I have never understood what hello packets are. I know OSPF and EIGRP routers will establish adjacencies through hello packets. Can Somebody explain what they are? Thanks. Matt
hello packets have appropriate info for two neighboring routers to become neighbors and exchange routes; Routers receive hello packet and compare their fields; if specific values are match, routers agree on becoming neighbors and start exchange routes.
EIGRP will include IP address, K values, AS number, and some other info.
OSPF have Area number and mtu besides the IP address, plus other info;
W.Odom in CCNA book has nice table with values in hello packets and which ones have to match.