[CentOS] Info about the NIC

If you do a ifconfig eth0 you get some info about the eth0 nic

eth0 Link encap:Ethernet HWaddr 00:02:B3:63:EF:43 inet addr:x.x.x.x Bcast:x.x.x.x Mask:x.x.x.x UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1166 errors:0 dropped:0 overruns:0 frame:0 TX packets:268 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:100 RX bytes:104255 (101.8 Kb) TX bytes:19936 (19.4 Kb) Interrupt:5 Base address:0x2000

I wounder about RX bytes and TX bytes, what does it mean, how does it collect its data How often does it zero the counters, every boot, hour or somethings else?. Is the information reliable

Thanks

Tronn