Re: Me versus UPC (ziggo)

Hi,

You generally want to set the MTU as high as possible, i.e. as large as is
supported along the routes which you want to send traffic. This is because
every packet has overhead, so sending fewer larger packets means less
overhead, which means you're using your connection more efficiently.

ping supports setting the DF (Do not Fragment) bit on most distributions,
which you can use to test and discover your largest available MTU.

For example: on my (Debian Jessie) system:  ping -M do -s 1472 google.com
- where the number after -s is the number of bytes to send. Increasing it
on this system shows that 1500 bytes is my MTU (1472 data bytes + 28 bytes
of overhead.)

### Finding your MTU by experimenting with ping and packet sizes. Increase
-s nnn until it breaks...
### 1472 bytes works (as with 20 bytes + 8 bytes overhead, this makes 1500
bytes total)
$ ping -M do google.com -s 1472
PING google.com (159.134.168.110) 1472(1500) bytes of data.
1480 bytes from 159.134.168.110: icmp_seq=1 ttl=60 time=13.3 ms
1480 bytes from 159.134.168.110: icmp_seq=2 ttl=60 time=13.4 ms
^C
--- google.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 13.389/13.443/13.497/0.054 ms

### 1473 data bytes (+28 bytes = 1501 total bytes) does not work. My local
interface complains as its MTU is 1500 bytes...
$ ping -M do google.com -s 1473
PING google.com (159.134.168.96) 1473(1501) bytes of data.
ping: local error: Message too long, mtu=1500
ping: local error: Message too long, mtu=1500
^C
--- google.com ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 1007ms


You can also set your local MTU higher to make sure that you're getting a
useful path MTU (rather than being limited by configuration on your local
host:
e.g.
### Look at my interface MTU setting - looks like it's the ethernet default
of 1500 bytes...
# ip link show dev wlan0
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode
DORMANT group default qlen 1000
    link/ether 00:1d:e0:36:79:f9 brd ff:ff:ff:ff:ff:ff

### Set it to something larger, so we'll hit the MTU limit of the next
upstream device, not the local interface...
# ip link set dev wlan0 mtu 2000
# ip link show dev wlan0
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 2000 qdisc mq state UP mode
DORMANT group default qlen 1000
    link/ether 00:1d:e0:36:79:f9 brd ff:ff:ff:ff:ff:ff

### Ping wit something slightly larger than 1500. 1474+28 bytes overhead =
1502, a great place to start...
# ping -M do google.com -s 1474
PING google.com (159.134.168.52) 1474(1502) bytes of data.
From MitraStar.Home (192.168.1.254) icmp_seq=1 Frag needed and DF set (mtu
= 1500)
ping: local error: Message too long, mtu=1500
ping: local error: Message too long, mtu=1500
^C
--- google.com ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2009ms


### Note the useful error from my local router stating (fairly and
correctly) that it's receiving packets it needs to fragment, but I've
explicitly told it not to fragment (ping -M do), so it has to drop the
packets and respond with an error.


Hope this helps.

Best regards,
-->Gar


2015-10-23 10:55 GMT+01:00 Paul Mc Auley <[email protected]>:

