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Chapter 2 - TCP/IP Concepts

Introduction

Internet Protocol - IP
Internet Control Message Protocol - ICMP
Transmission Control Protocol - TCP
User Datagram Protocol - UDP

Address Resolution
TCP/IP Options and VINES

Note: This chapter is mainly background conceptual material designed to give network administrators with little background in TCP/IP the information they require to construct a TCP/IP network. If you are a very experienced TCP/IP network manager, and you have a firm knowledge of how TCP/IP works, you can skip this chapter.

Internet Protocol

Addressing Packets

Figure 2-1. Addressing Packets

Figure 2-2. Sample IP Packet

Decimal Dot Notation

160.134.1.1

Figure 2-3. Sample IP Address in Decimal Dot Notation

255.255.0.0

Figure 2-4. Sample Subnetwork Mask in Decimal Dot Notation

IP Addressing

All IP addresses have a network ID and a host ID. Some IP addresses also have a subnetwork ID.
All network addresses used in a VINES network belong to one of three address classes: Class A, Class B, or Class C.
Each address has a corresponding subnetwork mask.

Networks, Subnetworks, and Hosts

1. Network ID. This number identifies the network in which the host or gateway resides. Class A, B, and C addresses are distinguished by the range of network numbers that they support.

2. Subnetwork ID. The subnetwork ID is optional. If used, it takes up a portion of the host ID. How many bits are used to specify subnetworks, and which bits are used, is specified by the subnetwork mask.

3. Host ID. This number uniquely identifies a host within a network, or within a subnetwork.

The IP address class
The subnetwork mask

IP Address Classes

Class A Addresses

Figure 2-5. Class A Address: 16.4.0.12

Class B Addresses

Figure 2-6. Class B Address: 144.133.1.13

Class C Addresses

Figure 2-7. Class C Address: 195.15.80.3

Subnetworks and Subnetwork Masks

Note: You actually control bit usage only for the subnetwork portion of the address, even though the mask also pertains to the network portion. This is because the size of the network ID field is predetermined by the IP address class.

Example 1 Class B Address 144.133.17.1 with No Subnetwork Field

Figure 2-8. Address 144.133.17.1 with No Subnetworks

Example 2 Class B Address 144.133.17.1 with 4-bit Subnetwork Field

Figure 2-9. Address 144.133.17.1 with Four Bits of Subnetwork

Example 3 Class B Address 144.133.17.1 with 8-bit Subnetwork Field

Figure 2-10. Address 144.133.17.1 with Eight Bits of Subnetwork

Specific Values for Subnetwork Masks

Table 2-1. Common Subnetwork Mask Values

IP Address Class No Subnetwork Field 4-bit Subnetwork Field 8-bit Subnetwork Field
Class A 255.0.0.0 255.240.0.0 255.255.0.0
Class B 255.255.0.0 255.255.240.0 255.255.255.0
Class C 255.255.255.0 255.255.255.240 Not supported

IP Addressing - An Example

Figure 2-11. Two Subnetworks of Network 160.134.1

Routing Packets

Figure 2-12. Server Acting as a Gateway

1. The gateway software looks at the destination address enclosed in the packet.

2. It compares the destination address in the packet with the gateway's own IP addresses.

3. If a match is found, the gateway keeps the packet. If not, the gateway knows that the packet is destined for a host or another gateway. It must then look in its routing table to determine how to route the packet.

Routing Table

All the IP interfaces on the gateway and their IP addresses.
The addresses of all the gateways that can be reached through each interface.
The addresses of destinations that can be reached through each gateway. Destinations can be either networks, subnetworks, or individual hosts or gateways.

Routing Table Decisions

A specific host route entry
A subnetwork route entry
The first matching network route

Routing Tables on Hosts

Figure 2-13. Network End Points

Routing Tables on Gateways

Figure 2-14. Sample Network with Three Gateways

Table 2-2. Routing Table for Gateway 1

Table 2-3. Routing Table for Gateway 2

Example Routing a Packet

1. The PC/TCP workstation addresses the packet to the UNIX workstation, and forwards the packet to Server 1.

2. After receiving the packet, Server 1 looks in its routing table:

Server 1 sees that the network address in the packet is for network 160.134.2, and forwards the packet to the foreign host gateway.

