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:
- Enter global configuration mode.
- 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.
- Exit
global configuration mode.
- 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: - In privileged mode enter the
command show running-config to view the active
configuration.
- Verify that the static route has been
correctly entered. If the route is not correct, it will be
necessary to go back into global configuration mode to remove
the incorrect static route and enter the correct one.
- Enter the command show ip route.
- Verify
that the route that was configured is in the routing
table.
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:
- Routing Information Protocol (RIP)
- Interior
Gateway Routing Protocol (IGRP)
- Enhanced Interior
Gateway Routing Protocol (EIGRP)
- Open Shortest Path
First (OSPF)
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: - Internet Protocol
(IP)
- Internetwork Packet Exchange (IPX)
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.