> So generally different delivery mechanisms add different encapsulation
> overheads and sometimes fragmentation isn't well served.
> I'd expect 1450 to be a fairly reliable size, but generally you should be
> able to narrow down the optimal size by repeatedly halving
> the difference between what works and what doesn't, (so 500, 1000, 1250,
> 1375...)
>
> Paul
>
> On 21 October 2015 at 06:59, Rob Stocker <[email protected]> wrote:
>
>> Hi Guys,
>>
>> I reduced the MTU and it seems to work!!!  I started at 576 (a truly
>> random number) and will try increasing it this evening (out of curiosity).
>>
>> 1) Can you confirm that it makes sense? Is the fragmentation issue a
>> router/connection issue that would be unique (in this case) to ziggo?
>>
>> So I will change the MTU on each of my machines (2 desktops, 4 laptops).
>>
>> 2) What is the trade-off with a smaller MTU.
>>
>> thank you so much.
>> The thought of dealing with customer service in a foreign language, with
>> a use case as obscure as this, meant I was gonna cancel my account first
>> and ask questions later.
>>
>>
>> @Techbot <https://twitter.com/techbot>
>> ----------------------------------------------
>> The Eclectic Meme Conspiracy <http://www.eclecticmeme.com>
>> ----------------------------------------------
>>
>> On Wed, Oct 21, 2015 at 12:30 AM, Paul Mc Auley <[email protected]>
>> wrote:
>>
>>> It was sort of called out earlier by David K above, but you might want
>>> to try dropping the MTU on your laptop and trying to connect again.
>>> If it's a combination of encapsulation and poor fragmentation handling
>>> that could cause something like this.
>>> I'd expect something on the order of 1400-1450 to get around most such
>>> cases.
>>>
>>> Paul
>>>
>>> On 20 October 2015 at 22:47, Jean-François Bucas <[email protected]>
>>> wrote:
>>>
>>>> do you have an extract of the log where the login succeeded?
>>>>
>>>> Perhaps you can try to start another SSH daemon no a different port
>>>> (eg: 443) and see how it goes?
>>>>
>>>> 2015-10-20 21:55 GMT+01:00 Rob Stocker <[email protected]>:
>>>>
>>>>> 46.19.37.66 is my server MrJigs
>>>>>
>>>>> My laptop is never on the same network as 46'.
>>>>>
>>>>>  46' is a VPS on tilaa.nl
>>>>>
>>>>> Normally I would not use any form of port forwarding at any of my
>>>>> connection points. (Ireland, previous flat,work etc)
>>>>>
>>>>> I logged in to '46 from work today and it was instantly business as
>>>>> usual, this issue is unique to my connection in new home.
>>>>>
>>>>> I cannot SSH into my work server either (not owned or run by me, so
>>>>> completely different location and config),  I'm still thinking it's related
>>>>> to router or connection.
>>>>>
>>>>> ** I can use SSH via Phpstorm to upload a file provided it is really
>>>>> small , 600 bytes.**
>>>>>
>>>>> The screen shot below is of /var/logs/auth.log on 46'. it repeats for
>>>>> 3 days . There are 110,000 lines for 3 days 18th,19th and 20th
>>>>>
>>>>> [image: Inline image 1]
>>>>>
>>>>> @Techbot <https://twitter.com/techbot>
>>>>> ----------------------------------------------
>>>>> The Eclectic Meme Conspiracy <http://www.eclecticmeme.com>
>>>>> ----------------------------------------------
>>>>>
>>>>> On Tue, Oct 20, 2015 at 6:02 PM, Maciej (Matchek) Bliziński <
>>>>> [email protected]> wrote:
>>>>>
>>>>>> Is your server and your laptop in the same internal network? If so,
>>>>>> you need to set up hairpin nat. Microtik wiki has an explanation.
>>>>>>
>>>>>> A ter, 20/10/2015, 16:52, David Kernan <[email protected]>
>>>>>> escreveu:
>>>>>>
>>>>>>> So seeing a connection closed result would mean you're being sent a
>>>>>>> TCP RST packet somewhere, which is closing the connection.
>>>>>>> Is there anything useful in /var/log/auth.log log file?
>>>>>>>
>>>>>>> On Tue, Oct 20, 2015 at 4:49 PM, Jean-François Bucas <
