03-23-2026 12:30 AM - edited 03-23-2026 03:14 AM
Goog day!
FMC 7.6.5 (build 106)
NAT from local net working fine.
Need to NAT server from another vlan to another public IP, not on FTDv OUTSIDE interface ip.
on ASA5550 this works by
nat (inside,outside) source dynamic NAT-SOURCE-SRV NAT-PUB-SRV
I have made same on FMC
> show running-config nat
nat (INSIDE,OUTSIDE) source dynamic NAT-SOURCE-SRV NAT_PUBLIC_SRV
i see xlates to another public ip, also see connections.
but no interfnet on PC....ERR_CONNECTION_TIMED_OUT
no ping outside...
looks like I forgot something..somewhere...
Solved! Go to Solution.
03-24-2026 12:02 AM
there was:
sysopt noproxyarp OUTSIDE
sysopt noproxyarp INSIDE
sysopt noproxyarp management
so I have made a Flexconfig to disable it.
then removed the route and NAT starts to work.
Someone switched off same setting on ASA5550, that's why same config works on asa.
And it is strange, that settings in NAT does not work, untill proxyarp globally disabled.
03-23-2026 01:19 AM - edited 03-23-2026 01:20 AM
FTDv CLI, we see that NAT is going to be .60.40 that is the goal. IP add 60.126 it is ip of FTDv OUTSIDE interface.
But no internet.
packet-tracer shows all "as green and passed"
03-23-2026 01:43 AM
@s_SiD_s I assume 10.201.213.249 is NAT-SOURCE-SRV? Is 60.40 in the same network as the outside IP address of the FTD - therefore the upstream router has a route back via the FTD?
Can you run packet tracer from the CLI and provide the full output (mask your public IP addresses) but provide the full output.
03-23-2026 01:59 AM
03-23-2026 02:27 AM
@s_SiD_s Is proxy arp disabled on that nat rule?
Run "show nat detail" and provide the output.
03-23-2026 03:08 AM - edited 03-23-2026 03:13 AM
> show nat detail
Manual NAT Policies Implicit (Section 0)
1 (nlp_int_tap) to (INSIDE) source static nlp_server__snmp_32_10.201.213.11_intf3 interface destination static 0_10.201.213.11_2 0_10.201.213.11_2 service udp snmp snmp
translate_hits = 0, untranslate_hits = 0
Source - Origin: 169.254.1.2/32, Translated: 10.201.98.101/29
Destination - Origin: 10.201.213.11/32, Translated: 10.201.213.11/32
Service - Protocol: udp Real: snmp Mapped: snmp
2 (nlp_int_tap) to (OUTSIDE) source static nlp_server__ssh_10.129.0.0_intf2 interface destination static 0_10.129.0.0_3 0_10.129.0.0_3 service tcp ssh ssh
translate_hits = 0, untranslate_hits = 0
Source - Origin: 169.254.1.2/32, Translated: xx.xx.60.126/25
Destination - Origin: 10.129.0.0/16, Translated: 10.129.0.0/16
Service - Protocol: tcp Real: ssh Mapped: ssh
3 (nlp_int_tap) to (INSIDE) source static nlp_server__ssh_10.129.0.0_intf3 interface destination static 0_10.129.0.0_5 0_10.129.0.0_5 service tcp ssh ssh
translate_hits = 0, untranslate_hits = 0
Source - Origin: 169.254.1.2/32, Translated: 10.201.98.101/29
Destination - Origin: 10.129.0.0/16, Translated: 10.129.0.0/16
Service - Protocol: tcp Real: ssh Mapped: ssh
4 (nlp_int_tap) to (INSIDE) source static nlp_server__ssh_10.201.64.0_intf3 interface destination static 0_10.201.64.0_4 0_10.201.64.0_4 service tcp ssh ssh
translate_hits = 0, untranslate_hits = 0
Source - Origin: 169.254.1.2/32, Translated: 10.201.98.101/29
Destination - Origin: 10.201.64.0/24, Translated: 10.201.64.0/24
Service - Protocol: tcp Real: ssh Mapped: ssh
5 (nlp_int_tap) to (OUTSIDE) source dynamic nlp_client_0_10.129.0.0_6proto22_intf2 interface destination static nlp_client_0_ipv4_2 nlp_client_0_ipv4_2 service nlp_client_0_6svc22_1 nlp_client_0_6svc22_1
translate_hits = 0, untranslate_hits = 0
Source - Origin: 169.254.1.2/32, Translated: xx.xx.60.126/25
Destination - Origin: 10.129.0.0/16, Translated: 10.129.0.0/16
Service - Origin: tcp destination eq ssh , Translated: tcp destination eq ssh
