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HP 5500 Ei 5500 Si Switch Series Configuration Guide

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Step Command Remarks 
3.  Configure a timeout waiting 
for ping responses.  dhcp server ping timeout
 
milliseconds   Optional. 
500 ms by default. 
The value 
0 indicates that no ping 
operation is performed. 
 
Enabling client offline detection 
With this feature enabled, the DHCP server considers a DHCP client goes offline when the ARP entry for  
the client ages out. In addition, it removes the client’s IP-to-MAC binding entry. 
Removing an ARP entry manually does not remove  the corresponding client’s IP-to-MAC binding. 
To  e n ab l e  of fl i n e  d e te ct io n : 
 
Step Command Remarks 
1.   Enter system view. 
system-view N/A 
2.  Enter interface view.  interface
 interface-type 
interface-number   N/A 
3.
  Enable offline detection. 
dhcp server client-detect enable Disabled by default 
 
Enabling handling of Option 82 
With Option 82 handling enabled, when the DHCP server receives a request with Option 82, it adds 
Option 82 into the response.  
If the server is configured to ignore Option 82, it will assign an IP address to the client without adding 
Option 82 in the response message. 
Configuration prerequisites 
Before you enable Option 82 handling, complete the following tasks: 
•
  Configure the DHCP server —Enable DHCP and configure the DHCP address pool. 
•   Configure the relay agent or the device enabled with DHCP snooping —For more information, see 
 Configuring DHCP relay agent  and Configuring DHCP snooping .
 
Enabling Option 82 handling  
Step Command Remarks 
1.  Enter system view. 
system-view  N/A 
2.  Enable the server to handle 
Option 82.  dhcp server relay information 
enable  Optional. 
Enabled by default.
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Specifying the threshold for sending trap messages 
Configuration prerequisites 
Before you perform the configuration, use the snmp-agent target-host command to specify the 
destination address of the trap messages. For more information about the command, see the  Network 
Management and Monitoring Command Reference . 
Configuration procedure 
A DHCP server sends trap messages to the network management server when one of the following items 
reaches the specified threshold: 
•   The ratio of successfully allocated IP addresses to received DHCP requests 
•   The average IP address utilization of the address pool 
•   The maximum IP address utilization of the address pool 
Trap messages help network administrators know th e latest usage information of the DHCP server. 
To specify the threshold for sending trap messages: 
 
Step Command Remarks 
1.   Enter system view. 
system-view  N/A 
2.  Specify the threshold for 
sending trap messages to the 
network management server.  dhcp server threshold
 { allocated-ip 
threshold-value  | average-ip-use  
threshold-value  | max-ip-use  threshold-value  } Optional. 
Disabled by default. 
 
Setting the DSCP value for DHCP packets 
 
Step Command Remarks 
1.
  Enter system view. 
system-view N/A 
2.  Set the DSCP value for DHCP packets 
sent by the DHCP server.  dhcp dscp
 dscp-value  Optional. 
By default, the DSCP value is 56. 
 
Displaying and maintaining the DHCP server 
 
 
IMPORTANT: 
A restart of the DHCP serv
er or execution of the reset dhcp server ip-in-use  command deletes all lease 
information. The DHCP server denies any DHCP reques t for lease extension, and the client must request an
IP address again. 
 
Task Command  Remarks 
Display information about IP address 
conflicts.  display dhcp server conflict
 { all |  ip 
ip-address  } [ | { begin |  exclude | include  } 
regular-expression  ]  Available in any view
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Task Command  Remarks 
Display information about lease 
expiration. display dhcp server expired 
{ all  |  ip 
ip-address  |  pool  [ pool-name  ] } [ | { begin | 
exclude  | include  } regular-expression ]  Available in any view 
Display information about assignable 
IP addresses.  display dhcp server free-ip
 [ | { begin | 
exclude  | include  } regular-expression ]  Available in any view 
Display IP addresses excluded from 
automatic allocation in the DHCP 
address pool.  display dhcp server forbidden-ip
 [ | { begin  | 
exclude  | include  } regular-expression ]  Available in any view
 
