Users Guide

NOTE: Management routes added by the DHCP client include the specific routes to reach a DHCP server in a different subnet
and the management route.
DHCP Client on a VLAN
The following conditions apply on a VLAN that operates as a DHCP client:
• The default VLAN 1 with all ports auto-configured as members is the only L3 interface on the Aggregator.
• When the default management VLAN has a DHCP-assigned address and you reconfigure the default VLAN ID number, the Aggregator:
• Sends a DHCP release to the DHCP server to release the IP address.
• Sends a DHCP request to obtain a new IP address. The IP address assigned by the DHCP server is used for the new default
management VLAN.
DHCP Packet Format and Options
DHCP uses the user datagram protocol (UDP) as its transport protocol.
The server listens on port 67 and transmits to port 68; the client listens on port 68 and transmits to port 67. The configuration parameters
are carried as options in the DHCP packet in Type, Length, Value (TLV) format; many options are specified in RFC 2132. To limit the
number of parameters that servers must provide, hosts specify the parameters that they require, and the server sends only those
parameters. Some common options are shown in the following illustration.
Figure 6. DHCP packet Format
The following table lists common DHCP options.
Option
Number and Description
Subnet Mask Option 1
Specifies the client’s subnet mask.
Router Option 3
Specifies the router IP addresses that may serve as the client’s default gateway.
Domain Name
Server
Option 6
Specifies the domain name servers (DNSs) that are available to the client.
Domain Name Option 15
Specifies the domain name that clients should use when resolving hostnames via DNS.
IP Address Lease
Time
Option 51
Specifies the amount of time that the client is allowed to use an assigned IP address.
74 Dynamic Host Configuration Protocol (DHCP)