6 (nlp_int_tap) to (INSIDE) source dynamic nlp_client_0_10.129.0.0_6proto22_intf3 interface destination static nlp_client_0_ipv4_6 nlp_client_0_ipv4_6 service nlp_client_0_6svc22_5 nlp_client_0_6svc22_5
translate_hits = 0, untranslate_hits = 0
Source - Origin: 169.254.1.2/32, Translated: 10.201.98.101/29
Destination - Origin: 10.129.0.0/16, Translated: 10.129.0.0/16
Service - Origin: tcp destination eq ssh , Translated: tcp destination eq ssh
7 (nlp_int_tap) to (INSIDE) source dynamic nlp_client_0_10.201.64.0_6proto22_intf3 interface destination static nlp_client_0_ipv4_4 nlp_client_0_ipv4_4 service nlp_client_0_6svc22_3 nlp_client_0_6svc22_3
translate_hits = 0, untranslate_hits = 0
Source - Origin: 169.254.1.2/32, Translated: 10.201.98.101/29
Destination - Origin: 10.201.64.0/24, Translated: 10.201.64.0/24
Service - Origin: tcp destination eq ssh , Translated: tcp destination eq ssh
Manual NAT Policies (Section 1)
1 (INSIDE) to (OUTSIDE) source dynamic VLAN_213 NAT_125 dns
translate_hits = 371, untranslate_hits = 0
Source - Origin: 10.201.213.0/24, Translated: xx.xx.60.125/32
Auto NAT Policies (Section 2)
1 (INSIDE) to (OUTSIDE) source dynamic SPB_BELL_NETWORK interface
translate_hits = 0, untranslate_hits = 0
Source - Origin: 10.206.64.0/24, Translated: xx.xx.60.126/25
2 (INSIDE) to (OUTSIDE) source dynamic NAT_BELL_NETWORK interface
translate_hits = 90770, untranslate_hits = 10777
Source - Origin: 10.201.0.0/16, Translated: xx.xx.60.126/25
>
>
> Proxy ARP is grayed out on that NAT rule
03-23-2026 03:55 AM
03-23-2026 05:18 AM
packet capture/
no reply ...
> capture CAPI trace interface INSIDE match ip host 10.201.213.249 host 77.88.8.8
> capture CAPO interface OUTSIDE match ip any host 77.88.8.8
>
> show capture CAPI
1: 12:08:46.342755 10.201.213.249 > 77.88.8.8 icmp: echo request
2: 12:08:51.339582 10.201.213.249 > 77.88.8.8 icmp: echo request
3: 12:08:56.343106 10.201.213.249 > 77.88.8.8 icmp: echo request
4: 12:09:01.340726 10.201.213.249 > 77.88.8.8 icmp: echo request
5: 12:09:06.341031 10.201.213.249 > 77.88.8.8 icmp: echo request
6: 12:09:11.345593 10.201.213.249 > 77.88.8.8 icmp: echo request
>
> show capture CAPO
1: 12:08:56.343457 xx.xx.60.125 > 77.88.8.8 icmp: echo request
2: 12:09:01.341062 xx.xx.60.125 > 77.88.8.8 icmp: echo request
3: 12:09:06.341397 xx.xx.60.125 > 77.88.8.8 icmp: echo request
4: 12:09:11.346005 xx.xx.60.125 > 77.88.8.8 icmp: echo request
5: 12:09:16.352246 xx.xx.60.125 > 77.88.8.8 icmp: echo request
6: 12:09:21.355480 xx.xx.60.125 > 77.88.8.8 icmp: echo request
> no capture /all
03-23-2026 09:36 AM
Is your outside network a /24? Just asking to confirm that the various addresses you have tested are indeed in the same subnet.
03-23-2026 10:06 AM - edited 03-23-2026 10:27 AM
public network /25
I think proxy arp does not working at all on FMC\FTDv
I have added static route to Border GW - xx.xxx60.125 255.255.255.255 xx.xx.60.126
poiting that .125 in behind OUTSIDE int of FTDv
now, NAT with .125 working as per config.
it is odd...
03-23-2026 07:23 PM
Check your running config for potentially hidden sysopt proxyarp commands:
show running-config all | include sysopt
03-24-2026 12:02 AM
there was:
sysopt noproxyarp OUTSIDE
sysopt noproxyarp INSIDE
sysopt noproxyarp management
so I have made a Flexconfig to disable it.
then removed the route and NAT starts to work.
Someone switched off same setting on ASA5550, that's why same config works on asa.
And it is strange, that settings in NAT does not work, untill proxyarp globally disabled.
03-24-2026 02:28 AM
yeap)
after that, i see a lot of tries or sniff high tcp port on ip .60.125 )
how to stop this nightmare?
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