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Author Topic: modem/router/PC MTU size  (Read 1774 times)

neil

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modem/router/PC MTU size
« on: November 29, 2019, 03:31:51 PM »

MTU size in modem settings and router settings and PC settings has any effect on pkt loss in games and stuff? please share any suggestions
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burakkucat

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Re: modem/router/PC MTU size
« Reply #1 on: November 29, 2019, 06:40:05 PM »

As I use an ADSL2 (ITU-T G.992.3) service, with PPPoA, I have the modem/router's MTU configured as 1500.

All devices connected to my LAN have their MTU settings configured as "Auto".
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neil

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Re: modem/router/PC MTU size
« Reply #2 on: November 30, 2019, 04:30:13 PM »

As I use an ADSL2 (ITU-T G.992.3) service, with PPPoA, I have the modem/router's MTU configured as 1500.

All devices connected to my LAN have their MTU settings configured as "Auto".
whats the difference between PPPoE and PPPoA?

in my modem it is default at 1400. Is it OK?

[Moderator edited to merge two consecutive posts into one.]
« Last Edit: November 30, 2019, 05:27:46 PM by burakkucat »
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jelv

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Re: modem/router/PC MTU size
« Reply #3 on: November 30, 2019, 05:16:50 PM »

The largest MTU for PPPoA is 1500, for PPPoE it is 1492 - the difference is because of the header contents.

Generally the larger the MTU the better the speed although the difference is marginal. One thing is that the larger each block the higher the possibility it may get corrupted and need re-transmission. Interleaving etc. reduce the likelihood of this so there's no reason these days to not go for the largest that works.

Have you read Kitz's pages about MTU? https://kitz.co.uk/adsl/MTU2.htm
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burakkucat

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Re: modem/router/PC MTU size
« Reply #4 on: November 30, 2019, 05:34:47 PM »

whats the difference between PPPoE and PPPoA?

There are descriptions of PPPoE, PPPoA and PPPoEoA available on Wikipedia, which should answer your query far better than anything I could type.
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Chrysalis

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Re: modem/router/PC MTU size
« Reply #5 on: December 01, 2019, 03:31:26 PM »

For me mtu is about compatibility more than anything.

As jelv said the performance differential from a few bytes isnt going to be noticeable, the issues with mtu is always about fragmentation handling.

I had a discussion on pfsense recently about ipv6 mtu in which I said everyone should have just used 1280 as thats compatible with all types of broadband and tunnels, but companies like cloudflare and a few users have started migrating to 1500 which in my view will just create the same issues as ipv4 had down the line.
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neil

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Re: modem/router/PC MTU size
« Reply #6 on: December 02, 2019, 08:13:37 PM »

in one game pubg i do get pkt loss on upstream and after google search there were some posts about MTU size
i tried setting different MTU size but i still face pkt loss
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d2d4j

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Re: modem/router/PC MTU size
« Reply #7 on: December 02, 2019, 08:36:57 PM »

Hi

Please remember MTU is limited usually by your dsl provider and some modems-routers cannot be set to mtu 1500

Who is your dsl provider

Many thanks

John
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neil

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Re: modem/router/PC MTU size
« Reply #8 on: December 03, 2019, 05:09:28 PM »

Hi

Please remember MTU is limited usually by your dsl provider and some modems-routers cannot be set to mtu 1500

Who is your dsl provider

Many thanks

John
i am from Pakistan and the highest MTU i can set in my modem is 1492 but after setting this vlaue my pkt loss increased so i set it at 1480 for now but i still face pkt loss in pubg lite before it was default at 1400
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d2d4j

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Re: modem/router/PC MTU size
« Reply #9 on: December 03, 2019, 07:07:41 PM »

Hi

Many thanks

Please could I ask how you know you have packet loss

If 1492 gives fragmented I would think 1480 would also

So first you need to do the following test from your computer

(As MTU is set at 1480 in router, do not go above 1480 as it will fail)

ping bbc.co.uk -f -l 1440

If 1440 gives fragmented lower it until you find the MTU value without fragment then set your router MTU to that value.

Restart router and test once more

To find where packet loss may be happening run from command prompt

pathping bbc.co.uk

The result should show you where your packet loss is occurring

Many thanks

John
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neil

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Re: modem/router/PC MTU size
« Reply #10 on: December 03, 2019, 09:11:41 PM »

Hi

Many thanks

Please could I ask how you know you have packet loss

If 1492 gives fragmented I would think 1480 would also

So first you need to do the following test from your computer

(As MTU is set at 1480 in router, do not go above 1480 as it will fail)

ping bbc.co.uk -f -l 1440

If 1440 gives fragmented lower it until you find the MTU value without fragment then set your router MTU to that value.

Restart router and test once more

To find where packet loss may be happening run from command prompt

pathping bbc.co.uk

The result should show you where your packet loss is occurring

Many thanks

John
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.
« Last Edit: December 03, 2019, 09:14:10 PM by neil »
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d2d4j

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Re: modem/router/PC MTU size
« Reply #11 on: December 03, 2019, 09:17:57 PM »

Hi

So you need to set router MTU to 1452 and restart router

Then run pathping to see where packets are lost

Many thanks

John
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neil

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Re: modem/router/PC MTU size
« Reply #12 on: December 03, 2019, 11:15:01 PM »

Hi

So you need to set router MTU to 1452 and restart router

Then run pathping to see where packets are lost

Many thanks

John
i read somewhere 18 bytes are overhead for header and other stuff
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Alex Atkin UK

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Re: modem/router/PC MTU size
« Reply #13 on: December 04, 2019, 10:09:11 AM »

For me mtu is about compatibility more than anything.

As jelv said the performance differential from a few bytes isnt going to be noticeable, the issues with mtu is always about fragmentation handling.

I had a discussion on pfsense recently about ipv6 mtu in which I said everyone should have just used 1280 as thats compatible with all types of broadband and tunnels, but companies like cloudflare and a few users have started migrating to 1500 which in my view will just create the same issues as ipv4 had down the line.

I'm guessing from a backhaul perspective, a 1500 MTU is going to be lighter on the CPU of the routers plus more efficient use of bandwidth?

So I guess Cloudflare are going to be more concerned with keeping the costs of their network down rather than end-user issues.
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neil

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Re: modem/router/PC MTU size
« Reply #14 on: December 04, 2019, 01:03:41 PM »

Hi

So you need to set router MTU to 1452 and restart router

Then run pathping to see where packets are lost

Many thanks

John
path ping ends after 2 hops my routerand modem. 100% pkt loss at modem because it is in bridge mode?
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