4.3. IPv6-ready test/debug programs

4.3.1. IPv6 ping

This program is normally included in package iputils. It is designed for simple transport tests sending ICMPv6 echo-request packets and wait for ICMPv6 echo-reply packets.

Usage

# ping6 <hostwithipv6address>
# ping6 <ipv6address>
# ping6 [-I <device>] <link-local-ipv6address>

Example

# ping6 -c 1 ::1 
PING ::1(::1) from ::1 : 56 data bytes 
64 bytes from ::1: icmp_seq=0 hops=64 time=292 usec
--- ::1 ping statistics --- 
1 packets transmitted, 1 packets received, 0% packet loss 
round-trip min/avg/max/mdev = 0.292/0.292/0.292/0.000 ms

Hint: ping6 needs raw access to socket and therefore root permissions. So if non-root users cannot use ping6 then there are two possible problems:

1. ping6 is not in users path (probably, because ping6 is generally stored in /usr/sbin -> add path (not really recommended)

2. ping6 doesn't execute properly, generally because of missing root permissions -> chmod u+s /usr/sbin/ping6

# ping6 fe80::212:34ff:fe12:3456 
connect: Invalid argument

# ping6 -I eth0 -c 1 fe80::2e0:18ff:fe90:9205 
PING fe80::212:23ff:fe12:3456(fe80::212:23ff:fe12:3456) from
╛ fe80::212:34ff:fe12:3478 eth0: 56 data bytes 
64 bytes from fe80::212:23ff:fe12:3456: icmp_seq=0 hops=64 time=445 usec
--- fe80::2e0:18ff:fe90:9205 ping statistics --- 
1 packets transmitted, 1 packets received, 0% packet loss round-trip
╛ min/avg/max/mdev = 0.445/0.445/0.445/0.000 ms

# ping6 -I eth0 ff02::1 PING ff02::1(ff02::1) from fe80:::2ab:cdff:feef:0123
╛ eth0: 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.104 ms
64 bytes from fe80::212:34ff:fe12:3450: icmp_seq=1 ttl=64 time=0.549 ms (DUP!) 

4.3.2. IPv6 traceroute6

This program is normally included in package iputils. It's a program similar to IPv4 traceroute. Below you will see an example:

# traceroute6 www.6bone.net 
traceroute to 6bone.net (3ffe:b00:c18:1::10) from 3ffe:ffff:0000:f101::2, 30
╛ hops max, 16 byte packets 
 1 localipv6gateway (3ffe:ffff:0000:f101::1) 1.354 ms 1.566 ms 0.407 ms 
 2 swi6T1-T0.ipv6.switch.ch (3ffe:2000:0:400::1) 90.431 ms 91.956 ms 92.377 ms 
 3 3ffe:2000:0:1::132 (3ffe:2000:0:1::132) 118.945 ms 107.982 ms 114.557 ms 
 4 3ffe:c00:8023:2b::2 (3ffe:c00:8023:2b::2) 968.468 ms 993.392 ms 973.441 ms 
 5 3ffe:2e00:e:c::3 (3ffe:2e00:e:c::3) 507.784 ms 505.549 ms 508.928 ms 
 6 www.6bone.net (3ffe:b00:c18:1::10) 1265.85 ms * 1304.74 ms

Note: unlike some modern versions of IPv4 traceroute, which can use ICMPv4 echo-request packets as well as UDP packets (default), current IPv6-traceroute is only able to send UDP packets. As you perhaps already know, ICMP echo-request packets are more accepted by firewalls or ACLs on routers inbetween than UDP packets.

4.3.3. IPv6 tracepath6

This program is normally included in package iputils. It's a program like traceroute6 and traces the path to a given destination discovering the MTU along this path. Below you will see an example:

# tracepath6 www.6bone.net 
 1?: [LOCALHOST] pmtu 1480 
 1: 3ffe:401::2c0:33ff:fe02:14 150.705ms 
 2: 3ffe:b00:c18::5 267.864ms 
 3: 3ffe:b00:c18::5 asymm 2 266.145ms pmtu 1280 
 3: 3ffe:3900:5::2 asymm 4 346.632ms 
 4: 3ffe:28ff:ffff:4::3 asymm 5 365.965ms 
 5: 3ffe:1cff:0:ee::2 asymm 4 534.704ms 
 6: 3ffe:3800::1:1 asymm 4 578.126ms !N 
Resume: pmtu 1280

4.3.4. IPv6 tcpdump

On Linux, tcpdump is the major tool for packet capturing. Below you find some examples. IPv6 support is normally built-in in current releases of version 3.6.

tcpdump uses expressions for filtering packets to minimize the noise:

• icmp6: filters native ICMPv6 traffic

• ip6: filters native IPv6 traffic (including ICMPv6)

• proto ipv6: filters tunneled IPv6-in-IPv4 traffic

• not port ssh: to suppress displaying SSH packets for running tcpdump in a remote SSH session

Also some command line options are very useful to catch and print more information in a packet, mostly interesting for digging into ICMPv6 packets:

• "-s 512": increase the snap length during capturing of a packet to 512 bytes

• "-vv": really verbose output

• "-n": don't resolve addresses to names, useful if reverse DNS resolving isn't working proper

# tcpdump -t -n -i eth0 -s 512 -vv ip6 or proto ipv6 
tcpdump: listening on eth0 
3ffe:ffff:100:f101:2e0:18ff:fe90:9205 > 3ffe:ffff:100:f101::1: icmp6: echo
╛ request (len 64, hlim 64) 
3ffe:ffff:100:f101::1 > 3ffe:ffff:100:f101:2e0:18ff:fe90:9205: icmp6: echo
╛ reply (len 64, hlim 64)

# tcpdump -t -n -i ppp0 -s 512 -vv ip6 or proto ipv6 
tcpdump: listening on ppp0 
1.2.3.4 > 5.6.7.8: 2002:ffff:f5f8::1 > 3ffe:ffff:100::1: icmp6: echo request
╛ (len 64, hlim 64) (DF) (ttl 64, id 0, len 124) 
5.6.7.8 > 1.2.3.4: 3ffe:ffff:100::1 > 2002:ffff:f5f8::1: icmp6: echo reply (len
╛ 64, hlim 61) (ttl 23, id 29887, len 124) 
1.2.3.4 > 5.6.7.8: 2002:ffff:f5f8::1 > 3ffe:ffff:100::1: icmp6: echo request
╛ (len 64, hlim 64) (DF) (ttl 64, id 0, len 124) 
5.6.7.8 > 1.2.3.4: 3ffe:ffff:100::1 > 2002:ffff:f5f8::1: icmp6: echo reply (len
╛ 64, hlim 61) (ttl 23, id 29919, len 124)