Operation Manual DHCP H3C S5500-SI Series Ethernet Switches. Table of Contents. Table of Contents

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1 Table of Contents Table of Contents Chapter 1 DHCP Overview Introduction to DHCP DHCP Address Allocation Allocation Mechanisms Dynamic IP Address Allocation Procedure IP Address Lease Extension DHCP Message Format Protocols and Standards Chapter 2 DHCP Relay Agent Configuration Introduction to DHCP Relay Agent Application Environment Fundamentals Configuring the DHCP Relay Agent Configuration Task List Enabling DHCP Enabling the DHCP Relay Agent on Interfaces Correlating a DHCP Server Group with Relay Agent Interfaces Configuring the Relay Agent to Forward a DHCP-Release Request Configuring the DHCP Relay Agent Security Functions Configuring the DHCP Relay Agent to Support Option Displaying and Maintaining the DHCP Relay Agent Configuration DHCP Relay Agent Configuration Example Troubleshooting DHCP Relay Agent Configuration Chapter 3 DHCP Snooping Configuration DHCP Snooping Overview Function of DHCP Snooping How Does DHCP Snooping Work Configuring DHCP Snooping Displaying DHCP Snooping DHCP Snooping Configuration Example Chapter 4 DHCP Client Configuration Introduction to DHCP Client Enabling the DHCP Client on an Interface Displaying the DHCP Client DHCP Client Configuration Example i

2 Table of Contents Chapter 5 BOOTP Client Configuration Introduction to BOOTP Client BOOTP Application Obtaining an IP Address Dynamically Protocols and Standards Configuring an Interface to Dynamically Obtain an IP Address through BOOTP Displaying BOOTP Client Configuration ii

3 Chapter 1 DHCP Overview Chapter 1 DHCP Overview 1.1 Introduction to DHCP The fast expansion and growing complexity of networks result in scarce IP addresses assignable to hosts. Meanwhile, with the wide application of the wireless network, the frequent movement of laptops across the network requires that the IP addresses be changed accordingly. Therefore, related configurations on hosts become more complex. Dynamic host configuration protocol (DHCP) was introduced to ease network configuration by providing a framework for passing configuration information to hosts on a TCP/IP network. DHCP is built on a client-server model, in which the client sends a configuration request and then the server returns a reply to send configuration parameters such as an IP address to the client. A typical DHCP application, as shown in Figure 1-1, includes a DHCP server and multiple clients (PCs and laptops). DHCP Client DHCP Client DHCP Server LAN DHCP Client DHCP Client Figure 1-1 A typical DHCP application 1.2 DHCP Address Allocation Allocation Mechanisms DHCP supports three mechanisms for IP address allocation. Manual allocation: The network administrator assigns an IP address to a client like a WWW server, and DHCP conveys the assigned address to the client. Automatic allocation: DHCP assigns a permanent IP address to a client. Dynamic allocation: DHCP assigns an IP address to a client for a limited period of time, which is called a lease. Most clients obtain their addresses in this way. 1-1

4 Chapter 1 DHCP Overview Dynamic IP Address Allocation Procedure For dynamic allocation, a DHCP client obtains an IP address from a DHCP server via four steps: 1) The client broadcasts a DHCP-DISCOVER message to locate a DHCP server. 2) A DHCP server offers configuration parameters such as an IP address to the client in a DHCP-OFFER message. 3) If several DHCP servers send offers to the client, the client accepts the first received offer, and broadcasts it in a DHCP-REQUEST message to formally request the IP address. 4) All DHCP servers receive the DHCP-REQUEST message, but only the server to which the client sent a formal request for the offered IP address returns a DHCP-ACK message to the client confirming that the IP address has been allocated to the client, or returns a DHCP-NAK unicast message denying the IP address allocation. If the client receives the DHCP-ACK message, it will probe the IP address using gratuitous ARP with destination address as the IP address assigned by the server to check whether the IP address is in use. If the client receives no response within specified time, the client can use this IP address. f there are multiple DHCP servers in the network, the IP addresses offered by other DHCP servers are still assignable to other clients IP Address Lease Extension The IP address dynamically allocated by a DHCP server to a client has a lease. After the lease duration elapses, the IP address will be reclaimed by the DHCP server. If the client wants to use the IP address again, it has to extend the lease duration. After the half lease duration elapses, the DHCP client will send the DHCP server a DHCP-REQUEST unicast message to extend the lease duration. Upon availability of the IP address, the DHCP server returns a DHCP-ACK unicast confirming that the client s lease duration has been extended, or a DHCP-NAK unicast denying the request. If the client receives the DHCP-NAK message, it will broadcast another DHCP-REQUEST message for lease extension after 7/8 lease duration elapses. The DHCP server will handle the request as above mentioned. 1-2

