What can limit the upload speed on a computer through a linux gateway?

Question

Computer networks

There is an Internet gateway on Debian. Traffic is redirected through iptables. On the gateway, the upload is 2 times higher than on the computer. What could be the problem?

Answer 1

For example, if the speed and duplex are set manually, it can be stupid. Try doing auto-negotiation.

Answer 2

Compare "pings" to the target server when working through the gateway and directly. Also check the interfaces for errors (using the ifconfig command).
UPD :

https://cloud.mail.ru/public/3VZDQKLZM2Wb/cap_eth0.pcap - listening to eth0 (Internet)
https://cloud.mail.ru/public/2MTN9apktN8U/cap_eth1.pcap - listening to eth1 (LAN)

Specify, are these traffic dumps only from the server or from the server (eth0) and the client computer too (eth1)?
I ask because I did not find a difference in the transfer rate of useful data twice here.
Graph of the traffic transfer rate from server 213.180.204.183 from eth0:
From eth1:
I have not found any obvious problems with TCP yet, as well as with MTU (the HTTP payload size in each packet is the same in both dumps, 1410 bytes)
UPD2 :

gateway - https://cloud.mail.ru/public/5VsPnm4QmaRp/gateway.pcap
computer - https://cloud.mail.ru/public/yy6WtAZgbKc5/computer.pcap

So, now I see:
gateway:
computer:
If I'm not mistaken, it follows from the dumps that you:
1) raise an l2tp session from the gateway and download the file through it, your MAC address is 14:cc:20:03:c0:aa, the nearest router - 84:
c9 :b2:22:a6:02, the speed is about 5 MB / sec , the nearest router - 84:c9:b2:22:a6:02, the speed is about 2.5 MB / s
In this regard, it is not clear how your connection is organized? If the computer is connected via a linux gateway (this is not visible from the dumps, see MAC addresses of Ethernet frames), then why are you raising a session from it (the computer), instead of raising it on the gateway and sending traffic to the computer through a regular IPoE ?
Please explain clearly what exactly is the problem? For example, before it was so-and-so, now it has become so-and-so. Or is the problem that the performance of the L2TP tunnel is different when it is raised from the computer and from the gateway?
PS I can answer no earlier than Monday, April 27 this year, do not lose.
UPD3 : I apologize for the delay in responding.

The problem lies somewhere in the forwarding of frames to eth1 from ppp0 at the software level.

I can't help you with this problem. As an attempt to grasp at straws - do you happen to have qos / tc not configured on the gateway?

Answer 3

habrahabr.ru/post/133076