Troubleshooting Mastery - Routing, Switching & IP Services

Assign unique IP addresses to router interfaces to enable inter-network connectivity, and ensure every LAN and WAN uses a different subnet to support end-to-end routing.

Troubleshoot IPv4 addressing by ensuring devices share the same subnet and mask, verify correct gateway, and use ipconfig and ping to isolate misconfigurations in a practical lab.

Master Layer 2 troubleshooting by identifying network prerequisites, verifying VLAN and trunk configurations, and diagnosing issues across VLANs, trunk links, spanning tree, EtherChannel, and inter-VLAN routing.

Verify connectivity by checking interface status and vlan membership, ensure ports are up, devices share the same subnet, and ip addressing is correct.

Troubleshoot vlan reachability by verifying physical connectivity and port status, correcting vlan assignments, and restoring up ports to ensure inter-vlan reachability for vlan ten, twenty, and thirty.

Troubleshoot trunk links by validating encapsulation, native VLAN, and allowed VLAN across switches with show interface trunk, and apply manual trunking to ensure connectivity.

verify trunking between switches to resolve vlan ten reachability issues by correcting native vlan mismatch and allowed vlan settings, and confirm dot1q encapsulation and trunk mode.

Configure VTP in server, client, and transparent modes across three switches, create VLANs on the server, verify trunk links, domain name, password, and version settings, and observe VLAN propagation behavior.

Configure a BTP server and three BTP clients on a multilayer switch, set up trunking and VLANs 10, 20, 30, 40, 50, and verify cross-switch VLAN synchronization and host reachability.

Troubleshoot VTP by verifying case-sensitive domain names, matching versions (1/2/3) across switches, and consistent passwords (MD5), and understand how DTP, transparent mode, and revision numbers influence VLAN synchronization.

Diagnose STP issues by gathering spanning-tree and MSTP data and detecting MAC address table corruption. Identify broadcast storms causing loops; isolate ports and reboot switches to confirm root cause.

Identify routing troubleshooting prerequisites, verify LAN connectivity, and systematically isolate WAN issues by analyzing static and dynamic routing, including OSPF, BGP, and redistribution, through selective device checks.

Verify the wan link by using show ip interface brief and ping to confirm interfaces are up and reachable; differentiate administrative down from down and use no shutdown to fix.

Troubleshoot wan connectivity by diagnosing interface status, encapsulation mismatches, and authentication issues, using show interface and show ip interface brief to verify and fix links.

Troubleshoot static routing by validating network ID and subnet mask, next-hop or exit interface, and ensure the WAN link and next hop are up; verify with show ip route.

learn to troubleshoot IPv4 static routing in Packet Tracer, verify reachability, and fix issues like incorrect subnet masks and wrong next-hop configurations.

Troubleshoot IPv6 static routing by verifying destination prefix and next hop, checking link local and global addresses, and ensuring the exit interface and WAN connectivity are correct.

Troubleshoot IPv6 static routing by verifying routes and next-hop reachability, using tracert and show ipv6 route to compare administrative distance and route IDs, and reconfigure to prefer the path.

Identify and fix EIGRP interface down issues by verifying neighbor adjacencies with show IP neighbors, confirming interfaces are up, and issuing no shutdown to restore route exchange.

Identify and fix EIGRP neighbor issues by verifying interfaces, ARP settings, and matching the autonomous system number, then re-advertise routes to establish neighbor adjacency.

Troubleshoot router neighborship by verifying interfaces and ARP, ensuring correct network statements are advertised, and correcting misconfigurations to establish neighbor relations between routers.

Troubleshoot router neighborship by ensuring connected interfaces share the same /30 subnet, verify interface status and reachability, and correct erroneous IP addressing to restore neighbor adjacency.

Troubleshoot router neighborship by resolving authentication mismatches: align key number and key string on both sides, and verify interface status and reachability with show and debug commands.

Understand how mismatched k values disrupt ERP neighborship, review default k values used in metric calculations, and learn to fix configurations with metric weights to restore neighborship.

Learn how a passive interface stops hello messages while advertising its subnet, preserving neighbor relationships; verify with show run and show ip protocols, then disable the wrong WAN interface.

Troubleshoot EIGRP neighborship by checking inbound and outbound ACLs on WAN interfaces, ensuring ARP and IP hello messages are permitted, and removing or modifying ACL lines as needed.

Adjust hello and hold on timers to speed up convergence and avoid adjacency flaps, and verify by using show IP interface detail to check timer settings.

Verify ARP neighborship and ensure the interface is up to enable EIGRP route exchange; if the route is missing, confirm advertisement and apply no shutdown.

Identify missing network statements and advertise all relevant interfaces to ensure routes propagate across routers; verify correct network IDs and wildcard masks, noting no auto summary in iOS.

Understand how routers choose routes from multiple sources using administrative distance, and how tweaking static and redistributed routes affects the routing table and traffic.

Troubleshoot route filtering by examining ACL, prefix list, and route-map configurations to ensure correct direction and interface, and verify with show commands to fix routes not being advertised.

Configure edge routers as stubs to minimize unnecessary neighbor queries and prevent incorrect route advertising; verify with show IP protocols and show IP enabled detail.

Identify how split horizon prevents routing updates from returning on the interface in hub and spoke networks, including vpn and frame relay, and disable it with no ip split horizon.