5 Chapter 1 DHCP Overview 1.3 DHCP Message Format The figure below gives the DHCP message format, which is based on the BOOTP message format and involves eight types. These types of messages have the same format except that some fields have different values. The numbers in parentheses indicate the size of each field in octets. op: Message type defined in option field. 1 = REQUEST, 2 = REPLY htype,hlen: Hardware address type and length of a DHCP client. hops: Number of relay agents a request message traveled. xid: Transaction ID, a 32 bit random number chosen by the client to identify an IP address allocation. secs: Filled in by the client, the number of seconds elapsed since the client began address acquisition or renewal process. Currently this field is reserved and set to 0. flags: The leftmost bit is defined as the BROADCAST (B) flag. If this flag is set to 1, the DHCP server sent a reply back by broadcast. The remaining bits of the flags field are reserved for future use. Currently, the BROADCAST flag is always set to 1. ciaddr: Client IP address. yiaddr: 'your' (client) IP address, assigned by the server. siaddr: Server IP address, from which the clients obtained configuration parameters. giaddr: The first relay agent IP address a request message traveled. chaddr: Client hardware address. sname: The server host name, from which the client obtained configuration parameters. file: Bootfile name and routing information, defined by the server to the client. options: Optional parameters field that is variable in length; parameters include the message type, lease, DNS IP address, WINS IP address and so forth. 1-3

6 Chapter 1 DHCP Overview 1.4 Protocols and Standards RFC2131:Dynamic Host Configuration Protocol RFC2132:DHCP Options and BOOTP Vendor Extensions RFC1542:Clarifications and Extensions for the Bootstrap Protocol RFC 3046: DHCP Relay Agent Information Option 1-4

7 Chapter 2 DHCP Relay Agent Configuration Chapter 2 DHCP Relay Agent Configuration When configuring the DHCP relay agent, go to these sections for information you are interested in: Introduction to DHCP Relay Agent Configuring the DHCP Relay Agent Displaying and Maintaining the DHCP Relay Agent Configuration DHCP Relay Agent Configuration Example Troubleshooting DHCP Relay Agent Configuration The DHCP relay agent configuration is supported only on VLAN interfaces. DHCP Snooping must be disabled on the DHCP relay agent. 2.1 Introduction to DHCP Relay Agent Application Environment Since DHCP clients request IP addresses via broadcast messages, the DHCP sever and clients must be on the same subnet. Therefore, a DHCP server must be available on each subnet. It is not practical. DHCP relay agent solves the problem. Via a relay agent, DHCP clients communicate with a DHCP server on another subnet to obtain configuration parameters. Thus, DHCP clients on different subnets can contact the same DHCP server for ease of centralized management and cost reduction Fundamentals A typical application of the DHCP relay agent is shown below. 2-1

8 Chapter 2 DHCP Relay Agent Configuration DHCP client DHCP client Ethernet Internet Switch ( DHCP Relay) DHCP client DHCP client DHCP Server Figure 2-1 DHCP relay agent application No matter whether a relay agent exists or not, the DHCP server and client interact with each other in a similar way (see Dynamic IP Address Allocation Procedure). The following describes the forwarding process on the DHCP relay agent. The DHCP client broadcasts the DHCP-DISCOVER or DHCP-REQUEST packet. After receiving the packet, the DHCP relay-enabled network device unicasts the packet to a specified DHCP server based on the configuration. The DHCP server returns an IP address to the relay agent, which conveys it to the client via broadcast. 2.2 Configuring the DHCP Relay Agent Configuration Task List Complete the following tasks to configure the DHCP relay agent: Task Remarks Enabling DHCP Enabling the DHCP Relay Agent on Interfaces Correlating a DHCP Server Group with Relay Agent Interfaces Configuring the Relay Agent to Forward a DHCP-Release Request Configuring the DHCP Relay Agent Security Functions Configuring the DHCP Relay Agent to Support Option 82 Optional Optional Optional 2-2

