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Standard User Ripley
(committed) Wed 05-Feb-14 21:48:44
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: XRaySpeX] [link to this post]
 
In reply to a post by XRaySpeX:
In reply to a post by Chrysalis:
cannot ping with unfragmented 1460 bytes then its not working as it should.

ping -f -l 1460 bbc.co.uk

if that fails set mtu back to 1492.
Shouldn't the 1460 above be 1465 or more? 1492 MTU -28 = 1464 packet size.

If your MTU is actually 1492:
then ping -f -l 1465 bbc.co.uk should give 'Packet needs to be fragmented but DF set.'
but ping -f -l 1464 bbc.co.uk should be OK.

For an actual MTU of 1500 the biggest unfragmented packet is 1472.


So only out of interest how come I can ping Zen with a different packet size to BBC.co.uk?

Freeserve Dial-Up --> BTopenworld --> <n>ildram -->Talk Talk LLU --> ZeN
ASUS RT-AC66U
Standard User XRaySpeX
(eat-sleep-adslguide) Wed 05-Feb-14 23:57:26
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: Ripley] [link to this post]
 
Probably cuz it's fragmenting the packet and it's the 1st or early hop in Zen's network.

The proper test for MTU size is to use the '-f' flag in the ping and see when it stops fragmenting.

Don't confuse the MTU size with the ping's packet size; the former is +28 bytes larger than the latter to accommodate the protocol overheads.

1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC
Standard User Chrysalis
(legend) Thu 06-Feb-14 20:31:12
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: XRaySpeX] [link to this post]
 
if I get enough free time I will try to upgrade to this firmware this weekend and give a direct opinion on if it works with gui only configuration.


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Standard User rhetherington
(member) Sun 23-Feb-14 08:04:18
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: Chrysalis] [link to this post]
 
Nice to see RFC 4638 support gaining some traction.

I switched from an Asus to TPLink router running OpenWRT so can't take advantage of it, but hopefully OpenWRT will also support it soon.
Standard User CharlesBrown
(newbie) Mon 24-Feb-14 14:26:03
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: Chrysalis] [link to this post]
 
Got this working with an RT-AC66U running Merlin 3.0.0.4.374.39.

This firmware does not fully support the enabling of RFC 4638 in the web interface because it only lets you set the ppp0 MTU/MRU to 1500.
For it to work properly you also need to enable baby jumbo frames on the WAN interface eth0.
I haven't enabled jumbo frames on the LAN switch yet as I don't understand why it would be needed.

Steps:
1) Set the MTU and MRU to 1500 in the web interface WAN settings for the ppp0 interface.
2) Enable baby jumbo frames (1508) on the WAN interface eth0 and set it every time the WAN interface starts. Create a UNIX text file /jffs/scripts/wan-start and insert the following:

#!/bin/sh
ifconfig eth0 mtu 1508 up


After rebooting, run ifconfig and check that the appropriate interfaces show the correct MTU.

On a connected device, test with: ping -f -l 1472 bbc.co.uk
and http://www.letmecheck.it/mtu-test.php

Pinging bbc.co.uk [212.58.244.20] with 1472 bytes of data:
Reply from 212.58.244.20: bytes=1472 time=8ms TTL=53
Reply from 212.58.244.20: bytes=1472 time=8ms TTL=53
Reply from 212.58.244.20: bytes=1472 time=8ms TTL=53
Reply from 212.58.244.20: bytes=1472 time=8ms TTL=53

Ping statistics for 212.58.244.20:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 8ms, Maximum = 8ms, Average = 8ms

Full support in OpenWRT is probably going to take forever but you can patch it yourself with this guide:
http://monki.org.uk/blog/2013/04/14/patching-openwrt...

Plusnet Unlimited Fibre 80/20
Asus RT-AC66U

Edited by CharlesBrown (Mon 24-Feb-14 14:32:33)

Standard User Chrysalis
(legend) Sat 01-Mar-14 15:23:50
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: CharlesBrown] [link to this post]
 
this is working 100% now in 374.40 beta

quote from changelog

- FIXED: PPPoE with an MTU of 1500 requires the WAN interface
to have its MTU set at 1508 (patch by pinwing)


So I set 1500 mtu and 1500 mru in gui, thats it, no cli commands needed, no extra ppp options needed.
Since my windows is set to auto mtu, I checked on speedguide,net and 1500 bytes reported.

C:\windows\system32>ping -f -l 1472 bbc.co.uk

Pinging bbc.co.uk [212.58.246.104] with 1472 bytes of data:
Reply from 212.58.246.104: bytes=1472 time=21ms TTL=56
Reply from 212.58.246.104: bytes=1472 time=20ms TTL=56
Reply from 212.58.246.104: bytes=1472 time=20ms TTL=56
Reply from 212.58.246.104: bytes=1472 time=20ms TTL=56

Ping statistics for 212.58.246.104:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 20ms, Maximum = 21ms, Average = 20ms

Edited by Chrysalis (Sat 01-Mar-14 15:25:20)

Standard User CharlesBrown
(newbie) Sun 02-Mar-14 10:43:41
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: Chrysalis] [link to this post]
 
Thanks Chrysalis.
I'll stick with the stable version for now but can you check something for me with the beta please?
Type ifconfig at the shell and post the MTU values for all of the interfaces.
Cheers!

Plusnet Unlimited Fibre 80/20
Asus RT-AC66U
Standard User Chrysalis
(legend) Mon 03-Mar-14 20:00:31
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: CharlesBrown] [link to this post]
 
br0 1500
eth0 1508
eth1 1500
eth2 1500
lo 16436
ppp0 1500
vlan1 1500

normally I wouldnt use beta firmwares but I needed to test this as the previous build had broken ipv6.

Standard User CharlesBrown
(newbie) Mon 03-Mar-14 20:29:57
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: Chrysalis] [link to this post]
 
Great, thanks - same as mine - looks like I've set it up correctly then smile

Plusnet Unlimited Fibre 80/20
Asus RT-AC66U
Standard User Chrysalis
(legend) Wed 05-Mar-14 08:33:41
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Re: mtu 1500 FTTC RFC RFC 4638 - asus routers


[re: CharlesBrown] [link to this post]
 
I am back on the older nov firmware I was using before, I was using the beta to confirm the ipv6 (and pppoe) are fine which they are but on ac66 routers its buggy on the wireless, the extension channel doesnt work on 5ghz when a channel is manually configured.

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