO
    network-object 10.30.0.0 255.255.255.0
    network-object 10.20.0.0 255.255.255.0

  object network BAR
    host 77.77.77.77

  nat (inside,any) source dynamic FOO BAR
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  • Hey, I know it's been a while since the post. How would this change if "BAR" was a DHCP address? Also, if the two subnets in FOO are in different zones? One inside, one DMZ Sep 18 '16 at 22:25

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