CCNA v5.0 modul 2 Chapter: 6 - Static Routing

    1. Introduction

Routers learn about remote networks either dynamically, using routing protocols, or manually, or using static routes. In many cases, routers use a combination of both dynamic routing protocols and static routes.

Static routes do not require the same amount of processing and overhead as dynamic routing protocols.

CCNA: methods: Classless Inter-Domain Routing (CIDR) and the variable-length subnet mask (VLSM).

1   1.1 Static Routing Implementation

A router can learn about remote networks in one of two ways: 

·      Manually - Remote networks are manually entered into the route table using static routes.

·      Dynamically - Remote routes are automatically learned using a dynamic routing protocol.

Static route = Reach specific networks and manually configured

1   1.2 Why Use Static Routing?

Administrative distance (AD) of a static route is 1. Static for small network and with only one path to an outside network.

    1.3 When to Use Static Routes

Static routing has three primary uses: 

·      Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly.

·      Routing to and from stub networks. A stub network is a network accessed by a single route, and the router has only one neighbor.

·      Using a single default route to represent a path to any network that does not have a more specific match with another route in the routing table. Default routes are used to send traffic to any destination beyond the next upstream router.

2   2.     Types of Static Routes

2   2.1 Static Route Applications

Static route are used to: -       Connect stub networks. -       Connect to a specific network -       Summarize routing table entry -       Create backup route

CCNA: IPv4 and IPv6 static routes: - Standard static - route Default - static route - Summary static route - Floating static route

2   2.2 Standard Static Route

A static route can be used to connect to any network.

2   2.3 Default Static Route

Static route is a route that matches all packets. A default route identifies the gateway IP address to which the router sends all IP packets that it does not have a learned or static route. A default static route is simply a static route with 0.0.0.0/0 as the destination IPv4 address. Configuring a default static route creates a Gateway of Last Resort.

Note: route for larger subnets takes preference over default static route

Default static routes are used: 

-       Only one other router to which it is connected. This condition is known as a stub router.

-       Default exit: routerß--àISP (An edge router to a service provider network)

2   2.4 Summary Static Route

To reduce the number of routing table entries, multiple static routes can be summarized into a single static route if: -       Destination networks are contiguous and can be summarized into a single network address. -       The multiple static routes all use the same exit interface or next-hop IP address.

2   2.5 Floating Static Route

Floating static routes are static routes that are used to provide a backup path to a primary static or dynamic route, in the event of a link failure. The floating static route is only used when the primary route is not available. Example: AD:95 Static route entry AD: 90 EIGRP static route entry. If learned route fails static route is the backup.

3   3.   Configure Static and Default Routes

3   3.1 ip route Command

R1(config)#ip route network-address network-mask {ip-address | exit-interface}

3   3.2 Next-Hop Options

The next hop can be identified by an IP address, exit interface, or both. How the destination is specified creates one of the three following route types: 

-       Next-hop route - Only the next-hop IP address is specified.

-       Directly connected static route - Only the router exit interface is specified.

-       Fully specified static route - The next-hop IP address and exit interface are specified.

3   3.3 Configure a Next-Hop Static Route

Before any packet is forwarded by a router, the routing table process must determine the exit interface to use to forward the packet. This is known as route resolvability. The route resolvability process will vary depending upon the type of forwarding mechanism being used by the router. CEF (Cisco Express Forwarding) is the default behavior on most platforms running IOS 12.0 or later.

R1(config)#ip route network-address network-mask ip-address

AD=1

3   3.4 Configure a Directly Connected Static Route

This method is used to avoid the recursive lookup problem.

R1(config)#ip route network-address network-mask exit-interface

       AD=0

3   3.5 Configure a Fully Specified Static Route

In a fully specified static route, both the output interface and the next-hop IP address are specified. This is another type of static route that is used in older IOSs, prior to CEF

R1(config)# ip route 192.168.2.0 255.255.255.0 GigabitEthernet 0/1

3   3.6 Verify a Static Route

Along with ping and traceroute, useful commands to verify static routes include: 

-       show ip route

-       show ip route static

-       show ip route network

4   4.  Configure IPv4 Default Routes

4   4.1 Default Static Route (code “S”)

A default route is a static route that matches all packets

R1(config)# ip route 0.0.0.0  0.0.0.0  { ip-address | exit-intf }

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)

5   5.  Configure IPv6 Static Routes

5   5.1 The ipv6 route Command

Static routes for IPv6 are configured using the ipv6 route global configuration command.

Router(config)# ipv6 route ipv6-prefix/prefix-length { ipv6-address | exit-intf }

Most of parameters are identical to the IPv4 version of the command. IPv6 static routes can also be implemented as: 

-       Standard IPv6 static route Default

-       IPv6 static route Summary

-       IPv6 static route Floating

-       IPv6 static route

-        

R1(config)#ipv6 unicast-routing command enable the router to forward IPv6 packets

5.2 Verify IPv6 Static Routes

verify static routes include: 

show ipv6 route

show ipv6 route static

show ipv6 route network

5   5.3 Default Static IPv6 Route

R1(Config)# ipv6 route ::/0 { ipv6-address | exit-intf }

6   6.  CIDR

Will be developed soon.

7   7.  VLSM

      Will be developed soon.