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New Member

PIX 6.3 Overlapping network config

I have a PIX 506 running 6.3 with multiple  VPN tunnels. On one we are attempting to nat two network to a single and the other network to as below. The nat is working and the tunnel is sending the traffic to the remote end, we are also recieving something back according to the IPSec SA but the source PC is receiving nothing.

Is my NAT configured correctly?

Do I need to NAT the returning traffic back to the real network?

What am I missing?

access-list 199 permit ip host

access-list fcpa_NAT2 permit ip

global (outside) 16

nat (inside) 16 access-list fcpa_NAT2 0 0

  local  ident (addr/mask/prot/port): (

   remote ident (addr/mask/prot/port): (


     PERMIT, flags={origin_is_acl,}

    #pkts encaps: 1443, #pkts encrypt: 1443, #pkts digest 1443

    #pkts decaps: 1430, #pkts decrypt: 1430, #pkts verify 1430

    #pkts compressed: 0, #pkts decompressed: 0

    #pkts not compressed: 0, #pkts compr. failed: 0, #pkts decompress failed: 0

    #send errors 2, #recv errors 0

     local crypto endpt.:, remote crypto endpt.:

     path mtu 1500, ipsec overhead 56, media mtu 1500

     current outbound spi: 2a59d3a

     inbound esp sas:

      spi: 0x827c5c51(2189188177)

        transform: esp-3des esp-sha-hmac ,

        in use settings ={Tunnel, }

        slot: 0, conn id: 11, crypto map: banctecmap

        sa timing: remaining key lifetime (k/sec): (4607838/26451)

        IV size: 8 bytes

        replay detection support: Y

  • VPN
Super Bronze

PIX 6.3 Overlapping network config


Are you sure that the traffic inbound is not something initated from the remote site? (Even though it could naturally not reach anything since only a Dynamic Policy PAT is facing the remote site)

What are you using to test the connection?

Have you been taking capture on the actual local host and seen that there is no return traffic?

- Jouni

New Member

PIX 6.3 Overlapping network config


Thanks for responding. I'm in contact with the other end and they are saying they see my traffice come into thier firewall as wchich they nat to a 10.X.X.X, they are also seeing the return traffic to me. I see this traffic on the ipsec sa on my end as shown on the original post.

I've set up a capture as below on my end.

PIX515# sh access-l test

access-list test; 5 elements

access-list test line 1 permit ip any host (hitcnt=0)

access-list test line 2 permit ip any (hitcnt=14693)

access-list test line 3 permit ip any (hitcnt=0)

access-list test line 4 permit ip any host (hitcnt=0)

access-list test line 5 permit ip host any (hitcnt=0)

This is what I capture

-PIX515# sh cap gtest

13 packets captured

15:33:41.696115 > icmp: echo request

15:33:42.695993 > icmp: echo request

15:33:43.695963 > icmp: echo request

15:33:44.696939 > icmp: echo request

15:33:45.696817 > icmp: echo request

15:33:46.696802 > icmp: echo request

15:33:47.696680 > icmp: echo request

15:33:48.696588 > icmp: echo request

Super Bronze

PIX 6.3 Overlapping network config


Did you have the "fixup protocol icmp" and "fixup protocol icmp error" configured on your PIX?

- Jouni

New Member

PIX 6.3 Overlapping network config

I did not have either. I put fixup protocol icmp error in but the PIX will not take "fixup protocol icmp".

PIX515(config)# fixup protocol icmp

Usage: [no] fixup protocol icmp error


Super Bronze

PIX 6.3 Overlapping network config


I guess it might have been only a single command in the older software.

From 7.x onwards they have have been separate and used the format "inspect icmp" and "inspect icmp error"

I assume this did not have any affect on the ICMP going through?

- Jouni

New Member

PIX 6.3 Overlapping network config

No, I'm still stuck on this one. I'm not understanding, I see the xlate being done on this end and going through the tunnel, they see it translate it to thier destination and then see the response translating back to our end. I see the decryption on the tunnel to me but from there it's lost. We get no response to the original source pc.


New Member

PIX 6.3 Overlapping network config

Is there a way to actually capture the traffic returning to us other than what I have already done in my capture?

Super Bronze

PIX 6.3 Overlapping network config


You have the ACL lines for both direction so you should see everything that goes between these networks. You can only really capture the traffic that has already passed the firewall since if you captured the traffic from the WAN interface of the PIX then it would be encrypted.

The capture seems to indicate that the traffic is not getting through the PIX.

I would perhaps consider adding additional NAT IP address on your side of the L2L VPN and configuring Static Policy NAT to this IP address for a single internal host. This should probably tell if the problem is with the current NAT.

But do my understanding your setup should work too.

- Jouni

New Member

PIX 6.3 Overlapping network config

Thank's Jonui,

I really appericiate your help.I'm not sure what you mean though, I found another post you helped on mentioning the static NAT but when I try it I get the following.

PIX515(config)# static (inside,outside) access-l fcpa_NAT1

number of maximum connections should lie between 0 and 65535

access-list 199 line 1 permit ip host (hitcnt=229)

access-list 199 line 2 permit ip host (hitcnt=291375)

access-list fcpa_NAT1 line 1 permit ip (hitcnt=219)

access-list fcpa_NAT2 line 1 permit ip (hitcnt=291520)

Do I need to remove this first?

nat (inside) 15 access-list fcpa_NAT1 0 0

nat (inside) 16 access-list fcpa_NAT2 0 0

nat (inside) 10 0 0

PIX515(config)# sh global

global (outside) 10 interface

global (outside) 15

global (outside) 16