Speed HALFED again

[#1]

Not yet...I am checking with Asus in Taiwan on that.
There's a few IPv6 things I've asked them to look at (MTU/Packet Too Big Messages/Ping Spikes).

[#2]

Quote from: chrcoluk

andy you figured a way to get our asus routers to set a seperate ipv6 mtu to ipv4 mtu?

I haven't been through the thread so I might be taking that question out of context but it wouldn't make sense to have separate MTU values for IPv4 and IPv6 because they are carried over the same Layer 2 link and hence there can only be a single MTU value by definition.

[#3]

normally I would expect both to use the same, but for whatever reason plusnet's network now has different mtu sizes for ipv4 and ipv6.

[#4]

I don't think they do - I've tried that MTU testing site the Plusnet gateways/core routers (other servers in a v6 traceroute) and they all show a max MTU value of 1500 for v6 traffic.
I am wondering if there is a change somewhere else that might have caused this (our traffic passes through a lot of links before it even gets into PN's network).

Quote

One answer I want is why when I set the ipv6 mtu on windows its not overiding the higher mtu on the router.

Interesting question. What if you try this http://ccie-in-3-months.blogspot.co.uk/2011/06/debugging-ipv6-mtu-issues-in-windows.html ?
Another thing:
Is anyone here on ADSL and have they tried playing around with a 1500 MTU for v6?

[#5]

The MTU on windows should not override the router - that is the point of path discovery. The MTU to be used is the LOWEST handled by all the devices between (and including) source and destination.

[#6]

In theory, what should happen is that if your router MTU is 1492 and your Windows PC is 1500 (for IPv6), then the router should drop the 1500 packet and send back a "Packet too big" message telling what size it will accept.
This should be easy to test with Wireshark.

[#7]

On IPv4 at least that depends on the DF (don't fragment) flag being set. If it isn't set the packet will be split.

[#8]

I think if you try something like (assuming a router MTU of 1492):
ping -l 1445 2a02:68:1::4
The the first ping response should be:
Packet needs to be fragmented but DF set.
The rest of the pings should be normal (as they will be sent with MTU of 1492).

[#9]

On Windows 7:

C:\Users\John>ping -6 -l 10000 2a02:68:1::4
Pinging 2a02:68:1::4 with 10000 bytes of data:
Request timed out.
Reply from 2a02:68:1::4: time=146ms
Reply from 2a02:68:1::4: time=148ms
Reply from 2a02:68:1::4: time=149ms
Ping statistics for 2a02:68:1::4:
    Packets: Sent = 4, Received = 3, Lost = 1 (25% loss),
Approximate round trip times in milli-seconds:
    Minimum = 146ms, Maximum = 149ms, Average = 147ms
C:\Users\John>ping -6 -f -l 10000 2a02:68:1::4
The option -f is only supported for IPv4.

[#10]

Quote from: AndyH

I don't think they do - I've tried that MTU testing site the Plusnet gateways/core routers (other servers in a v6 traceroute) and they all show a max MTU value of 1500 for v6 traffic. I am wondering if there is a change somewhere else that might have caused this (our traffic passes through a lot of links before it even gets into PN's network). Quote One answer I want is why when I set the ipv6 mtu on windows its not overiding the higher mtu on the router. Interesting question. What if you try this http://ccie-in-3-months.blogspot.co.uk/2011/06/debugging-ipv6-mtu-issues-in-windows.html ? Another thing: Is anyone here on ADSL and have they tried playing around with a 1500 MTU for v6?

I expect this is related to traffic management configuration, so eg. pinging border routers doesnt really show anything. it only takes one intermediate device to not handle the larger mtu size to be incompatible or to forcefully resize the packets to break it.  This may be only occuring on tcp traffic, which might explain why mtu discovery isnt working as well.

[#11]

well I put 1500 back on the router and youtube is going at linespeed with 4 or 6 reporting ipv6 been used, however the tbb speedtester is still forcing the ipv4 tester on me for some reason so cant do a tbb ipv6 speedtest.  I can telnet to the webserver on the tbb ipv6 address.
speedtested ok here.
http://ipv6-test.com/speedtest/
by ok I mean it matched the ipv4 result, both on that site didnt hit line speed.
I made a post on the tbb forums about the tbb speedtest issue (which also occurs when I am on mtu 1492).