Display information about bindings. 
display dhcp server ip-in-use
 { all | ip 
ip-address  | pool [ pool-name  ] } [ | { begin | 
exclude  | include  } regular-expression ]  Available in any view
 
Display information about DHCP 
server statistics.  display dhcp server statistics
 [ | { begin | 
exclude  | include  } regular-expression ]  Available in any view 
Display tree organization 
information of address pool(s).  display dhcp server tree
 { all  |  pool  
[ pool-name  ] } [ | { begin |  exclude | 
include  } regular-expression ]  Available in any view 
Clear information about IP address 
conflicts. 
reset dhcp server conflict
 { all |  ip  ip-address  }  Available in user view 
Clear information about dynamic 
bindings.  reset dhcp server ip-in-use { all
 | ip 
ip-address  |  pool  [ pool-name  ] }  Available in user view 
Clear information about DHCP server 
statistics.  reset dhcp server statistics 
Available in user view 
 
DHCP server configuration examples 
DHCP networking involves the following two types: 
•  The DHCP server and client are on the same  subnet and exchange messages directly. 
•   The DHCP server and client are not on the same subnet and they communicate with each other via 
a DHCP relay agent.  
The DHCP server configuration for the two types is the same. 
Static IP address assignment configuration example 
Network requirements 
As shown in  Figure 29, S witch B (DHCP client) and Switch C (BOOTP client) obtain the static IP address, 
DNS server address, and gateway address from Switch A (DHCP server). 
The client ID of VLAN-interface 2 on Switch B is: 
3030 -3066 -2e65-3234 -392e -3830 -3530 -2d56 -6c61-6e2d-696e -7465-7266 -6163-6532.  
The MAC address of VLAN-interface 2 on Switch C is 000f-e249-8050.
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Figure 29 Network diagram 
 
 
Configuration procedure 
1. Configure the IP address of VLAN -interface 2 on Switch A. 
 system-view 
[SwitchA] interface vlan-interface 2 
[SwitchA-Vlan-interface2] ip address 10.1.1.1 25 
[SwitchA-Vlan-interface2] quit 
2. Configure the DHCP server: 
# Enable DHCP. 
[SwitchA] dhcp enable 
# Enable the DHCP server on VLAN-interface 2. 
[SwitchA] interface vlan-interface 2 
[SwitchA-Vlan-interface2] dhcp select server global-pool 
[SwitchA-Vlan-interface2] quit 
# Create DHCP address pool 0,  configure a static binding, DNS server and gateway in it. 
[SwitchA] dhcp server ip-pool 0 
[SwitchA-dhcp-pool-0] static-bind ip-address 10.1.1.5 
[SwitchA-dhcp-pool-0] static-bind client-identifier 
3030-3066-2e65-3234-392e-3830-3530-2d56-6c61-6e2d-696e-7465-7266-6163-65\
32 
[SwitchA-dhcp-pool-0] dns-list 10.1.1.2 
[SwitchA-dhcp-pool-0] gateway-list 10.1.1.126 
[SwitchA-dhcp-pool-0] quit 
# Create DHCP address pool 1, configure a static binding, DNS server and gateway in it. 
[SwitchA] dhcp server ip-pool 1 
[SwitchA-dhcp-pool-1] static-bind ip-address 10.1.1.6 
[SwitchA-dhcp-pool-1] static-bind mac-address 000f-e249-8050 
[SwitchA-dhcp-pool-1] dns-list 10.1.1.2 
[SwitchA-dhcp-pool-1] gateway-list 10.1.1.126 
Verifying the configuration 
After the preceding configuration is complete, Switch B can obtain IP address 10.1.1.5 and other network 
parameters, and Switch C can obtain IP address 10.1.1.6 and other network parameters from Switch A. 
You can use the display dhcp server ip-in-use command on the DHCP server to view the IP addresses 
assigned to the clients. 
 
