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New Member

PIX 6.3(1) isakmp nat-traversal Problem

I have problem with the PIX Firewall 515 running 6.3(1). I can not use the VPN Client behind any NAT or PAT firewall. I make a connection but can not pass any traffic to my private addresses. I am using the command :

isakmp nat-traversal

Still no sucess, everything works great when I use a public address. For example a dial up connection.

I have included my configuration file. Any help would be appreciated.


PIX Version 6.3(1)

interface ethernet0 auto

interface ethernet1 auto

nameif ethernet0 outside security0

nameif ethernet1 inside security100

hostname calprovpix

clock timezone PST -8

clock summer-time PDT recurring

fixup protocol ftp 21

fixup protocol h323 h225 1720

fixup protocol h323 ras 1718-1719

fixup protocol http 80

fixup protocol icmp error

fixup protocol ils 389

fixup protocol rsh 514

fixup protocol rtsp 554

fixup protocol sip 5060

no fixup protocol sip udp 5060

fixup protocol skinny 2000

fixup protocol smtp 25

fixup protocol sqlnet 1521

names removed

object-group service Exchange tcp

port-object eq 135

port-object range 1096 1098

port-object eq smtp

port-object eq www

object-group service RadiusServer udp

description Radius Authentication Server

port-object eq radius

port-object eq radius-acct

access-list shjc_outbound_nat0_acl permit ip 25

access-list calprov_splitTunnelAcl permit ip any

access-list outside_access_in permit ip any

access-list outside_access_in deny ip PrivateNetwork any log

access-list outside_access_in permit icmp any any unreachable

access-list outside_access_in permit icmp any any time-exceeded

access-list outside_access_in permit icmp any any source-quench

access-list outside_access_in permit icmp any any echo

access-list outside_access_in permit esp any any

access-list outside_access_in permit udp any any eq 4500

access-list outside_access_in permit tcp any host cpsj-exchange-1P object-group


access-list outside_access_in permit tcp any host WWWP eq www

access-list outside_access_in permit tcp any host cpsj-server-1 eq 1099

access-list outside_access_in permit ip host Router any

access-list outside_access_in permit udp host QwestDNS eq domain any

access-list inside_nat0_outbound permit ip any

pager lines 24

logging on

logging monitor debugging

logging trap debugging

logging facility 7

logging host inside 6/1468

mtu outside 1500

mtu inside 1500

mtu test 1500

ip address outside xxx xxx

ip address inside

ip audit info action alarm

ip audit attack action alarm

ip local pool calprov-vpn

pdm history enable

arp timeout 14400

global (outside) 1

global (outside) 1 interface

nat (inside) 0 access-list inside_nat0_outbound

nat (inside) 1 0 0

static (inside,outside) cpsj-exchange-1P netmask 0 0

static (inside,outside) WWWP netmask 0 0

static (inside,outside) cpsj-server-1 netmask 0 0

static (inside,outside) cpsj-server-2P netmask 0 0

static (inside,outside) cpsj-server-3P netmask 0 0

static (inside,outside) cpsj-server-4P netmask 0 0

access-group outside_access_in in interface outside

route outside Router 1

timeout xlate 1:00:00

timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h225 1:00:00

timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00

timeout uauth 0:05:00 absolute

aaa-server TACACS+ protocol tacacs+

aaa-server RADIUS protocol radius

aaa-server LOCAL protocol local

aaa-server AuthInbound protocol radius

aaa-server AuthInbound (inside) host

aaa authentication telnet console AuthInbound

aaa authentication http console AuthInbound

ntp server Router source outside prefer

http server enable

http inside

no snmp-server location

no snmp-server contact

snmp-server community public

no snmp-server enable traps

floodguard enable

sysopt connection permit-ipsec

crypto ipsec transform-set ESP-DES-MD5 esp-des esp-md5-hmac

crypto dynamic-map outside_dyn_map 20 set transform-set ESP-DES-MD5

crypto map outside_map 65535 ipsec-isakmp dynamic outside_dyn_map

crypto map outside_map client authentication AuthInbound

crypto map outside_map interface outside

isakmp enable outside

isakmp nat-traversal 20

isakmp policy 20 authentication pre-share

isakmp policy 20 encryption des

isakmp policy 20 hash md5

isakmp policy 20 group 2

isakmp policy 20 lifetime 86400

vpngroup calprov address-pool calprov-vpn

vpngroup calprov dns-server

vpngroup calprov default-domain xxx

vpngroup calprov split-tunnel calprov_splitTunnelAcl

vpngroup calprov idle-time 1800

vpngroup calprov password

telnet inside

telnet timeout 5

ssh timeout 5

console timeout 0

terminal width 80

Cisco Employee

Re: PIX 6.3(1) isakmp nat-traversal Problem

Config looks OK. what version of teh VPN client are you using, NAT-T was only introduced in the 3.6 release so make sure it's something after that. After the tunnel is built, ensure that they've negotiated NAT-T by double-clicking on th epadlock icon and it should show something about encapsulation (can't remember exactly what it is). In fact, make sure the client has Enable Transparent Tunnelling checked.

