If you want to filter ICMP echo-requests with tcpdump, you can use this command:

tcpdump -i em0 "icmp[0] == 8"

But it doesn’t work if you try the same syntax with ICMPv6:

tcpdump -i em0 "icmp6[0] == 128"
tcpdump: IPv6 upper-layer protocol is not supported by proto[x]

Instead you can parse directly the IPv6 payload. An IPv6 packet is 40 bytes long, and the first 8 bits of the ICMPv6 header specify its type:

tcpdump -i eth0 "icmp6 && ip6[40] == 128"

The most common ICMPv6 types are:

• unreachable: 1
• too-big: 2
• time-exceeded: 3
• echo-request: 128
• echo-reply: 129
• router-solicitation: 133
• router-advertisement: 134
• neighbor-solicitation: 135
• neighbor-advertisement: 136