Static Routes and Packet Forwarding

• Packet forwarding with static routes. (recall Zinin’s 3 routing principles)

•  Router 1 Packet arrives on R1’s Fastethernet 0/0 interface R1 does not have a route to the destination network, 192.168.2.0/24 R1 uses the default static route.

•  Packet forwarding with static routes. (recall Zinin’s 3 routing principles)

• Router 2

•  The packet arrives on the Serial 0/0/0 interface on R2
• .R2 has a static route to 192.168.2.0/24 out Serial0/0/1.

•  Packet forwarding with static routes. (recall Zinin’s 3 routing principles)

• Router 3
• The packet arrives on the Serial0/0/1 interface on R3.
• R3 has a connected route to 192.168.2.0/24 out Fastethernet 0/1

• Troubleshooting a Missing Route

• Tools that can be used to isolate routing problems include:
• Ping– tests end to end connectivity
• Traceroute– used to discover all of the hops (routers) along the path between 2 points
• Show IP route– used to display routing table & ascertain forwarding process
• Show ip interface brief- used to show status of router interfaces
• Show cdp neighbors detail– used to gather configuration information about directly connected neighbors
• Solving a Missing Route
• Finding a missing or mis-configured route requires methodically using the correct tools
  -Start with PING. If ping fails then use traceroute to determine where packets are failing to arrive
•  Issue: show ip route to examine routing table.
  -If there is a problem with a mis-configured static route remove the static route then reconfigure the new static route

• Solving a Missing Route

  

 Summary

• Routers
• Operate at layer 3
• Functions include best path selection & forwarding packets

•  Connecting Networks
• WANs Serial cables are connected to router serial ports. In the lab environment clock rates must be configured for DCE
• LANs Straight through cables or cross over cables are used to connect to fastethernet port. (The type of cable used depends on what devices are being connected)

• Cisco Discovery Protocol
• A layer 2 proprietary protocol Used to discover information about directly connected Cisco devices

• Static Routes
• This is a manually configured path that specifies how the router will get to a certain point using a certain path.

• Summary static routes
• This is several static routes that have been condensed into a single static route.

• Default route
• It is the route packets use if there is no other possible match for their destination in the routing table.

• Forwarding of packets when static route is used
• Zinin’s 3 routing principles describe how packets are forwarded

• Troubleshooting static routes may require some of the following commands:
• Ping 
• Traceroute
• Show cdp neighbors detail 
• Show IP route 
• Show ip interface brief