RT-N66W, Gaming Consoles and Packet Fragmentation

[Elite49]

Just picked this up and after an entire day of trying to get it customized so it ran at least as good as my 5 year old router I realize there are no MTU settings. The PS3/4 and Xbox 360 all need specific MTU settings that I guess this router is not giving it.

The PS3/4 give me a "Your router doesn't support packet fragmentation, contact the router company this will effect online multiplayer, etc" message. Tried Auto and every custom MTU setting I could find online. Tested old router and it doesn't give me this warning.

All wireless, and while I get really good speeds I also get really bad lag spikes. Anyone know a remedy for this?

 

[jlake]

Check to see if Merlin firmware allows you to change MTU. I assume you don't have PPPoE Internet connection type.

I have RT-N66u (same router) and I've always found the ping to very consistent without spikes and no lag, so maybe once you get the MTU sorted out, it will work better.

When I have used the Qos for gaming, I always use the default Qos settings. I just enter ISP upload and download speeds and that's it. No tinkering for me.

I think most n66 owners are using Merlin's latest experimental SDK 5 build which is located in his experimental folder.

https://www.mediafire.com/folder/bkfq2a6aebq68//Asuswrt-Merlin

 

[Elite49]

Yeah no PPPoE for me, surprised this feature isn't on this router since it was on my really old one. Does anyone know the default MTU for this router?

 

[RMerlin]

Yeah no PPPoE for me, surprised this feature isn't on this router since it was on my really old one. Does anyone know the default MTU for this router?

It's the standard Ethernet value - 1500.

 

[sinshiva]

hey,

you must be on dsl; whether you are using pppoe or not, your MTU settings probably need to be tweaked. (dsl should have below 1488 for max efficiency, without baby jumbos) You generally need cable for 1500. are you setting the MTU at the wan port? i've set it manually on all my devices locally and couldn't on the xbox, but i haven't seen any errors coming from it. i'd obviously prefer if the router would set mtu locally for me. did yourr old router let you specify wan and lan, or is it that the lan side would be updated if you set it on the wan side and the asus routers aren't doing it? i'm new to dsl; is this something that can mess with devices learning the mtu if the immediate interface to them doesn't have this set?

almighty merlin, if such is the case, would you know a fix?

[edit] forgot about lan side jumbo frames as im not using them; can this setting be modified to also let you specify mtu? [/edit]

[edit2/] actually, i had jumbo frames enabled. waiting for somebody to get off netflix to reboot with jumbo disabled to see if that changes things.

 

[jlake]

hey,

you must be on dsl; whether you are using pppoe or not, your MTU settings probably need to be tweaked. (dsl should have below 1488 for max efficiency, without baby jumbos) You generally need cable for 1500. are you setting the MTU at the wan port? i've set it manually on all my devices locally and couldn't on the xbox, but i haven't seen any errors coming from it. i'd obviously prefer if the router would set mtu locally for me. did yourr old router let you specify wan and lan, or is it that the lan side would be updated if you set it on the wan side and the asus routers aren't doing it? i'm new to dsl; is this something that can mess with devices learning the mtu if the immediate interface to them doesn't have this set?

almighty merlin, if such is the case, would you know a fix?

[edit] forgot about lan side jumbo frames as im not using them; can this setting be modified to also let you specify mtu? [/edit]

[edit2/] actually, i had jumbo frames enabled. waiting for somebody to get off netflix to reboot with jumbo disabled to see if that changes things.

Where are you getting the info that MTU for DSL should be below 1488 for max efficiency? Can you post a link? You're new to DSL?

 

[sinshiva]

yea, i always had cable before.

here's an example of information i found on how i arrived at my MTU settings;

https://learningnetwork.cisco.com/thread/25798

the first guy is pretty much right, the guy answering him is trying to calculate crap on his own and is way off, but has the right idea. the problem is that there are additional parameters to set for various kinds of encapsulation that alter payload size as well as some forms of encapsulation can expand their padding, again shrinking the payload size.

so, what i accept to be absolutely certain when calculating MTU is that if there aren't baby jumbo frames implemented by the ISP allowing greater than 1500 MTUs, but not nearly as high as jumbo frame mtus, then you can have an MTU greater than 1488. you could potentially have an MTU of 48bytes x 32 for 1536 MTU, IF there is ABSOLUTELY NO encapsulation in use. Which is never the case, even without PPPoE. To find MTU, i set the router's WAN MTU to 1500 and configured it at the interface of the machine i was testing from.

in this case, windows with the command

netsh interface ipv4 set subinterface "Local Area Connection" MTU=1456 store=persistent

you can verify with

netsh interface ipv4 show subinterfaces

so, since MTU can't be greater than 1500, all dsl travels over atm which divides packets into payloads of 48bytes, (+5 bytes making 53byte atm 'cells', but this is not important.) leaving me a starting point of 1488. then, find your favorite speedtest that has been most successful testing your maximum downstream bandwidth and keep dropping your MTU between speedtests a few bytes at a time. when your downstream bandwidth launches back up despite a lower MTU, you'll know you are at your maximum efficient MTU with DSL. After, set the WAN MTU on the router to what you got.

back to the topic;

i disabled jumbo frames under LAN > Switch Control, set this computer's MTU to 1500, but with

netsh interface ipv4 set subinterface "Local Area Connection" mtu=1500 store=active

i then disabled and re-enabled the the interface and used

netsh interface ipv4 show subinterfaces

again and this time my computer took the 1456 MTU automatically.

so, it looks like as long as you have jumbo frames disabled, the LAN ports take on the MTU set at the WAN side

1456 MTU is what i arrived at for my connection in my testing. you can try it, but i'd definitely advise testing others to make sure.

