Table of Contents

Chapter 1 IP Routing Protocol Overview.. 1-1

1.1 Introduction to IP Route and Routing Table. 1-1

1.1.1 IP Route. 1-1

1.1.2 Routing Table. 1-1

1.1.3 Routing Protocols and Routing Priority. 1-3

1.1.4 Route Backup. 1-4

1.2 Displaying and Maintaining a Routing Table. 1-4

Chapter 2 Static Route Configuration. 2-1

2.1 Introduction to Static Route. 2-1

2.1.1 Static Route. 2-1

2.1.2 Default Route. 2-2

2.2 Static Route Configuration. 2-2

2.2.1 Configuration Prerequisites. 2-2

2.2.2 Configuring a Static Route. 2-2

2.3 Displaying and Maintaining Static Routes. 2-3

2.4 Static Route Configuration Example. 2-3

2.5 Troubleshooting a Static Route. 2-5

 

Chapter 1  IP Routing Protocol Overview

Go to these sections for information you are interested in:

l           Introduction to IP Route and Routing Table

l           Displaying and Maintaining a Routing Table

 

 

1.1  Introduction to IP Route and Routing Table

1.1.1  IP Route

Routers are used for route selection on the Internet. As a router receives a packet, it selects an appropriate route (through a network) according to the destination address of the packet and forwards the packet to the next router. The last router on the route is responsible for delivering the packet to the destination host.

1.1.2  Routing Table

I. Function

The key for a router to forward packets is the routing table. Each router maintains a routing table. Each entry in this table contains an IP address that represents a host/subnet and specifies which physical port on the router should be used to forward the packets destined for the host/subnet. And the router forwards those packets through this port to the next router or directly to the destination host if the host is on a network directly connected to the router.

II. Routing entry

Each routing entry in a routing table contains:

l           Destination: It identifies the address of the destination host or network of an IP packet.

l           Mask: Along with the destination address, it identifies the address of the network segment where the destination host or router resides. By performing a logical AND operation between destination address and network mask, you can get the address of the network segment where the destination host or router resides. For example, if the destination address is 129.102.8.10 and the mask is 255.255.0.0, the address of the network segment where the destination host or router resides is 129.102.0.0. A mask consists of some consecutive 1s, represented either in dotted decimal notation or by the number of the consecutive 1s in the mask.

l           Interface: It indicates through which interface IP packets should be forwarded to the destination.

l           Nexthop: It indicates the next router that IP packets will pass through to reach the destination.

l           Preference: There may be multiple routes with different next hops to the same destination. These routes may be discovered by different routing protocols, or be manually configured static routes. The one with the highest preference (the smallest numerical value) will be selected as the current optimal route.

According to different destinations, routes fall into the following categories:

l           Subnet route: The destination is a subnet.

l           Host route: The destination is a host.

In addition, according to whether the network where the destination resides is directly connected to the router, routes fall into the following categories:

l           Direct route: The router is directly connected to the network where the destination resides.

l           Indirect route: The router is not directly connected to the network where the destination resides.

In order to avoid an oversized routing table, you can set a default route. All the packets for which the router fails to find a matching entry in the routing table will be forwarded through this default route.

Figure 1-1 shows a relatively complicated internet environment, the number in each network cloud indicate the network address. Router G is connected to three networks, and so it has three IP addresses and three physical ports. Its routing table is shown in Figure 1-1.

Destination Network	Nexthop	Interface
11.0.0.0	14.0.0.1	3
12.0.0.0	14.0.0.1	3
13.0.0.0	16.0.0.1	2
14.0.0.0	14.0.0.3	3
15.0.0.0	17.0.0.2	1
16.0.0.0	16.0.0.2	2
17.0.0.0	17.0.0.1	1

Figure 1-1 Routing table

1.1.3  Routing Protocols and Routing Priority

Different routing protocols may find different routes (including static routes) to the same destination. However, not all of those routes are optimal. In fact, at a particular moment, only one protocol can uniquely determine the current optimal routing to the destination. For the purpose of route selection, each routing protocol (including static routes) is assigned a priority. The route found by the routing protocol with the highest priority is preferred.

The following table lists some routing protocols and the default priorities for routes found by them:

Table 1-1 Routing protocols and priorities of their default route

Routing approach	Priority
DIRECT	0
STATIC	60

 

 

1.1.4  Route Backup

You can configure multiple routes to the same destination, expecting the one with the highest priority to be the primary route and all the rest backup routes.

Route backup can help improve network reliability. Automatic switching can happen between the primary route and a backup route.

Under normal circumstances, packets are forwarded through the primary route. When the primary route goes down, the route with the highest priority among the backup routes is selected to forward packets. When the primary route recovers, the route selection process is performed again and the primary route is selected again to forward packets.

1.2  Displaying and Maintaining a Routing Table

To do…	Use the command…	Remarks
Display brief information about a routing table	display ip routing-table [ | { begin | exclude | include } regular-expression ]	Available in any view
Display detailed information about a routing table	display ip routing-table verbose
Display information about routes permitted by a basic ACL	display ip routing-table acl acl-number [ verbose ]
Display routes to a specified destination	display ip routing-table ip-address [ mask | mask-length ] [ longer-match ] [ verbose ]
Display routes to specified destinations	display ip routing-table ip-address1 { mask1 | mask-length1 } ip-address2 { mask2 | mask-length2 } [ verbose ]
Display routes discovered by a routing protocol	display ip routing-table protocol protocol [ inactive | verbose ]
Display the tree-structured routing table information	display ip routing-table radix
Display statistics about a routing table	display ip routing-table statistics
Clear statistics about a routing table	reset ip routing-table statistics protocol { all | protocol }	Available in user view

 

Chapter 2  Static Route Configuration

When configuring a static route, go to these sections for information you are interested in:

l           Introduction to Static Route

l           Static Route Configuration

l           Displaying and Maintaining Static Routes

l           Static Route Configuration Example

l           Troubleshooting a Static Route

 

 

2.1  Introduction to Static Route

2.1.1  Static Route

Static routes are special routes. They are manually configured by the administrator. In a relatively simple network, you only need to configure static routes to make routers work normally. Proper configuration and usage of static routes can improve network performance and ensure sufficient bandwidth for important applications.

