Overview
This lecture covers routing tables, troubleshooting routing issues, DHCP addressing, and managing IP conflicts in network environments.
Routing Tables and Their Importance
- Routing tables determine the best next hop for forwarding traffic through routers.
- Routers use information such as static routes and default gateways to build a forwarding map.
- Troubleshooting routing requires checking routing tables on all routers along the data path.
- Routers drop traffic with no matching route and may send an ICMP host unreachable message.
- A default route, or Gateway of Last Resort (0.0.0.0), handles unmatched traffic.
- Default routes are usually configured statically.
Routing Table Example
- Routers may have directly connected routes, static routes, and routes learned via routing protocols (e.g., RIP).
- If no Gateway of Last Resort is set, unmatched traffic is dropped.
- Setting a static route to 0.0.0.0 ensures traffic has a default path if no specific route exists.
DHCP Addressing and Troubleshooting
- If a device receives an APIPA address (169.254.x.x), the DHCP address pool may be exhausted.
- APIPA addresses are non-routable and only allow local subnet communication.
- Organizations use IP Address Management (IPAM) tools to monitor DHCP address pools.
- Shorter DHCP lease times can reduce address pool exhaustion.
Verifying and Troubleshooting IP Configuration
- Always verify IP address, subnet mask, and default gateway assignments.
- Use packet captures or check other devices to confirm correct network configuration.
- Begin troubleshooting by pinging the local address, then the gateway, then external addresses.
Resolving Duplicate IP Address Issues
- Duplicate IPs may come from overlapping DHCP pools or manual misconfiguration.
- Modern systems usually prevent duplicates by detecting conflicts during connection.
- To troubleshoot, check configuration and use ping and ARP tables to locate conflicting devices.
Key Terms & Definitions
- Routing Table — A database used by routers to decide the next hop for forwarding packets.
- Default Gateway/Gateway of Last Resort — A catch-all route used if no specific route matches a destination.
- Static Route — A manually configured route in a router's table.
- APIPA (Automatic Private IP Addressing) — An IPv4 address (169.254.x.x) assigned when DHCP fails.
- IPAM (IP Address Management) — A tool for monitoring and managing IP address pools.
Action Items / Next Steps
- Review routing tables on all routers for required destination networks.
- Check DHCP server address availability and adjust lease times if needed.
- Verify network device IP settings and resolve any conflicts detected.