H3C S3600 Series Operating instructions

Operation Manual – DHCP

H3C S3600 Series Ethernet Switches-Release 1510 Table of Contents

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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 DHCP Packet Processing Modes...................................................................................... 1-4

1.5 Protocol Specification........................................................................................................1-4

Chapter 2 DHCP Server Configuration........................................................................................2-1

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

2.1.1 Usage of DHCP Server...........................................................................................2-1

2.1.2 IRF Support.............................................................................................................2-1

2.1.3 DHCP Address Pool................................................................................................ 2-2

2.1.4 DHCP IP Address Preferences...............................................................................2-3

2.2 Global Address Pool-Based DHCP Server Configuration.................................................2-4

2.2.1 Configuration Overview........................................................................................... 2-4

2.2.2 Enabling DHCP.......................................................................................................2-4

2.2.3 Configuring Global Address Pool Mode on Interface(s)..........................................2-5

2.2.4 Configuring How to Assign IP Addresses in a Global Address Pool ...................... 2-6

2.2.5 Configuring DNS Services for the DHCP Server....................................................2-9

2.2.6 Configuring DHCP Server to Assign WINS Server Addresses.............................2-10

2.2.7 Customizing DHCP Service..................................................................................2-11

2.2.8 Configuring Gateway Addresses for DHCP Clients..............................................2-11

2.2.9 Configuring Connection Between a DHCP Global Address Pool and a BIMS Server2-12

2.3 Interface Address Pool-based DHCP Server Configuration............................................2-13

2.3.1 Configuration Overview......................................................................................... 2-13

2.3.2 Enabling DHCP.....................................................................................................2-14

2.3.3 Configuring to Assign the IP Addresses of Interface Address Pools to DHCP Clients2-14

2.3.4 Configuring the Mode to Assign IP Addresses to DHCP Clients..........................2-15

2.3.5 Configuring DNS Services for the DHCP Server..................................................2-17

2.3.6 Configuring DHCP Servers to Assign WINS Server Addresses...........................2-18

2.3.7 Customizing DHCP Service..................................................................................2-20

2.3.8 Configuring Connection Between the DHCP Interface Address Pool and the BIMS

Server............................................................................................................................. 2-20

2.4 DHCP Security Configuration..........................................................................................2-21

2.4.1 Prerequisites .........................................................................................................2-21

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2.4.2 Configuring Private DHCP Server Detecting ........................................................2-21

2.4.3 Configuring IP Address Detecting.........................................................................2-21

2.5 Option 82 Supporting Configuration................................................................................2-22

2.5.1 Introduction to DHCP-Server Option 82................................................................ 2-22

2.5.2 Configuration Prerequisites...................................................................................2-22

2.5.3 Configuring the Option 82 Supporting Function.................................................... 2-22

2.6 Option 184 Supporting Configuration..............................................................................2-23

2.6.1 Introduction to Option 184..................................................................................... 2-23

2.6.2 Prerequisites .........................................................................................................2-25

2.6.3 Configuring the Option 184 Supporting Function.................................................. 2-25

2.6.4 Configuration Example.......................................................................................... 2-28

2.7 Displaying and Debugging a DHCP Server..................................................................... 2-30

2.8 DHCP Server Configuration Example..............................................................................2-31

2.9 Troubleshooting a DHCP Server..................................................................................... 2-33

Chapter 3 DHCP Relay Configuration .........................................................................................3-1

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

3.1.1 Usage of DHCP Relay ............................................................................................3-1

3.1.2 DHCP Relay Fundamentals....................................................................................3-1

3.1.3 Option 82 Supporting.............................................................................................. 3-2

3.2 DHCP Relay Configuration................................................................................................3-4

3.2.1 DHCP Relay Configuration Tasks........................................................................... 3-4

3.2.2 Enabling DHCP....................................................................................................... 3-4

3.2.3 Configuring an Interface to Operate in DHCP Relay Mode....................................3-4

3.2.4 Configuring DHCP Relay Security..........................................................................3-6

3.2.5 Configuring Option 82 Supporting...........................................................................3-9

3.3 Displaying and Debugging DHCP Relay.........................................................................3-10

3.4 DHCP Relay Configuration Example............................................................................... 3-10

3.5 Troubleshooting DHCP Relay..........................................................................................3-12

