In tcp/ip which protocol is the routing protocol

To pass on information, the gateway receives datagrams through one network interface and sends them out through the other network interface. Gateways periodically verify their network connections through interface status messages.

Gateways route packets according to the destination network, not according to the destination host. That is, a gateway machine is not required to keep track of every possible host destination for a packet. Instead, a gateway routes packets according to the network of the destination host. The destination network then takes care of sending the packet to the destination host. Thus, a typical gateway machine requires only limited disk storage capacity if any and limited main memory capacity.

The distance a message must travel from originating host to destination host depends upon the number of gateway hops it must make. A gateway is zero hops from a network to which it is directly attached, one hop from a network that is reachable through one gateway, and so on.

Message distance is usually expressed in the number of gateway hops required, or hop counts also called the metric. Interior gateways are gateways that belong to the same autonomous system. Exterior gateways belong to different autonomous systems. For example, consider two autonomous systems. The first is all the networks administered by the Widget Company.

The second is all the networks administered by the Gadget Company. The Widget Company has one machine, called apple, which is Widget's gateway to the Internet. The Gadget Company has one machine, called orange, which is Gadget's gateway to the Internet. Both companies have several different networks internal to the companies.

The gateways connecting the internal networks are interior gateways. But apple and orange are exterior gateways. Each exterior gateway does not communicate with every other exterior gateway. Instead, the exterior gateway acquires a set of neighbors other exterior gateways with which it communicates. These neighbors are not defined by geographic proximity, but rather by their established communications with each other.

The neighboring gateways, in turn, have other exterior gateway neighbors. In fact, it is really much easier to understand routing protocols once you have a good background on the entire process of routing. You may notice that in the title of this section I refer to both routing protocols and gateway protocols.

These terms are interchangeable, and in fact, the word gateway appears in the name of several of the protocols. Today, the term gateway normally refers not to a router, but to a different type of network interconnection device, so this can be particularly confusing. Note: Some of the protocols in this section are generic enough that they could be applied to support the routing of any network layer protocol. Also, this section focuses primarily on the routing protocols used in Internet Protocol version 4.

There is limited discussion of IPv6 versions of the protocols at this time. Note: Strictly speaking, an argument could be made that some routing protocols don't belong in layer three.

Despite this, routing is inherently a layer three activity and for this reason, it is traditional to consider routing protocols part of layer three. Note: Like all topics related to routing, routing protocols are generally quite complex. I cover the major ones here in more detail than most general networking references, but even so, you should recognize that I am only scratching the surface, especially of the more complicated ones like OSPF.

The subnet mask that specifies 16 bits of subnetting for Class A address Both of these subnet masks are pictured in Figure 5. Subnet masks can be passed through a network on demand so that new nodes can learn how many bits of subnetting are being used on their network. Traditionally, all subnets of the same network number used the same subnet mask.

In other words, a network manager would choose an eight-bit mask for all subnets in the network. This strategy is easy to manage for both network administrators and routing protocols. However, this practice wastes address space in some networks.

Some subnets have many hosts and some have only a few, but each consumes an entire subnet number. Serial lines are the most extreme example, because each has only two hosts that can be connected via a serial line subnet.

As IP subnets have grown, administrators have looked for ways to use their address space more efficiently. With VLSM, a network administrator can use a long mask on networks with few hosts and a short mask on subnets with many hosts. However, this technique is more complex than making them all one size, and addresses must be assigned carefully. Of course in order to use VLSM, a network administrator must use a routing protocol that supports it.

ARP uses broadcast messages to determine the hardware MAC layer address corresponding to a particular network-layer address. ARP is sufficiently generic to allow use of IP with virtually any type of underlying media access mechanism. RARP uses broadcast messages to determine the network-layer address associated with a particular hardware address. RARP is especially important to diskless nodes, for which network-layer addresses usually are unknown at boot time.

An "internet" is a group of interconnected networks. The Internet, on the other hand, is the collection of networks that permits communication between most research institutions, universities, and many other organizations around the world. Credits Transactions Credits: 0.

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