Chapter 2: Static Routing

Static routing occurs when a

router uses a manually-

configured routing entry, done

by a human being

Advantages of Static Routing

Dynamic versus Static Routing

When to Use Static Routes

a. In Smaller networks that are not

expected to grow

b. When routing to and from stub networks

• Stub network is one that can be accessed

by a single route, and has only one

neighbour

• 172.16.3.0 is a stub network

c. A single default route to any network not

found in the routing table

Stub Networks and

Stub Routers

Standard Static Route

R2 is configured with a static route to reach the stub network 172.16.3.0/24

A router learns about remote networks in two ways:

a. Using manually entered entries in the routing table - static

routes

• Static routes must be reconfigured when topology changes

b. Uisng dynamically (Automatically) entered entries in the

routing table

Reach Remote Networks

4 Uses of Static Routes

Static Routes are used to:

Connect to a specific network

Connect a stub router

Summarize routing table entries

Create a backup route in case a primary route link fails

The default route is used when a packet does

not match a specific route in the routing table

It can be dynamically learned or statically

configured

The Default Static route uses 0.0.0.0/0 as the

destination IPv4 address

It creates a Gateway of Last Resort

It is commonly used when connecting a

company’s edge router to the ISP network

It is also used when a router is connected to

only one other router.

Default Static Route – 0.0.0.0/0

A few static routes can be summarized into a single network address when,

• Destination networks are next to each other

• Multiple static routes must use the same exit interface or next hop

In figure, four networks are summarized into one summary static route

Summary Static Route

A floating static route is one used to

provide a backup path

It is used when the primary route is

not available

It is configured with a higher

administrative distance

(trustworthiness) than the primary

route

Example: EIGRP administrative

distance equals 90. A floating static

route with an AD of 91 or higher

would serve as backup route and will

be used if EIGRP route goes down.

Floating Static Route

Floating

Static Route

ConfiguringStatic and Default Routes

IPv4 Static Routes can be configured using a CLI command

’ip route’ Command

IPv4 Static Routes can be configured using a CLI command

’ip route’ Command

IPv4 Static Routes

Next-Hop Options

In a static route, next-hop

can be identified by

• Next-hop IP address

• Router exit interface

next hop is an IP address

entry in a router's routing

table

it specifies the next

closest/most optimal router

in its routing path.

To configure a Directly Connected Static Route,

The exit interface is used to specify the

next-hop

The Administrative distance of a

static route is 1

Configure IPv4 Static Routes

Cisco Express Forwarding (CEF)

• provides optimized lookup

• uses a Forwarding Information Base (FIB)

(which is a copy of the routing table and an adjacency table that includes Layer 2 addresses)

• no recursive lookup is needed for next-hop IP address lookups

Cisco Express Forwarding (CEF) is a packet-switching technique used within Cisco routers.

The main purpose of CEF is to optimize the forwarding of packets and increase the packet

switching speed.

CEF technique can be used to Configure a Directly Connected Static Route

Both the exit interface and the next-hop IP address

are specified

When exit interface is an Ethernet network, fully

specified static route is used

Note: With CEF, a next-hop address could be used

instead

To configure a Fully Specified Static Route

Command to Verify a Static Route (1/3)

‘show ip route static’ command

Command to Verify a Static Route (2/3)

‘show ip route 192.168.2.1’

Command to Verify a Static Route (3/3)

‘show running-config’

Configure IPv4 Default Routes

Default Static Route

Default static routes are commonly used when connecting:

• An edge router to a service provider network

• A stub router (a router with only one upstream neighbor router)

Default route is used when no other routes in the routing table match the destination IP

An edge router is a specialized router

residing

at the edge or boundary of a network.

Configure a Default Static Route

R1#(config)# ip route 0.0.0.0.0.0.0.0 172.16.2.2

Any packets

not matching

route entries

are forwarded

to 172.16.2.2

show ip route static

• S indicates static route

• candidate default route indicated

by *

• /0 mask in route entry indicates

none of the bits are required to

match

Last Slide

To display Default Static Route

Static Routing, Static route

Default static route 0.0.0.0/0 (IPv4)

Directly Connected Static Route

Administrative distance of a static route

Stub Network

Dynamic routing

Hop

Next hop

Gateway of Last Resort

Summary of Terms Used Summary Static Route

Floating Static Route

CEF – Cisco Express Forwarding

Exit interface

‘Ip route’ command

‘show ip route static’ command

‘show ip route <ip address>’ command

‘show running-config’ command