Chapter 4 DHCP Snooping Configuration .................................................................................. 4-1

4.1 Introduction to DHCP Snooping.........................................................................................4-1

4.2 DHCP Snooping Configuration..........................................................................................4-3

4.3 Displaying DHCP Snooping...............................................................................................4-3

4.4 Configuration Example ......................................................................................................4-4

Chapter 5 DHCP Accounting Configuration............................................................................... 5-1

5.1 Introduction to DHCP Accounting...................................................................................... 5-1

5.1.1 DHCP Accounting Fundamentals...........................................................................5-1

5.2 DHCP Accounting Configuration .......................................................................................5-1

5.2.1 Prerequisites ...........................................................................................................5-1

5.2.2 Configuring DHCP Accounting................................................................................ 5-2

5.2.3 DHCP Accounting Configuration Example..............................................................5-2

Operation Manual – DHCP

H3C S3600 Series Ethernet Switches-Release 1510 Chapter 1

DHCP Overview

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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 DHCP

ient

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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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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gs(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)

flasecs(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)

flasecs(2)

xid(4)

gs(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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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 request packet sent by the

DHCP client passes.

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 DHCP Packet Processing Modes

After the DHCP is enabled on a device, the device processes the DHCP packet

received from a DHCP client in one of the following three modes depending on your

configuration:

z Global address pool: In response to the DHCP packets received from DHCP

clients, the DHCP server picks IP addresses from its global address pools and

assigns them to the DHCP clients.

z Interface address pool: In response to the DHCP packets received from DHCP

clients, the DHCP server picks IP addresses from the interface address pools and

assigns them to the DHCP clients. If there is no available IP address in the

interface address pools, the DHCP server picks IP addresses from its global

address pool that contains the interface address pool segment and assigns them

to the DHCP clients.

z Relay: DHCP packets received from DHCP clients are forwarded to an external

DHCP server, which assigns IP addresses to the DHCP clients.

You can specify the mode to process DHCP packets. For the configuration of the first

two modes, see

Chapter 2 DHCP Server Configuration. For the configuration of the

trunk mode, see

Chapter 3 DHCP Relay Configuration.

One interface only corresponds to one mode. In this case, the new configuration

overwrites the previous one.

1.5 Protocol Specification

Protocol specifications related to DHCP include:

z RFC2131: Dynamic Host Configuration Protocol

z RFC2132: DHCP Options and BOOTP Vendor Extensions

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z RFC1542: Clarifications and Extensions for the Bootstrap Protocol

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H3C S3600 Series Ethernet Switches-Release 1510 Chapter 2

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Chapter 2 DHCP Server Configuration

 Note:

The contents of this chapter are only applicable to the S3600-EI series among S3600

series switches.

2.1 Introduction to DHCP Server

2.1.1 Usage of DHCP Server

Generally, DHCP servers are used in the following networks to assign IP addresses:

z Large-sized networks, where manual configuration method bears heavy load and

is difficult to manage the whole network in centralized way.

z Networks where the number of available IP addresses is less than that of the hosts.

In this type of networks, IP addresses are not enough for all the hosts to obtain a

fixed IP address, and the number of on-line users is limited (such is the case in an

ISP network). In these networks, a great number of hosts must dynamically obtain

IP addresses through DHCP.

z Networks where only a few hosts need fixed IP addresses and most hosts do not

need fixed IP addresses.

2.1.2 IRF Support

In an IRF (intelligent resilient framework) system, DHCP servers operate in a

centralized way to fit the IRF environment.

z DHCP servers run (as tasks) on all the units (including the master unit and the

slave units) in a Fabric system. But only the one running on the master unit

receives/sends packets and carries out all functions of a DHCP server. Those

running on the slave units only operate as the backup tasks of the one running on

the master unit.

z When a slave unit receives a DHCP-REQUEST packet, it redirects the packet to

the DHCP server on the master unit, which returns a DHCP-ACK/DHCP-NAK

packet to the DHCP client and at the same time backs up the related information to

the slave units. In this way, when the current master unit fails, one of the slaves

can change to the master and operates as the DHCP server immediately.

z DHCP is an UDP-based protocol operating at the application layer. When a DHCP

server in a fabric system runs on a Layer 2 network device, DHCP packets are

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directly forwarded by hardware instead of being delivered to the DHCP server, or

being redirected to the master unit by UDP HELPER. This idles the DHCP server.