9 Chapter 2 DHCP Relay Agent Configuration Enabling DHCP Enable DHCP before performing other DHCP-related configurations. Enter system view system-view Enable DHCP dhcp enable Disabled by default Enabling the DHCP Relay Agent on Interfaces With this task completed, upon receiving a DHCP request from an enabled interface, the relay agent will forward the request to an outside DHCP server for address allocation. To enable the DHCP relay agent on interfaces, use the following commands: Enter system view system-view Enter interface view Enable the DHCP relay agent on the current interface interface interface-type interface-number dhcp select relay Disabled by default. When a DHCP client obtains an IP address from a DHCP server through the DHCP relay, an IP address pool with the same network segment (network number and mask) as that of the IP address of the DHCP relay interface connecting the client must has already been configured on the DHCP server. Otherwise, the DHCP client cannot obtain a correct IP address Correlating a DHCP Server Group with Relay Agent Interfaces To improve reliability, you can specify several DHCP servers as a group on the DHCP relay agent and correlate a relay agent interface with the server group. When the interface receives requesting messages from clients, the relay agent will forward them to all the DHCP servers of the group. To correlate a DHCP server group with relay agent interfaces, use the following commands: 2-3

10 Chapter 2 DHCP Relay Agent Configuration Enter system view system-view Specify a DHCP server group number and servers in the group Enter interface view Correlate the DHCP server group with the Current interface dhcp relay server-group group-id ip ip-address interface interface-type interface-number dhcp relay server-select group-id Not specified by default Not correlated by default You can specify up to twenty DHCP server groups on the relay agent. You can configure up to eight DHCP servers for a server group. The IP address of any DHCP server in a DHCP server group cannot be on the same network segment with that of a DHCP relay interface connecting with DHCP clients; otherwise, the DHCP clients may not be able to obtain IP addresses. A DHCP server group can correlate with one or multiple DHCP relay agent interfaces, while a relay agent interface can only correlate with one DHCP server group. Using the dhcp relay server-select command repeatedly overwrites the previous configuration. However, if the specified DHCP server group does not exist, the interface still uses the previous correlation. The group-id in the dhcp relay server-select command was specified by the dhcp relay server-group command Configuring the Relay Agent to Forward a DHCP-Release Request Sometimes, you need to release a client s IP address manually on the DHCP relay agent. With this task completed, the DHCP relay agent can actively send a DHCP-RELEASE request that contains the client s IP address to the DHCP server. The DHCP server then releases the IP address for the client. I. Configure to release a client s IP address through the DHCP relay (in system view) In system view, when you configure to release a client s IP address through DHCP relay, if you do not specify the IP address of the DHCP server, the DHCP relay will send a DHCP-RELEASE request to the DHCP servers of DHCP server groups that correspond to all interfaces working in the DHCP relay mode. 2-4

11 Chapter 2 DHCP Relay Agent Configuration Table 2-1 Configure to release a client s IP address through the DHCP relay (in system view) To do Use the command... Remarks Enter system view system-view Request DHCP server to release the IP address applied and used by a client dhcp relay release client-ip client-mac [ server-ip ] II. Configure to release a client s IP address through the DHCP relay (in interface view) In interface view, when you configure to release a client s IP address through DHCP relay, if you do not specify a DHCP server, the DHCP relay will send a DHCP-RELEASE request to all the DHCP servers of DHCP server group that correspond to the interface. If you specify a DHCP server, the DHCP relay will send the DHCP-RELEASE request to the specified DHCP server only. Table 2-2 Configure to release a client s IP address through the DHCP relay (in interface view) To do Use the command... Remarks Enter system view system-view Enter interface view Request DHCP server to release the IP address applied and used by a client interface interface-type interface-number dhcp relay release client-ip client-mac [ server-ip ] Configuring the DHCP Relay Agent Security Functions I. Creating static bindings and enabling invalid IP addresses check The DHCP relay agent can dynamically record IP-to-MAC bindings after clients got IP addresses. You can also create static bindings on the DHCP relay agent. For avoidance of invalid IP address configuration, you can configure the DHCP relay agent to check whether a requesting client s IP and MAC addresses match a binding on it (both dynamic and static bindings). If not, the client cannot access outside networks via the DHCP relay agent. To create a static binding and enable invalid IP address check, use the following commands: 2-5

