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reset

Cisco ASA – Reset TCP connection

“Normal” TCP applications use a three-way handshake to establish a session. After data has been send the session is closed. Some legacy applications don’t always close a TCP session. They keep the session open, even when the session is idle for a long time (+ 2 hours). When the session is idle and a client wants to send data, the clients sends a PSH packet followed by the new data. Both stations use the original session information to maintain the connection.

This behavior is problematic when components, like firewalls are along the path between the two clients. A Cisco ASA firewall for example automatically flushes a TCP session when it’s idle for 1 hour. When the clients start sending data after an idle period of 1 hour, by starting with a PSH command, the firewall doesn’t recognize the session anymore and drops the traffic. Both clients need to flush / restart their TCP session to establish a new valid session through the firewall.

The Cisco ASA firewall has the option to change the default idle timers and even send a reset (RSET) to both clients when the idle timer is reached. The Reset bit in TCP is designed to allow a client to abort / terminate the TCP session with another client. This forces both clients to re-establish a new session, which is learned and maintained by the firewall. This prevents a session from getting dropped in the firewall when it’s idle for more than one hour.

To configure a TCP reset you need to specify the “interesting” traffic for a reset through an access-list and specify the reset parameters via a policy-map like shown below.

access-list reset_tcp extended permit ip 192.168.10.0 255.255.255.0 host 10.10.10.205
!
class-map cm_reset_tcp
match access-list reset_tcp
!
policy-map global_policy
class cm_reset_tcp
set connection timeout idle 0:15:00 reset

The configuration snippet resets a connection when it’s idle for 15 minutes between the network 192.168.10.0/24 and the host 10.10.10.205. The sessions are initiated by the remote network. You can view the connection parameters with the show conn command.

fw01# show conn address 192.168.10.2 address 10.10.10.205 detail
TCP DMZ:192.168.10.2/31731 Inside:10.10.10.205/4000,
flags UIOB, idle 3m11s, uptime 51m56s, timeout 15m0s, bytes 165157

The output shows the configured idle timeout of 15 minutes, the real idle timeout and the uptime of the connection.

Reset Nokia E71

Are you having weird problems with your Nokia E71 that you didn’t have when you first got it? Maybe it is time to reset your phone. There are two ways of resetting, a soft and a hard reset. You should always backup your phone, before resetting it.

Soft reset

A soft reset only reboots your phone, but leaves all messages, contacts, calls, applications, themes and so on. Follow the following steps to perform a soft reset:

  1. Type *#7780# from the standby screen
  2. Enter the security code (default 12345)
  3. Confirm the soft reset

Hard reset

When performing a hard reset, your phone gets restored to its factory default settings. You will loose all your messages, contacts, calls, applications, themes and so on. Follow this steps to perform a hard reset:

  1. Type *#7370# from the standby screen
  2. Enter the security code (default 12345)
  3. Confirm the hard reset

I hope this helps solve your weird problems with your Nokia E71. It always helps me to boost my Nokia E71…