DHCP packets can be redirected to the DHCP server on the master unit by UDP

HELPER only when the Layer 2 device is upgraded to a Layer 3 device.

Caution:

z When you merge two or more IRF systems into one IRF system, a new master unit

is elected, and the new IRF system adopts new configurations accordingly. This

may result in the existing system configurations (including the address pools

configured for the DHCP servers) being lost. As the new IRF system cannot inherit

the original DHCP server configurations, you need to perform DHCP server

configurations for it.

z When an IRF system is split into multiple new IRF systems, some of the new IRF

systems may be degraded to Layer 2 devices. For a new IRF system degraded to

Layer 2 device, although the original DHCP server still exists in the new system, it

runs idle for being unable to receive any packets. When the IRF system restores to

a Layer 3 device due to being merged into a new IRF system, it adopts the

configurations on the new IRF system. And you need to perform DHCP server

configurations if the new IRF system does not have DHCP server-related

configurations.

z In an IRF system, the UDP HELPER function must be enabled on the DHCP servers

that are in fabric state.

2.1.3 DHCP Address Pool

A DHCP address pool holds the IP addresses to be assigned to DHCP clients. When a

DHCP server receives a DHCP request from a DHCP client, it selects an address pool

depending on the configuration, picks an IP address from the pool and sends the IP

address and other related parameters (such as the IP address of the DNS server, and

the lease time of the IP address) to the DHCP client.

I. Types of address pool

The address pools of a DHCP server fall into two types: global address pool and

interface address pool.

z A global address pool is created by executing the dhcp server ip-pool command

in system view. It is valid on the current device.

z If an interface is configured with a valid unicast IP address, you can create an

interface-based address pool for the interface by executing the dhcp select

interface command in interface view. The IP addresses an interface address pool

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holds belong to the network segment the interface resides in and are available to

the interface only.

II. The structure of an address pool

The address pools of a DHCP server are hierarchically organized in a tree-like structure.

The root holds the IP address of the natural network segment, the branches hold the

subnet IP addresses, and the leaves holds the IP addresses that are manually bound to

specific clients. The address pools that are of the same level are sorted by their

configuration precedence order. Such a structure enables configurations to be inherited.

That is, the configurations of the natural network segment can be inherited by its

subnets, whose configurations in turn can be inherited by their client address. So, for

the parameters that are common to the whole network segment or some subnets (such

as domain name), you just need to configure them on the network segment or the

corresponding subnets. The following is the details of configuration inheritance.

1) A newly created child address pool inherits the configurations of its parent address

pool.

2) For an existing parent-child address pool pair, when you performs a new

configuration on the parent address pool:

z The child address pool inherits the new configuration if there is no corresponding

configuration on the child address pool.

z The child address pool does not inherit the new configuration if there is already a

corresponding configuration on the child address pool.

2.1.4 DHCP IP Address Preferences

Interfaces of the DHCP server can work in the global address pool mode or in the

interface address pool mode. If the DHCP server works in the interface address pool

mode, it picks IP addresses from the interface address pools and assigns them to the

DHCP clients. If there is no available IP address in the interface address pools, the

DHCP server picks IP addresses from its global address pool that contains the interface

address pool segment and assigns them to the DHCP clients.

A DHCP server assigns IP addresses in interface address pools or global address

pools to DHCP clients in the following sequence:

z IP addresses that are statically bound to the MAC addresses of DHCP clients or

client IDs

z IP addresses that are ever used by DHCP clients. That is, those in the assigned

leases recorded by the DHCP server. If there is no record in the leases and the

DHCP-DISCOVER packets sent by DHCP clients contain option 50 fields, the

DHCP server assigns the IP address requested by option 50.

z The first IP address found among the available IP addresses in the DHCP address

pool.

