Книга: Windows Server 2012 R2 Storage, Security, & Networking Pocket Consultant

Understanding scopes

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Understanding scopes

Scopes are pools of IPv4 or IPv6 addresses you can assign to clients through leases. DHCP also provides a way to permanently assign a lease on an address. To do this, you need to create a reservation by specifying the IPv4 address to reserve and the media access control (MAC) address of the computer that will hold the IPv4 address. The reservation thereafter ensures that the client computer with the specified MAC address always gets the designated IPv4 address. With IPv6, you can specify that a lease is temporary or nontemporary. A nontemporary lease is similar to a reservation.

You create scopes to specify IP address ranges that are available for DHCP clients. For example, you could assign the IP address range 192.168.12.2 to 192.168.12.250 to a scope called Enterprise Primary. Scopes can use public or private IPv4 addresses on the following networks:

? Class A networks IP addresses from 1.0.0.0 to 126.255.255.255

? Class B networks IP addresses from 128.0.0.0 to 191.255.255.255

? Class C networks IP addresses from 192.0.0.0 to 223.255.255.255

? Class D networks IP addresses from 224.0.0.0 to 239.255.255.255

NOTE The IP address 127.0.0.1 is used for local loopback (and so are any other IP addresses in the 127.x.y.z address range).

Scopes can also use link-local unicast, global unicast, and multicast IPv6 addresses. Link-local unicast addresses begin with FE80. Multicast IPv6 addresses begin with FF00. Global (site-local) unicast addresses include all other addresses except:: (unspecified) and::1 (loopback) addresses.

A single DHCP server can manage multiple scopes. With IPv4 addresses, four types of scopes are available:

? Normal scopes Used to assign IPv4 address pools for class A, B, and C networks.

? Multicast scopes Used to assign IP address pools for IPv4 class D networks. Computers use multicast IP addresses as secondary IP addresses in addition to a standard IP address.

? Superscopes Containers for other scopes that are used to simplify management of multiple scopes and also support DHCP clients on a single physical network where multiple logical IP networks are used.

? Failover scopes Scopes split between two DHCP servers to increase fault tolerance, provide redundancy, and enable load balancing.

With IPv6, only normal scopes are available. Although you can create scopes on multiple network segments, you’ll usually want these segments to be in the same network class, such as all IP addresses that are class C.

TIP Don’t forget that you must configure DHCPv4 and DHCPv6 relays to relay DHCPv4 and DHCPv6 broadcast requests between network segments. You can configure relay agents with the Routing and Remote Access Service (RRAS) and the DhCP Relay Agent Service. You can also configure some routers as relay agents. These services can be installed as part of the Remote Access role. On a server with no other policy and access role services configured, you can install the Remote Access role by using the Add Roles And Features Wizard.

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