I initially sent this to Paul & Chris because I am unable to read (sorry). Forwarded to the list.

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It's possible to compile libpcap without ipv6 via a configure flag. This is the default at least on the hardened flavor of Gentoo, but users are able to disable ipv6, too, and a lot of people do.

For the moment, this results in a runtime crash:

iftop-1.0pre2 $ ./configure && make iftop-1.0pre2 $ sudo ./iftop Password: interface: eth0 Unable to get IP address for interface: eth0 ioctl(SIOCGIFADDR): Cannot assign requested address MAC address is: e0:cb:4e:c3:cb:6b set_filter_code: ip6 not supported

Ideally, iftop could check for ipv6 support in libpcap and fall back to ipv4-only if it doesn't exist. On the other hand, that's a pain in your butt, and introduces another configuration you have to support.

It "should be" (ha ha!) easy enough to fail ./configure if libpcap is missing ipv6 support though. Unfortunately, autotools are dark magic to me, so I can't provide any insights there.