H3C S3100-52P Operating instructions

Brand: H3C

Model: S3100-52P

Category: Routers

Type: Operating instructions

Operation Manual – DLDP

H3C S3100-52P Ethernet Switch Table of Contents

Table of Contents

Chapter 1 DHCP Overview............................................................................................................ 1-1

1.1 Introduction to DHCP.........................................................................................................1-1

1.2 DHCP IP Address Assignment..........................................................................................1-1

1.2.1 IP Address Assignment Policy................................................................................1-1

1.2.2 Obtaining IP Addresses Dynamically...................................................................... 1-2

1.2.3 Updating IP Address Lease ....................................................................................1-2

1.3 DHCP Packet Format........................................................................................................1-3

1.4 Protocol Specification........................................................................................................1-4

Chapter 2 DHCP Snooping Configuration .................................................................................. 2-1

2.1 Introduction to DHCP Snooping.........................................................................................2-1

2.2 DHCP Snooping Configuration..........................................................................................2-2

2.3 Displaying DHCP Snooping...............................................................................................2-3

2.4 Configuration Example ......................................................................................................2-3

Chapter 3 DHCP/BOOTP Client Configuration........................................................................... 3-1

3.1 Introduction to DHCP Client...............................................................................................3-1

3.2 Introduction to BOOTP Client............................................................................................3-3

3.3 DHCP/BOOTP Client Configuration..................................................................................3-4

3.3.1 Prerequisites ...........................................................................................................3-4

3.3.2 Configuring a DHCP/BOOTP Client........................................................................3-4

3.3.3 Configuration Example............................................................................................3-5

3.4 Displaying the Information about a DHCP/BOOTP Client.................................................3-5

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H3C S3100-52P Ethernet Switch Chapter 1

DHCP Overview

1-1

Chapter 1 DHCP Overview

1.1 Introduction to DHCP

With networks getting larger in size and more complicated in structure, lack of available

IP addresses becomes the common situation the network administrators have to face,

and network configuration becomes a tough task for the network administrators. With

the emerging of wireless networks and the using of laptops, the position change of

hosts and frequent change of IP addresses also require new technology. Dynamic host

configuration protocol (DHCP) is developed in this background.

DHCP adopts a client/server model, where DHCP clients send requests to DHCP

servers for configuration parameters; and the DHCP servers return the corresponding

configuration information such as IP addresses to configure IP addresses dynamically.

A typical DHCP application includes one DHCP server and multiple clients (such as

PCs and laptops), as shown in

Figure 1-1.

LAN

DHCP Server

DHCP Client DHCP Cl

DHCP Client DH

ient

CP Client

Figure 1-1 Typical DHCP application

1.2 DHCP IP Address Assignment

1.2.1 IP Address Assignment Policy

Currently, DHCP provides the following three IP address assignment policies to meet

the requirements of different clients:

z Manual assignment. The administrator statically binds IP addresses to few clients

with special uses (such as WWW server). Then the DHCP server assigns these

fixed IP addresses to the clients.

z Automatic assignment. The DHCP server assigns IP addresses to DHCP clients.

The IP addresses will be occupied by the DHCP clients permanently.

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DHCP Overview

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z Dynamic assignment. The DHCP server assigns IP addresses to DHCP clients for

predetermined period of time. In this case, a DHCP client must apply for an IP

address again at the expiration of the period. This policy applies to most clients.

1.2.2 Obtaining IP Addresses Dynamically

A DHCP client undergoes the following four phases to dynamically obtain an IP address

from a DHCP server:

1) Discover: In this phase, the DHCP client tries to find a DHCP server by

broadcasting a DHCP-DISCOVER packet.

2) Offer: In this phase, the DHCP server offers an IP address. After the DHCP server

receives the DHCP-DISCOVER packet, it chooses an unassigned IP address

according to the priority order of IP address assignment and then sends the IP

address and other configuration information together in a DHCP-OFFER packet to

the DHCP client. The sending mode is decided by the flag filed in the

DHCP-DISCOVER packet, refer to section

1.3 "DHCP Packet Format” for detail.

