H3C S3100-52P Manuale utente

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Table of Contents

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

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Chapter 1 IP Routing Protocol Overview

1-1

Chapter 1 IP Routing Protocol Overview

Go to these sections for information you are interested in:

zIntroduction to IP Route and Routing Table

zDisplaying and Maintaining a Routing Table

Note:

The term router in this chapter refers to a router in a generic sense or an Ethernet

switch running a routing protocol.

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:

zDestination: It identifies the address of the destination host or network of an IP

packet.

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Chapter 1 IP Routing Protocol Overview

1-2

zMask: 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.

zInterface: It indicates through which interface IP packets should be forwarded to

the destination.

zNexthop: It indicates the next router that IP packets will pass through to reach the

destination.

zPreference: 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:

zSubnet route: The destination is a subnet.

zHost 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:

zDirect route: The router is directly connected to the network where the destination

resides.

zIndirect 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.

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Chapter 1 IP Routing Protocol Overview

1-3

Router A

Router B

Router H

Router E

16.0.0.2

17.0.0.2

15.0.0.0

12.0.0.0 17.0.0.0

11.0.0.0 16.0.0.0

13.0.0.0

14.0.0.0

Router C

Router D

Router F

Router G

11.0.0.1

11.0.0.2

12.0.0.1

12.0.0.2 15.0.0.1 15.0.0.2

17.0.0.1

16.0.0.1

13.0.0.1 13.0.0.2

13.0.0.3

14.0.0.1 14.0.0.3

15.0.0.3

14.0.0.2

14.0.0.4

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

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Chapter 1 IP Routing Protocol Overview

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Note:

zThe smaller the priority value, the higher the priority.

zThe priority for a direct route is always 0, which you cannot change. Any other type

of routes can have their priorities manually configured.

zEach static route can be configured with a different priority.

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 ]

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

Available in

any view

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Chapter 1 IP Routing Protocol Overview

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To do… Use the command… Remarks

Clear statistics about a

routing table reset ip routing-table statistics

protocol {all |protocol }Available in

user view

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Chapter 2 Static Route Configuration

2-1

Chapter 2 Static Route Configuration

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

in:

zIntroduction to Static Route

zStatic Route Configuration

zDisplaying and Maintaining Static Routes

zStatic Route Configuration Example

zTroubleshooting a Static Route

Note:

The term router in this chapter refers to a router in a generic sense or an Ethernet

switch running a routing protocol.

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:

zReachable 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.

zUnreachable 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.

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Chapter 2 Static Route Configuration

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zBlackhole 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,

zIf there is default route in the routing table, the default route will be selected to

forward the packet.

zIf 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:

zConfiguring the physical parameters of related interfaces

zConfiguring 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.

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Chapter 2 Static Route Configuration

2-3

Note:

zUse the ip route-static command to configure a default route by setting the

destination IP address and the mask to 0.0.0.0.

zAvoid configuring the next hop address of a static route to the address of an

interface on the local switch.

zDifferent preferences can be configured to implement flexible route management

policies.

2.3 Displaying and Maintaining Static Routes

To do... Use the command... Remarks

Display the current

configuration information display current-configuration

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 ]

Available in

any view

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.

Operation Manual – Static Route

H3C S3100-52P Ethernet Switch Chapter 2 Static Route Configuration

2-4

Figure 2-1 Network diagram for static route configuration

III. Configuration procedure

Note:

When only one interface of the device is interconnected with another network segment,

you can implement network communication by configuring either a static route or

default route.

1) Perform the following configurations on the switch.

# Approach 1: Configure static routes on SwitchA.

<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

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