such as those made with Hurricane Electric for ipv6 connectivity

to reproduce:

my /etc/network/interfaces

iface he-ipv6 inet6 v4tunnel
    address 2001:470:c:238::2
    netmask 64
#LA 0.5ms
    endpoint 66.220.18.42
    local 198.46.198.198
    ttl 255
    gateway 2001:470:c:238::1
    up ip addr add 2001:470:d:238::1 dev he-ipv6

iftop -i he-ipv6

(nothing shows)

reported to debian here https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=901283

it works with tcpdump/libpcap