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Slow TFTP between zones

Tony Ayre

We currently have our XG set up with 2 LAN zones - 1 is a normal LAN, plugged in to the switch in the normal manner. The other is on the end of a PTP leased line and has its own core switch handling routing.

We are seeing an issue when trying to boot via PXE/tftp on that remote site. PXE/TFTP is incredibly slow. The SCCM boot file being sent is about 360MB in size, but even when booting a single PC from it, it takes 10+ minutes to transfer. Once in the Windows PE environment and downloading the image files themselves, things speed up though (those files being transferred over HTTP). SMB traffic over the same links are also fine. 

The link is a 1Gbps link, so with a single PC getting data, it shouldn't be taking 5 minutes.

I have 2 rules in place on the XG for this link - allowing all traffic from LAN to DMS (the PTP linked LAN), and one allowing all traffic from DMS to LAN, with now intrusion protection enabled in either direction (turned off to eliminate possible causes).

To eliminate it being the TFTP server or the PXE client, I have set up a TFTP server on a different machine, and a TFTP client at the remote end and tried transferring a file. ~450MB took 11 minutes or so to transfer. There is also nothing in the log viewer being blocked between the sites (nothing logged anyway).

Does anyone have any ideas what could be causing this slowness?



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  • 0

    To troubleshoot such issues, you would have to look for different issues. 

    Most likely this could be caused by Redirect / retransmissions. 

    If you start to tcpdump such traffic and read it in wireshark, you could see retransmissions (so to speak, packets are to big or something like that, and the other site have to resent it). 

    Or maybe the issue is not XG, instead the PC to Switch communication? Could you verify, which speed is negotiation between Switch and PC? For PXE, you are in a boot state, maybe there is an issue. I saw couple of issues there, because the BIOS / UEFI was not able to negotiate a proper speed (half duplex etc). 

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  • 0

    To troubleshoot such issues, you would have to look for different issues. 

    Most likely this could be caused by Redirect / retransmissions. 

    If you start to tcpdump such traffic and read it in wireshark, you could see retransmissions (so to speak, packets are to big or something like that, and the other site have to resent it). 

    Or maybe the issue is not XG, instead the PC to Switch communication? Could you verify, which speed is negotiation between Switch and PC? For PXE, you are in a boot state, maybe there is an issue. I saw couple of issues there, because the BIOS / UEFI was not able to negotiate a proper speed (half duplex etc). 

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