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Re: Debugging ipv6



On Mon, Feb 09, 2015 at 12:50:19PM +0000, Tony van der Hoff wrote:
> I have a VPS, with an ipv6 address. It responds correctly to ping packets:
> 
> tony@tony-lx:~$ ping6 vanderhoff.org
> PING vanderhoff.org(2a03:9800:10:54::1) 56 data bytes
> 64 bytes from 2a03:9800:10:54::1: icmp_seq=1 ttl=58 time=13.6 ms
> 64 bytes from 2a03:9800:10:54::1: icmp_seq=2 ttl=58 time=12.1 ms
> 64 bytes from 2a03:9800:10:54::1: icmp_seq=3 ttl=58 time=11.8 ms
> 
> However, when I attempt to ssh into it, it baulks:
> tony@tony-lx:~$ ssh -6 vanderhoff.org
> ssh: connect to host vanderhoff.org port 22: Connection refused
> 
> ssh -4 works fine:
> tony@tony-lx:~$ ssh -4 vanderhoff.org
> Linux shell 3.2.0-4-amd64 #1 SMP Debian 3.2.65-1+deb7u1 x86_64
> 
> /etc/sshd_config has ipv6 enabled:
> # What ports, IPs and protocols we listen for
> Port 22
> # Use these options to restrict which interfaces/protocols sshd will bind to
> ListenAddress ::
> ListenAddress 0.0.0.0
> 
> My firewall should let ssh6 packets through (I think):
> tony@shell:~$ sudo ip6tables -L -v
> [sudo] password for tony:
> Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
>  pkts bytes target     prot opt in     out     source
> destination
>     0     0 ACCEPT     udp      any    any     anywhere
> anywhere             udp dpt:openvpn
>     0     0 ACCEPT     tcp      any    any     anywhere
> anywhere             tcp spt:https
>  2421  301K ACCEPT     tcp      any    any     anywhere
> anywhere             tcp spt:http
>  3955  350K ACCEPT     tcp      any    any     anywhere
> anywhere             tcp dpt:http
>     0     0 ACCEPT     tcp      any    any     anywhere
> anywhere             tcp spt:domain
>     0     0 ACCEPT     udp      any    any     anywhere
> anywhere             udp spt:domain
>     0     0 ACCEPT     tcp      any    any     anywhere
> anywhere             tcp dpt:domain
>     0     0 ACCEPT     udp      any    any     anywhere
> anywhere             udp dpt:domain
>     0     0 ACCEPT     tcp      any    any     anywhere
> anywhere             tcp dpt:http
>     0     0 ACCEPT     all      any    any     anywhere
> tony-lx.magpieway.net/128
>     0     0 ACCEPT     all      any    any     tony-lx.magpieway.net/128
>  anywhere
>    25  4458 ACCEPT     tcp      any    any     anywhere
> anywhere             tcp dpt:smtp
>     0     0 ACCEPT     udp      any    any     anywhere
> anywhere             udp dpt:ntp
>     0     0 ACCEPT     tcp      any    any     anywhere
> anywhere             tcp dpt:ntp
> 38640   96M ACCEPT     all      any    any     localhost/128
> localhost/128
>     0     0 ACCEPT     ipv6-icmp    any    any     anywhere
> anywhere
>     0     0 ACCEPT     tcp      any    any     anywhere
> anywhere             tcp dpt:ssh
>     0     0 LOG        all      any    any     anywhere
> anywhere             limit: avg 5/min burst 5 LOG level debug prefix
> "ip6tables denied: "
>     0     0 DROP       all      any    any     anywhere
> anywhere
> 
> I get no ip6tables reject entries in my log.
> 
> I used to be able to access this server over ipv6, so something's
> broken. Can anyone please suggest where else to look, or how to diagnose
> this problem.

According to nmap, the only port you have open is port 179 (bgp). So I'd
start by checking netstat to confirm that sshd IS listening on IPv6

Next, it may help to run tshark (or wireshark or some other packet
sniffer) and make sure that those pings come in to the host you're
expecting (it's conceivable, for example, that there's some other device
at that address that's actually the one you're pinging). If it is, then
you know packets are getting to your machine and you just need to alter
the firewall rules.

> 
> Cheers, Tony.
> -- 
> Tony van der Hoff        | mailto:tony@vanderhoff.org
> Buckinghamshire, England |
> 
> 
> -- 
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