12 Chapter 2 DHCP Relay Agent Configuration Enter system view system-view Create a static binding Enter interface view Enable invalid IP address check dhcp relay security static ip-address mac-address interface interface-type interface-number dhcp relay address-check { disable enable } Optional Not created by default Disabled by default The dhcp relay address-check command is independent of other commands of the DHCP relay agent. That is, the invalid address check takes effect when this command is executed, regardless of whether other commands are used. Before executing the dhcp relay address-check enable command on the DHCP relay interface connected to the DHCP server, you need to configure the static binding between the IP address and MAC address of the DHCP server. Otherwise, the DHCP client will fail to obtain an IP address. II. Configuring dynamic binding update interval Via the DHCP relay agent, a DHCP client sends a DHCP-RELEASE unicast message to the DHCP server to relinquish its IP address. In this case the DHCP relay agent simply conveys the message to the DHCP server, thus it does not remove the IP address from its bindings. To solve this, the system provides the function of updating relay agent binding entries at a specified interval. The DHCP relay agent regularly sends a DHCP-REQUEST message using its own MAC address and a client s IP address to the DHCP server. If the server returns a DHCP-ACK message, which means the client s IP address is assignable now, the DHCP relay agent will update its bindings by aging out the binding entry of the client s IP address. If the server returns a DHCP-NAK message, which means the IP address is still in use, the relay agent will not age it out. To configure dynamic binding update interval, use the following commands: Enter system view system-view 2-6

13 Chapter 2 DHCP Relay Agent Configuration Configure binding update interval dhcp relay security tracker { interval auto } Optional auto by default (auto interval is calculated by the relay agent according to the number of bindings) III. Enabling pseudo DHCP servers detection There are invalid DHCP servers on networks, which reply DHCP clients with wrong IP addresses. These invalid DHCP servers are pseudo DHCP servers. With this task completed, upon receiving a DHCP-REQUEST message from a client, the DHCP relay agent will record from the message the IP address that the server has ever offered to the client and the receiving interface address. The administrator can use this information to check out any DHCP pseudo servers. To enable pseudo DHCP server detection, use the following commands: Enter system view system-view Enable pseudo DHCP server detection dhcp server-detect relay Disabled by default With pseudo DHCP server detection enabled, the device puts a record once for each DHCP server. The administrator needs to find pseudo DHCP servers from the records Configuring the DHCP Relay Agent to Support Option 82 I. Introduction to option 82 Option 82 is the relay agent option in the Options field of the DHCP message. It involves 255 sub-options. At least one sub-option must be defined. Now the DHCP relay agent supports two sub-options: sub-option 1 and sub-option 2. Option 82 has no unified definition. Its padding formats vary with venders. Currently the device supports two padding formats: normal and verbose. The padding contents for sub-options in the normal padding format are: sub-option 1: padded with the number of the port that receives the DHCP client s request, and the number of the VLAN that the port belongs to. sub-option 2: padded with the MAC address of the interface that received the client s request. 2-7

14 Chapter 2 DHCP Relay Agent Configuration The padding contents for sub-options in the verbose padding format are: sub-option 1: padded with specified access node identifier, the type and number of the port that receives the DHCP client s request, and the number of the VLAN that the port belongs to. sub-option 2: padded with the MAC address of the interface that received the client s request. II. Handling strategies for option 82 on the relay agent If the DHCP relay agent supports option 82, it will handle a client s requesting message according to the contents defined in option 82, if any. The handling strategies are described in the table below. If a reply returned by the DHCP server contains option 82, the DHCP relay agent will remove the option 82 before forwarding the reply to the client. If a client s requesting message has Handling strategy Padding format The DHCP relay agent will Drop Drop the message. Keep Forward the message without changing Option 82. Option 82 Replace Normal Verbose Forward the message after replacing the original Option 82 with the Option 82 padded in normal format. Forward the message after replacing the original Option 82 with the Option 82 padded in verbose format. no option 82 Normal Verbose Forward the message after adding the Option 82 padded in normal format. Forward the message after adding the Option 82 padded in verbose format. III. Prerequisites You need to complete the following tasks before configuring the DHCP relay agent to support option 82 Enabling DHCP Enabling the DHCP relay agent on the specified interface Configure network parameters for DHCP relay agent to ensure the route between the DHCP relay and the DHCP server is reachable. 2-8