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z If no IP address is available, the DHCP server queries lease-expired and

conflicted IP addresses. If the DHCP server finds such IP addresses, it assigns

them; otherwise the DHCP server does not assign an IP address.

2.2 Global Address Pool-Based DHCP Server Configuration

2.2.1 Configuration Overview

Table 2-1 Configure global address pool-based DHCP server

Configuration task Description Related section

Enable DHCP Required 2.2.2 “Enabling DHCP”

Configure global address pool mode

on interface(s)

Optional

2.2.3 “Configuring Global

Address Pool Mode on

Interface(s)

”

Configure to bind IP

address statically to

a DHCP client

Configure the

interface(s) to

operate in

global

address pool

mode

Configure to assign

IP addresses

dynamically

One of the two

options is

required. Only

one mode can

be selected

for the same

global

address pool.

2.2.4 “Configuring How to

Assign IP Addresses in a

Global Address Pool

”

Configure DNS services for the

DHCP server

Optional

2.2.5 “Configuring DNS

Services for the DHCP

”

Configure NetBIOS services for the

DHCP server

Optional

2.2.6 “Configuring DHCP

Server

”

Customize DHCP service Optional

2.2.7 “Customizing DHCP

Service

”

Configure the gateway IP address

for DHCP clients

Optional

2.2.8 “Configuring

Gateway Addresses for

DHCP Clients

”

Configure the connection between

the DHCP global address pool and

the BIMS server

Optional

2.2.9 “Configuring

Connection Between a

DHCP Global Address

Pool and a BIMS Server

”

2.2.2 Enabling DHCP

You need to enable DHCP before performing other DHCP-related configurations, which

takes effect only after DHCP is enabled.

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Table 2-2 Enable DHCP

Operation Command Description

Enter system view

system-view

—

Enable DHCP

dhcp enable

Required

By default, DHCP is enabled

 Note:

To improve security and avoid malicious attack to the unused SOCKETs, S3600

Ethernet switches provide the following functions:

z UDP 67 and UDP 68 ports used by DHCP are enabled only when DHCP is enabled.

z UDP 67 and UDP 68 ports are disabled when DHCP is disabled.

The corresponding implementation is as follows:

z After DHCP is enabled by executing the dhcp enable command, if the DHCP server

and DHCP relay functions are not configured, UDP 67 and UDP 68 ports are kept

disabled; if the DHCP server / DHCP relay function is configured, UDP 67 and UDP

68 ports are enabled.

z After DHCP is disabled by executing the undo dhcp enable command, even if the

DHCP server and DHCP relay functions are configured, UDP 67 and UDP 68 ports

will be disabled.

2.2.3 Configuring Global Address Pool Mode on Interface(s)

You can configure the global address pool mode on the specified or all interfaces of a

DHCP server. After that, when the DHCP server receives DHCP packets from DHCP

clients through these interfaces, it assigns IP addresses in the global address pool to

the DHCP clients.

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Table 2-3 Configure the global address pool mode on interface(s)

Operation Command Description

Enter system view

system-view

—

interface interface-type

nterface-number

i

dhcp select global

Configure the

current

interface

quit

Configure

the specified

interface(s)

or all the

interfaces to

operate in

global

address pool

mode

Configure

multiple

interfaces

simultaneously

in system view

dhcp select global

{ interface interface-type

interface-number [ to

interface-type

interface-number ] | all }

Optional

By default, the

interface operates in

global address pool

mode.

2.2.4 Configuring How to Assign IP Addresses in a Global Address Pool

You can specify to bind an IP address in a global address pool statically to a DHCP

client or assign IP addresses in the pool dynamically to DHCP clients as needed. In a

global address pool, you can only bind one IP address statically to a DHCP client and

assign other IP addresses in the pool dynamically to DHCP clients.

For dynamic IP address assigning, you need to specify the range of the IP addresses to

be dynamically assigned. But for static IP address binding, you can regard that the IP

address statically bound to a DHCP client comes from a special DHCP address pool

that contains only one IP address.

