I gathered these notes to mentally prepare my Troubleshooting methodology on the exam day:

  • Follow the path
  • divide and conquer
  • Move the problem
  • Bottom up
  • Top down After watching Kevin Wallace Bull’s Eye videos and INE Tshoot Exam Demo video, the best method is to use a combination of Divide and Conquer-Bottom up/Top Down-Follow the path. There’s not really one single method that will lead to finding where the problem lies.

This is a collection of possible troubleshooting tips I collected over my studies. They are organized by OSI layer:

Layer 1

  • interface is down? admin down?
  • interfaces along layer2 path: down?
  • cable is in place? (not for Tshoot exam)
  • Portchannel is up?down? admin down?
  • Etherchannel member ports are all up? is one member port down?

Layer 2

  • Spanning-tree running on the vlan/the interface?
  • Spanning-tree is blocking the interface/the vlan?
  • vlan exists on switch?
  • port in correct mode (trunk/access)?
  • trunk interface exists?
  • vlan is allowed on trunk?
  • Etherchannel member ports have same config?
  • Etherchannel vlan mask is the same as member ports?
  • Etherchannel, on both ends, has same vlan mask? is trunking on both sides?
  • Frame-relay mapping exists?
  • for IPv6: frame-relay is done with link-local addresses?

Layer 3

  • client has correct ip address? correct subnet mask and gateway?
  • Duplicate IP address? duplicate IPv6 address?
  • Static routes misconfigured?
  • IPv6 enabled globally?
  • routing enabled on router/L3switch?
  • ip address on interface exists? wrong subnet?
  • OSPF/EIGRP neighborship up? is there passive-interface?
  • OSPF network type on interfaces match? beware of default OSPF network interface types
  • Frame-relay mapping contain broadcast keyword?
  • OSPF Hello&Dead timers match?
  • OSPF authentication implemented?
  • OSPF authentication type match?
  • OSPF authentication keys/key-strings match?
  • OSPF/EIGRP advertises default route?
  • OSPF network statement correct?
  • OSPF area numbers match?
  • OSPF area types match?
  • OSPF into EIGRP: metric defined?
  • Route redistribution: distribute-list prevents correct route injection? misconfigred route-map?
  • Vlan access-map blocks traffic?
  • Router ACL blocks traffic? misconfigred? placed under wrong interface?
  • HSRP group has correct vIP? has correct priority? has preemption?
  • HSRP object tracking (and interface tracking): decrement value is correct?
  • DHCP service exists?
  • DHCP pool correct?
  • DHCP excluded-addresses correct?
  • DHCP ip helper-address exists? on the right vlan?
  • NAT access-list matches correct traffic to be translated?
  • NAT inside/outside interface placement?
  • NAT pool of global inside addresses correct?
  • Old NAT translation entries still exist?
  • GRE tunnel up on both sides?
  • GRE tunnel mode matches on both sides?
  • GRE tunnel interfaces reach each other? –> IPv4 network (GRE transport protocol) is correct?

Layer 3/4

  • BGP neighbor statement correct?
  • BGP source IP of update packets reachable?
  • BGP network statement: matches ip route in RIB?
  • BGP authentication: same type? same digest?