15 Chapter 2 DHCP Relay Agent Configuration IV. Configuring the DHCP relay agent to support option 82 Use the following commands for this configuration: Enter system view system-view Enter interface view Enable the relay agent to support option 82 Configure the handling strategy for requesting messages containing option 82 Configure the padding format for option 82 interface interface-type interface-number dhcp relay information enable dhcp relay information strategy { drop keep replace } dhcp relay information format { normal verbose [ node-identifier { mac sysname user-defined node-identifier } ] } Disabled by default Optional replace by default Optional normal by default To support option 82, it is required to perform related configuration on both the DHCP server and relay agent. Since the DHCP server configuration varies with devices, it is not mentioned here. If the handling strategy of the DHCP relay agent is configured as replace, you need to configure a padding format for option 82. If the handling strategy is keep or drop, you need not configure any padding format. 2.3 Displaying and Maintaining the DHCP Relay Agent Configuration Display information about DHCP server groups correlated to a specified or all interfaces Display information about bindings of DHCP relay agents display dhcp relay { all interface interface-type interface-number } display dhcp relay security [ ip-address dynamic static ] Available in any view Available in any view 2-9

16 Chapter 2 DHCP Relay Agent Configuration Display statistics information about bindings of DHCP relay agents Display information about the refreshing interval for entries of dynamic IP-to-MAC bindings Display information about the configuration of a specified or all DHCP server groups Display packet statistics on relay agent Clear packet statistics from relay agent display dhcp relay security statistics display dhcp relay security tracker display dhcp relay server-group { group-id all } display dhcp relay statistics [ server-group { group-id all } ] reset dhcp relay statistics [ server-group group-id ] Available in any view Available in any view Available in any view Available in user view Available in user view 2.4 DHCP Relay Agent Configuration Example I. Network requirements Vlan-interface1 on the DHCP relay agent (a switch) connects to the network where DHCP clients reside. The IP address of Vlan-interface1 is /24 and IP address of Vlan-interface2 is /24 that communicates with the DHCP server /24. As shown in the figure below, the DHCP relay agent forwards messages between DHCP clients and the DHCP server. 2-10

17 Chapter 2 DHCP Relay Agent Configuration II. Network diagram DHCP Client DHCP Client DHCP Server Ethernet DHCP Relay /24 Vlan-interface /24 Vlan-interface /24 Ethernet Figure 2-2 Network diagram for DHCP relay agent III. Configuration procedure # Enable DHCP. <Sysname> system-view [Sysname] dhcp enable # Enable the DHCP relay agent on Vlan-interface1. [Sysname] interface vlan-interface 1 [Sysname-Vlan-interface1] dhcp select relay [Sysname-Vlan-interface1] quit # Configure DHCP server group 1 with the DHCP server , and correlate the DHCP server group 1 with Vlan-interface1. [Sysname] dhcp relay server-group 1 ip [Sysname] interface vlan-interface 1 [Sysname-Vlan-interface1] dhcp relay server-select 1 Performing the configuration on the DHCP server is also required to guarantee the client-to-server communication via the relay agent. Since the DHCP server configuration varies with devices, it is not mentioned here. In this example, the DHCP relay agent and server are on the same subnet. If they are on different subnets, the routes in between must be reachable. 2-11

18 Chapter 2 DHCP Relay Agent Configuration 2.5 Troubleshooting DHCP Relay Agent Configuration I. Symptom DHCP clients cannot obtain any configuration parameters via the DHCP relay agent. II. Analysis Some problems may occur with the DHCP relay agent or server configuration. Enable debugging and execute the display command on the DHCP relay agent to view the debugging information and interface state information for locating the problem. III. Solution Check that: The DHCP is enabled on the DHCP server and relay agent. The address pool on the same subnet where DHCP clients reside is available on the DHCP server. The routes between the DHCP server and DHCP relay agent are reachable. The relay agent interface connected to DHCP clients is correlated with correct DHCP server group and IP addresses for the group members are correct. 2-12

