Slow upload speeds (Download speed are fine)

[ThePro]

A client did an upgrade to their bandwidth (50/50) and although download speeds are fine 50-52Mbps, upload speeds are always between 10-12Mbps (on any workstation/server).

If I connect a laptop directly do the ISPs ethernet cable I get 50Mbs up. Its only when connected via the FortiGate 60D.

I didn't setup this FortiGate initially. I tried disabling all policies except the default ones (no change). MTU is set to the default 1500. Should I mess with the MTU or TCP-MSS values? I read a couple of thread mentioning messing around with those value, but I'm not sure if it would help in this case. Like I mentioned download speeds reach 50-52Mbps easily, its the upload speed that are being capped for some reason.

[PerthNSE]

Have you checked that there is no Traffic Shaping set? 

[FatalHalt]

Did you ever get a resolution to this - feel like I'm encountering something very similar. 

[hpearce]

I have the same thing going on for over a month now, downloads are in the 300Mbps range and the upload is 34Mbps on the back of the Comcast modem, but is only 9 to 10Mbps from anything on the network, unless I just rebooted the the Fortigate 60E, then I can get 34Mbps up. But after a few minutes it drops down. There also seem to be times when it just goes back up to 34Mbps on various PCs but doesn't stay there. This seemed to happen when I upgraded from 7.0.2 to 7.0.3. Support doesn't have any great ideas other than for me to run diagnostics and reimage the unit. I've pulled everything out of the policies, there's no traffic shaping, etc. I hope to run the diags soon, not thrilled about reimaging, but I have all the pieces ready - finding the serial cable and adding a USB COM port were the hardest part so far.

[FuriousRabbit]

Did you ever find the solution to this. I’m having the exact same problem with a comcast modem.

[Toshi_Esumi]

I don't think your case is the same as the OP's situation. OP's case is "always" slow upload.
When you test with your 60E, make sure you disconnect everything else other than your device to test the speed.

[BrianSDX2]

I had the exact same problem as the OP and ended up solving it by putting a dumb gig switch in between the fortigate and the ISP device. I honestly don't know who to blame at this point the ISP or Foritnet.

[SysAdminSarr]

I realize this is old, but curious if anyone has found an answer.  

I am using a 100E running 7.0.5 and experiencing very slow upload speed with download fine.  I have tried a dumb gig switch between the Fortigate and the ISP router, but no change.  I have changed the interfaces from auto negotiate to full and 1000 still no change.  I can connect to the ISP on their router and get 100 up and down on a 100mb nic so I don't think it is on their end.  But through the Fortigate I get at most 25mb up and around 300mb down with a gig connection.  I created a policy specifically for traffic from one server for cloud backups without any inspection on the policy and still no go.  

[SysAdminSarr]

I am answering my own question here.  This was a config error on an ether channel in my org.  One side of the ether channel was setup as both a trunk and access.  The problem was it was hard to find due to no errors on the interfaces.  I ended up going through the running config to find it.

[FuriousRabbit]

Interesting. Did you end up changing the config to access solely or trunk solely? Currently, we are access solely and still having this problem.

This is the switch port config to the fortigate:

interface GigabitEthernet1/0/47
switchport mode access
spanning-tree portfast edge