6.1.4 Configuring default route forwarding Default routes are used to route packets with destinations that do not match any of the other routes in the routing table. Routers are typically configured with a default route for Internet-bound traffic, since it is often impractical and unnecessary to maintain routes to all networks in the Internet. A default route is actually a special static route that uses this format: ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface] The 0.0.0.0 mask, when logically ANDed to the destination IP address of the packet to be routed, will always yield the network 0.0.0.0. If the packet does not match a more specific route in the routing table, it will be routed to the 0.0.0.0 network. Use the following steps to configure default routes:
  1. Enter global configuration mode.
  2. Type the ip route command with 0.0.0.0 for the destination network address and 0.0.0.0 for the subnet mask. The gateway for the default route can be either the local router interface that connects to the outside networks or the IP address of the next-hop router. In most cases, it is preferred that the IP address of the next hop router is specified.
  3. Exit global configuration mode.
  4. Save the active configuration to NVRAM by using the copy running-config startup-config command.
In the section Configuring Static Routes, static routes were configured on Hoboken to make networks 172.16.1.0 on Sterling and 172.16.5.0 on Waycross accessible. It should now be possible to route packets to both of these networks from Hoboken. However, neither Sterling nor Waycross will know how to return packets to any non-directly connected network. A static route could be configured on Sterling and Waycross for each of the non-directly connected destination networks. This would not be a scalable solution on a larger network. Sterling connects to all non-directly connected networks via interface Serial 0. Waycross has only one connection to all non-directly connected networks. This is through interface Serial 1. A default route on both Sterling and Waycross will provide routing for all packets that are destined for non-directly connected networks. Lab Activity e-Lab Activity: Configuring Default Route Forwarding In this lab, the students will configure a default static route. Web Links ip default-network Command http://www.cisco.com/en/US/products/sw/ iosswrel/ps1835/products_command_reference_ chapter09186a00800ca75a.html#1017820
Content 6.1 Introduction to Static Routing 6.1.5 Verifying static route configuration After static routes are configured it is important to verify that they are present in the routing table and that routing is working as expected. The command show running-config is used to view the active configuration in RAM to verify that the static route was entered correctly. The show ip route command is used to make sure that the static route is present in the routing table.Use the following steps to verify static route configuration: Lab Activity e-Lab Activity: Verifying Static Route Configuration In this lab, the students will use show commands to verify the default static route configuration created in the previous lab.
Content 6.1 Introduction to Static Routing 6.1.6 Troubleshooting static route configuration In the section "Configuring Static Routes", static routes were configured on Hoboken to make networks 172.16.1.0 on Sterling and 172.16.5.0 on Waycross accessible . Using this configuration, nodes on Sterling’s 172.16.1.0 network cannot reach nodes on the 172.16.5.0 network. From privileged EXEC mode on the Sterling router, execute a ping to a node on the 172.16.5.0 network. The ping fails. Now run a traceroute from Sterling to the same address used in the previous ping statement. Note where the traceroute fails. The traceroute indicates that the ICMP packet was returned from Hoboken but not from Waycross. This implies that the trouble exists either on Hoboken or Waycross. Telnet to the Hoboken router. Try again to ping the node on the 172.16.5.0 network connected to the Waycross router. This ping should succeed because Hoboken is directly connected to Waycross. Lab Activity Lab Exercise: Configuring Static Routes In this lab, the students will configure static routes between routers to allow data transfer between routers without the use of dynamic routing protocols. Lab Activity e-Lab Activity: Static Routes In this lab, the students will configure static routes between routers to allow data transfer between routers without the use of dynamic routing protocols. Web Links Troubleshooting http://www.cisco.com/en/US/ tech/tk826/tk365/ tech_troubleshooting.html
Content 6.2 Dynamic Routing Overview 6.2.1 Introduction to routing protocols Routing protocols are different from routed protocols in both function and task.A routing protocol is the communication used between routers. A routing protocol allows one router to share information with other routers regarding the networks it knows about as well as its proximity to other routers. The information a router gets from another router, using a routing protocol, is used to build and maintain a routing table. Examples of routing protocols are: A routed protocol is used to direct user traffic. A routed protocol provides enough information in its network layer address to allow a packet to be forwarded from one host to another based on the addressing scheme. Examples of routed protocols are: Web Links Introduction to Routing http://www.cisco.com/ networkers/ nw99_pres/301.pdf
Content 6.2 Dynamic Routing Overview 6.2.2 Autonomous systems An autonomous system (AS) is a collection of networks under a common administration sharing a common routing strategy. To the outside world, an AS is viewed as a single entity. The AS may be run by one or more operators while presenting a consistent view of routing to the external world.The American Registry of Internet Numbers (ARIN), a service provider, or an administrator assigns an identifying number to each AS. This autonomous system number is a 16 bit number. Routing protocols, such as Cisco’s IGRP, require assignment of a unique, autonomous system number. Web Links Autonomous System http://searchnetworking.techtarget.com/ sDefinition/ 0,,sid7_gci213662,00.html
Content 6.2 Dynamic Routing Overview 6.2.3 Purpose of a routing protocol and autonomous systems The goal of a routing protocol is to build and maintain the routing table.