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[PacketTracer]

Hi,

here is how you can determine the MTU of your Internet uplink in case it is smaller than 1500 which is the Ethernet-MTU of your LAN.

At a Windows PC open a command prompt and type the following command:

     ping -f -l 1472 <target>

where <target> is some Internet destination you know you'll get a ping reply from (often the administrators of <target> block ping responses). For example <target>=www.heise.de should work (just test it typing ping <target> whithout any options).

If you see ping replies coming back, you know that the MTU of your Internet uplink is at least 1500 and hence there is no MTU problem.

Otherwise, you might see some error message saying that fragmentation is needed but the DF flag is set or you might run into a timeout getting no reply. In this case you know, that some link in the path through the Internet to <target> has a smaller MTU than 1500. Now start to repeat the command decreasing the l-value by 1 (1471, 1470, 1469, ...) until you find a value l=LMIN, where you get a ping reply.

Then you know, that PTMU=LMIN+28 is the so called Path-MTU to <target> which means the smallest MTU of all links that form the path to <target> through the Internet.

Now repeat the test for several other targets. If you always end up with the same value l=LMIN, then probability is high that LMIN+28 is the MTU of your Internet uplink. In my case I get LMIN=1464 for any <target> which means that my Internet uplink (PPPoE/DSL) has a MTU of 1464+28=1492 (this is Ethernet(1500) minus PPPoE/PPP-Overhead (=8)).

If you can determine the MTU of your Internet uplink this way, put this value into the configuration of your router and see, if things get better.

PT

[chali]

in terms of d link router, you need to put a switch in between.
the same goes for cisco, zyxel etc.

I've had the same problem with the following servers / nas,
seagate black armor, Thecus 7700pro, ubuntu server.

Fix the problem by putting a dlinkswitch in between (connect all computers / servers to the switch and have only one cable from the router to the switch and your problem should be solved.

would like to point out that this little nugget is the first router that can handle my network without causing lag or die. (Over 50 clients that streams and plays, samba, wingftp, subsonic, plex, etc.)

can also mention the various routers I used before I found this. zyxel nbg5715, netgear wndr4500, Cisco E4200, jensen 89300th

/ Chali

[Hecro]

Hi,

here is how you can determine the MTU of your Internet uplink in case it is smaller than 1500 which is the Ethernet-MTU of your LAN.

At a Windows PC open a command prompt and type the following command:

     ping -f -l 1472 <target>

where <target> is some Internet destination you know you'll get a ping reply from (often the administrators of <target> block ping responses). For example <target>=www.heise.de should work (just test it typing ping <target> whithout any options).

If you see ping replies coming back, you know that the MTU of your Internet uplink is at least 1500 and hence there is no MTU problem.

Otherwise, you might see some error message saying that fragmentation is needed but the DF flag is set or you might run into a timeout getting no reply. In this case you know, that some link in the path through the Internet to <target> has a smaller MTU than 1500. Now start to repeat the command decreasing the l-value by 1 (1471, 1470, 1469, ...) until you find a value l=LMIN, where you get a ping reply.

Then you know, that PTMU=LMIN+28 is the so called Path-MTU to <target> which means the smallest MTU of all links that form the path to <target> through the Internet.

Now repeat the test for several other targets. If you always end up with the same value l=LMIN, then probability is high that LMIN+28 is the MTU of your Internet uplink. In my case I get LMIN=1464 for any <target> which means that my Internet uplink (PPPoE/DSL) has a MTU of 1464+28=1492 (this is Ethernet(1500) minus PPPoE/PPP-Overhead (=8)).

If you can determine the MTU of your Internet uplink this way, put this value into the configuration of your router and see, if things get better.

PT

Thanks for the incredible detailed post - much much appreciated!
Unfortunately I have a MTU of atleast 1500 following your post, but it was a great suggestion!

[PacketTracer]

Hm, here are two other ideas:

• Maybe Ethernet datarate and duplex mode autonegotiation between your wired LAN devices and the Ethernet ports of your router may not work. So if possible try to adjust speed (1GB/s) and duplex mode (full) within the driver settings of your network adapters manually instead of doing autonegotiation by default.
  
  
• Maybe SPI within your router drops TCP segments that are okay and shouldn't get dropped. So for a test, disable SPI within the router's firewall settings. If this does not improve the situation, return to enabled SPI.

Edit:

Are there any differences between using active or passive FTP? Meaning slow if passive and fast if active or vice versa?

PT

[FurryNutz]

Maybe someone can review your router settings with you using Link> teamviewer if your interested. Its safe and secure.