[SOLVED] Hidden (default) NAT-Rule?

kroerig · ‎12-27-2021

Hello,

are there any hidden (default) NAT rules on an ASA 5506-X with software 9.14?

I didn't configure any NAT rules but any device on the inside net can access the outside network.

packet trace says:

Phase: 1
Type: ACCESS-LIST
Subtype:
Result: ALLOW
Config:
Implicit Rule
Additional Information:
 Forward Flow based lookup yields rule:
 in  id=0x7f870f22e200, priority=1, domain=permit, deny=false
        hits=1654056, user_data=0x0, cs_id=0x0, l3_type=0x8
        src mac=0000.0000.0000, mask=0000.0000.0000
        dst mac=0000.0000.0000, mask=0100.0000.0000
        input_ifc=inside, output_ifc=any

Phase: 2
Type: INPUT-ROUTE-LOOKUP
Subtype: Resolve Egress Interface
Result: ALLOW
Config:
Additional Information:
Found next-hop 62.156.244.XXX using egress ifc  outside

Phase: 3
Type: NAT
Subtype: per-session
Result: ALLOW
Config:
Additional Information:
 Forward Flow based lookup yields rule:
 in  id=0x7f870de469c0, priority=0, domain=nat-per-session, deny=false
        hits=266366, user_data=0x0, cs_id=0x0, reverse, use_real_addr, flags=0x0, protocol=6
        src ip/id=0.0.0.0, mask=0.0.0.0, port=0, tag=any
        dst ip/id=0.0.0.0, mask=0.0.0.0, port=0, tag=any, dscp=0x0
        input_ifc=any, output_ifc=any

Phase: 4
Type: IP-OPTIONS
Subtype:
Result: ALLOW
Config:
Additional Information:
 Forward Flow based lookup yields rule:
 in  id=0x7f870f235880, priority=0, domain=inspect-ip-options, deny=true
        hits=38871, user_data=0x0, cs_id=0x0, reverse, flags=0x0, protocol=0
        src ip/id=0.0.0.0, mask=0.0.0.0, port=0, tag=any
        dst ip/id=0.0.0.0, mask=0.0.0.0, port=0, tag=any, dscp=0x0
        input_ifc=inside, output_ifc=any

Phase: 5
Type: NAT
Subtype: per-session
Result: ALLOW
Config:
Additional Information:
 Reverse Flow based lookup yields rule:
 in  id=0x7f870de469c0, priority=0, domain=nat-per-session, deny=false
        hits=266368, user_data=0x0, cs_id=0x0, reverse, use_real_addr, flags=0x0, protocol=6
        src ip/id=0.0.0.0, mask=0.0.0.0, port=0, tag=any
        dst ip/id=0.0.0.0, mask=0.0.0.0, port=0, tag=any, dscp=0x0
        input_ifc=any, output_ifc=any

Phase: 6
Type: IP-OPTIONS
Subtype:
Result: ALLOW
Config:
Additional Information:
 Reverse Flow based lookup yields rule:
 in  id=0x7f870f131390, priority=0, domain=inspect-ip-options, deny=true
        hits=332920, user_data=0x0, cs_id=0x0, reverse, flags=0x0, protocol=0
        src ip/id=0.0.0.0, mask=0.0.0.0, port=0, tag=any
        dst ip/id=0.0.0.0, mask=0.0.0.0, port=0, tag=any, dscp=0x0
        input_ifc=outside, output_ifc=any

Phase: 7
Type: FLOW-CREATION
Subtype:
Result: ALLOW
Config:
Additional Information:
New flow created with id 246500, packet dispatched to next module
Module information for forward flow ...
snp_fp_inspect_ip_options
snp_fp_tcp_normalizer
snp_fp_translate
snp_fp_adjacency
snp_fp_fragment
snp_fp_tracer_drop
snp_ifc_stat

Module information for reverse flow ...
snp_fp_inspect_ip_options
snp_fp_translate
snp_fp_tcp_normalizer
snp_fp_adjacency
snp_fp_fragment
snp_fp_tracer_drop
snp_ifc_stat

Phase: 8
Type: INPUT-ROUTE-LOOKUP-FROM-OUTPUT-ROUTE-LOOKUP
Subtype: Resolve Preferred Egress interface
Result: ALLOW
Config:
Additional Information:
Found next-hop 62.156.244.XXX using egress ifc  outside

Result:
input-interface: inside
input-status: up
input-line-status: up
output-interface: outside
output-status: up
output-line-status: up
Action: allow

But there is no NAT rule for the inside network, so why does NAT happen?