Vlan-int2
10.1.1.1/25
Switch B
DHCP Client
DNS server
10.1.1.2/25
Switch A
DHCP server Gateway
10.1.1.126/25
Switch C
BOOTP Client
Vlan-int2 Vlan-int2
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Dynamic IP address assignment configuration example 
Network requirements 
•  As shown in  Figure 30, the DHCP s erver (Switch A) assigns IP addresses to clients in subnet 
1 0 .1.1. 0 / 2 4 ,  w h i c h  i s  s u b n e t t e d  i n t o  1 0 .1.1. 0 / 2 5  a n d  1 0 .1.1.12 8 / 2 5 .  
•   The IP addresses of VLAN-interfaces 1 and 2 on Switch A are 10.1.1.1/25 and 10.1.1.129/25 
respectively.  
•   In address pool 10.1.1.0/25, configure the address lease duration as ten days and twelve hours, 
domain name suffix aabbcc.com, DNS server address 10.1.1.2/25, gateway 10.1.1.126/25, and 
W I N S  s e r v e r  1 0 .1.1. 4 / 2 5 .  
•   In address pool 10.1.1.128/25, configure the address lease duration as five days, domain name 
suffix aabbcc.com, DNS server address 10.1.1.2/25, and gateway address 10.1.1.254/25, and 
there is no WINS server address. 
•   The domain name and DNS server address on subnets 10.1.1.0/25 and 10.1.1.128/25 are the same. 
Therefore, the domain name suffix and DNS server address can be configured only for subnet 
1 0 .1.1. 0 / 2 4 .  S u b n e t  1 0 .1.1.12 8 / 2 5  c a n  i n h e r i t  t h e  c o n f i g u r a t i o n  o f  s u b n e t  1 0 .1.1. 0 / 2 4 .  
Figure 30  Network diagram 
 
 
Configuration procedure 
1. Specify IP addresses for VLAN interfaces. (Details not shown.) 
2. Configure the DHCP server: 
# Enable DHCP. 
 system-view 
[SwitchA] dhcp enable 
# Enable the DHCP server on VLAN-interface 1 and VLAN-interface 2. 
[SwitchA] interface vlan-interface 1 
[SwitchA-Vlan-interface1] dhcp select server global-pool 
[SwitchA-Vlan-interface1] quit 
[SwitchA] interface vlan-interface 2 
[SwitchA-Vlan-interface2] dhcp select server global-pool 
[SwitchA-Vlan-interface2] quit 
# Exclude IP addresses (addresses of the  DNS server, WINS server and gateways). 
[SwitchA] dhcp server forbidden-ip 10.1.1.2 
[SwitchA] dhcp server forbidden-ip 10.1.1.4 
WINS server
10.1.1.4/25
Client
Switch BClient
DNS server
10.1.1.2/25
Switch A
DHCP server
Vlan-int2
10.1.1.129/25
Vlan-int1
10.1.1.1/25
ClientClient
ClientClient
Vlan-int1
Gateway B
Gateway A
10.1.1.126/25 10.1.1.254/25
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[SwitchA] dhcp server forbidden-ip 10.1.1.126 
[SwitchA] dhcp server forbidden-ip 10.1.1.254 
# Configure DHCP address pool 0 (subnet, client domain name suffix, and DNS server address). 
[SwitchA] dhcp server ip-pool 0 
[SwitchA-dhcp-pool-0] network 10.1.1.0 mask 255.255.255.0 
[SwitchA-dhcp-pool-0] domain-name aabbcc.com 
[SwitchA-dhcp-pool-0] dns-list 10.1.1.2 
[SwitchA-dhcp-pool-0] quit 
# Configure DHCP address pool 1 (subnet, gateway, lease duration, and WINS server). 
[SwitchA] dhcp server ip-pool 1 
[SwitchA-dhcp-pool-1] network 10.1.1.0 mask 255.255.255.128 
[SwitchA-dhcp-pool-1] gateway-list 10.1.1.126 
[SwitchA-dhcp-pool-1] expired day 10 hour 12 
[SwitchA-dhcp-pool-1] nbns-list 10.1.1.4 
[SwitchA-dhcp-pool-1] quit 
# Configure DHCP address pool 2 (subnet, gateway, and lease duration). 
[SwitchA] dhcp server ip-pool 2 
[SwitchA-dhcp-pool-2] network 10.1.1.128 mask 255.255.255.128 
[SwitchA-dhcp-pool-2] expired day 5 
[SwitchA-dhcp-pool-2] gateway-list 10.1.1.254 
Verifying the configuration 
A f t e r  t h e  p r e c e d i n g  c o n f i g u r a t i o n  i s  c o m p l e t e ,  c l i e n t s  o n  n e t w o r k s  1 0 .1.1. 0 / 2 5  a n d  1 0 .1.1.12 8 / 2 5  c a n  
obtain IP addresses on the corresponding network and  other network parameters from Switch A. You can 
use the  display dhcp server ip-in-use command on the DHCP server to view the IP addresses assigned to 
the clients. 
Self-defined option configuration example 
Network requirements 
As shown in  Figure 31, the D HCP client (Switch B) obtains an IP address and PXE server addresses from 
the DHCP server (Switch A). The IP address belongs to subnet 10.1.1.0/24. The PXE server addresses are 
1. 2.3. 4  a n d  2. 2. 2. 2.  
The DHCP server assigns PXE server addresses to DHCP clients through Option 43, a self-defined option. 
The format of Option 43 and that of the PXE server address sub-option are shown in  Figure 19 and Figure 
21 , r

