HP 5500 Ei 5500 Si Switch Series Configuration Guide

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Step Command Remarks 
2.  Enter interface view.  interface
 interface-type 
interface-number   N/A 
3.
  Enable the DHCP relay agent 
on the current interface.  dhcp select
 relay  With DHCP enabled, interfaces 
operate in the DHCP server mode.
 
 
Correlating a DHCP server group with a relay 
agent interface 
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 gr
oup. When the interface receives...

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Configuring the DHCP relay agent security 
functions 
Configuring address check 
Address check can block illegal hosts from accessing external networks.  
With this feature enabled, the DHCP relay agent can dynamically record clients’ IP-to-MAC bindings 
after they obtain IP addresses through DHCP. This feature also supports static bindings. You can also 
configure static IP-to-MAC bindings on the DHCP relay agent, so users can access external networks 
using fixed IP addresses. 
Upon receiving a...

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When this feature is enabled, the DHCP relay agent uses the IP address of a client and the MAC address 
o f  t h e  D H C P  r e l a y  i n t e r f a c e  t o  s e n d  a  D H C P- R E Q U EST  m essage to the DHCP server at specified intervals.   
•   If the server returns a DHCP-ACK message or does not return any message within a specified 
interval, the DHCP relay agent ages out the entry. 
•   If the server returns a DHCP-NAK message, the relay agent keeps the entry. 
To configure periodic...

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•  To prevent a DHCP starvation attack that uses DH CP requests encapsulated with the same source 
MAC address, enable MAC address check on the DHCP relay agent. With this function enabled, 
the DHCP relay agent compares the chaddr field of a received DHCP request with the source MAC 
address field of the frame. If they are the same, the DHCP relay agent decides this request as valid 
and forwards it to the DHCP server; if  not, it discards the DHCP request. 
To enable MAC address check: 
 
Step...

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To configure the DHCP relay agent to send DHCP-RELEASE messages:  
Step Command Remarks 
1.  Enter system view. 
system-view N/A 
2.  Configure the DHCP relay agent to 
release an IP address.  dhcp relay release ip
 client-ip The IP address must be in a 
dynamic client entry. 
 
Configuring the DHCP relay agent to support 
Option 82 
Configuration prerequisites 
Before you perform this configuration, complete the following tasks: 
•   Enable DHCP. 
•   Enable the DHCP relay agent on the specified...

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Step Command Remarks 
5.  Configure 
non-user-defined 
Option 82. 
• Configure the padding format for 
Option 82: 
dhcp  relay  information  format 
{  normal  | verbose  [ node-identifier  
{  mac  | sysname  | user -defined  
node-identifier  } ] } 
• Configure the code type for the 
circuit ID sub-option:  
dhcp relay information circuit-id 
format-type  { ascii  | hex  } 
• Configure the code type for the 
remote ID sub-option: 
dhcp relay information remote-id 
format-type  { ascii  | hex  }...

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Task Command Remarks 
Display statistics about bindings of 
DHCP relay agents. display dhcp relay security
 statistics  [ | 
{  begin |  exclude | include  } 
regular-expression  ]  Available in any view
 
Display information about the 
refreshing interval for entries of 
dynamic IP-to-MAC bindings.  display dhcp relay security 
tracker [ | { begin  
|  exclude  | include  } regular-expression ]  Available in any view
 
Display information about the 
configuration of a specified DHCP 
server group...

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Configurations on the DHCP server are also required to guarantee the client-server communication via 
the DHCP relay agent. For DHCP server configuration information, see  Configuring DHCP server. 
# S

pecify IP addresses for the interfaces. (Details not shown.) 
# Enable DHCP. 
 system-view 
[SwitchA] dhcp enable 
#  A d d  D H C P  s e r v e r  1 0 .1.1.1  i n t o  D H C P  s e r v e r  g r o u p  1.  
[SwitchA] dhcp relay server-group 1 ip 10.1.1.1 
# Enable the DHCP relay agent on...

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[SwitchA-Vlan-interface1] dhcp relay information enable 
[SwitchA-Vlan-interface1] dhcp relay information strategy replace 
[SwitchA-Vlan-interface1] dhcp relay information circuit-id string compa\
ny001 
[SwitchA-Vlan-interface1] dhcp relay information remote-id string device\
001 
Troubleshooting DHCP relay agent configuration 
Symptom 
DHCP clients cannot obtain any configuration parameters via the DHCP relay agent. 
Analysis 
Problems may occur with the DHCP relay agent or server configuration....

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Configuring DHCP client 
With DHCP client enabled, an interface uses DHCP to obtain configuration parameters such as an IP 
address from the DHCP server. 
Configuration restrictions 
•  The DHCP client configuration is supported only on Layer 3 Ethernet ports, Layer 3 aggregate 
interfaces, and 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 Server 2000 or Windows Server 2003....