Troubleshooting Quick Fixes

IDK man

No IP connectivity between routers?

Check “no shutdown”, correct IP/mask, clock rate on DCE

OSPF neighbors stuck in INIT?

ACL blocking protocol 89 or MTU mismatch

OSPF not forming adjacency?

Mismatched subnet mask, area ID, hello/dead timers, authentication

EIGRP no neighbor?

Mismatched AS number, passive-interface, ACL blocking 88

RIP not working?

Version mismatch (R1 v1, R2 v2), no “network” statement

Switch ports not in right VLAN?

Access port wrong VLAN or still in default VLAN 1

Trunk not passing VLANs?

Allowed VLAN list missing, native VLAN mismatch

Cannot ping across VLANs?

Missing subinterface or SVI, no ip routing on switch

NAT not translating?

Missing ip nat inside/outside, ACL wrong, no route back

DHCP not giving addresses?

ip helper-address missing on SVI, pool wrong network

Serial link down/down?

No clock rate on DCE, encapsulation mismatch (HDLC vs PPP)