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[Weaver]

Are you using an IP MTU below 1492 bytes? Is that for IPv4, IPv6 or both? What are the circumstances ? Any problems encountered in the Internet as a result?

I ask because if I were to start combining technologies, like DSL and LTE then I assume that would mean using L2TP and hence reduced MTU.

[neil]

Are you using an IP MTU below 1492 bytes? Is that for IPv4, IPv6 or both? What are the circumstances ? Any problems encountered in the Internet as a result?

I ask because if I were to start combining technologies, like DSL and LTE then I assume that would mean using L2TP and hence reduced MTU.

i am using 1452 i tried using 1492 but i was getting pkt loss in my games and i also faced websites not loading properly when i tried different MTU sizes dont know it is related or not
and in my modem and router i can select 1492 as max and also i changed MTU size in windows settings too

[Weaver]

Thanks Neil. You had certain problems with particular website before with MTU 1492 ?

[burakkucat]

Replying on behalf of neil . . .

He started a thread, "modem/router/PC MTU size", late last November (2019) and in Reply #10 posted the following --

i have turned on ping and other stats in game settings it shows pkt loss for upstream 1-10-15% and sometimes it hit 50% during start of game for downstream it is all fine

and i am getting fragmented after 1452
>ping bbc.co.uk -f -l 1453

Pinging bbc.co.uk [151.101.0.81] with 1453 bytes of data:
Reply from 192.168.1.1: Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.

[Weaver]

Thank you my friends. One adds on 20+8 to that, is that correct? So what is the significance of 1452 + 20 + 8 = 1480 ?

[burakkucat]

I'm not sure as to the significance but the evidence is clear . . . with a MTU set greater than 1452 fragmentation would occur. Of course we do not have any knowledge of how the ISP/CP deploys a service in Pakistan. 

[Weaver]

Indeed

[neil]

Thanks Neil. You had certain problems with particular website before with MTU 1492 ?

it was default 1400 in my modem before any changes. And in windows it was 1500. I will test again with 1492. Not just 1492 i tried different values randomly i think i also set very low value too less than 1000 Websites were not loading properly had to refresh a few times.

I am using 1452+28 header because it is default in my router. 1480 is mentioned in router settings

[neil]

now i am using 1492 MTU size in router settings. And after windows update MTU size of windows has been reset to 1500

[Weaver]

[neil]

[Weaver]

[burakkucat]

Many years ago, TalkTalk required a silly-low MTU setting. Fortunately that has long been consigned to history.

As PPPoA user I can, with my ZyXEL VMG1312-B10A, have a full 1500 bytes MTU --

[bcat ~]$ ping -c1 -Mdo -s1473 forum.kitz.co.uk
PING forum.kitz.co.uk (185.24.98.37) 1473(1501) bytes of data.
ping: local error: Message too long, mtu=1500

--- forum.kitz.co.uk ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 999ms

[bcat ~]$ ping -c1 -Mdo -s1472 forum.kitz.co.uk
PING forum.kitz.co.uk (185.24.98.37) 1472(1500) bytes of data.
1480 bytes from kitz.servers.eqx.misp.co.uk (185.24.98.37): icmp_seq=1 ttl=55 time=56.5 ms

--- forum.kitz.co.uk ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 99ms
rtt min/avg/max/mdev = 56.592/56.592/56.592/0.000 ms
[bcat ~]$

[ejs]

I use an MTU of 1478, set on the wlan0 interface of my computer. It results in very slightly more usable bandwidth for larger bulk downloads due to less wastage on ATM cell padding. I've done this for the past few years and not noticed any problems due to it. I don't think an MTU of 1500 is advantageous on ADSL due to the aforementioned ATM cell padding.

[Weaver]