Torrent Upload Speed Change When Changing Routers

[fromport]

I am running openmediavault with transmission as torrent software.

I exchanged my router a couple of weeks ago for a version with more ethernet ports.

Yesterday I exchanged it back for the "old" router and the upload traffic of my torrent server is now only 1/10 of the capacity of yesterday.

 

My connection is 75/35 megabit/s from verizon (fios)

Instead of the provided router/wifi gateway I used these: 

http://www.ubnt.com/edgemax#EdgeMAXhardware

 

I have of those:

the "small" one: edgerouter-PoE (5 ports gig-E)

rated as 1.000.000 pps for 64-byte packets

I call this the ERL-POE

 

and

 

the "big" one: edgerouter (8 ports gig-E)

rated as 2.000.000 pps for 64-byte packets

I call this the ER8

 

Both routers are running the same firmware version (although the cpus in both routers are differen) and the same config. Including an ipv6 tunnel to he.net

 

This is a graph of the ethernet traffic on my openmediavault server. I did not reboot the server.

Traffic of the 101 torrents resumes as soon as it gets reconnected:

 

 

As you can see, as soon at I switch the 2 ethernet cables over, traffic changes significantly.

With both routers, when I initiate a big download or upload, i am able to saturate my 75/35 easily.

 

So upload torrent traffic goes down to 1/10 with the lighter router. 

The router cpu is about 1-8% busy when I look.

This is speedtest result on the erl-poe while serving 2 megabit/s torrent upload:

http://www.speedtest.net/my-result/3519269056

The router runs debian based linux os, and #conntrack -C 

shows : 2121

Nothing out of the ordinary

When people download iso from my server my uplink goes strait to the ceiling, no problem.

 

It almost seems that maybe something else (latency ?) is influencing how much torrent traffic is being pulled from my server. 

Could someone give me a hint why this is happening and how to debug this further ?

 

 

[fromport]

*update*

 

On the small router I ran this from a machine behind it:

 

http://n3.netalyzr.icsi.berkeley.edu/summary/id=36ea240d-20088-694f26e7-cf42-4132-af6a

 

This shows UDP fragmentation problems.

 

With the bigger router I don't have those problems:

 

http://n3.netalyzr.icsi.berkeley.edu/summary/id=36ea240d-20088-b3f06d4a-e0ce-4e30-b847

 

Still figuring out more and will report when I find out more.