03-Layer 3 Configuration Guide

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08-IP Routing Basics Configuration
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08-IP Routing Basics Configuration 78.58 KB

This chapter includes these sections:

·          IP routing overview

·          Displaying and maintaining a routing table

 

 

NOTE:

·      The term "switch" or "device" in this chapter refers to the switching engine on a WX3000E wireless switch.

·      The WX3000E series comprises WX3024E and WX3010E wireless switches.

·      The port numbers in this chapter are for illustration only.

IP routing overview

Upon receiving a packet, a router determines the optimal route based on the destination address and forwards the packet to the next router in the path. When the packet reaches the last router, it then forwards the packet to the destination host.

Routing provides the path information that guides the forwarding of packets.

Routes can be divided into the following categories by destination:

·          Network route—The destination is a network. The subnet mask is less than 32 bits.

·          Host route—The destination is a host. The subnet mask is 32 bits.

Based on whether the destination is directly connected to the router, routes can be divided into the following types:

·          Direct routes—The destination is directly connected to the router.

·          Indirect routes—The destination is not directly connected to the router.

Routing table

Introduction to routing table

A router selects optimal routes from the routing table, and sends them to the forwarding information base (FIB) table to guide packet forwarding. Each router maintains a routing table and a FIB table.

Routes in a routing table can be divided into the following categories by origin:

·          Direct routes—Routes discovered by data link protocols, also known as “interface routes”

·          Static routes—Routes manually configured. Static routes are easy to configure and require less system resources. They work well in small and stable networks. Static routes cannot adjust to network changes. You must manually configure the routes again whenever the network topology changes.

·          Dynamic routes—Routes that are discovered dynamically by routing protocols

Each entry in the FIB table specifies a physical interface that packets destined for a certain address should go out to reach the next hop—the next router—or the directly connected destination.

 

 

NOTE:

For more information about the FIB table, see the Layer 3—IP Services Configuration Guide.

 

Routing table information

Display the brief information of a routing table by using the display ip routing-table command.

For example:

<Sysname> display ip routing-table

Routing Tables: Public

         Destinations : 7       Routes : 7

 

Destination/Mask    Proto  Pre  Cost         NextHop         Interface

 

1.1.1.0/24          Direct 0    0            1.1.1.1         GE1/0/1

2.2.2.0/24          Static 60   0            12.2.2.2        GE1/0/2

…(Part of the output information is omitted)

A route entry includes the following key items:

·          Destination—Destination IP address or destination network

·          Mask—The network mask specifies, in company with the destination address, the address of the destination network. A logical AND operation between the destination address and the network mask yields the address of the destination network. For example, if the destination address is 129.102.8.10 and the mask 255.255.0.0, the address of the destination network is 129.102.0.0. A network mask is made up of a certain number of consecutive 1s. It can be expressed in dotted decimal format or by the number of the 1s.

·          Pre—Preference of the route. Among routes to the same destination, the one with the highest preference is optimal.

·          Cost—When multiple routes to a destination have the same preference, the one with the smallest cost becomes the optimal route.

·          NextHop—Specifies the IP address of the next hop

·          Interface—Specifies the interface through which a matching IP packet is to be forwarded

Dynamic routing protocols

Based on dynamic routing protocols, dynamic routing can detect network topology changes and recalculate the routes, so it is suitable for large networks. However, dynamic routing is difficult to configure. It not only imposes higher requirements on the system, but also consumes a certain amount of network resources.

Dynamic routing protocols can be classified based on different criteria, as shown in Table 1:

Table 1 Dynamic routing protocols

Criterion

Categories

Optional scope

·      Interior gateway protocols (IGPs)—Work within an autonomous system (AS). Examples include RIP, OSPF, and IS-IS.

·      Exterior gateway protocols (EGPs)—Work between ASs. The most popular one is BGP.

Routing algorithm

·      Distance-vector protocols—RIP and BGP. BGP is also considered a path-vector protocol.

·      Link-state protocols—OSPF and IS-IS

Destination address type

·      Unicast routing protocols—RIP, OSPF, BGP, and IS-IS

·      Multicast routing protocols—PIM-SM and PIM-DM

IP version

·      IPv4 routing protocols—RIP, OSPF, BGP, and IS-IS

·      IPv6 routing protocols—RIPng, OSPFv3, IPv6 BGP, and IPv6 IS-IS

 

 

NOTE:

The WX3000E Series Wireless Switches support only RIP.

 

Routing preference

Different routing protocols may find different routes to the same destination. However, not all of those routes are optimal. For route selection, routing protocols, direct routes, and static routes are assigned different preferences. The route with the highest preference is preferred.

The preference of a direct route is always 0 and cannot be changed. All other types of routes can have their preferences manually configured. Each static route can be configured with a different preference. The following table lists the types of routes and the default preferences. The smaller the preference value, the higher the preference.

Routing approach

Preference

Direct route

0

Static route

60

RIP

100

 

Load sharing

A routing protocol can be configured with multiple equal-cost routes to the same destination. These routes have the same preference and will all be used to accomplish load sharing if there is no route with a higher preference available.

Route backup

Route backup can help improve network reliability. With route backup, you can configure multiple routes to the same destination, expecting the one with the highest preference to be the main route and all the rest backup routes.

Under normal circumstances, packets are forwarded through the main route. When the link fails, the route with the highest preference among the backup routes is selected to forward packets. When the link recovers, the route selection process is performed again and the main route is selected again to forward packets.

Route recursion

The next hops of static routes configured with next hops may not be directly connected. The outgoing interface to reach the next hop must be available. Route recursion is used to find the outgoing interface based on the next hop information of the route.

Route redistribution

Different routing protocols running on a network learn route information from each other through route redistribution. Each routing protocol can redistribute routes from other protocols, direct routes, and static routes. For more information, see relevant protocols in this configuration guide.

Displaying and maintaining a routing table

To do…

Use the command…

Remarks

Display information about the routing table

display ip routing-table [ verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display information about routes permitted by an IPv4 basic ACL

display ip routing-table acl acl-number [ verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display information about routes to the specified destination

display ip routing-table ip-address [ mask | mask-length ] [ longer-match ] [ verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display information about routes with destination addresses in the specified range

display ip routing-table ip-address1 { mask | mask-length } ip-address2 { mask | mask-length } [ verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display routes of a routing protocol

display ip routing-table protocol protocol [ inactive | verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display statistics about the routing table

display ip routing-table statistics [ | { begin | exclude | include } regular-expression ]

Available in any view

Clear statistics for the routing table

reset ip routing-table statistics protocol { protocol | all }

Available in user view

Display IPv6 routing table information

display ipv6 routing-table [ verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display routing information permitted by an IPv6 ACL

display ipv6 routing-table acl acl6-number [ verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display routing information for a specified destination IPv6 address

display ipv6 routing-table ipv6-address prefix-length [ longer-match ] [ verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display IPv6 routing information for an IPv6 address range

display ipv6 routing-table ipv6-address1 prefix-length1 ipv6-address2 prefix-length2 [ verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display IPv6 routing information of a routing protocol

display ipv6 routing-table protocol protocol [ inactive | verbose ] [ | { begin | exclude | include } regular-expression ]

Available in any view

Display IPv6 routing statistics

display ipv6 routing-table statistics [ | { begin | exclude | include } regular-expression ]

Available in any view

Clear specified IPv6 routing statistics

reset ipv6 routing-table statistics protocol { protocol | all }

Available in user view

 

 

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