Default iptraf build that comes with RedHat or CentOS does not support bondX interfaces, or vlan (ethX.Y) interfaces, however there's a version on that does support it. More details: Also, for you the lazy ones out there, quick install procedure (done on CentOS5 x86_64) :

#remove current iptraf version
root@host ~# yum remove iptraf
root@host ~# wget "" -O iptraf-3.0.0-6.el5.src.rpm
root@host ~# rpmbuild --rebuild iptraf-3.0.0-6.el5.src.rpm
root@host ~# rpm -Uvh /usr/src/redhat/RPMS/x86_64/iptraf-3.0.0-6.x86_64.rpm

Ready to go. If there's no rpmbuild command, install rpm-build, and also you'll have to add some packages like ncurses-devel