Thanks,

Klaus

Rob Ingram · ‎12-27-2021

@kroerig is this a fresh install of ASA software and did you run through the wizard to complete the setup?

Can you provide the output of "show nat detail".

kroerig · ‎12-27-2021

Manual NAT Policies (Section 1)
1 (dmz) to (outside) source static transfer-net transfer-net  destination static Server-Net Server-Net no-proxy-arp route-lookup
    translate_hits = 39127, untranslate_hits = 39127
    Source - Origin: 192.168.113.0/24, Translated: 192.168.113.0/24
    Destination - Origin: 10.11.120.0/22, Translated: 10.11.120.0/22
2 (dmz) to (outside) source static transfer-net transfer-net  destination static admin-net admin-net no-proxy-arp route-lookup
    translate_hits = 0, untranslate_hits = 0
    Source - Origin: 192.168.113.0/24, Translated: 192.168.113.0/24
    Destination - Origin: 10.11.150.0/24, Translated: 10.11.150.0/24
3 (inside) to (outside) source static inside-net inside-net  destination static Server-Net Server-Net no-proxy-arp route-lookup
    translate_hits = 164919, untranslate_hits = 261328
    Source - Origin: 192.168.13.0/24, Translated: 192.168.13.0/24
    Destination - Origin: 10.11.120.0/22, Translated: 10.11.120.0/22
4 (inside) to (outside) source static inside-net inside-net  destination static admin-net admin-net no-proxy-arp route-lookup
    translate_hits = 0, untranslate_hits = 0
    Source - Origin: 192.168.13.0/24, Translated: 192.168.13.0/24
    Destination - Origin: 10.11.150.0/24, Translated: 10.11.150.0/24
5 (inside) to (outside) source static inside-net inside-net  destination static TK-Net TK-Net no-proxy-arp route-lookup
    translate_hits = 1, untranslate_hits = 2
    Source - Origin: 192.168.13.0/24, Translated: 192.168.13.0/24
    Destination - Origin: 10.11.102.0/24, Translated: 10.11.102.0/24

Auto NAT Policies (Section 2)
1 (inside) to (outside) source dynamic tk01 interface
    translate_hits = 1243, untranslate_hits = 48
    Source - Origin: 192.168.13.10/32, Translated: 87.139.216.XXX/32
2 (dmz) to (outside) source dynamic sunny-box interface
    translate_hits = 336, untranslate_hits = 0
    Source - Origin: 192.168.113.20/32, Translated: 87.139.216.XXX/32
3 (dmz) to (outside) source dynamic protone-nat interface
    translate_hits = 2, untranslate_hits = 0
    Source - Origin: 192.168.113.21/32, Translated: 87.139.216.XXX/32
4 (inside) to (outside) source dynamic Telefone interface
    translate_hits = 1273, untranslate_hits = 47
    Source - Origin: 192.168.13.150-192.168.13.170, Translated: 87.139.216.XXX/32
5 (Hotspot) to (outside) source dynamic hotspot interface
    translate_hits = 3799, untranslate_hits = 31
    Source - Origin: 10.11.50.0/24, Translated: 87.139.216.XXX/32

I tested with source ip 192.168.113.7.

I manually migrated this config from an ASA 5505. I removed the brigde interface config.

kroerig · ‎12-27-2021

OK. My mistake. Everything' fine. Packet-trace is of course right. The packet is allowed to exit the outside interface, there's no NAT.