I. Configuring to assign IP addresses by static binding

Some DHCP clients, such as WWW servers, need fixed IP addresses. This can be

achieved by binding IP addresses to the MAC addresses of these DHCP clients. When

such a DHCP client applies for an IP address, the DHCP server searches for the IP

address corresponding to the MAC address of the DHCP client and assigns the IP

address to the DHCP client.

When some DHCP clients send DHCP-DISCOVER packets to the DHCP server to

apply for IP addresses, they construct client IDs and add them in the

DHCP-DISCOVER packets. The DHCP server finds the corresponding IP addresses

based on the client IDs and assigns them to the DHCP clients.

Currently, only one IP address in a global DHCP address pool can be statically bound to

a MAC address or a client ID.

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Table 2-4 Configure to assign IP addresses by static binding

Operation Command Description

Enter system view

system-view

—

Create a DHCP address pool and

enter DHCP address pool view

dhcp server ip-pool

pool-name

Required

By default, no

global DHCP

address pool is

created.

Configure an IP address to be

statically bound

static-bind ip-address

ip-address [ mask

mask ]

Required

By default, no IP

address is statically

bound.

Configure the MAC

address to which

e IP address is to

be statically bound

th

static-bind

mac-address

Bind an IP

address to

the MAC

address of

a DHCP

client or a

client ID

statically

Configure the

client ID to which

the IP address is to

be statically bound

static-bind

client-identifier

One of these two

options is required.

By default, no MAC

address or client ID

to which an IP

address is to be

statically bound is

configured.

 Note:

z The static-bind ip-address command and the static-bind mac-address

command or the static-bind client-identifier command must be coupled.

z In the same global DHCP address pool, if you configure the static-bind

client-identifier command after configuring the static-bind mac-address

command, the new configuration overwrites the previous one, and vice versa.

z In the same global DHCP address pool, if the static-bind ip-address command,

the static-bind mac-address command, or the static-bind client-identifier is

executed repeatedly, the new configuration overwrites the previous one.

z The IP address to be statically bound cannot be an interface IP address of the

DHCP server; otherwise static binding does not take effect.

z A client can permanently use the statically-bound IP address that it has obtained.

The IP address is not limited by the lease time of the IP addresses in the address

pool.

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 Note:

To improve security and avoid malicious attack to the unused SOCKETs, S3600

Ethernet switches provide the following functions:

z UDP 67 and UDP 68 ports used by DHCP are enabled only when DHCP is enabled.

z UDP 67 and UDP 68 ports are disabled when DHCP is disabled.

The corresponding implementation is as follows:

z After a DHCP address pool is created by executing the dhcp server ip-pool

command, the UDP 67 and UDP 68 ports used by DHCP are enabled.

z After a DHCP address pool is deleted by executing the undo dhcp server ip-pool

command and all other DHCP functions are disabled, UDP 67 and UDP 68 ports

used by DHCP are disabled accordingly.

II. Configuring to assign IP addresses dynamically

IP addresses dynamically assigned to DHCP clients (including those that are

permanently leased and those that are temporarily leased) belong to addresses

segments that are previously specified. Currently, an address pool can contain only one

address segment, whose ranges are determined by the subnet mask.

To avoid IP address conflicts, the IP addresses to be dynamically assigned to DHCP

clients are those that are not occupied by specific network devices (such as gateways

and FTP servers).

The lease time can differ with address pools. But that of the IP addresses of the same

address pool are the same. Lease time is not inherited, that is to say, the lease time of

a child address pool is not affected by the configuration of the parent address pool.

