DHCP Messages
Table of Contents
10.1
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- Tap Interfaces
-
- Layer 2 and Layer 3 Packets over a Virtual Wire
- Port Speeds of Virtual Wire Interfaces
- LLDP over a Virtual Wire
- Aggregated Interfaces for a Virtual Wire
- Virtual Wire Support of High Availability
- Zone Protection for a Virtual Wire Interface
- VLAN-Tagged Traffic
- Virtual Wire Subinterfaces
- Configure Virtual Wires
- Configure an Aggregate Interface Group
- Configure Bonjour Reflector for Network Segmentation
- Use Interface Management Profiles to Restrict Access
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- DNS Overview
- DNS Proxy Object
- DNS Server Profile
- Multi-Tenant DNS Deployments
- Configure a DNS Proxy Object
- Configure a DNS Server Profile
- Use Case 1: Firewall Requires DNS Resolution
- Use Case 2: ISP Tenant Uses DNS Proxy to Handle DNS Resolution for Security Policies, Reporting, and Services within its Virtual System
- Use Case 3: Firewall Acts as DNS Proxy Between Client and Server
- DNS Proxy Rule and FQDN Matching
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- NAT Rule Capacities
- Dynamic IP and Port NAT Oversubscription
- Dataplane NAT Memory Statistics
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- Translate Internal Client IP Addresses to Your Public IP Address (Source DIPP NAT)
- Enable Clients on the Internal Network to Access your Public Servers (Destination U-Turn NAT)
- Enable Bi-Directional Address Translation for Your Public-Facing Servers (Static Source NAT)
- Configure Destination NAT with DNS Rewrite
- Configure Destination NAT Using Dynamic IP Addresses
- Modify the Oversubscription Rate for DIPP NAT
- Reserve Dynamic IP NAT Addresses
- Disable NAT for a Specific Host or Interface
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- Network Packet Broker Overview
- How Network Packet Broker Works
- Prepare to Deploy Network Packet Broker
- Configure Transparent Bridge Security Chains
- Configure Routed Layer 3 Security Chains
- Network Packet Broker HA Support
- User Interface Changes for Network Packet Broker
- Limitations of Network Packet Broker
- Troubleshoot Network Packet Broker
DHCP
Messages
DHCP uses eight standard message types, which are identified
by an option type number in the DHCP message. For example, when
a client wants to find a DHCP server, it broadcasts a DHCPDISCOVER
message on its local physical subnetwork. If there is no DHCP server
on its subnet and if DHCP Helper or DHCP Relay is configured properly,
the message is forwarded to DHCP servers on a different physical
subnet. Otherwise, the message will go no further than the subnet
on which it originated. One or more DHCP servers will respond with
a DHCPOFFER message that contains an available network address and
other configuration parameters.
When the client needs an IP address, it sends a DHCPREQUEST to
one or more servers. Of course if the client is requesting an IP
address, it doesn’t have one yet, so RFC 2131 requires that the broadcast
message the client sends out have a source address of 0 in its IP
header.
When a client requests configuration parameters from a server,
it might receive responses from more than one server. Once a client
has received its IP address, it is said that the client has at least
an IP address and possibly other configuration parameters bound to
it. DHCP servers manage such binding of configuration parameters
to clients.
The following table lists the DHCP messages.
DHCP Message | Description |
|---|---|
DHCPDISCOVER | Client broadcast to find available DHCP
servers. |
DHCPOFFER | Server response to client’s DHCPDISCOVER,
offering configuration parameters. |
DHCPREQUEST | Client message to one or more servers to
do any of the following:
|
DHCPACK | Server to client acknowledgment message
containing configuration parameters, including a confirmed network
address. |
DHCPNAK | Server to client negative acknowledgment
indicating the client’s understanding of the network address is
incorrect (for example, if the client has moved to a new subnet),
or a client’s lease has expired. |
DHCPDECLINE | Client to server message indicating the
network address is already being used. |
DHCPRELEASE | Client to server message giving up the user
of the network address and canceling the remaining time on the lease. |
DHCPINFORM | Client to server message requesting only
local configuration parameters; client has an externally configured
network address. |