Cisco ASA Static NAT

[Kenneth Goh]

Please help (refer to attached diagram) as I need client 10.2.6.42 to telnet to 172.16.44.100 and the traffic will be NATed (which telnet into R2) to 172.26.32.5 (lookback interface).

It is not working, not sure did I miss out any thing? Thanks in advanced

interface GigabitEthernet0
 nameif inside
 security-level 0
 ip address 10.2.6.22 255.255.255.248
!
interface GigabitEthernet1
 nameif outside
 security-level 0
 ip address 172.16.44.254 255.255.255.0

same-security-traffic permit inter-interface

object network Telnet_172.26.32.5
 host 172.26.32.5

object network Telnet_172.26.32.5
 nat (inside,outside) static 172.16.44.100 service tcp telnet telnet
access-list outside_To_inside extended permit tcp any host 172.26.32.5 eq telnet
access-group outside_To_inside in interface outside

[Flavio Miranda]

Hi @Kenneth Goh

Does firewall is able to ping 172.26.32.5?

Does R2 have route to 172.16.44.0 ?

-If I helped you somehow, please, rate it as useful.-

[Kenneth Goh]

Does firewall is able to ping 172.26.32.5?

yes

Does R2 have route to 172.16.44.0 ?

R2 has a default route to the firewall.

[Flavio Miranda]

Try to run a packet tracer from ASA.

packet-tracer input [src_int] protocol src_addr src_port dest_addr  dest_port [detailed] 

packet-tracer input outside  tcp 10.2.6.42 1024 172.16.44.100 23 detailed

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[Kenneth Goh]

Unable to establish telnet session on R2

client#telnet 172.16.44.100
Trying 172.16.44.100 ...
% Connection timed out; remote host not responding

--------------------------------------------------------------------------

ciscoasa# packet-tracer input outside tcp 10.2.6.42 1024 172.16.44.100 23 detailed

Phase: 1
Type: ACCESS-LIST
Subtype:
Result: ALLOW
Config:
Implicit Rule
Additional Information:
 Forward Flow based lookup yields rule:
 in  id=0xbc2d21e8, priority=1, domain=permit, deny=false
        hits=14, 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=outside, output_ifc=any

Phase: 2
Type: UN-NAT
Subtype: static
Result: ALLOW
Config:
object network Telnet_172.26.32.5
 nat (inside,outside) static 172.16.44.100 service tcp telnet telnet
Additional Information:
NAT divert to egress interface inside
Untranslate 172.16.44.100/23 to 172.26.32.5/23

Phase: 3
Type: ACCESS-LIST
Subtype: log
Result: ALLOW
Config:
access-group outside_To_inside in interface outside
access-list outside_To_inside extended permit tcp any host 172.26.32.5 eq telnet
Additional Information:
 Forward Flow based lookup yields rule:
 in  id=0xbb980028, priority=13, domain=permit, deny=false
        hits=1, user_data=0xb9466b40, cs_id=0x0, use_real_addr, flags=0x0, protocol=6
        src ip/id=0.0.0.0, mask=0.0.0.0, port=0
        dst ip/id=172.26.32.5, mask=255.255.255.255, port=23, dscp=0x0
        input_ifc=outside, output_ifc=any

Phase: 4
Type: IP-OPTIONS
Subtype:
Result: ALLOW
Config:
Additional Information:
 Forward Flow based lookup yields rule:
 in  id=0xbc2d60e0, priority=0, domain=inspect-ip-options, deny=true
        hits=12, 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
        dst ip/id=0.0.0.0, mask=0.0.0.0, port=0, dscp=0x0
        input_ifc=outside, output_ifc=any

Phase: 5
Type: NAT
Subtype: rpf-check
Result: ALLOW
Config:
object network Telnet_172.26.32.5
 nat (inside,outside) static 172.16.44.100 service tcp telnet telnet
Additional Information:
 Forward Flow based lookup yields rule:
 out id=0xbc2dd058, priority=6, domain=nat-reverse, deny=false
        hits=2, user_data=0xbcabb3e0, cs_id=0x0, use_real_addr, flags=0x0, protocol=6
        src ip/id=0.0.0.0, mask=0.0.0.0, port=0
        dst ip/id=172.26.32.5, mask=255.255.255.255, port=23, dscp=0x0
        input_ifc=outside, output_ifc=inside

Phase: 6
Type: IP-OPTIONS
Subtype:
Result: ALLOW
Config:
Additional Information:
 Reverse Flow based lookup yields rule:
 in  id=0xbc2a9578, priority=0, domain=inspect-ip-options, deny=true
        hits=3, 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
        dst ip/id=0.0.0.0, mask=0.0.0.0, port=0, dscp=0x0
        input_ifc=inside, output_ifc=any

Phase: 7
Type: FLOW-CREATION
Subtype:
Result: ALLOW
Config:
Additional Information:
New flow created with id 14, packet dispatched to next module
Module information for forward flow ...
snp_fp_tracer_drop
snp_fp_inspect_ip_options
snp_fp_tcp_normalizer
snp_fp_translate
snp_fp_adjacency
snp_fp_fragment
snp_ifc_stat

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

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

[Flavio Miranda]

Perfect. Now, try do enable debug on R2 and test again.

terminal monitor

debug telnet

-If I helped you somehow, please, rate it as useful.-

[Kenneth Goh]

There is no output.

R2#debug telnet
Incoming Telnet debugging is on

[Flavio Miranda]

Show conn

Show xlate

Show nat

On ASA?

[Kenneth Goh]

On ASA

ciscoasa# show conn
0 in use, 1 most used
ciscoasa# show xlate
1 in use, 1 most used
Flags: D - DNS, i - dynamic, r - portmap, s - static, I - identity, T - twice
TCP PAT from inside:172.26.32.5 23-23 to outside:172.16.44.100 23-23
    flags sr idle 0:04:58 timeout 0:00:00
ciscoasa# show nat

Auto NAT Policies (Section 2)
1 (inside) to (outside) source static Telnet_172.26.32.5 172.16.44.100   service tcp telnet telnet
    translate_hits = 0, untranslate_hits = 0

[Flavio Miranda]

The problem may be this:

nat (inside,outside) static 172.16.44.100 service tcp telnet telnet

Looks like the NAT will match the rule if the connection start from port 23 to port 23.

 PAT from inside:172.26.32.5 23-23 to outside:172.16.44.100 23-23

However, the source port must be any so that the source port can be any port above 1024, (random ports).

Try to change this and try again.

-If I helped you somehow, please, rate it as useful.-

[Kenneth Goh]

Tried changing the NAT below and also don't work, I am not sure how can I change the source port? Please help.

nat (inside,outside) static 172.16.44.100

[Flavio Miranda]

Let me correct something I said. Your NAT config was not wrong sorry. For this version of firewall, you let as is.

nat (outside,inside) source static <real-ip> <mapped-ip> destination static interface <real-ip> service <real-service> <mapped-service>

NAT must be ok as per the packet traced. But, for some reason the packet is not getting in to the r2.

Can you send me the GNS3 file?

[Kenneth Goh]

Some problems with GNS3, but I have attached the config files.

[Kenneth Goh]

sorry can't seems to be able to attach the zip file here.

[Flavio Miranda]

You need to rename file and change the extension to .txt.