Lecture Notes: Understanding Router Routing Tables and DHCP Configuration

Importance of Routing Tables

• Routing Tables Role:
  • Determine the best next hop for forwarding traffic.
  • Build a map of data forwarding within a router.
• Components:
  • Default gateways.
  • Static routes.

Troubleshooting Routing Problems

• Steps for Troubleshooting:
  • Check routing tables of each router along the data path.
  • Ensure proper routes for return to the original workstation.
• Handling Missing Routes:
  • Without a route, the router drops traffic and may send an ICMP host unreachable message.

Network Configuration Example

• Example Setup:
  • Two laptops separated by three routers and switches.
  • Required routing table entries to reach specific subnets (e.g., 10.3.1.0/24).

Routing Table Management

• Large Networks:
  • Use summarized routes or default routes (Gateway of Last Resort).
• Configuring Default Routes:
  • Static route destination: 0.0.0.0/0 encompasses all networks.

DHCP Addressing Issues

• Automatic Private IP Addressing (APIPA):
  • Used when DHCP address pool is exhausted.
  • Allows local subnet communication but is non-routable.
• Address Pool Management:
  • Use IPAM to monitor available addresses.
  • Decrease lease time to prevent exhaustion.

Troubleshooting IP Address Issues

• Incorrect DHCP Configuration:
  • Verify with network administrator.
  • Perform packet capture to check subnet configuration.
• Basic Troubleshooting Steps:
  • Ping local address, default gateway, and beyond.

Handling Duplicate IP Addresses

• Causes of Duplicate IPs:
  • Manual configuration conflict.
  • Overlapping DHCP pools.
  • Accidental DHCP service activation on new devices.
• Resolution:
  • Investigate configurations.
  • Use ARP and MAC address tables to locate devices.
  • Capture packets to identify DHCP server issues.