3. After receiving the packet, the Foreign Host Gateway looks in its routing table.

The Foreign Host Gateway forwards the packet to the UNIX workstation.

Figure 2-15. Server Forwarding a Packet

Fragmenting Packets

Internet Control Message Protocol

Transmission Control Protocol

User Datagram Protocol

Address Resolution

Proxy ARP

Direct Mapping

TCP/IP Options and VINES

Figure 2-16. VINES IP and IP in the VINES Architecture

Figure 2-17. Sample IP Backbone

TCP/IP Routing Option

Note: Throughout most of this discussion, the term "IP" is used instead of "TCP/IP." The routing functions discussed here apply to IP only. TCP is a transport layer protocol that does not perform routing.

Two VINES servers equipped with the TCP/IP Routing option
Workstations running VINES
One PC running PC/TCP from FTP Software, Inc.
Foreign hosts

Figure 2-18. Sample Network with Routing Option

PC/TCP

Workstations running the VINES Transport version of PC/TCP can reside anywhere in a VINES network.
Workstations running the Ethernet-only version must be on the same LAN as a VINES server running the VINES TCP/IP Routing option or a foreign host gateway.

Figure 2-19. Sample VINES Network

Note: ln examples that follow, PC/TCP enables workstations to reside anywhere in the VINES network.

The names (or serial numbers) of all servers in the VINES network that have the TCP/IP Routing option, their IP addresses, and IP destinations reachable through them. These gateways are associated with the interface to the VINES network.
The interfaces to physical media that connect the server directly to foreign host gateways, the IP addresses of the gateways, and IP destinations reachable through them.
The interface to VINES with a unique IP address, if the server provides routing services to workstations equipped with the VINES Transport version of PC/TCP.

Encapsulation and TCP/IP Routing

Figure 2-20. Routing an IP Packet Without Encapsulation

Figure 2-21. Encapsulating an IP Packet in a VINES IP Packet

1. The packet leaves Foreign Host 1 as an IP packet.

2. When the packet arrives at Server 1, the IP packet is encapsulated in a VINES IP packet (that is, a VINES header is added). The packet is then routed through VINES to Server 2.

Note: When encapsulated, the IP packet is treated as user data in the VINES IP packet.

3. When the packet arrives at Server 2, the VINES IP header is stripped off. The packet is then routed to its destination via IP.

Network Addressing and TCP/IP Routing

TCP/IP Server-to-Server Option

Figure 2-22. Sample Network with Routing and Server-to-Server Options

Encapsulation and the TCP/IP Server-to-Server Option

1. Workstation 1 sends a VINES packet to Server 1.

2. Server 1 encapsulates the VINES packet in an IP packet, and routes the packet to Foreign Host Gateway 1.

3. Foreign Host Gateway 1 routes the packet to Server 2.

4. Server 2 strips off the IP header, then routes the remaining VINES IP packet to Workstation 2.

Figure 2-23. Routing VINES Packets Through an IP Network

Network Addressing and the TCP/IP Server-to-Server Option

The destination server. In this case, the destination server must be running the TCP/IP Server-to-Server option.
A VINES gateway server that runs the TCP/IP Server-to-Server option and acts as a gateway to the destination server. This server will strip the IP header and route the remaining packet to its destination through VINES.

Figure 2-24. Addressing Services for Routing a VINES IP Packet

Note: It is recommended that only servers that share a physical interface with a foreign host gateway be chosen to route VINES traffic across an IP backbone. In Figure 2-24, Server 2 and Server 3 are configured with the TCP/IP Server-to-Server option. All other servers in the network use the services of either Server 2 or Server 3 to route traffic across Foreign Host Gateway 1.

Table 2-4. Required Options for Servers in Figure 2-24

To reach Server 1, it must route through Server 2.
To reach Server 2, it must route through an IP backbone.
Server 2's IP address is 160.134.1.2.

The packet contains VINES data.
The packet is destined for Server 1.

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