espectively. The value of Option 43 configured on the DHCP server in this example is 80 0B 00 00 
02 01 02 03 04 02 02 02 02. The number 80 is the value of the sub-option type. The number 0B is the 
value of the sub-option length. The numbers 00 00 are the value of the PXE server type. The number 02 
indicates the number of servers. The numbers 01 02 03 04 02 02 02 02 indicate that the PXE server 
addresses are 1.2.3.4 and 2.2.2.2. 
Figure 31  Network diagram
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Configuration procedure 
1. Specify IP addresses for the interfaces. (Details not shown.) 
2. Configure the DHCP server: 
# Enable DHCP. 
 system-view 
[SwitchA] dhcp enable 
# Enable the DHCP server on VLAN-interface 2. 
[SwitchA] interface vlan-interface 2 
[SwitchA-Vlan-interface2] dhcp select server global-pool 
[SwitchA-Vlan-interface2] quit 
# Configure DHCP address pool 0. 
[SwitchA] dhcp server ip-pool 0 
[SwitchA-dhcp-pool-0] network 10.1.1.0 mask 255.255.255.0 
[SwitchA-dhcp-pool-0] option 43 hex 80 0B 00 00 02 01 02 03 04 02 02 02 \
02 
Verifying the configuration 
After the preceding configuration is complete, Switch B can obtain its IP address on 10.1.1.0/24 and PXE 
server addresses from the Switch A. You can use the  display dhcp server ip-in-use command on the 
DHCP server to view the IP addresses assigned to the clients. 
Troubleshooting DHCP server configuration 
Symptom 
A client’s IP address obtained from the DHCP server conflicts with another IP address. 
Analysis 
A host on the subnet may have the same IP address. 
Solution 
1.  Disable the client’s network adapter  or disconnect the client’s network cable. Ping the IP address 
of the client from another host to check whether there is a host using the same IP address. 
2.  If a ping response is received, the IP address ha s been manually configured on a host. Execute the 
dhcp server forbidden-ip command on the DHCP server to exclude the IP address from dynamic 
allocation. 
3.  Enable the network adapter or connect the network  cable. For example, to release the IP address 
and obtain another one on a Windows XP client: 
a.  Run  cmd to enter DOS window.  
b. Type  ipconfig/release  to relinquish the IP address. 
c. Type  ipconfig/renew  to obtain another IP address.
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Configuring DHCP relay agent 
The DHCP relay agent configuration is supported only on Layer 3 Ethernet ports, Layer 3 aggregate 
interfaces, and VLAN interfaces. 
The term interface in the DHCP features refers to Layer 3 interfaces, including VLAN interfaces and 
route-mode (or Layer 3) Ethernet ports. You can set an  Ethernet port to operate in route mode by using the 
port  link-mode  route  command (see the  Layer 2—LAN Switching Configuration Guide ). 
Only HP 5500 EI switches support Layer 3 Ethernet port configuration. 
Overview 
Via a relay agent, DHCP clients can communicate with a DHCP server on another subnet to obtain 
configuration parameters. DHCP clients on different subnets can contact the same DHCP server rather 
than having a DHCP server on each subnet. This centralizes management and reduces cost reduction. 
An MCE device serving as the DHCP relay agent can forward DHCP packets not only between a DHCP 
server and clients on a public network, but also betw een a DHCP server and clients on a private network. 
Note that the IP address ranges of the public and pr ivate networks or those of private networks cannot 
overlap each other. For more information about MCE, see  Layer 3—IP Routing Configuration Guide. 
Fundamentals 
Figure 32 DHCP relay agent application 
 
