Weblog entry #189 for Steve

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#189
IPv6 again. again.
Posted by Steve on Wed 31 Oct 2007 at 13:13
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Once more we have working IPv6 upon this site.

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#1
Re: IPv6 again. again.
Posted by philcore (70.106.xx.xx) on Thu 1 Nov 2007 at 17:22
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Hey Steve,

I seem to be having some connectivity issues via ipv6 to the site. It seems to be a pMTU issue. I'm using freenet6 via the tspc package. It sets mtu to 1280 for the tunnel.

If I try to ping6 your site with anything larger than around 1235, I don't get anything back. tcpdumping on the www connection, it looks like it dies right when you're trying to push the data packet right after the handshake, so it does /seem/ to be an mtu issue.

I'm not having any problems connecting to other ipv6 sites like kame.net or ipv6.org.



phil

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#2
Re: IPv6 again. again.
Posted by Steve (80.68.xx.xx) on Thu 1 Nov 2007 at 17:29
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On my side the MTU is set to the standard/default size of 1500...

I'm not familiar enough with IPv6 to know whether this problem is caused by your tunnel, or something with the setup here. But I'd certainly accept suggestions.

To the best of my testing things work correctly from ipv6 locations, for example this online ping test.

Steve

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#3
Re: IPv6 again. again.
Posted by philcore (72.218.xx.xx) on Fri 2 Nov 2007 at 02:44
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well, I'm getting closer. let the record show that if i manually set my network mtu to be 1200, I have no problems. I was trying to do it initially on the tunnel interface, but couldn't since it was pure ipv6. (minimum packet size in v6 is 1280) I changed it to 1200 on the actual iface, and that seems good. We'll look into who's fault it is next. I suspect the magic of ipv6 is about the same as ipv4, and a lot of the same problems exist. Boy, I really would like the mtu problem to die with v4... Now we can get back to the real problems that exist like routing table size and churn...

phil

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#4
Re: IPv6 again. again.
Posted by rodaballo (213.73.xx.xx) on Mon 5 Nov 2007 at 11:20
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IPv6 doesn't work for me at all, I can ping6 your server but it never replies to my HTTP connections.

I have no problems with any other IPv6 site, but I need to disable IPv6 dns in FF to be able to visit debian-administration.org

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#5
Re: IPv6 again. again.
Posted by rodaballo (213.73.xx.xx) on Mon 5 Nov 2007 at 11:27
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Sorry, I forgot the "proof"...

rodaballo@dummie:~/Desktop$ telnet www.debian-administr ation.org 80
Trying 2001:41c8:108::1...
Connected to www.debian-administration.org.
Escape character is '^]'.
GET / HTTP/1.0
Host: www.debian-administration.org



...and it waits forever.


ping IPv4:

--- www.debian-administration.org ping statistics& nbsp;---
10 packets transmitted, 10 received, 0%& nbsp;packet loss, time 9000ms
rtt min/avg/max/mdev = 32.546/33.930/36.589/1.083& nbsp;ms


ping IPv6:

--- www.debian-administration.org ping statistics& nbsp;---
10 packets transmitted, 10 received, 0%& nbsp;packet loss, time 9037ms
rtt min/avg/max/mdev = 76.213/81.053/86.667/2.979& nbsp;ms

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#6
Re: IPv6 again. again.
Posted by Steve (80.68.xx.xx) on Mon 5 Nov 2007 at 11:31
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That's not good. I see it working just fine from my test sites... I have to say I'm not 100% with IPv6 so I'm not sure where the fault could lie, especially if you can ping6 the host.

Steve

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#7
Re: IPv6 again. again.
Posted by philcore (70.106.xx.xx) on Mon 5 Nov 2007 at 15:52
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I think it's the mtu issue. Ping[6] by default only sending 56 byte icmp[6] packets. See the first output below returns ping6 just fine. When I up the packet size, it times out. This is consistent with connecting to a web server which is trying to send back large amounts of data, like a web page. And I was wrong before when I said I had solved my problem. I thought it was fixed, but it was just resorting to ipv4.


with small packets...


 [root@firefoot mail] # ping6  www.debian-administration.org
PING www.debian-administration.org(www.debian-administration .org) 56 data bytes
64 bytes from www.debian-administration.org:  icmp_seq=1 ttl=42 time=143 ms
64 bytes from www.debian-administration.org:  icmp_seq=2 ttl=42 time=142 ms
64 bytes from www.debian-administration.org:  icmp_seq=3 ttl=42 time=138 ms
64 bytes from www.debian-administration.org:  icmp_seq=4 ttl=42 time=137 ms

--- www.debian-administration.org ping statistics& nbsp;---
4 packets transmitted, 4 received, 0%&nb sp;packet loss, time 3001ms
rtt min/avg/max/mdev = 137.610/140.550/143.541/2.6 73 ms



and then with 1400 byte icmp packets... it dies.


 [root@firefoot mail] # ping6  -s 1400 www.debian-administration.org
PING www.debian-administration.org(www.debian-administration .org) 1400 data bytes

--- www.debian-administration.org ping statistics& nbsp;---
10 packets transmitted, 0 received, 100%  packet loss, time 8999ms


Now if I use wget (with -6 to force ipv6) to connect and try to grab something over 1200 bytes, like the logo image, I time out. If I try to wget a very small image, like dt_open.gif, it works.


 [root@firefoot mail] # wget - 6 http://www.debian-administration.org/images/logo.png
--10:44:17--  http://www.debian-administration.org/images/logo.png
            ;=> `logo.png.2'
Resolving www.debian-administration.org... 2001:41c8:10 8::1
Connecting to www.debian-administration.org|2001:41c8:1 08::1|:80... connected.
HTTP request sent, awaiting response...


No response for logo...


 [root@firefoot mail] # wget - 6 http://www.debian-administration.org/images/dt_open.gif
--10:44:26--  http://www.debian-administration.org/images/dt_open.gif
            ;=> `dt_open.gif.3'
Resolving www.debian-administration.org... 2001:41c8:10 8::1
Connecting to www.debian-administration.org|2001:41c8:1 08::1|:80... connected.
HTTP request sent, awaiting response...  200 OK
Length: 100  [image/gif] 

100% [====================================>]&nb sp; 100          ;  --.--K/s

10:44:27 (11.48 MB/s) - `dt_open.gif.3'  saved  [100/100] 


No problem with smaller image.

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