Something doesn't quite add up

[Lean L]

In the spirit of setting up a network for many users, I did a couple of experiments with high connection counts. I tried a couple of moderate speed torrents at the same time. I used a broadcom based router with 16/4 ram/flash. Just two simultaneous torrents slowed the network down significantly. What I don't understand is why. I looked into the ddwrt specs and noticed that not only was the processor not being stressed (10% usage), there was still around 2MB of memory available. The connection count did not exceed 400 at any time.

Based on that, the router was sufficient for the task yet internet was noticeably slower. It seemed to be opening new connections that was the issue, as I could still use the remaining bandwidth using single connections. Could there be a connection limit on the isp's side or is ddwrt not reporting correctly?

 

[gsaldivar]

Each firmware build has the potential to contain bugs. Have you tried a different one, such as Tomato?

http://www.polarcloud.com/tomato

 

[Lean L]

Well, this particular router is not supported by tomato. At any rate, this is for a different network that I'm doing the research. I'm under the impression that a router with a lot of ram can handle p2p traffic without slowing down the whole network.

I'm actually thinking of using a wrtu54g tm which has 64MB of ram but no 3rd party support. Based on my results so far, I am confused. Would this router do a good job with multiple torrents/p2p connections while keeping latencies low enough to enjoy a lan game a possible a few streams? THanks

 

[ScottMac]

It's usually the NAT table being filled to capacity. Unless you limit the torrent connections, most BT clients will suck all available resources ... and grab any new translation slots that become available.

The processor is not (in this case) stressed, or the memory ... but the translation table has finite resources, frequently 1024 concurrent active translations ... if BT has most / all of them tied up, then any following sessions (web, mail, Skype ...) are starved for resources and have to compete with the BT client (looks like a major slowdown).

 

[gsaldivar]

It's usually the NAT table being filled to capacity. Unless you limit the torrent connections, most BT clients will suck all available resources ... and grab any new translation slots that become available.

The processor is not (in this case) stressed, or the memory ... but the translation table has finite resources, frequently 1024 concurrent active translations ... if BT has most / all of them tied up, then any following sessions (web, mail, Skype ...) are starved for resources and have to compete with the BT client (looks like a major slowdown).

I forgot about the NAT table. This is an excellent explanation and almost certainly the issue observed by the OP.

 

[Lean L]

It's usually the NAT table being filled to capacity. Unless you limit the torrent connections, most BT clients will suck all available resources ... and grab any new translation slots that become available.

The processor is not (in this case) stressed, or the memory ... but the translation table has finite resources, frequently 1024 concurrent active translations ... if BT has most / all of them tied up, then any following sessions (web, mail, Skype ...) are starved for resources and have to compete with the BT client (looks like a major slowdown).

That makes sense... the max connection setting in ddwrt refers to this though right? In the case of my test, I had set the max to 4096. Does the nat translations get slower as it fills up even if its not to capacity?

Is there a setting a way to set this in default linksys firmwares?

thanks

 

[spidey07]

A larger state table/nat table takes longer to process and there is more clean up work. This is true for all firewalls/routers that don't do it in hardware (and even in hardware it is a finite limit). Even in huge firewalls the size of your state table can cause problems and we're talking millions of states/connections.

 

[gsaldivar]

That makes sense... the max connection setting in ddwrt refers to this though right? In the case of my test, I had set the max to 4096. Does the nat translations get slower as it fills up even if its not to capacity?

Yes, a large (but not filled) table can cause a speed issue. There is also a complimentary setting to max connections called timeout I think. It refers to the amount of time (usually in seconds) before the connections are dropped, and room is made for new connections to be established. Setting the timeout too low causes the router to spend excessive amount of time needlessly pruning the table, while leaving it set too high can block new connections from being made if the table is maxxed by network traffic.

 

[JackMDS]

The problem is that people buy a MiniCooper and use it as a Bulldozer.

The Routers are minicomputers that are constantly over loaded by the users.

Actually the best way to handle them is to switch them Off once within 24 cycle (night/day) for the duration that they do not work.

That cleans all the overload data, and the GIGO.