WRT54Gv2 Problem: High connection count = long ping times

Discussion in 'Cisco/Linksys Wireless Routers' started by matthawke, Oct 16, 2006.

  1. matthawke

    matthawke LI Guru Member

    Hi all,

    Have experienced an issue with my WRT54Gv2 over the last few weeks which is somewhat peculiar. I'm hoping the combined knowledge of this forum's readership can tell me if my router is doomed...

    I am using the router to connect to Telstra Bigpond Cable, and have been testing it with the Linksys 4.00.7, DD-WRT v23 SP1 and SP2, and Thibor 15c firmwares. It has operated just fine on DD-WRT v23 SP1 since SP1 was released, but I upgraded to SP2 at or around the time the problems started. With the problems continuing, I've gone ahead tested all the firmwares I can think of, but I think the problems started before I went to SP2 and so I doubt it was the upgrade which damaged it.

    Here's the symptoms. When I power my router from "cold", it operates fine. Net connection is great, nice and fast, and if I ping continuously to an IP addresses on my home network (www.bigpond.com, for example) the times are in the 45ms range. However, after some time (anywhere from 3 - 20 mins) the ping times to the same site suddenly increase to an average of 1900 - 2300ms, and there is approximately a 15% dropout rate. The net connection slows from ~2.5Mbps to just 5kbps - so slow it's unusable.

    I have noticed that every time the slowdown occurs, the number of tracked IP connections (from /proc/net/ip_conntrack) has risen above ~100 or so. When the connection speed has slowed, I seem have an idle connection count of about 400, but have seen up to 800, and that just from pinging. Have tried setting my TCP and UDP timeouts to 600 with no change.

    So, is there something seriously wrong with my router? Anybody think of a way to fix it?


    Matt Hawke
  2. jchuit

    jchuit Network Guru Member

    You could try the Tarifa firmware:

    1. This is patched agains Dos attatcks.
    2. short time out.
    3. big hashtable, can hold up to 1543 connections.
    4. Hashtable size is set to a prime number to handle large amount of traffic without performance decrease.

  3. matthawke

    matthawke LI Guru Member

    Thanks jchuit - might give that a go if I have no success otherwise.

    I have done some more testing over the last few days and have observed some interesting things.

    It appears that the slowdown and excess of tracked connections has to do with the use of wireless. If I leave my only wireless connection switched off, the only other wired connection to the router works fine and the number of connections does not rise too high. However, if I enable and attempt to use the wireless connection on my laptop, the connection count rises dramatically. Furthermore, my wireless connection starts continually exchanging packets, as demonstrated by the Windows wireless connection status dialog.

    So I'm guessing the next step would be to get a packet sniffer set up and figure out what's going back and forth between the laptop and the router over the wireless connection... Any suggestions?


  4. matthawke

    matthawke LI Guru Member

    I've been doing some more investigation and have noticed a pattern in the high amount of connections held by the router. While looking at the count of IP connections tracked I happened also to look at the ip_conntrack file's contents (see attached). A large proportion of the connections are UDP Port 53, going out to one of the three DNS servers which are provided to the router upon connection to Bigpond Cable internet. The attachment shows a representative sample. In a file of 384 connections, 267 of them were these port 53 requests.

    Is it usual for the router to make so many DNS requests spontaneously? As soon as I connect to the net using the router's Bigpond Cable connection client, the connection count starts to rise...

    - M

    Attached Files:

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