awful slow on lines with reduced MTU

(Dirk2358) #1

Meanwhile I could find, why is awful slow for me and many others probably, too: There are problems with the host if the MTU is smaller than 1500 Bytes (if you are using DSL with pppoe e.g.).
Problem is, ( ignores the MSS TCP option and always uses the MTU 1500. I’m currently using a VPN (OpenVPN) as workaround, with additional use of fragment option. This option turned on forcefully fragments each packet > 1500 Bytes - if the server ignores MSS.
Could you please fix the problem?
BTW: ( doesn’t show the problem.

How to test?
You can test it with wget and parallel tcp trace (tcpdump). You can see the MSS problem, if you are seeing TCP Retransmissions or if the throughput is just a few KB/s (<70 KB/s - > 200 MB/s if it works as it should).

(Dirk2358) #2

I’m wondering why there isn’t any response to this problem. Maybe I wrote it not understandable enough? Please tell me if this is the problem!

My hope was, that the people technically providing this site read along here - but this seems to be not true. Would it be possible that some of the Sangoma people here could contact the responsible peoples?



I am not one of the maintainers of this site but did want to see what you are experiencing. I set my MTU to 1280 and loaded the site and found no slowdown at all, including on a purged browser with no cache.

(Dirk2358) #4

Did you ensure, that the reduced MTU actually takes any effect? Did you do a wireshark trace and verified, that the packages sent by the server have been actually reduced? Did you compare it? I have traces, which definitely show the problem (several upcoming ICMP frag needed).

BTW: testing is best done using wget e.g. Using a tool like this one guarantees that there is no caching at all and you can measure the time used for the download with time.

But even if it really works for you: It’s not a solution to provide a website, which doesn’t work globally - and many other hosts on freepbx do work fine - why not

Would be really nice, if the responsible person would take a look at the problem!



I confirm in my wireshark trace that regardless of local MTU and MSS, I receive > 1500 byte segments from the forum site. For me it does not create a slowdown because it is an artificial limitation (the network path has internet MTU of 1500 from here; there is no actual bottleneck).