If they do show as running over UDP 4500 then you need to check the stats on both the client and the PIX to see where the packet is being dropped. Check outbound packets on the client, Pkts Decaps on the PIX, then Pkts Encaps on the PIX and inbound packets on the client. You should be able to figure out where the packets are dropped by checking these.

Could be that your ISP is blocking NAT-T packets, but doubtful.

New Member

Re: PIX 6.3(1) isakmp nat-traversal Problem

Thank you for your response. I am currently using VPN Client 3.6.4. When I connect it does show tunnel port UDP 4500. No packets will pass to the network. Everything shows up as Packets Bypassed. This same configuration works as long as I am not behind NAT. Anything more help would be appreciated.



Re: PIX 6.3(1) isakmp nat-traversal Problem


Please double check that if your "Packets encrypted" counter stays at Zero, if yes, you can try changing the split tunnel list to :

access-list calprov_splitTunnelAcl permit ip

If it doesn't stay at Zero, and you do see packet encrypted increasing with the bypass counter increasing as well(which is normall)... then make sure that NAT-T (UDP 4500) is not being blocked anywhere inside your network (client/pix side).

let us know.



New Member

Re: PIX 6.3(1) isakmp nat-traversal Problem

Yes Packets do start encrypting but do not ever decrypt. I have look at each side client/pix and both sides start encrypting but never decrypt. I do not have anything else blocked on the network for UDP 4500, except what I have put on the PIX Firewall. If I can give you any more information please let me know.



New Member

Re: PIX 6.3(1) isakmp nat-traversal Problem

Hi Paul,

which OS are you using on the client side?

I had a problem similar to yours with Windows XP. If you're using Windows Xp, ensure that the Internet Connection Firewall is not enabled on your REmote access connection or Local Area Network Connection.

Hope it helps.


New Member

Re: PIX 6.3(1) isakmp nat-traversal Problem

I have Windows 2000. I do not have any Firewall Enabled.



Cisco Employee

Re: PIX 6.3(1) isakmp nat-traversal Problem

If both sides are sending out UDP 4500 packets (you mention they're both encrypting), but neither side is receiving them (you mention neither side is decrypting), then it looks like UDP 4500 is being blocked somewhere in between your client and the PIX. How is your client connected to the Internet, can you verify that your ISP is not blocking anything. What about the router outside the PIX, does it have any ACL's on it?

New Member

Re: PIX 6.3(1) isakmp nat-traversal Problem

I have used UDP 4500 through my ISP on a router with Nat-T. I am pretty sure it can not be the ISP. The router on it does have an access list. Even when i remove the access list it still does not work. I do not know where this could be being blocked if that is what is wrong.


New Member

Re: PIX 6.3(1) isakmp nat-traversal Problem

I just found some new information. If I ping from the PIX side of network to the VPN Client, the stats say they are decrypting on the client but no ping replys on th PIX side of the network. It is almost like the PIX is the only one that is not decrypting the packets. I hope this helps.


New Member

Re: PIX 6.3(1) isakmp nat-traversal Problem

I am having the exact same problem. It wasn't solved by 6.3(2) for the pix .Could it be a bug?

Please someone help us on that.


New Member

Re: PIX 6.3(1) isakmp nat-traversal Problem

with regard to the problem that you are having, I have configured a few VPN Client to PIX scenarios that work. I must be doing something right, or just good luck on my part.

the original configuration lists two different acaa-lists that are used for the nat0 and the split tunneling.

The following lines have been taken from one of my working configs. I only use one access-list for both purposes.

name inside-network

access-list 110 permit ip inside-network

ip local pool home

nat (inside) 0 access-list 110

vpngroup pix506 address-pool home

vpngroup pix506 split-tunnel 110

Please try the above scenario on your PIX, with the addresses applicable for your network.

the two different access-lists that are listed in the configuration have the source and destination networks reversed.



New Member

Re: PIX 6.3(1) isakmp nat-traversal Problem

Sorry forgot to say that for me it is Pix to cisco router conf (And I am aware af the thing with different access-lists for nat 0 and for the vpn).


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