Table 2-5 Configure to assign IP addresses dynamically

Operation Command Description

Enter system view

system-view

—

Create a DHCP

address pool and

enter DHCP

address pool view

dhcp server ip-pool

pool-name

Required

By default, no global DHCP

address pool is created

Set the IP address

segment whose IP

address are to be

assigned

dynamically

network ip-address [ mask

mask ]

Required

By default, no IP address

segment is set. That is, no IP

address is available for being

assigned

Configure the

lease time

expired { day day [ hour

hour [ minute minute ] ] |

unlimited }

Optional

The default lease time is one

day

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DHCP Server Configuration

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Operation Command Description

Return to system

view

quit

—

Specify the IP

addresses that are

not dynamically

assigned

dhcp server forbidden-ip

low-ip-address

[ high-ip-address ]

Optional

By default, all IP addresses in

a DHCP address pool are

available for being

dynamically assigned

 Note:

z In the same DHCP global address pool, the network command can be executed

repeatedly. In this case, the new configuration overwrites the previous one.

z The dhcp server forbidden-ip command can be executed repeatedly. That is, you

can configure multiple IP addresses that are not dynamically assigned to DHCP

clients.

z If an IP address that is not to be automatically assigned has been configured as a

statically-bound IP address, the DHCP server still assigns this IP address to the

client whose MAC address has been bound.

2.2.5 Configuring DNS Services for the DHCP Server

If a host accesses the Internet through domain names, DNS (domain name system) is

needed to translate the domain names into the corresponding IP addresses. To enable

DHCP clients to access the Internet through domain names, a DHCP server is required

to provide DNS server addresses while assigning IP addresses to DHCP clients.

Currently, you can configure up to eight DNS server addresses for a DHCP address

pool.

On a DHCP server, you can configure domain names to be used by DHCP clients for

address pools. After you do this, the DHCP server provides the domain names together

with the assigned IP addresses to the DHCP clients.

Table 2-6 Configure DNS services for the DHCP server

Operation Command Description

Enter system view

system-view

—

Create a DHCP

address pool and

enter DHCP

address pool view

dhcp server ip-pool

pool-name

Required

By default, no global DHCP

address pool is created.

Operation Manual – DHCP

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Operation Command Description

Configure a

domain name for

DHCP clients

domain-name

Required

By default, no domain name is

configured for DHCP clients.

Configure DNS

server addresses

for DHCP clients

dns-list ip-address&<1-8>

Required

By default, no DNS server

address is configured.

2.2.6 Configuring DHCP Server to Assign WINS Server Addresses

For Microsoft Windows-based DHCP clients that communicate through NetBIOS

protocol, the host name-to-IP address translation is carried out by Windows internet

naming service (WINS) servers. So you need to perform WINS-related configuration for

most Windows-based hosts. Currently, you can configure up to eight WINS addresses

for a DHCP address pool.

Host name-to-IP address mappings are needed for DHCP clients communicating

through NetBIOS protocol. According to the way to establish the mapping, NetBIOS

nodes fall into the following four categories:

z B-node. Nodes of this type establish their mappings through broadcasting (The

character b stands for the word broadcast). The source node obtains the IP

address of the destination node by sending the broadcast packet containing the

host name of the destination node. After receiving the broadcast packet, the

destination node returns its IP address to the source node.

z P-node. Nodes of this type establish their mappings by sending unicast packets to

WINS servers. (The character p stands for peer-to-peer). The source node sends

the unicast packet to the WINS server. After receiving the unicast packet, the

WINS server returns the IP address corresponding to the destination node name

to the source node.

z M-node. Nodes of this type are p-nodes mixed with broadcasting features (The

character m stands for the word mixed), that is to say, this type of nodes obtain

mappings by sending broadcast packets first. If they fail to obtain mappings, they

send unicast packets to the WINS server to obtain mappings.

z H-node. Nodes of this type are b-nodes mixed with peer-to-peer features. (The

character h stands for the word hybrid), that is to say, this type of nodes obtain

mappings by sending unicast packets to WINS servers first. If they fail to obtain

mappings, they send broadcast packets to obtain mappings.

Operation Manual – DHCP

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Table 2-7 Configure DHCP server to assign WINS server addresses

Operation Command Description

Enter system view

system-view

—

Create a DHCP

address pool and

enter DHCP

address pool view

dhcp server ip-pool

pool-name

Required

By default, no global DHCP

address pool is created.

Configure WINS

server addresses

for DHCP clients

nbns-list ip-address&<1-8>

Required

By default, no WINS server

address is configured.

