Router Slowdown

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Revision as of 19:52, 26 November 2006


A lot of people have issues with their router, some symptoms can be

  • Slow web-interface
  • Slow transfer of data, e.g. browsing
  • Not responding to ping
  • Crash or even rebooting

Usually these people are running P2P software like Emule, Bittorrent, Shareaza or something else. These programs require a lot of connections which could cause the ip_conntrack-table to get full.


Even if it happens the router doesn't answer pings anymore and no more HTTP, you still can check what's going on through syslogd.

To view syslog messages, Telnet or SSH into your router, login and run the following command:

cat /var/log/messages

Here is a brief description of what's going on :

  1. First, you'll see 'full, dropping packet.' messages followed by 'messages suppressed.'
  2. Eventually, it will get verbose and you'll see logs similar to the following :
<4>kernel: ip_conntrack: table full, dropping packet.
<4>kernel: NET: 15 messages suppressed.
<4>kernel: ip_conntrack: table full, dropping packet.
<4>kernel: NET: 12 messages suppressed.

Solution 1

  • Go to the Web-Admin and log in
  • Go to 'Administration'
  • Go to 'Management'
  • Enter the following values at 'IP Filter Settings'
    • Maximum Ports: 4096
    • TCP Timeout (s): 90 or 120
    • UDP Timeout (s): 90 or 120


alt IP Filter Settings at DD-WRT v23

AIM, ICQ and other IM programs

If you're using certain IM clients such as ICQ or AIM (or other applications which do not send frequent keep-alive packets), you should set timeout to 300 or 600 to help them stay connected. As this will decrease the router's performance when you're dealing with heavy P2P traffic, you might want to experiment with these values.

Solution 2

DD-WRT has an inbuild proxy feature that allows rewriting of HTML content to filter ActiveX cookies, etc. As this is load-intensive, you may want to disable this feature. This should be done under Security->Firewall.

Unfortunately this function has 3 bugs:

  • Though all 4 checkboxes are unchecked the rewriting proxy is still running (you might have to reboot)
  • It drops connections if under heavy load
  • It probably runs haywire checking traffic on other ports than 80, hence the slowdown with P2P applications (unconfirmed)

The only solution is to totally disable the firewall (which I do not recommend) in Security->Firewall. This fixes all slowdowns.

This behavior has been seen in v22 and v23. Please report this to the maintainer and put it in the bug database.

Solution 3

Apparently there is a bug in the WRT54GS v2.2. The bug involves a fatal memory access error due to a difference in the CPU clock speed and the clock speed on the memory bus. This bug causes connections to be dropped when transferring large files. New versions of the Linksys firmware overclock the CPU to 216 MHz. This can be fixed by logging into the router via SSH or Telnet and executing the following commands:

nvram set clkfreq=216
nvram commit

Extra Information

The line

echo '600 1800 120 60 120 120 10 60 30 120' > /proc/sys/net/ipv4/ip_conntrack_tcp_timeouts

is often recommended in forums, but precious few know what it really does. Here is the explanation.

It is a list for all the possible TCP states and their time outs in seconds. See my table below (they are in the correct order):

State		Timeout value

NONE		10 minutes
ESTABLISHED	30 minutes (default is 5 days)
SYN_SENT	2 minutes
SYN_RECV	60 seconds
FIN_WAIT	2 minutes
TIME_WAIT	2 minutes
CLOSE		10 seconds
CLOSE_WAIT	60 seconds (default is 12 hours)
LAST_ACK	30 seconds
LISTEN		2 minutes

You can check what your router is set to by printing the same device used above. (I recommend checking the values on your router before you change them):

cat /proc/sys/net/ipv4/ip_conntrack_tcp_timeouts
300     600     120     60      120     120     10      60      30      120