 

[sm00thpapa]

Use F/W .276, factory set your settings and re-configure. Have this router for 2 years and never had a problem with Xbox 360 or PS3. 66W same butt 66U.

 

[Pericynthion]

FWIw If you have QOS enabled on any ASUS router (from what I can tell) the packet fragmentation test will always fail. Without QOS it works just fine.


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[sinshiva]

ok, so good news and bad news.

While my windows computer for whatever reason kept reverting to the 1456 MTU, i don't know if that's because it was intelligent or just using old settings because i didn't reboot the whole computer. That said, with my android devices, they wouldn't update their MTU automatically.

during my tests, i actually set the MTU on my attached WAP and that didn't help automagically change my device's MTU. worse, when i changed my android's MTU to 1500 while the WAP was set for 1456 (via startup-script), the phone would only connect to the WAP and nowhere else.

luckily, i figured out how to leave the android set for 1500, the WAP set for 1456 and still connect to the internet by tweaking the n66. unfortunately, it's stuff that needs to be added to a startup script in jffs or something, so i'm about to start looking into that.

to get devices working properly with an outside MTU different from the inside MTU without setting the MTU on each device, from the Asus router; under the 'Tools > Run CMD' menu, i had to do;

ifconfig eth1 mtu 1456 up
ifconfig eth2 mtu 1456 up
ifconfig br0 mtu 1456 up

and now my devices can have whatever MTU on the inside and still be efficient connecting to the outside. one or both of those eth interfaces had to be set to get the br0 mtu set, which was required to make everything perfect.

[edit] let me know if using the above commands to set your mtu + setting the mtu on wan page fixes your xbox problems. this isn't yet a permanent solution.

 

[sinshiva]

okie dokie, making it permanent is easy enough;

you have to enable jffs under Administration > System, leave format on boot disabled.

you then have to telnet or ssh into the router and create init-start under /jffs/scripts

#!/bin/sh
ifconfig eth1 mtu 1456 up
ifconfig eth2 mtu 1456 up
ifconfig br0 mtu 1456 up

and make it executable with the command;

chmod a+rx /jffs/scripts/init-start

that should take care of things. additionally, thanks to merlin for providing a comprehensive guide instead of making me look around for everything.

[edit] i do still see a performance gain manually setting the MTU on devices, but this way at least things will work if they don't have it

 

[Elite49]

FWIw If you have QOS enabled on any ASUS router (from what I can tell) the packet fragmentation test will always fail. Without QOS it works just fine.


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Thought this would be 1500 MTU.

@sm00thpapa do you use QOS and if so does it give you that error?
Should QOS generally be used or is that something that doesn't need to be? I have Comcast as well not DSL.

Thanks for all your help.

 

[sinshiva]

hey, you said you are on cable, but are getting fragmentation issues... is the mtu on the wan page set for 1492 or something when it should be 1500? i'd have thought comcast mtu would always be 1500 so everything should pretty much work out of the box if it's all set for 1500

besides these qos issues, whatever they are.

 

[Elite49]

hey, you said you are on cable, but are getting fragmentation issues... is the mtu on the wan page set for 1492 or something when it should be 1500? i'd have thought comcast mtu would always be 1500 so everything should pretty much work out of the box if it's all set for 1500

besides these qos issues, whatever they are.

Comcast I'm pretty sure is 1500 as my last router was at 1500. Gonna downgrade to the older version and see if turning QOS off helps. Funny I turned ON QOS to help with the overall speeds. Before it was on trying to upload a 500 MB clip on PSN took around 30 minutes. Turning it on resulted in normal speeds.

 

[Pericynthion]

There is a post (somewhere on the inter web) - another firmware found that the fragmentation test failures (PSN etc) are caused by an issue with handling UDP fragmentation. This is something embedded within the core firmware (ie not something I believe Merlin can compensate for) - I spent a few days myself trying to hack QOS to handle PSN type traffic but in the end the only way I could get it to pass the console test was by disabling QOS entirely.


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[Elite49]

There is a post (somewhere on the inter web) - another firmware found that the fragmentation test failures (PSN etc) are caused by an issue with handling UDP fragmentation. This is something embedded within the core firmware (ie not something I believe Merlin can compensate for) - I spent a few days myself trying to hack QOS to handle PSN type traffic but in the end the only way I could get it to pass the console test was by disabling QOS entirely.


Sent from my iPhone using Tapatalk

Did everything stated went to the older firmware, dropped QOS and while I don't get the error message anymore my upload speed went from a solid 9-10 to a fluctuating 500 kb to 10. Turning on QOS seemed to fix this. Anyone have any tips on settings that should be changed for better all around performance?