 
The DHCP server and client interact with each other in the same way with or without a relay agent (see 
DHCP overview )
 .
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Figure 33 DHCP relay agent work process 
 
 
1. After receiving a DHCP-DISCOVER or DHCP-REQUE ST broadcast message from a DHCP client, 
the DHCP relay agent fills the giaddr field of th e message with its IP address and forwards the 
message to the designated DHCP server in unicast mode. 
2.  Based on the giaddr field, the DHCP server  returns an IP address and other configuration 
parameters to the relay agent, and the relay agent conveys them to the client. 
DHCP relay agent support for Option 82 
Option 82 records location information of the DHCP  client, letting the administrator locate the DHCP 
client for security control and accounting purposes. For more information, see DHCP overview  
If the D

HCP relay agent supports Option 82, it handles a client’s request according to the contents 
defined in Option 82, if any. The handling strategies are described in  Tabl e  3.  
If a r

eply returned by the DHCP server contains Option 82, the DHCP relay agent removes the Option 82 
before forwarding the reply to the client. 
Table 3  Handling strategies of the DHCP relay agent 
If a client’s 
requesting 
messa
ge has…  Handling 
strategy 
Padding format  The DHCP relay agent will… 
Option 82  Drop  Random  Drop the message. 
Keep Random 
Forward the message without changing 
Option 82. 
Replace normal 
Forward the message after replacing the 
original Option 82 with the Option 82 
padded in normal format. verbose Forward the message after replacing the 
original Option 82 with the Option 82 
padded in verbose format. 
user-defined Forward the message after replacing the 
original Option 82 with the user-defined 
Option 82. 
no Option 82  N/A 
normal Forward the message after adding the 
Option 82 padded in normal format.
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If a client’s 
requesting 
messa
ge has… Handling 
strategy 
Padding format  The DHCP relay agent will… 
N/A verbose  Forward the message after adding the 
Option 82 padded in verbose format. 
N/A user-defined Forward the message after adding the 
user-defined Option 82. 
 
DHCP relay agent configuration task list 
 
Task Remarks 
Enabling DHCP 
Required 
Enabling the DHCP relay agent on an interface Required 
Correlating a DHCP server group with a relay agent interface  Required 
Configuring the DHCP relay agent security functions  Optional 
Enabling offline detection Optional 
Configuring the DHCP relay agent to release an IP address Optional 
Configuring the DHCP relay agent to support Option 82 Optional 
Setting the DSCP value for DHCP packets Optional 
 
Enabling DHCP 
Enable DHCP before performing other configurations related to the DHCP relay agent. 
To enable DHCP: 
 
Step Command Remarks 
1.   Enter system view. 
system-view  N/A 
2.  Enable DHCP. 
dhcp enable  Disabled by default 
 
Enabling the DHCP relay agent on an interface 
With the DHCP relay agent enabled, an interface fo rwards incoming DHCP requests to a DHCP server 
for address allocation. 
The IP address pool containing the IP address of the DHCP relay agent enabled interface must be 
configured on the DHCP server. Otherwise, the DHCP clients connected to the relay agent cannot obtain 
correct IP addresses. 
To enable the DHCP relay agent on an interface: 
 
Step Command Remarks 
1.   Enter system view. 
system-view  N/A
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