Section 11 – Static Routing

Section 11 Tasks

  • Read today’s lesson notes (below)
  • Review yesterday’s lesson notes
  • Complete today’s lab
  • Read the ICND1 cram guide
  • Spend 15 minutes on the subnetting.org website

Your choices as a network administrator are to use dynamic routing protocols on your network or stick to static routing, which is where you manually add each route for your network onto each router.

I’m often asked which routing protocol is the “best.” There is no method which will suit every network, as even a particular company’s network requirements will change over time. Static routing will take time and effort to configure, but you will save on network bandwidth and CPU cycles. If a new route is added, then you will have to add this manually to every router. In addition, if a route goes down, static routing has no method to deal with this, so it will continue to send traffic to the down network (reliable static routing is outside the CCNA syllabus).

Today you will learn about the following:

  • Configuring static routes
  • Troubleshooting static routes

This module maps to the following CCNA syllabus requirements:

  • Configure and verify the routing configuration for a static or default route given specific
    routing requirements
  • Differentiate methods of routing and routing protocols
    • Static vs. dynamic
    • Next hop

If you look back at the administrative distances table in Day 10, you will see that manually configured networks are preferred over routing protocols. The reason for this is, as a network administrator, you will be expected to know your network better than any protocol can and to understand what you want to achieve. By now, it should be clear that you can use static routing with dynamic routing if your needs require it.

Configuring Static Routes

The commands to configure a static route (see Figure 11.1 below) include the following:

  • network address/prefix mask
  • address or exit interface
  • distance (optional)

Here is an example of these commands in use:

RouterA(config)#ip route network prefix mask {address | interface} [distance]

Figure 11.1 – Sample Network for Static Routes

To add a static route for the network above, you would write the following line of configuration on the router on the left:

Router(config)#ip route 192.168.1.0 255.255.255.0 172.16.1.2

With static routes, you can specify a next-hop IP address the router needs to go to on the way to the destination address, or you can specify an exit interface. Often, you won’t know your next hop because it is your ISP, or your IP address will change over time (see Figure 11.2 below). If this is the case, use an exit interface.

Figure 11.2 – You Might Not Always Know Your Next-Hop Address

Router(config)#ip route 192.168.1.0 255.255.255.0 s0/0

The command line above tells the router to send traffic destined for the 192.168.1.0 network out of the Serial interface. The next command tells the router to send all traffic for all networks out of the Serial interface:

Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0

The route above is actually a default route. Default routes are used to direct packets addressed to networks not explicitly listed in the routing table.

Configuring Static IPv6 Routes

The configuration of static IPv6 routes follows similar logic to that of static IPv4 routes. In Cisco IOS software, the ipv6 route [ipv6-prefix/prefix-length] [next-hop-address | interface] [distance <1-254> | multicast | tag | unicast] global configuration command is used to configure static IPv6 routes. While the other keywords are familiar, because they are also applicable to IPv4 static routes, the [multicast] keyword is exclusive to IPv6 and is used to configure an IPv6 static Multicast route. If this keyword is used, the route will not be entered into the Unicast routing table and will never be used to forward Unicast traffic. To ensure that the route is never installed into the Unicast RIB, Cisco IOS software sets the administrative distance value for the route to 255.

Inversely, the [unicast] keyword is used to configure an IPv6 static Unicast route. If this keyword is used, the route will not be entered into the Multicast routing table and will be used only to forward Unicast traffic. If neither the [multicast] keyword nor the [unicast] keyword is used, by default, the route will be used for both Unicast and Multicast packets.

The following configuration example illustrates how to configure three static IPv6 routes. The first route, to subnet 3FFF:1234:ABCD:0001::/64, will forward traffic out of the FastEthernet0/0 interface. This route will be used only for Unicast traffic. The second route, to subnet 3FFF:1234:ABCD:0002::/64, will forward packets to that subnet out of Serial0/0 using the Link- Local address of the next-hop router as the IPv6 next-hop address. This route will be used only for Multicast traffic. Finally, a default route pointing out of interface Serial0/1 is alsoconfigured. This default route will forward packets to unknown IPv6 destinations via Serial0/1 using the Link-Local address of the next-hop router as the IPv6 next-hop address. These routes are illustrated below:

