741 Chapter 4: Implementing DHCP

hot standby mode

A DHCP failover mode in which one server is assigned as the active server to provide DHCP services to clients and the other server is placed in standby mode.

DHCP filters

A DHCP server feature that allows administrators to restrict which computers on a network are leased UP addresses

conflict detection

A DHCP server property that causes the DHCP server to attempt to ping an IP address before it's offered to a client to ensure that the address isn't already in use

name squatting

A DNS problem that occurs when a non-Windows computer registers its name with a DNS server, but that name has already been registered by a Windows computer

Dynamic Host Configuration Protocol (DHCP)

A component of the TCP/IP protocol suite used to assign an IP address to a host automatically from a defined pool of addresses

User class

A custom value you create on the DHCP server and then configure on a DHCP client

DHCP relay agent

A device that listens for broadcast DHCPDISCOVER and DHCPREQUEST messages and forwards them to a DHCP server on another subnet

split scope

A fault-tolerant DHCP configuration in which two DHCP servers share the same scope information, allowing both servers to offer DHCP services to clients.

DHCP name protection

A feature in DHCP that prevents name squatting by non-Windows computers by using the DHCP resource record Dynamic Host Configuration Identifier (DHCID)

DHCP failover

A feature in Windows Server 2016 that allows two DHCP servers to share the pool of IP addresses in a scope, giving both servers access to all addresses in the pool.

DHCP policies

A feature in Windows Server 2016 that gives administrators more fine-tuned control over IP address lease options with conditions based on criteria

DHCPACK

Fourth packet in sequence for DHCP address assignment. Server that made the offer acknowledges the transaction and sends any other requested IP params to the client.

Preboot Execution Environment (PXE)

A network environment built into many NICs that allows a computer to boot from an image stored on a network server

lease duration

A parameter o the DHCP IP address lease that specifies how long a DHCP client an keep an address

superscope

A special type of scope consisting of one or more member scopes; it allows a DHCP server to service multiple IP subnets on a single physical network

multicast scope

A type of DHCP scope that allows assigning multicast addresses dynamically to multicast servers and clients by using Multicast Address Dynamic Client Allocation Protocol (MADCAP)

Two ranges of multicast addresses you can use to create a multicast scope

Administrative scopes- Composed of multicast addresses intended to be used in a private network (must contain at least 256 addresses) Global scopes- Multicast application is used across the public internet. No minimum number of addresses.

003 router

Almost always requested by client and supplied by server b/c it configures the client's default gateway setting

reservation

An IP address associated with a DHCP client's MAC address to ensure that when the client requests an IP address, it always gets the same one along with any configured options

DHCPDISCOVER

First packet in sequence for DHCP address assignment. The client transmits a broadcast packet via UDP source port 68/destination port 67 asking for IP address.

Reasons why you would want to have shorter lease times

An unpredictable environment where many computers are used for brief periods and then not used again for long periods A wireless network in a public setting where mobile devices come and go constantly If you're planning on making changes to the IP addressing scheme that requires a major scope change

Troubleshooting IP address conflicts

Can happen if there is a rogue DHCP server on the network or if the database needs to be reconciled. Ensure that exclusions are created for statically assigned addresses.

exclusion ranges

Certain addresses or range of addresses that are excluded from the DHCP scope for use in static address assignments

Troubleshooting a client receiving an incorrect DHCP address.

Check to see if another DHCP server is operating on the subnet

How to configure DHCP when a network has multiple subnets

Configure a DHCP server for each subnet Configure a single DHCP server with network interfaces connected to each subnet and scopes defined for each subnet Configure DHCP relay agents on subnets that don't have a DHCP server

DHCPINFORM

DHCP client which already has an IP address can use this message to request more information from the server.

policy options

DHCP policies allow an administrator to assign IP address options to clients based on client properties, such as device type, MAC address, or OS. DHCP policies are discussed later in "Configuring Policies." Options specified at the policy level can be overridden only by reservation options.

Reasons why a renewal request might fail

If the requested address has been deleted or deactivated from scope If the server doesn't respond

044 WINS/NBNS Servers

Only used on networks with WINS Servers

060 PXEClient

Option required for some configurations of WDS

DHCP scope

Pool of IP addresses and optionally other IP configuration parameters from which a DHCP server leases addresses to DHCP clients

015 DNS Domain Name

Provides a domain name, such as csmtech.local, to DHCP clients. The DNS Domain Name option configures the client domain name, which a client needs when performing a DNS query with a single-label name. Unnecessary if all computers receiving DHCP are domain members.

DHCPOFFER

Second packet in sequence for DHCP address assignment. DHCP server responds with an offer of IP/subnet mask from pool of addresses and is broadcast on source port 67 and destination port 68.

006 DNS Servers

The DNS Servers option consists of a list of IP addresses of DNS servers the client can use for name resolution.

load-balancing mode

The default DHCP failover mode in which both DHCP servers participate in address leasing at the same time from a shared pool of addresses.

maximum client lead time

The maximum amount of time a DHCP server can extend a lease for a DHCP client without the partner server's knowledge. It also defines the amount of time a server waits before assuming control over all DHCP services if its partner is in Partner Down state.

DHCP server authorization

The process of enabling a DHCP server in a domain environment to prevent rogue DHCP servers from operating on the network

DHCPREQUEST

Third packet in sequence for DHCP address assignment. The client responds by requesting the offered address. Possible for multiple offers to be made to the client from different servers but it will only accept one.

DHCP troubleshooting tools

Third-party protocol analyzer (Wireshark) Built-in DHCP audit logging feature

Troubleshooting no addresses being leased

Verify service is running, authorized, scope is activated and addresses are available in that scope.

Troubleshooting a client not receiving a DHCP address

Verify the DHCP service is running, authorized, scope is activated, and addresses are available in that scope If a client moved to a new subnet but had a reservation for the old one, it will not work.

Vendor Class

a field in the DHCP packet that device manufacturers or OS vendors can use to identify a device model or an OS version

lease renewal

the process of a DHCP client renewing its IP address lease by using unicast DHCPREQUEST messages. Packet 1-DHCPREQUEST: Client sends request to server when the lease is 50% expired Packet 2- DHCPACK- If server responds and can honor request, sends unicast packet ot client granting and awkknowledging the renewal requset