Ubuntu 11.10 - Can ping but something seriously wrong!

[johnsnider]

Hi,

Basically after 5 minutes or so of ping6 running, I got one ICMP return packet. Not sure what's going wrong. Any suggestions?

root@ubuntu:/home/jd# ping6 ipv6.google.com
PING ipv6.google.com(2404:6800:4006:801::1013) 56 data bytes
64 bytes from 2404:6800:4006:801::1013: icmp_seq=396 ttl=55 time=416 ms
^C
--- ipv6.google.com ping statistics ---
728 packets transmitted, 1 received, 99% packet loss, time 728365ms
rtt min/avg/max/mdev = 416.184/416.184/416.184/0.000 ms


Here's my ifconfig

root@ubuntu:/home/jd# ifconfig sit0 and sit1

sit0      Link encap:IPv6-in-IPv4 
          inet6 addr: ::192.168.2.6/96 Scope:Compat
          inet6 addr: ::127.0.0.1/96 Scope:Unknown
          UP RUNNING NOARP  MTU:1480  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

sit1      Link encap:IPv6-in-IPv4 
          inet6 addr: fe80::c0a8:206/64 Scope:Link
          inet6 addr: 2001:470:1f04:211::2/64 Scope:Global
          UP POINTOPOINT RUNNING NOARP  MTU:1480  Metric:1
          RX packets:1 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1219 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:104 (104.0 B)  TX bytes:123752 (123.7 KB)

[kasperd]

Try traceroute6 or mtr to get a bit more information about where the packet loss is happening.

[johnsnider]

I was just looking at the RX/TX values on SIT0 and they were 0. That's also interesting, considering the one ICMP echo request/reply surely would have incremented it?

The traceroute6 isn't encouraging. I can't understand why this isn't working. *scratches head*

root@ubuntu:/home/jd# traceroute6 ipv6.google.com
traceroute to ipv6.l.google.com (2404:6800:4006:802::1011) from 2001:470:1f04:211::2, 30 hops max, 16 byte packets
1  * * *
2  * * *
3  * * *

[nickbeee]

The traceroute6 isn't encouraging. I can't understand why this isn't working. *scratches head*

On unix (like) systems, traceroute uses UDP by default (unlike tracert on Windows). If you want it to use ICMP echo then you need to call it with the -I option.

[kasperd]

The traceroute6 isn't encouraging. I can't understand why this isn't working.

Judging from the traceroute, the problem is on the tunnel link. That is hardly surprising. It just sounds very unlikely that you should have been able to get one single echo through.

I think for now we should just ignore that one echo you got through and focus on narrowing down the problem. Once we have identified the problem, we may or may not understand why you got one echo through.

All symptoms so far are pointing at a problem with the tunnel. That means either one end of the tunnel is misconfigured, or there is a problem on the path between the two endpoints.

The next thing you should do is a tcpdump on the physical network interface on which you will be sending packets to the tunnel server. If for example eth0 is the interface you would use to communicate with the tunnel server, then you could try:

tcpdump -pni eth0 'proto 41'

Then in parallel try a ping or a traceroute. Question number one then is, are you sending any 6in4 packets over that interface. Question number two is, are you receiving any replies.