3) Select: In this phase, the DHCP client selects an IP address. If more than one

DHCP server sends DHCP-OFFER packets to the DHCP client, the DHCP client

only accepts the DHCP-OFFER packet that first arrives, and then broadcasts a

DHCP-REQUEST packet containing the assigned IP address carried in the

DHCP-OFFER packet.

4) Acknowledge: In this phase, the DHCP servers acknowledge the IP address.

Upon receiving the DHCP-REQUEST packet, only the selected DHCP server

returns a DHCP-ACK packet to the DHCP client to confirm the assignment of the

IP address to the client, or returns a DHCP-NAK packet to refuse the assignment

of the IP address to the client. When the client receives the DHCP-ACK packet, it

broadcasts an ARP packet with the assigned IP address as the destination

address to detect the assigned IP address, and uses the IP address only if it does

not receive any response within a specified period.

 Note:

The IP addresses offered by other DHCP servers but not used by the DHCP client are

still available to other clients.

1.2.3 Updating IP Address Lease

After a DHCP server dynamically assigns an IP address to a DHCP client, the IP

address keeps valid only within a specified lease time and will be reclaimed by the

DHCP server when the lease expires. If the DHCP client wants to use the IP address for

a longer time, it must update the IP lease.

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DHCP Overview

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ags(2)

By default, a DHCP client updates its IP address lease automatically by unicasting a

DHCP-REQUEST packet to the DHCP server when half of the lease time elapses. The

DHCP server responds with a DHCP-ACK packet to notify the DHCP client of a new IP

lease if the server can assign the same IP address to the client. Otherwise, the DHCP

server responds with a DHCP-NAK packet to notify the DHCP client that the IP address

will be reclaimed when the lease time expires.

If the DHCP client fails to update its IP address lease when half of the lease time

elapses, it will update its IP address lease by broadcasting a DHCP-REQUEST packet

to the DHCP servers again when seven-eighths of the lease time elapses. The DHCP

server performs the same operations as those described above.

1.3 DHCP Packet Format

DHCP has eight types of packets. They have the same format, but the values of some

fields in the packets are different. The DHCP packet format is based on that of the

BOOTP packets. The following figure describes the packet format (the number in the

brackets indicates the field length, in bytes):

option(variable)

file(128)

sname(64)

chaddr(16)

giaddr(4)

siaddr(4)

yiaddr(4)

ciaddr(4)

flsecs(2)

xid(4)

hops(1)hlen(1)htype(1)op(1)

option(variable)

file(128)

sname(64)

chaddr(16)

giaddr(4)

siaddr(4)

yiaddr(4)

ciaddr(4)

flsecs(2)

xid(4)

ags(2)

hops(1)hlen(1)htype(1)op(1)

Figure 1-2 DHCP packet format

The fields are described as follows:

z op: Operation types of DHCP packets, 1 for request packets and 2 for response

packets.

z htype, hlen: Hardware address type and length of the DHCP client.

z hops: Number of DHCP relays which a DHCP packet passes. For each DHCP

relay that the DHCP request packet passes, the field value increases by 1.

z xid: Random number that the client selects when it initiates a request. The number

is used to identify an address-requesting process.

z secs: Elapsed time after the DHCP client initiates a DHCP request.

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DHCP Overview

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z flags: The first bit is the broadcast response flag bit. It is used to identify that the

DHCP response packet is sent in the unicast or broadcast mode. Other bits are

reserved.

z ciaddr: IP address of a DHCP client.

z yiaddr: IP address that the DHCP server assigns to a client.

z siaddr: IP address of the DHCP server.

z giaddr: IP address of the first DHCP relay that the DHCP client passes after it sent

the request packet.

z chaddr: Hardware address of the DHCP client.

z sname: Name of the DHCP server.

z file: Path and name of the boot configuration file that the DHCP server specifies for

the DHCP client.

z option: Optional variable-length fields, including packet type, valid lease time, IP

address of a DNS server, and IP address of the WINS server.

