Question

Deny TCP (no connection) from x.x.x.x to x.x.x.x flag SYN ACK on interface inside issue

Asked by: rigneydolphin

Hi,

I'm receiving the following error on our Cisco ASA 5520 ever since we moved our email traffic from our other ASA to this one. This seems only to be affecting TLS email coming from our email server, all other mail traffic is fine.

Anybody have any ideas? Could it be on the clients side?

Any help on this is much appreciated

7|Aug 12 2009 12:25:16|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:24:52|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:24:52|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12283 flags SYN ACK  on interface inside
7|Aug 12 2009 12:24:52|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:24:40|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:24:40|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12283 flags SYN ACK  on interface inside
7|Aug 12 2009 12:24:40|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:24:31|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:24:31|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12283 flags SYN ACK  on interface inside
7|Aug 12 2009 12:24:31|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:24:27|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:24:27|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12283 flags SYN ACK  on interface inside
7|Aug 12 2009 12:24:27|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:24:18|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:24:18|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12283 flags SYN ACK  on interface inside
7|Aug 12 2009 12:24:18|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:21:50|609002: Teardown local-host outside:x.x.x.x duration 0:00:30
6|Aug 12 2009 12:21:50|302014: Teardown TCP connection 117683815 for outside:x.x.x.x/25 to inside:10.0.26.9/40070 duration 0:00:30 bytes 0 SYN Timeout
6|Aug 12 2009 12:21:38|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12091 flags SYN ACK  on interface inside
6|Aug 12 2009 12:21:29|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12091 flags SYN ACK  on interface inside
6|Aug 12 2009 12:21:26|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12091 flags SYN ACK  on interface inside
6|Aug 12 2009 12:21:22|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12091 flags SYN ACK  on interface inside
7|Aug 12 2009 12:21:19|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:21:19|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/12091 flags SYN ACK  on interface inside
7|Aug 12 2009 12:21:19|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:19:28|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:19:28|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/11967 flags SYN ACK  on interface inside
7|Aug 12 2009 12:19:28|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:19:25|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:19:25|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/11967 flags SYN ACK  on interface inside
7|Aug 12 2009 12:19:25|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:19:22|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
7|Aug 12 2009 12:19:19|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:19:19|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/11967 flags SYN ACK  on interface inside
7|Aug 12 2009 12:19:19|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:13:37|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:13:37|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/11476 flags SYN ACK  on interface inside
7|Aug 12 2009 12:13:37|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:13:25|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:13:25|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/11476 flags SYN ACK  on interface inside
7|Aug 12 2009 12:13:25|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:13:19|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:13:19|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/11476 flags SYN ACK  on interface inside
7|Aug 12 2009 12:13:19|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:13:09|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:13:09|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/11476 flags SYN ACK  on interface inside
7|Aug 12 2009 12:13:09|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:09:07|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:09:07|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/11096 flags SYN ACK  on interface inside
7|Aug 12 2009 12:09:07|609001: Built local-host outside:x.x.x.x
7|Aug 12 2009 12:09:04|609002: Teardown local-host outside:x.x.x.x duration 0:00:00
6|Aug 12 2009 12:09:04|106015: Deny TCP (no connection) from y.y.y.y/25 to x.x.x.x/11096 flags SYN ACK  on interface inside
7|Aug 12 2009 12:09:04|609001: Built local-host outside:x.x.x.x

                                  
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Asked On
2009-08-12 at 04:34:46ID24646019
Tags

cisco

,

tcp no connection local-host

Topics

Consumer Firewalls

,

Cisco PIX Firewall

,

TCP/IP

Participating Experts
2
Points
500
Comments
4

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Answers

 

by: asavenerPosted on 2009-08-12 at 05:48:48ID: 25078119

This looks to be a problem with asymmetric routing.  The SYN packet is taking a different route, and the ASA is blocking the SYN ACK response.

ASAs want all traffic to be stateful, so if it does not see the packet that initiates the connection it will block any returning traffic.

 

by: rigneydolphinPosted on 2009-08-12 at 06:02:36ID: 25078252

That make sense, I have two IP's on the one interface on my mail server, so maybe it's replying using the other interface.

Do you know the command to specify which IP to use? I try route add x.x.x.x mask y.y.y.y z.z.z.z metric 10 IF q.q.q.q but it wont accept it

 

by: asavenerPosted on 2009-08-12 at 07:45:49ID: 25079257

Try enabling Routing and Remote Access Service and adding the static route there.

 

by: chechillPosted on 2011-07-13 at 00:03:57ID: 36178436

I have the same problem but i don't know how solve it.

I've a asa 5510 with these interfaces:
0 -> Inside (vlan99)
1 -> Students (vlan98)
2 -> E2 (vlan trunk 999)
3 -> Outside (to router)

I need do a vnc connection from vlan 5 (interface inside) to vlan 15 (interface trunk 999)

Message "Deny TCP (no connection) from 192.168.15.10/5900 to 192.168.5.200/1465 flags SYN ACK on interface Vlan_15"

20120131-EE-VQP-002

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