1.Common network problem:
ping 127.0.0.1 to verify the TCP/IP protocol irt,
ping local host address to verify the NIC irt,
ping gateway address to verify the LAN network irt,
tracert to destination address to learn which node's configuration is incorrect irt,
check the DNS setttings
2.Netflow data problem:
sh ip flow interface
sh ip flow export
sh ip cache flow
3.VLAN problem:
sh vlan
sh mac address-table
4.Trunking problem:
switchport mode:auto, desirable, trunk, nonegotiate
show int trunk
5.Routing problem:
show ip protocols
show ip route
6.OSPF problem
show ip ospf neighor
show ip ospf database
show ip ospf interfaces
Network Types: p2p, p2mp, broadcast, nonbroadcast multi-access (NBMA)
7.EIGRP problem
show ip eigrp neighor
show ip eigrp interfaces
show ip eigrp topology
show ip eigrp traffic
8.InterVLAN routing problem
show vlan (brief)
show interfaces (interface) switchport
show interfaces trunk
show mac address-table
6.ACL problem
show access-list (ACL#)
show ip access-list
7.PPP problem
mismatch encapsulation protocol: ppp & hdlc ?
mismatch authentication protocol: chap & pap ?
mismatch username & password
8.Interfaces problem
sh interfaces
sh ip interfaces brief
sh controllers
9.Etherchannel problem
sh etherchannel port-channel
sh etherchannel summary