R1(config)#ipv6 route 3FFF:1234:ABCD:0001::/64 Fa0/0 unicast
R1(config)#ipv6 route 3FFF:1234:ABCD:0002::/64 Se0/0 FE80::2222 multicast
R1(config)#ipv6 route ::/0 Serial0/1 FE80::3333

Following this configuration, the show ipv6 route command can be used to verify the static route configuration implemented on the local router, as illustrated below:

R1#show ipv6 route static
IPv6 Routing Table - 13 entries
Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP
U - Per-user static route
I1 - ISIS L1, I2 - ISIS L2, IA - ISIS inter area, IS - ISIS summary
O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
S   ::/0 [1/0]
via FE80::3333, Serial0/1
S   3FFF:1234:ABCD:1::/64 [1/0]
via ::, FastEthernet0/0
S   3FFF:1234:ABCD:2::/64 [1/0]
via FE80::2222, Serial0/0

In addition to using the show ipv6 route command, the show ipv6 static [prefix] [detail] command can also be used to view detailed information about all or just specified static routes. The following output illustrates how to use this command:

R1#show ipv6 static 3FFF:1234:ABCD:1::/64 detail
IPv6 static routes
Code: * - installed in RIB
* 3FFF:1234:ABCD:1::/64 via interface FastEthernet0/0, distance 1

Troubleshooting Static Routes

Troubleshooting will almost always involve a configuration issue (unless your interface is down). If traffic isn’t arriving at the destination, you can test the route with the traceroute command or tracert command for a Windows PC.

NOTE – Today is a very short day so please move ahead to Day 12 because it’s a very meaty subject.

Section 11 Questions

1. Name the three parameters needed to configure a static route.
2. What is the command used to configure a static route?
3. What is the command used to configure a default static route?
4. What is the command used to configure an IPv6 static route?
5. What is the command used to view IPv6 static routes?

Section 11 Answers

1. Network address, subnet mask (prefix length), and next-hop address or exit interface.
2. The ip route command.
3. The ip route 0.0.0.0 0.0.0.0 command.
4. The ipv6 route command.
5. The show ipv6 route static command.

Section 11 Lab

Static Routes Lab

Topology

Purpose

Learn how to assign static routes to a router with a next-hop address and exit interface.

Walkthrough

1.  Assign all the IP addresses according to the above topology. Router A can be 192.168.1.1/30 and Router B can be .2.

2.  Ping across the Serial link to ensure that it is working.

3.  Assign a static route on Router A, sending all traffic for the 10.1.1.0/10 network out of the Serial interface. Use your own serial number, of course; don’t just copy mine if yours has a different number!

RouterA(config)#ip route 10.0.0.0 255.192.0.0 Serial0/1/0
RouterA(config)#exit
RouterA#ping 10.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 18/28/32 ms
RouterA#
RouterA#show ip route
Codes: C - Connected, S - Static, I - IGRP, R - RIP, M - Mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - Candidate default, U - Per-user static route, o - ODR
P - Periodic downloaded static route
Gateway of last resort is not set
10.0.0.0/10 is subnetted, 1 subnets
S       10.0.0.0 is directly connected, Serial0/1/0
172.16.0.0/24 is subnetted, 1 subnets
C       172.16.1.0 is directly connected, Loopback0
192.168.1.0/30 is subnetted, 1 subnets
C       192.168.1.0 is directly connected, Serial0/1/0
RouterA#
RouterA#show ip route 10.1.1.1
Routing entry for 10.0.0.0/10
Known via “static”, distance 1, metric 0 (connected)
Routing Descriptor Blocks:
* directly connected, via Serial0/1/0
Route metric is 0, traffic share count is 1
RouterA#

4. Configure a static route on Router B, sending all traffic for the 172.16.1.0/24 network to
next-hop address 192.168.1.1.

RouterB(config)#ip route 172.16.1.0 255.255.255.0 192.168.1.1
RouterB(config)#exit
RouterB#ping 172.16.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds:
!!!!!
RouterB#show ip route 172.16.1.1
Routing entry for 172.16.1.0/24
Known via “static”, distance 1, metric 0
Routing Descriptor Blocks:
* 192.168.1.1
Route metric is 0, traffic share count is 1
RouterB#


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