2016-04-10 - Re: [GRASE-Hotspot] Upload speed problem due to mtu?

Header Data

From: Timothy White <ti***8@gmail.com>
Message Hash: 08935ed263b37c082bc843ecf86462bfddf2081f990b394139046ffaf10ac797
Message ID: <CAESLx0+RnxZUKjEnUQ5t+_mDpkY=CRFpeKM8GT-visuGa7zxDg@mail.gmail.com>
Reply To: <47CB3802-43B2-4C8F-AF27-427C8C4436E5@argyle.com.au>
UTC Datetime: 2016-04-10 10:48:41 UTC
Raw Date: Mon, 11 Apr 2016 03:48:41 +1000

Raw message 

It may also be worth running
https://grasehotspot.org/support/collecting-support-information/ to show
your setup to us. It's possible that you are missing something obvious that
is causing your MTU issues.

I just did some tests on my devices, and pings of size 1472 all go through
my hotspots fine. What hardware are you using? Maybe it's a network card
driver bug?

Regards

Tim

On Sun, Apr 10, 2016 at 10:40 PM, David Wilson <da***e@argyle.com.au> wrote:

> MTU will normally always be 1500 for ethernet devices.
>
> MSS Clamping is different to the MTU.
> Getting an MTU of 576 from the client to the hotspot device is not that
> important, you need to know what size ping you can get out to somewhere on
> the internet (www.yahoo.com) without fragmentation.
>
> What was the result of running the pings (commands below) from a client on
> the LAN side of the hotspot?
> You can run the same from the firewall lan if you like, but if your issue
> is with Grase clients then best to do it from the client.
>
> Then you set the command in IPTables to Clamp all packets to that size.
>
> The first command probably won’t give you an output but will create a new
> firewall rule.
> Just make sure you runt that command without the initial # (The # is just
> a comment delimiter from where those commands came from
>
>
> Dave
>
>
> On 10 Apr 2016, at 8:46 pm, Ali Farajpahlou <al***u@gmail.com>
> wrote:
>
> thank you for your reply suggestions. i already tried pinging with
> different sizes, the problem is the hotspot device i think. the device is
> connected to the internet through a firewall (firewall is the dhcp server
> assigning ip to the wan side of the hotspot device). i tried connecting
> directly to the firewall and there was no issue with uploading and packet
> fragmentation. i have determined an mtu of 576 behind the hotspot device
> (pinging the hotspot device), and i think the probelm is that the device
> needs to fragment the packets, but they contain a DF header i think. so it
> drops them. i cant find where this mtu is set on the device, checking the
> interfaces mtu didnt solve the issue (they were already set at 1500 on
> every interface (yes even the tunnels xD )). havn't checked mss clampings
> but i'm assuming that it's not causing the problem.
>
> the first iptables command didnt output anyresponse. gonna search some
> more myself and see what more info i can find about this.
>
> btw i forgot to mention that im working on the latest Debian release with
> the latest version of grase (stable version not nightly)
>
>
> again, thanx for your help and suggestions.
>
> On Sunday, April 10, 2016 at 1:33:55 AM UTC+4:30, dave wrote:
>>
>> Hi Ali
>>
>>
>> MTU issues are normally related to additional overhead created by using
>> protocols on top of Ethernet.
>>
>> So If you have a pppoe connection to the internet, for example, then that
>> pppoe protocol will increase the packet size and possibly cause it to fail
>> to traverse the Internet.
>>
>> You should test to see what the maximum packet size is that you can send
>> through your internet connection from your Grase server
>> You can find this by trial and error
>>
>> The best value for MTU is that value just before your packets get
>> fragmented. How do you find that out? By using Ping at the command prompt.
>>
>> *Windows users:*
>> Go to Start/ Programs/ Accessories/ Command Prompt and type the following:
>> ping -f -l 1472 www.dslreports.com
>> (That is a dash lower case "L"  Also note the spaces in between the
>> sections.)
>>
>> *Linux users:*
>> ping -s 1472 www.dslreports.com
>>
>> *OS X users:*
>> ping -D -s 1472 www.dslreports.com
>>
>> Press Enter. Then reduce 1472 by 10 until you no longer get the "packet
>> needs to be fragmented" error message. Then increase by 1 until you are 1
>> less away from getting the "packet need to be fragmented" message again.  Add
>> 28 more to this (since you specified ping packet size, not including
>> IP/ICMP header of 28 bytes), and this is your MaxMTU.
>>
>>
>> Then you need to use iptables to implement the mss clamp unless you have
>> another router between your Grase server and the internet in which case you
>> may be able to do the MSS clamping on that router.
>> (I always setup this way so I have never used Grase to do the Clamping)
>> There are two options below - The first one is automatic and “may not
>> work” as some people have had issues with this.
>> The second option is based on you finding the correct value above and
>> then adding it to the command in place of the 1500 - Don’t forget to add
>> the 28 to the successful test result above.
>>
>> In order for this to work you need at least iptables-1.2.1a and Linux
>> 2.4.3 or higher. The basic command line is:
>>
>> 	# iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS  --clamp-mss-to-pmtu
>>
>> This calculates the proper MSS for your link. If you are feeling brave,
>> or think that you know best, you can also do something like this:
>>
>> # iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss
>> 1500
>>
>>
>>
>>
>> Dave
>>
>>
>> On 9 Apr 2016, at 7:46 pm, Ali Farajpahlou <al***.@gmail.com> wrote:
>>
>> hey there.
>>
>> I've Noticed a problem with uploading files though the hotspot (client
>> side) and after searching in the group and internet, and running some tests
>> with MTU and ping testing with different MTU's (ping packet size), i found
>> out that the problem is with mtu size.
>> all interfaces were set to MTU:1500 by default. changing them didn't fix
>> the issue, and after checking and adding header size i still get that the
>> MTU that is being applied to packets is 576.
>>
>> if anyone has any idea about this problem, i would appreciate any
>> suggestions. if u want more details about anything... I'm here :)
>>
>> many thanx in advance and if my writing has problems, sry for my bad
>> english :)
>>
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