1.4 Protocol Specification

Protocol specifications related to DHCP include:

z RFC2131: Dynamic Host Configuration Protocol

z RFC2132: DHCP Options and BOOTP Vendor Extensions

z RFC1542: Clarifications and Extensions for the Bootstrap Protocol

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H3C S3100-52P Ethernet Switch Chapter 2

DHCP Snooping Configuration

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Chapter 2 DHCP Snooping Configuration

2.1 Introduction to DHCP Snooping

For the sake of security, the IP addresses used by online DHCP clients need to be

tracked for the administrator to verify the corresponding relationship between the IP

addresses the DHCP clients obtained from DHCP servers and the MAC addresses of

the DHCP clients.

z Layer 3 switches can track DHCP client IP addresses through DHCP relay.

z Layer 2 switches can track DHCP client IP addresses through the DHCP snooping

function, which listens DHCP broadcast packets.

When an unauthorized DHCP server exists in the network, a DHCP client may obtains

an illegal IP address. To ensure that the DHCP clients obtain IP addresses from valid

DHCP servers, you can specify a port to be a trusted port or an untrusted port by the

DHCP snooping function.

z Trusted ports can be used to connect DHCP servers or ports of other switches.

Untrusted ports can be used to connect DHCP clients or networks.

z Untrusted ports drop the DHCP-ACK and DHCP-OFFER packets received from

DHCP servers. Trusted ports forward any received DHCP packets to ensure that

DHCP clients can obtain IP addresses from valid DHCP servers.

Figure 2-1 illustrates a typical network diagram for DHCP snooping application, where

Switch A is an S3100-52P series Ethernet switch.

Internet

DHCP client

Ethernet

DHCP client

DHCP server

Switch A (DHCP snooping)

Switch B (DHCP relay)

Internet

EthernetEthernet

Internet

DHCP client

Ethernet

DHCP client

DHCP server

Switch A (DHCP snooping)

Switch B (DHCP relay)

Internet

Ethernet

Internet

DHCP client

Ethernet

DHCP client

DHCP server

Switch A (DHCP snooping)

Switch B (DHCP relay)

Internet

EthernetEthernetEthernet

Figure 2-1 Typical network diagram for DHCP snooping application

Figure 2-2 illustrates the interaction between a DHCP client and a DHCP server.

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H3C S3100-52P Ethernet Switch Chapter 2

DHCP Snooping Configuration

2-2

DHCP client

DHCP server

DHCP client

DHCP server

DHCP client

DHCP server

DHCP client

DHCP server

DHCP client

DHCP server

DHCP client

DHCP server

Figure 2-2 Interaction between a DHCP client and a DHCP server

DHCP snooping listens the following two types of packets to retrieve the IP addresses

the DHCP clients obtain from DHCP servers and the MAC addresses of the DHCP

clients:

z DHCP-ACK packet

z DHCP-REQUEST packet

2.2 DHCP Snooping Configuration

Table 2-1 Configure the DHCP snooping function

Operation Command Description

Enter system view

system-view

—

Enable the DHCP

snooping function

dhcp-snooping

Required

By default, the DHCP

snooping function is disabled.

Enter Ethernet port

view

interface interface-type

interface-number

—

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DHCP Snooping Configuration

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Operation Command Description

Set the port

connected to a

DHCP server to a

trusted port

dhcp-snooping trust

Optional

By default, all ports of a

switch are untrusted ports.

 Note:

When you need to enable DHCP snooping on the switches in a fabric state, configure

the fabric ports on all devices to be trusted ports to ensure that the users connected to

each device can obtain IP addresses.

2.3 Displaying DHCP Snooping

After the above configurations, you can verify the configurations by executing the

display command in any view.

Table 2-2 Display DHCP snooping

Operation Command Description

Display the user IP-MAC address

mapping entries recorded by the

DHCP snooping function

display

dhcp-snooping [ unit

unit-id ]

Display the (enabled/disabled)

state of the DHCP snooping

function and the trusted ports

display

dhcp-snooping trust

You can execute the

display command in

any view

2.4 Configuration Example

I. Network requirements

As shown in Figure 2-1, the Ethernet1/0/1 port of Switch A ( S3100-52P ) is connected

to Switch B (acting as a DHCP relay). A network segment containing some DHCP

clients is connected to the Ethernet1/0/2 port of Switch A.

z Enable the DHCP snooping function on Switch A.

z Set the Ethernet1/0/1 port of Switch A to a trusted port.

