Intersegment packet routing

The addressing method depicted in Figure 4-9 is used when the two nodes reside on the same physical segment (or ring) or if they reside on separate segments interconnected by repeaters or bridges.

If the two nodes have different network numbers (reside on different network segments), the sending node must find a router on its own segment that can forward packets to the destination node's network segment. To find this router, the workstation broadcasts a RIP packet requesting the fastest route to the destination node's network number. This RIP request is responded to by the router residing on the sending node's segment with the shortest path to the desired segment; in the response, the router includes its node number.

Sending the packet

Once the sending node receives the router's node number, it is prepared to send packets to the destination node. The sending node addresses these packets by placing:

the node number of the router -- the one that responded to the RIP request -- in the destination address field of the MAC header.

its own node number in the source address field of the MAC header.

the destination node's IPX address (network, node and socket number) in the destination address fields of the IPX header.

its own IPX address in the source address fields of the IPX header.

Figure 4-10

Figure 4-10 Packet addressing through a router

Routing the packet

When a router receives a packet to be routed, it can take one of two possible actions. If the packet is destined for a network number to which the router is directly connected, the router will:

Place the destination node number from the IPX header in the destination address field of the MAC header.

Place its own node number in the source address field of the MAC header.

Transmit the packet.

Figure 4-10

Place the node number of that other router in the destination address field of the MAC header.

Place its own node number in the source address field of the MAC header.

Leave the IPX header as initially set by the sending node and sends the packet.

Network Access Protection Design Guide

Updated: October 6, 2008

Applies To: Windows 7, Windows Server 2008, Windows Server 2008 R2, Windows Vista

Network Access Protection (NAP) is one of the most anticipated features of the Windows Server� 2008 operating system. NAP is a new platform that allows network administrators to define specific levels of network access based on a client�s identity, the groups to which the client belongs, and the degree to which the client complies with corporate governance policy. If a client is not compliant, NAP provides a mechanism for automatically bringing the client into compliance (a process known as remediation) and then dynamically increasing its level of network access. NAP is supported by Windows Server 2008 R2, Windows Server 2008, Windows 7, Windows Vista�, and Windows� XP with Service Pack 3 (SP3). NAP includes an application programming interface that developers and vendors can use to integrate their products and leverage this health state validation, access enforcement, and ongoing compliance evaluation. For more information about the NAP API, see Network Access Protection (http://go.microsoft.com/fwlink/?LinkId=128423).

The following are key NAP concepts:

NAP Agent. A service included with Windows Server 2008, Windows Vista, and Windows XP with SP3 that collects and manages health information for NAP client computers.
NAP client computer. A computer that has the NAP Agent service installed and running, and is providing its health status to NAP server computers.
NAP-capable computer. A computer that has the NAP Agent service installed and running and is capable of providing its health status to NAP server computers. NAP-capable computers include computers running Windows Server 2008, Windows Vista, and Windows XP with SP3.
Non-NAP-capable computer. A computer that cannot provide its health status to NAP server components. A computer that has NAP agent installed but not running is also considered non-NAP-capable.
Compliant computer. A computer that meets the NAP health requirements that you have defined for your network. Only NAP client computers can be compliant.
Noncompliant computer. A computer that does not meet the NAP health requirements that you have defined for your network. Only NAP client computers can be noncompliant.
Health status. Information about a NAP client computer that NAP uses to allow or restrict access to a network. Health is defined by a client computer's configuration state. Some common measurements of health include the operational status of Windows Firewall, the update status of antivirus signatures, and the installation status of security updates. A NAP client computer provides health status by sending a message called a statement of health (SoH).
NAP health policy server. A NAP health policy server is a computer running Windows Server 2008 with the Network Policy Server (NPS) role service installed and configured for NAP. The NAP health policy server uses NPS policies and settings to evaluate the health of NAP client computers when they request access to the network, or when their health state changes. Based on the results of this evaluation, the NAP health policy server instructs whether NAP client computers will be granted full or restricted access to the network.