Configure DHCP

clients to be of a

specific NetBIOS

node type

netbios-type { b-node |

h-node | m-node | p-node }

Optional

By default, no NetBIOS node

type of the DHCP client is

specified and a DHCP client

uses an h-node.

2.2.7 Customizing DHCP Service

With the evolution of DHCP, new options are constantly coming into being. You can add

the new options as the properties of DHCP servers by performing the following

configuration.

Table 2-8 Customize DHCP service

Operation Command Description

Enter system view

system-view

—

Create a DHCP

address pool and

enter DHCP

address pool view

dhcp server ip-pool

pool-name

Required

By default, no global DHCP

address pool is created.

Configure

customized

options

option code { ascii

ascii-string | hex

hex-string&<1-10> |

ip-address

ip-address&<1-8> }

Required

By default, no customized

option is configured.

2.2.8 Configuring Gateway Addresses for DHCP Clients

Gateways are necessary for DHCP clients to access servers/hosts outside the current

network segment. After you configure gateway addresses on a DHCP server, the

DHCP server provides the gateway addresses to DHCP clients as well while assigning

IP addresses to them.

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You can configure gateway addresses for address pools on a DHCP server. Currently,

you can configure up to eight gateway addresses for a DHCP address pool.

Table 2-9 Configure gateway addresses for DHCP clients

Operation Command Description

Enter system view

system-view

—

Create a DHCP

address pool and

enter DHCP

address pool view

dhcp server ip-pool

pool-name

Required

By default, no global DHCP

address pool is created.

Configure gateway

addresses for

DHCP clients

gateway-list

ip-address&<1-8>

Required

By default, no gateway

address is configured.

2.2.9 Configuring Connection Between a DHCP Global Address Pool and a

BIMS Server

Branch intelligent management system (BIMS) is a kind of network management

software, provided by H3C Technologies Co., Ltd. With BIMS you can manage and

monitor network devices that dynamically obtain IP addresses universally and

effectively.

After configuring the connection between the DHCP global address pool and the BIMS

server, you can enable the BIMS server to manage the devices that have obtained IP

addresses from the global address pool.

Table 2-10 Configure connection between a DHCP global address pool and a BIMS

server

Operation Command Description

Enter system view

system-view

—

Create a DHCP address

pool and enter DHCP

address pool view

dhcp server ip-pool

pool-name

Required

By default, no DHCP

global address pool is

created.

Configure the connection

between the DHCP global

address pool and the

BIMS server

bims-server ip ip-address

[ port port-number ]

sharekey key

Required

By default, no

connection between

the DHCP global

address pool and the

BIMS server is

configured.

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2.3 Interface Address Pool-based DHCP Server

Configuration

Caution:

In the interface address pool mode, after the addresses in the interface address pool

have been assigned, the DHCP server picks IP addresses from the global interface

address pool containing the segment of the interface address pool and assigns them to

the DHCP clients. As a result, the IP addresses obtained from global address pools and

those obtained from interface address pools are not in the same network segment, so

the clients cannot interoperate with each other.

Therefore, in the interface address pool mode, if the IP addresses in the same address

pool are required to be assigned to the clients on the same VLAN interface, the number

of clients that obtain IP addresses automatically cannot exceed the number of the IP

addresses that can be assigned in the interface address pool.

2.3.1 Configuration Overview

An interface address pool is created when the interface is assigned a valid unicast IP

address and you execute the dhcp select interface command in interface view. The IP

addresses contained in it belong to the network segment where the interface resides in

and are available to the interface only.

You can perform certain configurations for DHCP address pools of an interface or

multiple interfaces within specified interface ranges. Configuring for multiple interfaces

eases configuration work load and makes you to configure in a more convenient way.

Table 2-11 Overview of interface address pool-based DHCP server configuration

Configuration task Description Related section

Enable DHCP Required 2.3.2 “Enabling DHCP”

Configure to assign the IP addresses

of the local interface-based address

pools to DHCP clients

Required

2.3.3 “Configuring to

Assign the IP Addresses of

Interface Address Pools to

DHCP Clients

”

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H3C S3600 Series Operating instructions

H3C S3600 Series Operating instructions

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