II. Configuration procedure

# Enter system view.

<H3C> system-view

# Enable the DHCP snooping function.

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DHCP Snooping Configuration

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[H3C] dhcp-snooping

# Enter Ethernet1/0/1 port view.

[H3C] interface Ethernet1/0/1

# Set the port to a trusted port.

[H3C-Ethernet1/0/1] dhcp-snooping trust

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H3C S3100-52P Ethernet Switch Chapter 3

DHCP/BOOTP Client Configuration

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Chapter 3 DHCP/BOOTP Client Configuration

3.1 Introduction to DHCP Client

As the network scale expands and the network complexity increases, the network

configurations become more and more complex accordingly. It is usually the case that

the computer locations change (such as the portable computers in wireless networks)

or the number of the computers exceeds that of the available IP addresses. The

dynamic host configuration protocol (DHCP) is developed to meet these requirements.

DHCP adopts the client/server model, where DHCP clients request DHCP servers

dynamically for configuration information, and the DHCP servers in turn return

corresponding configuration information based on policies.

A typical DHCP implementation usually involves a DHCP server and multiple clients

(such as PCs and portable computers), as shown in

Figure 3-1.

LAN

DHCP Server

DHCP Client DHCP Client

DHCP Client DHCP Cl

ient

Figure 3-1 A typical DHCP implementation

The interactions between a DHCP client and a DHCP server are shown in

Figure 3-2.

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H3C S3100-52P Ethernet Switch Chapter 3

DHCP/BOOTP Client Configuration

3-2

DHCP Client

DHCP Server

DHCP Client

DHCP Server

DHCP Client

DHCP Server

DHCP Client

DHCP Server

DHCP Client

DHCP Server

DHCP Client

DHCP Server

DHCP Client

DHCP Server

DHCP Client

DHCP Server

DHCP Client

DHCP Server

Figure 3-2 The interaction between a DHCP client and a DHCP server

To obtain a valid IP address dynamically, a DHCP client exchanges different

information with the DHCP server in different phases. Usually, the following three

phases are involved.

1) The DHCP client accesses the network for the first time

When a DHCP client accesses a network for the first time, it goes through the following

four phases to establish connections with the DHCP server.

z Discovery. The DHCP client tries to discover a DHCP server by broadcasting

DHCP-DISCOVER packets in the network. Only DHCP servers respond to this

type of packets.

z Offering IP addresses. Upon receiving DHCP-DISCOVER packets, each DHCP

server selects a free IP address from an address pool and sends a DHCP-OFFER

packet that carries the selected IP address and other configuration information to

the DHCP client.

z Selecting the IP address to be used. The DHCP client only accepts and processes

the first-arrived DHCP-OFFER packet (if multiple DHCP servers send

DHCP-OFFER packets to it), and broadcasts a DHCP-REQUEST packet to each

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DHCP/BOOTP Client Configuration

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DHCP server. The packet contains the IP address carried in the DHCP-OFFER

packet the DHCP client receives.

z Acknowledgement. Upon receiving the DHCP-REQUEST packet, the DHCP

server that owns the IP address carried in the DHCP-REQUEST sends a

DHCP-ACK packet to the DHCP client. The packet contains the IP address offered

and other configuration information. The DHCP client binds TCP/IP protocol

components to its MAC address after receiving the packet.

IP addresses offered by other DHCP servers (if any) through DHCP-OFFER packets

but not selected by the DHCP client are still available for other clients.

2) The DHCP client accesses the network for the second and the followed time

In this case, the DHCP client establishes connections with the DHCP server through

the following steps.

z After accessing the network successfully for the first time, the DHCP client can

access the network again by broadcasting a DHCP-REQUEST packet that

contains the IP address assigned to it last time instead of a DHCP-DISCOVER

packet.

z Upon receiving the DHCP-REQUEST packet and, when the IP address applied by

the client is available, the DHCP server that owns the IP address responds with a

DHCP-ACK packet to enable the DHCP client to use the IP address again.

z If the IP address is not available (for example, it is assigned to another DHCP

client), the DHCP server responds with a DHCP_NAK packet, which enables the

DHCP client to request for a new IP address by sending a DHCP-DISCOVER

packet once again.