>>>>>>> [email protected]> wrote:
>>>>>>>
>>>>>>>> anything in your 46.19.37.66:/etc/hosts.deny file?
>>>>>>>> do you have any relevant lines in 46.19.37.66:/var/log/auth.log ?
>>>>>>>>
>>>>>>>> 2015-10-20 16:38 GMT+01:00 Rob Stocker <[email protected]>:
>>>>>>>> >
>>>>>>>> >> Any firewall on your server in NL,  ie: fail2ban, denyhost, ... ?
>>>>>>>> >
>>>>>>>> >
>>>>>>>> > Nope.
>>>>>>>>
>>>>>>>> --
>>>>>>>> Irish Linux Users Group
>>>>>>>> ---
>>>>>>>> You received this message because you are subscribed to the Google
>>>>>>>> Groups "ILUG" group.
>>>>>>>> To unsubscribe from this group and stop receiving emails from it,
>>>>>>>> send an email to [email protected].
>>>>>>>> To post to this group, send an email to [email protected].
>>>>>>>> Visit this group at http://groups.google.com/a/linux.ie/group/ilug/
>>>>>>>> .
>>>>>>>> To view this discussion on the web, visit
>>>>>>>> https://groups.google.com/a/linux.ie/d/msgid/ilug/CAK_fzWqj3Jp-AXKKhDLYUHaOtAaBYyoj%3Ds2FZwOWccXASAb9Jw%40mail.gmail.com
>>>>>>>> .
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Best regards,
>>>>>>>
>>>>>>> David
>>>>>>>
>>>>>>> --
>>>>>>> Irish Linux Users Group
>>>>>>> ---
>>>>>>> You received this message because you are subscribed to the Google
>>>>>>> Groups "ILUG" group.
>>>>>>> To unsubscribe from this group and stop receiving emails from it,
>>>>>>> send an email to [email protected].
>>>>>>> To post to this group, send email to [email protected].
>>>>>>> Visit this group at http://groups.google.com/a/linux.ie/group/ilug/.
>>>>>>> To view this discussion on the web, visit
>>>>>>> https://groups.google.com/a/linux.ie/d/msgid/ilug/CABnDWJDg-ydGkJ5UgiZA%2BSzMZ%2BBaNixwT-_dbv5LYGKz%3DsmCXQ%40mail.gmail.com
>>>>>>> <https://groups.google.com/a/linux.ie/d/msgid/ilug/CABnDWJDg-ydGkJ5UgiZA%2BSzMZ%2BBaNixwT-_dbv5LYGKz%3DsmCXQ%40mail.gmail.com?utm_medium=email&utm_source=footer>
>>>>>>> .
>>>>>>>
>>>>>>
>>>>>
>>>> --
>>>> Irish Linux Users Group
>>>> ---
>>>> You received this message because you are subscribed to the Google
>>>> Groups "ILUG" group.
>>>> To unsubscribe from this group and stop receiving emails from it, send
>>>> an email to [email protected].
>>>> To post to this group, send email to [email protected].
>>>> Visit this group at http://groups.google.com/a/linux.ie/group/ilug/.
>>>> To view this discussion on the web, visit
>>>> https://groups.google.com/a/linux.ie/d/msgid/ilug/CAK_fzWr0pS2mxT9cUhxis_RkfP-V6wpAmnW4UoUaL7HgFzrKNw%40mail.gmail.com
>>>> <https://groups.google.com/a/linux.ie/d/msgid/ilug/CAK_fzWr0pS2mxT9cUhxis_RkfP-V6wpAmnW4UoUaL7HgFzrKNw%40mail.gmail.com?utm_medium=email&utm_source=footer>
>>>> .
>>>>
>>>
>>>
>>
> --
> Irish Linux Users Group
> ---
> You received this message because you are subscribed to the Google Groups
> "ILUG" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to [email protected].
> To post to this group, send email to [email protected].
> Visit this group at http://groups.google.com/a/linux.ie/group/ilug/.
> To view this discussion on the web, visit
> https://groups.google.com/a/linux.ie/d/msgid/ilug/CADuf5hk882p7fB5GHbsA%2B3%3DSU%2Bu3ebGd6oivx2MzoZ_mdu%3DhrA%40mail.gmail.com
> <https://groups.google.com/a/linux.ie/d/msgid/ilug/CADuf5hk882p7fB5GHbsA%2B3%3DSU%2Bu3ebGd6oivx2MzoZ_mdu%3DhrA%40mail.gmail.com?utm_medium=email&utm_source=footer>
> .
>



-- 
Gareth 'bigbro' Eason

-- 
Irish Linux Users Group
--- 
You received this message because you are subscribed to the Google Groups "ILUG" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
To post to this group, send an email to [email protected].
Visit this group at http://groups.google.com/a/linux.ie/group/ilug/.
To view this discussion on the web, visit https://groups.google.com/a/linux.ie/d/msgid/ilug/CAD4VSdgA6wPMG203iXhekHMtKB9gJuxfF8b9CO_2Sh9kKW8GOw%40mail.gmail.com.