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Chat => Tech Chat => Topic started by: banger on April 02, 2020, 08:48:37 PM

Title: IPV6 6to4 MTU tunnel setting on Asus router
Post by: banger on April 02, 2020, 08:48:37 PM
Using 6to4 IPV6 on my AC1200G+. When first configured the MTU setting is zero but googling suggests 1280. Both seem to work anyone know what the MTU setting should be?
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: Weaver on April 02, 2020, 09:06:15 PM
The MTU setting should be 20 bytes less than your normal setting. So if itís 1500, then 1480; or if itís 1492 then 1472. If youíre on ADSL as opposed to FTTC or FTTP, then you might want to tune the setting for the fastest performance according to ATM cell optimisation. Ask if that is the case.

[edit: used to read 40 bytes, which was my brain failure, changed to 20 bytes]
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: banger on April 02, 2020, 10:21:18 PM
Thanks Mr Weaver but this is an IPV6 tunnel which bears no relationship to normal IPV4 packets of 1500. Googling turns up 1280 for the tunnel but zero seems to work just as well.
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: Weaver on April 02, 2020, 10:56:07 PM
I use a proto 41 tunnel myself. I canít convince you other than asking you to read up on the subject. Maybe I have misunderstood your original post and if so I am sorry.
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: banger on April 02, 2020, 11:28:58 PM
http://lists.cluenet.de/pipermail/ipv6-ops/2010-March/003043.html

The above email is what is confusing me. My default is 1492 on the router, 1452 you say?
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: banger on April 02, 2020, 11:42:10 PM
And this http://test-ipv6.com/faq_pmtud.html

See DD-WRT section.
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: Weaver on April 02, 2020, 11:49:31 PM
Do you use ADSL ? Or FTTC or FTTP?

This is a very useful tool described at https://forum.kitz.co.uk/index.php/topic,16674.msg307531.html#msg307531
but it has serious bugs.
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: banger on April 03, 2020, 12:36:42 AM
I came across that site while googling. My Router for some reason doesn't allow ICMP V6 and I don't fancy turning off the firewall these days. So with ICMP V6 being blocked that site doesn't work.

I am on FTTC, I have asked Asus what the default setting is but as yet no reply. I expect them to say the default is zero and Windows will work out the correct packet size from any too big protocol receipts.
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: Alex Atkin UK on April 03, 2020, 03:33:04 AM
AFAIK ICMP is mandatory for IPv6 to work. https://tools.ietf.org/html/rfc4890
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: Weaver on April 03, 2020, 07:00:51 AM
With IPv6 PMTUD (path MTU discovery) is required, going along with what Alex said.
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: burakkucat on April 03, 2020, 05:36:56 PM
My Router for some reason doesn't allow ICMP V6 . . .

If the manufacturer does not have a firmware update available to fix that deficiency then it is time for a new device.  :-X
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: banger on April 03, 2020, 08:16:12 PM
If the manufacturer does not have a firmware update available to fix that deficiency then it is time for a new device.  :-X

Apparently it does allow ICMP as I found a thread on this very subject on the SNB Forums and it is a site issue.
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: burakkucat on April 03, 2020, 09:33:37 PM
So all is now sorted?
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: banger on April 03, 2020, 10:14:10 PM
I think so apart from max packet size on IPV6 which I assume the method to find that is the same as IPV4 which I can google.
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: banger on April 03, 2020, 10:26:15 PM
I think the packet size is 1424.

Code: [Select]
C:\Users\x_ban>ping ipv6.google.com -6 -l 1426

Pinging ipv6.l.google.com [2a00:1450:4009:816::200e] with 1426 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for 2a00:1450:4009:816::200e:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

C:\Users\x_ban>ping ipv6.google.com -6 -l 1424

Pinging ipv6.l.google.com [2a00:1450:4009:816::200e] with 1424 bytes of data:
Reply from 2a00:1450:4009:816::200e: time=30ms
Reply from 2a00:1450:4009:816::200e: time=30ms
Reply from 2a00:1450:4009:816::200e: time=31ms
Reply from 2a00:1450:4009:816::200e: time=30ms

Ping statistics for 2a00:1450:4009:816::200e:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 30ms, Maximum = 31ms, Average = 30ms

So do I add 28 for optimal tunnel size which would be 1452, oh my that's what Weaver said lol
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: burakkucat on April 03, 2020, 11:10:34 PM
So do I add 28 for optimal tunnel size which would be 1452, oh my that's what Weaver said lol

It looks that way and, yes, so he did!  :D
Title: Re: IPV6 6to4 MTU tunnel setting on Asus router
Post by: Weaver on April 05, 2020, 06:51:41 AM
 :-[ I must be going mad. When I said 40 bytes back their I should have said 20. My apologies

An IPv4 proto 41 tunnel, used to encapsulate IPv6, adds an IPv4 header to the start of an IPv6 packet. The IPv4 header is 20 bytes, so the tunnel payload, the IPv6 PDU, will have an MTU that is reduced by 20 bytes compared with the normal IPv6 PDU MTU.

So given my stupidity, I donít have an explanation for the numbers youíre getting. You do indeed add on 28, as you said,