Dhcp Packet Format And Options - Dell Force10 S4810P Configuration Manual

DHCP Packet Format and Options

DHCP uses UDP as its transport protocol. The server listens on port 67 and transmits to port 68; the client
listens on port 68 and dhcp snoopingtransmits 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; some common options are given in
Figure 15-1. DHCP Packet Format
htype
op
Table 15-1. 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
378
| Dynamic Host Configuration Protocol (DHCP)
hlen hops xid secs
Code
1
3
6
15
51
53
55
58
59
255
flags ciaddr yiaddr siaddr
Description
Specifies the client's subnet mask.
Specifies the router IP addresses that may serve as the client's default
gateway.
Specifies the DNS servers that are available to the client.
Specifies the domain name that clients should use when resolving hostnames
via DNS.
Specifies the amount of time that the client is allowed to use an assigned IP
address.
1: DHCPDISCOVER
2: DHCPOFFER
3: DHCPREQUEST
4: DHCPDECLINE
5: DHCPACK
6: DHCPNACK
7: DHCPRELEASE
8: DHCPINFORM
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.
Specifies the amount of time after the IP address is granted that the client
attempts to renew its lease with the original server.
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.
Signals the last option in the DHCP packet.
Table 15-1.
giaddr chaddr sname file
Code Length
options
Value