19 Chapter 3 DHCP Snooping Configuration Chapter 3 DHCP Snooping Configuration When configuring DHCP snooping, go to these sections for information you are interested in: DHCP Snooping Overview Configuring DHCP Snooping Displaying DHCP Snooping DHCP Snooping Configuration Example The DHCP snooping is supported no link aggregation. If an Ethernet port is added into an aggregation group, DHCP Snooping configuration on it will not take effect. When the port is removed from the group, DHCP Snooping can take effect. The DHCP snooping enabled device does not work if it is between the DHCP relay agent and DHCP server, and it can work when it is between the DHCP client and relay agent or between the DHCP client and server. The DHCP Snooping enabled device cannot be a DHCP server, DHCP relay agent, DHCP client, or BOOTP client. Therefore, DHCP Snooping must be disabled on a DHCP server, DHCP relay agent, DHCP client, and BOOTP client. 3.1 DHCP Snooping Overview Function of DHCP Snooping DHCP snooping is a DHCP security feature for preventing DHCP clients from receiving IP addresses provided by untrusted DHCP servers. It allows a device to: Drop DHCP responses received on untrusted ports, preventing DHCP clients from receiving IP addresses provided by untrusted DHCP servers. Listen to DHCP-REQUEST and DHCP-ACK messages, record and maintain binding information about MAC addresses of DHCP clients and the obtained IP addresses, so that network administrators can easily see which IP addresses are assigned to the DHCP clients. 3-1

20 Chapter 3 DHCP Snooping Configuration How Does DHCP Snooping Work On a network, DHCP servers fall into two categories: valid and invalid. With DHCP snooping, the ports of a device can be differentiated by whether they are trusted or untrusted: Trusted: A trusted port is connected to a valid DHCP server directly or indirectly. It forwards DHCP messages normally, guaranteeing that DHCP clients can obtain valid IP addresses. Untrusted: An untrusted port is connected to an invalid DHCP server. The DHCP-ACK or DHCP-OFFER packets received from the port are discarded, preventing DHCP clients from receiving invalid IP addresses. 3.2 Configuring DHCP Snooping Follow these steps to configure DHCP snooping: Enter system view system-view Enable DHCP snooping Enter Ethernet port view Specify the port as trusted dhcp-snooping interface interface-type interface-number dhcp-snooping trust Disabled by default Untrusted by default. You must specify the ports connected to the valid DHCP servers as trusted to ensure that DHCP clients can obtain valid IP addresses. The trusted port and the port connected to the DHCP client must be in the same VLAN. 3.3 Displaying DHCP Snooping Display DHCP snooping address binding information Display information about trusted ports display dhcp-snooping display dhcp-snooping trust Available in any view 3-2

21 Chapter 3 DHCP Snooping Configuration 3.4 DHCP Snooping Configuration Example I. Network requirements A device is connected to a DHCP server through GigabitEthernet1/0/1, and to two DHCP clients through GigabitEthernet1/0/2 and GigabitEthernet1/0/3. GigabitEthernet1/0/1 forwards DHCP server responses while the other two do not. II. Network diagram DHCP Server DHCP Snooping GE1/0/2 GE1/0/1 GE1/0/3 DHCP Client DHCP Client Figure 3-1 Network diagram for DHCP snooping configuration III. Configuration procedure # Enable DHCP snooping. <Sysname> system-view [Sysname] dhcp-snooping # Specify GigabitEthernet1/0/1 as trusted. [Sysname] interface GigabitEthernet1/0/ 1 [Sysname-GigabitEthernet1/0/1] dhcp-snooping trust 3-3

22 Chapter 4 DHCP Client Configuration Chapter 4 DHCP Client Configuration When configuring the DHCP client, go to these sections for information you are interested in: Introduction to DHCP Client Enabling the DHCP Client on an Interface Displaying the DHCP Client DHCP Client Configuration Example The DHCP client configuration is supported only on VLAN interfaces. When multiple VLAN interfaces with the same MAC address use DHCP for IP address acquisition via a relay agent, the DHCP server cannot be a Windows 2000 Server or Windows 2003 Server. DHCP Snooping must be disabled on the DHCP client. 4.1 Introduction to DHCP Client With the DHCP client enabled on an interface, the interface will use DHCP to obtain configuration parameters such as an IP address from the DHCP server. 4.2 Enabling the DHCP Client on an Interface Follow these steps to enable the DHCP client on an interface: Enter system view system-view Enter interface view Enable the DHCP client on the interface interface interface-type interface-number ip address dhcp-alloc [ client-identifier mac interface-type interface-number ] Disabled by default 4-1

