Pppoe mtu

chris890 · Post by **chris890** » Sun Apr 17, 2022 10:32 pm

Should I increase my default mtu from 1480 to 1492? 1492 being the maximum I can enter.

Would changing it from the default cause problems?

when I did a mtu test it said the value that didn't fragment was 1450. Do I add 28 bytes onto this to get my optimum mtu value and just tpe 1478 into my mtu setting on my router?

Post by **Philip** » Mon Apr 18, 2022 11:34 am

For general use, I would leave it at 1480 rather than 1492, it is a bit safer, and you're not losing much.
For testing, you can always set it to 1500 in your router/client, then see what the largest non-fragmented packet is.

You will not be able to see non-fragmented packets 28 bytes smaller than the MTU, because of additional headers. Not sure why it is 1450 and not 1452 is your MTU is 1480, some additional header likely.

chris890 · Post by **chris890** » Tue Apr 19, 2022 9:47 am

yes you are right it is 1452.

SO I wanted to enter the best mtu value for gaming.

Do you recomend I use 1492?

chris890 · Post by **chris890** » Tue Apr 19, 2022 9:48 am

I can't use a mtu value of 1500, that exceeds what I can enter in the field box.

Post by **Philip** » Tue Apr 19, 2022 5:06 pm

1492 is the max for PPPoE and it is ok to have it at that. It is also good to leave it slightly smaller at 1480 if you want to be more compatible, you won't see any noticeable reduction in speed, and for gaming latency is more important than the 0.01% potential throughput reduction.

chris890 · Post by **chris890** » Thu Apr 21, 2022 11:31 am

Philip wrote:1492 is the max for PPPoE and it is ok to have it at that. It is also good to leave it slightly smaller at 1480 if you want to be more compatible, you won't see any noticeable reduction in speed, and for gaming latency is more important than the 0.01% potential throughput reduction.

so your saying for latency I best leave it at 1480?

Post by **Philip** » Fri Apr 22, 2022 7:36 am

Yes, because it is less likely for packets to get re-packaged multiple times along the line between you and the game server.

chris890 · Post by **chris890** » Mon Apr 25, 2022 7:36 pm

Philip wrote:Yes, because it is less likely for packets to get re-packaged multiple times along the line between you and the game server.

Could it be lowered any lower from 1480 to produce better latency results?

Post by **Philip** » Tue Apr 26, 2022 6:33 pm

I doubt it will make a difference. The idea is to leave it large, so packet headers are small percentage of the total payload, while keeping it small enough to fit the underlying network encapsulations.
Most ISPs set their backbones to accommodate MTUs at least 1500 bytes (1492 for PPPoE, VPNs also chip away from the max size).

For illustration/historic purposes only:
There was some anecdotal evidence that lowering the MTU on PlayStation 4 from 1500 to 1473 would reduce latency, may have had something to do with encapsulation on their network.
Long time ago, with dial-up networks 576 MTU was used at times.
ATM/SONET backbones (not common today) had a fixed 48-byte MTU, so some people used MTUs of 1440 bytes (30x48bytes=1440 MTU, 31x48=1488 MTU).