Dhcp Packet Format And Options - Dell PowerEdge M IO Aggregator Command Reference Manual

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 parameters that servers must provide, hosts specify the parameters that
they require, and the server sends only those; some common options are given in
Figure 7-1. DHCP Packet Format
op htype hlen
Table 7-1. Common DHCP Options
Option
Subnet Mask
Router
Domain Name Server
Domain Name
IP Address Lease Time
DHCP Message Type
Parameter Request List
Renewal Time
Rebinding Time
End
84 | Dynamic Host Configuration Protocol (DHCP)
xid flags
hops secs
Code Description
1 Specifies the clients subnet mask.
3 Specifies the router IP addresses that may serve as the client's default
gateway.
6 Specifies the DNS servers that are available to the client.
15 Specifies the domain name that client should use when resolving hostnames
via DNS.
51 Specifies the amount of time that the client is allowed to use an assigned IP
address.
53 1: DHCPDISCOVER
2: DHCPOFFER
3: DHCPREQUEST
4: DHCPDECLINE
5: DHCPACK
6: DHCPNACK
7: DHCPRELEASE
8: DHCPINFORM
55 Clients use this option to tell the server which parameters it requires. It is a
series of octets where each octet is DHCP option code.
58 Specifies the amount of time after the IP address is granted that the client
attempts to renew its lease with the original server.
59 Specifies the amount of time after the IP address is granted that the client
attempts to renew its lease with any server, if the original server does not
respond.
255 Signals the last option in the DHCP packet.
ciaddr siaddr giaddr
yiaddr
Table 7-1.
chaddr sname file options
Code Length Value