3) The DHCP client extends the lease of an IP address

IP addresses assigned dynamically are only valid for a specified period of time and the

DHCP servers reclaim their assigned IP addresses at the expiration of these periods.

Therefore, a DHCP client need to extend the lease period if it is to use a dynamically

assigned IP address for a period longer than allowed.

By default, a DHCP client updates its IP address lease automatically by sending

DHCP-REQUEST packets to the DHCP server when half of the lease period expires.

The DHCP server, in turn, responds with a DHCP-ACK packet to notify the DHCP client

of the new lease if the IP address is still available. An S3100-52P switch operating as a

DHCP support this lease auto-update process.

3.2 Introduction to BOOTP Client

A BOOTP client can request the server for an IP address through BOOTP. It goes

through the following two phases to apply for an IP address.

z Sending a BOOTP request packet to the server

z Processing the BOOTP response packet received from the server

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DHCP/BOOTP Client Configuration

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To obtain an IP address through BOOTP, a BOOTP client first sends a BOOTP request

packet to the server. Upon receiving the request packet, the server returns a BOOTP

response packet. The BOOTP client then retrieves the assigned IP address from the

response packet.

The BOOTP packets are sent using user datagram protocol (UDP). To ensure reliable

packet transmission, a timer is triggered when a BOOTP client sends a request packet

to the server. If no response packet is received from the server after the timer times out,

the client sends the request packet again. BOOTP request packets are sent every five

seconds and three times at most. A BOOTP client stops sending BOOTP request

packets if it fails to obtain an IP address after sending three successive BOOTP request

packets.

3.3 DHCP/BOOTP Client Configuration

An S3100-52P Ethernet switch can operate as a DHCP client or BOOTP client. In this

case, the IP address of the management VLAN interface is obtained through DHCP or

BOOTP.

3.3.1 Prerequisites

Before configuring the management VLAN, you need to create the VLAN that is to act

as the management VLAN. As VLAN 1 is the default VLAN, there is no need to create it

if you configure VLAN 1 to be the management VLAN.

3.3.2 Configuring a DHCP/BOOTP Client

Table 3-1 Configure a DHCP/BOOTP client

Operation Command Description

Enter system view

system-view

Required

Configure a specified

VLAN to be the

management VLAN

management-vlan vlan-id

Required

By default, VLAN 1

operates as the

management VLAN.

Create the management

VLAN interface and enter

VLAN interface view

interface vlan-interface

vlan-id

Required

Configure the way in

which the management

VLAN interface obtains

an IP address

ip address { bootp-alloc |

dhcp-alloc }

Required

By default, no IP

address is assigned to

the management

VLAN interface.

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H3C S3100-52P Ethernet Switch Chapter 3

DHCP/BOOTP Client Configuration

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3.3.3 Configuration Example

I. Network requirements

To manage the Switch A remotely, which operates as a DHCP client, through Telnet,

The following are required:

z Switch A obtains an IP address through DHCP

z The route between Switch A and the remote console is reachable.

To achieve this, you need to perform the following configuration for the switch:

z Configuring the management VLAN interface to obtain an IP address through

DHCP

z Configuring a default route

II. Configuration procedures

# Enter system view.

<H3C> system-view

# Create VLAN 10 and configure VLAN 10 to be the management VLAN.

[H3C] vlan 10

[H3C-vlan10] quit

[H3C] management-vlan 10

# Create VLAN 10 interface and enter VLAN interface view.

[H3C] interface vlan-interface 10

# Configure the management VLAN interface to obtain an IP address through DHCP.

[H3C-Vlan-interface10] ip address dhcp-alloc

[H3C-Vlan-interface10] quit

# Configure the default route.

[H3C] ip route-static 0.0.0.0 0.0.0.0 1.1.1.2

3.4 Displaying the Information about a DHCP/BOOTP Client

Table 3-2 Display the information about a DHCP/BOOTP client

Operation Command Description

Display the information

about IP address

assignment on the DHCP

client

display dhcp client [ verbose ]

Display the information

about the BOOTP client

display bootp client [ interface

vlan-interface vlan-id ]

Optional

You can execute

the display

commands in any

view.

H3C S3100-52P Operating instructions

Brand: H3C

Model: S3100-52P

Category: Routers

Type: Operating instructions

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