Slow NAT transfer speeds

RouterOS General
1

When I go over a NATed port, my transfers don’t exceed 20Mbit/s. If I rsync from inside the network, I hit 60-70Mbit no problem, but from outside (port 11235 gets forwarded to 192.168.88.10:22 internally), I can’t get past 20Mbit.

/ip firewall nat print
Flags: X - disabled, I - invalid, D - dynamic
...
2   chain=dstnat action=dst-nat to-addresses=192.168.88.10 to-ports=22 protocol=tcp dst-port=11235
...

What can possibly be imposing this limit?

I’m on RB2011UAS with RouterOS 5.24.

2

Which ports are you using on the RB2011 ?

3

For NAT you mean?

This is the current situation:

remote-host → rb2011:11235 → 192.168.88.10:22

rsync --verbose --progress --human-readable -e 'ssh -p 11235' 100MB gerhard@rb2011:/tmp/
100MB
     104.86M 100%    2.01MB/s    0:00:49 (xfer#1, to-check=0/1)

sent 104.87M bytes  received 31 bytes  2.08M bytes/sec
total size is 104.86M  speedup is 1.00

192.168.88.10 ↔ remote-host

rsync --verbose --progress --human-readable remote-host:/tmp/100MB .
100MB
     104.86M 100%    7.17MB/s    0:00:13 (xfer#1, to-check=0/1)

sent 30 bytes  received 104.87M bytes  5.99M bytes/sec
total size is 104.86M  speedup is 1.00
4

no, I mean physically which ethernet ports on the device ?

5

ETH1 - internet
ETH2 - wireless AP
ETH3 - fileserver (192.168.88.10)
ETH4 - fileserver backup
ETH5 - desktop

ETH6 - 3G hotspot

6

Single TCP can’t be so high because of nature of TCP. Try running multiple TCP connections at the same time, you will see that the total speed will be higher.

7

OK, so when I parallelize, it takes 7 connections to saturate my upstream:

104.86M 100%    1.76MB/s    0:00:56 (xfer#1, to-check=0/1)
104.86M 100%    1.75MB/s    0:00:57 (xfer#1, to-check=0/1)
104.86M 100%    1.72MB/s    0:00:58 (xfer#1, to-check=0/1)
104.86M 100%    1.71MB/s    0:00:58 (xfer#1, to-check=0/1)
104.86M 100%    1.71MB/s    0:00:58 (xfer#1, to-check=0/1)
104.86M 100%    1.69MB/s    0:00:59 (xfer#1, to-check=0/1)
104.86M 100%    1.65MB/s    0:01:00 (xfer#1, to-check=0/1)
----------------------------------------------------------
734.02M 100%    11.99MB/s   0:00:58

There still must be a limit in the router for single TCP connections when going through the NAT, otherwise there wouldn’t be a 3.5x difference vs going direct.

Oh well, at least I have an acceptable solution. Cheers!