Got sar? Likely yes if youre using RHEL/CentOS.
No need for priv, dorky binaries, hacky scripts, libpcap, etc. Win.
$ sar -n DEV 1 3
Linux 2.6.18-194.el5 (localhost.localdomain) 10/27/2010
02:40:56 PM IFACE rxpck/s txpck/s rxbyt/s txbyt/s rxcmp/s txcmp/s rxmcst/s
02:40:57 PM lo 0.00 0.00 0.00 0.00 0.00 0.00 0.00
02:40:57 PM eth0 10700.00 1705.05 15860765.66 124250.51 0.00 0.00 0.00
02:40:57 PM eth1 0.00 0.00 0.00 0.00 0.00 0.00 0.00
02:40:57 PM IFACE rxpck/s txpck/s rxbyt/s txbyt/s rxcmp/s txcmp/s rxmcst/s
02:40:58 PM lo 0.00 0.00 0.00 0.00 0.00 0.00 0.00
02:40:58 PM eth0 8051.00 1438.00 11849206.00 105356.00 0.00 0.00 0.00
02:40:58 PM eth1 0.00 0.00 0.00 0.00 0.00 0.00 0.00
02:40:58 PM IFACE rxpck/s txpck/s rxbyt/s txbyt/s rxcmp/s txcmp/s rxmcst/s
02:40:59 PM lo 0.00 0.00 0.00 0.00 0.00 0.00 0.00
02:40:59 PM eth0 6093.00 1135.00 8970988.00 82942.00 0.00 0.00 0.00
02:40:59 PM eth1 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Average: IFACE rxpck/s txpck/s rxbyt/s txbyt/s rxcmp/s txcmp/s rxmcst/s
Average: lo 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Average: eth0 8273.24 1425.08 12214833.44 104115.72 0.00 0.00 0.00
Average: eth1 0.00 0.00 0.00 0.00 0.00 0.00 0.00