When the network topology changes, static routes may become unreachable because they cannot adapt themselves to the change automatically, thus resulting in network interruption. In this case, the network administrator needs to modify the configuration of static routes manually.

Static routes are divided into three types:

l           Reachable route: normal route. If a static route to a destination is of this type, the IP packets destined for this destination will be forwarded to the next hop. It is the most common type of static routes.

l           Unreachable route: route with the reject attribute. If a static route to a destination has the reject attribute, all the IP packets destined for this destination will be discarded, and the source hosts will be informed of the unreachability of the destination.

l           Blackhole route: route with blackhole attribute. If a static route destined for a destination has the blackhole attribute, the outgoing interface of this route is the Null 0 interface regardless of the next hop address, and all the IP packets addressed to this destination will be dropped without notifying the source hosts.

The attributes reject and blackhole are usually used to limit the range of the destinations this router can reach, and help troubleshoot the network.

2.1.2  Default Route

To avoid too large a routing table, you can configure a default route.

When the destination address of a packet fails to match any entry in the routing table,

l           If there is default route in the routing table, the default route will be selected to forward the packet.

l           If there is no default route, the packet will be discarded and an ICMP Destination Unreachable or Network Unreachable packet will be returned to the source.

2.2  Static Route Configuration

2.2.1  Configuration Prerequisites

Before configuring a static route, perform the following tasks:

l           Configuring the physical parameters of related interfaces

l           Configuring IP addresses for related interfaces

2.2.2  Configuring a Static Route

Follow these steps to configure a static route:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Configure a static route	ip route-static ip-address { mask | mask-length } { interface-type interface-number | next-hop } [ preference preference-value ] [ reject | blackhole ] [ description text ]	Required By default, the system can obtain the route to the subnet directly connected to the router.

 

 

2.3  Displaying and Maintaining Static Routes

To do...	Use the command...	Remarks
Display the current configuration information	display current-configuration	Available in any view
Display the brief information of a routing table	display ip routing-table
Display the detailed information of a routing table	display ip routing-table verbose
Display the information of static routes	display ip routing-table protocol static [ inactive | verbose ]
Delete all static routes	delete static-routes all	Available in system view

 

2.4  Static Route Configuration Example

I. Network requirements

A small company requires that any two nodes in its office network communicate with each other, and that the network structure be simple and stable. The company hopes that the existing devices that do not support any dynamic routing protocol can be fully utilized.

In this case, static routes can implement communication between any two nodes.

II. Network diagram

According to the network requirements, the network topology is designed as shown in Figure 2-1.

Figure 2-1 Network diagram for static route configuration

III. Configuration procedure

 

 

1)         Perform the following configurations on the switch.

# Approach 1: Configure static routes on Switch A.

<SwitchA> system-view

[SwitchA] ip route-static 1.1.3.0 255.255.255.0 1.1.2.2

[SwitchA] ip route-static 1.1.4.0 255.255.255.0 1.1.2.2

[SwitchA] ip route-static 1.1.5.0 255.255.255.0 1.1.2.2

# Approach 2: Configure a static route on Switch A.

<SwitchA> system-view

[SwitchA] ip route-static 0.0.0.0 0.0.0.0 1.1.2.2

# Approach 1: Configure static routes on Switch B.

<SwitchB> system-view

[SwitchB] ip route-static 1.1.2.0 255.255.255.0 1.1.3.1

[SwitchB] ip route-static 1.1.5.0 255.255.255.0 1.1.3.1

[SwitchB] ip route-static 1.1.1.0 255.255.255.0 1.1.3.1

# Approach 2: Configure a static route on Switch B.

<SwitchB> system-view

[SwitchB] ip route-static 0.0.0.0 0.0.0.0 1.1.3.1

# Configure static routes on Switch C.

<SwitchC> system-view

[SwitchC] ip route-static 1.1.1.0 255.255.255.0 1.1.2.1

[SwitchC] ip route-static 1.1.4.0 255.255.255.0 1.1.3.2

2)         Perform the following configurations on the host.

# Set the default gateway address of Host A to 1.1.5.1. Detailed configuration procedure is omitted.

# Set the default gateway address of Host B to 1.1.4.1. Detailed configuration procedure is omitted.

# Set the default gateway address of Host C to 1.1.1.1. Detailed configuration procedure is omitted.

Now, all the hosts and switches in the figure can communicate with each other.

2.5  Troubleshooting a Static Route

Symptom: The switch is not configured with a dynamic routing protocol. Both the physical status and the link layer protocol status of an interface are UP, but IP packets cannot be forwarded on the interface.

Solution: Perform the following procedure.

1)         Use the display ip routing-table protocol static command to view whether the corresponding static route is correctly configured.

2)         Use the display ip routing-table command to view whether the static route is valid.