23 Chapter 4 DHCP Client Configuration An interface can be configured to acquire an IP address in multiple ways, but these ways are exclusive. The IP address obtained in a new way overwrites the IP address obtained in the previous way. After the DHCP client is enabled on an interface, no secondary IP address is configurable for the interface. 4.3 Displaying the DHCP Client Display specified configuration information display dhcp client [ verbose ] [ interface interface-type interface-number ] Available in any view 4.4 DHCP Client Configuration Example I. Network requirements On a LAN, the DHCP client (S5500-SI) contacts the DHCP server via Vlan-interface1 to obtain an IP address. II. Network diagram WINS Server Client LAN V LAN-interface /25 VLAN-interface1 DHCP Server DNS Server Client Figure 4-1 A DHCP network( S5500-SI as the DHCP client) III. Configuration procedure The following is the configuration on the client switch shown in Figure 4-1. # Enable the DHCP client on Vlan-interface1. 4-2

24 Chapter 4 DHCP Client Configuration <Sysname> system-view [Sysname] interface vlan-interface 1 [Sysname-Vlan-interface1] ip address dhcp-alloc To implement the DHCP client-server model, you need to perform related configuration on the DHCP server. Since the DHCP server configuration varies with devices, it is not mentioned here. 4-3

25 Chapter 5 BOOTP Client Configuration Chapter 5 BOOTP Client Configuration While configuring a bootstrap protocol (BOOTP) client, go to these sections for information you are interested in: Introduction to BOOTP Client Configuring an Interface to Dynamically Obtain an IP Address through BOOTP Displaying BOOTP Client Configuration BOOTP client configuration only applies to VLAN interfaces. If several VLAN interfaces sharing the same MAC address obtain IP addresses through a BOOTP relay agent, the BOOTP server cannot be a Windows 2000 Server or Windows 2003 Server. DHCP Snooping must be disabled on the BOOTP client. 5.1 Introduction to BOOTP Client This section covers these topics: BOOTP Application Obtaining an IP Address Dynamically Protocols and Standards BOOTP Application After you specify an interface of the device as a BOOTP client, the interface can use BOOTP to get information (such as IP address) from the BOOTP server, which simplifies your configuration. Before using BOOTP, an administrator needs to configure a BOOTP parameter file for each BOOTP client on the BOOTP server. The parameter file contains information such as MAC address and IP address of a BOOTP client. When a BOOTP client originates a request to the BOOTP server, the BOOTP server will search for the BOOTP parameter file and return the corresponding configuration information. 5-1

26 Chapter 5 BOOTP Client Configuration Because you need to configure a parameter file for each client on the BOOTP server, BOOTP usually runs under a relatively stable environment. If the network changes frequently, dynamic host configuration protocol (DHCP) can be applied. For an introduction to DHCP, refer to Chapter 1 DHCP Overview Because a DHCP server can interact with a BOOTP client, you can use the DHCP server to configure an IP address for the BOOTP client, without any BOOTP server Obtaining an IP Address Dynamically A DHCP server can take the place of the BOOTP server in the following dynamic IP address acquisition. A BOOTP client dynamically obtains an IP address from a BOOTP server in the following way: 1) The BOOTP client broadcasts a BOOTP request, which contains its own MAC address. 2) The BOOTP server receives the request and searches the configuration file for the corresponding IP address according to the MAC address of the BOOTP client. The BOOTP server then returns a BOOTP response to the BOOTP client. 3) The BOOTP client obtains the IP address from the received the response Protocols and Standards Some protocols and standards related to BOOTP include: RFC 951: Bootstrap Protocol (BOOTP) RFC 2132: DHCP Options and BOOTP Vendor Extensions RFC 1542: Clarifications and Extensions for the Bootstrap Protocol 5.2 Configuring an Interface to Dynamically Obtain an IP Address through BOOTP Follow these steps to configure an interface to dynamically obtain an IP address: 5-2

27 Chapter 5 BOOTP Client Configuration Enter system view system-view Enter interface view Configure an interface to dynamically obtain IP address through BOOTP interface interface-type interface-number ip address bootp-alloc By default, an interface does not use BOOTP to obtain an IP address. 5.3 Displaying BOOTP Client Configuration Display related information on a BOOTP client display bootp client [ interface interface-type interface-number ] Available in any view 5-3

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