What layer is the routing protocol located in, and what is the core of the routing protocol?

The purpose of layering is to modularize complex functions that are easy to describe, easy to implement and maintain. It is generally believed that L3 is responsible for the Internetworking. For example, IP can realize the interconnection of global IP networks, and you only need an IP address.

That's where the problem comes in. All roads lead to Rome, how do you know which way to get to the IP you want to go to? So the dynamic routing protocol was invented and let it find its way.

But the dynamic routing protocol has its own packet.

table) is at the IP layer. If a node has a function, it will follow this table only when packets. But this ** table is not randomly generated, but learned by the dynamic routing protocol, or.

Generated by manually configured static routes. Therefore, the data structure of the table is at the IP layer, but the content is provided by the routing protocols.

If the message is wrapped in the order of zongzi, RIP and BGP can be regarded as the "application layer" because they are in the header of the transport layer. However, the purpose of layering was to distinguish the various functions (functionality) on the network, not to the number of layers of zongzi leaves. Therefore, a lot of literature counts the routing protocol in the network layer.

The concept of a control plane and a data plane has been proposed. The concept of facets is added to the original protocol layering. The process of packet representation and packaging belongs to the data plane

The third layer of the OSI. i.e. the network layer.

The routing protocols adopted by the Internet are mainly adaptive (i.e., dynamic) and distributed routing protocols. The Internet uses a hierarchical routing protocol for two reasons:

Dividing the entire Internet into many smaller autonomous systems is generally denoted as AS. An autonomous system as is a group of routers managed by a single technology that uses a routing protocol and common metrics within an autonomous system. An AS exhibits a single and consistent routing policy to the others.

In the current Internet, a large ISP is an autonomous system. In this way, the Internet divides routing protocols into two main categories, namely:

i) Interior Gateway Protocol (IGP) is a routing protocol used within an autonomous system, regardless of the routing protocol used by other autonomous systems on the Internet. Currently, such routing protocols are the most commonly used, such as RIP and OSPF.

2) External Gateway Protocol (EGP)If the source host and the destination host are in different autonomous systems (the two autonomous systems may use different internal gateway protocols), when the datagram is transmitted to the boundary of one autonomous system, it is necessary to use one protocol to pass the routing information to the other autonomous system. Such a protocol is the external gateway protocol EGP. The most commonly used external gateway protocol today is version 4 of BGP (BGP4).

Routing between autonomous systems is also called interdomain routing, while routing within an autonomous system is called intradomain routing.

Figure 4-31 shows a schematic diagram of the interconnection of two autonomous systems. Each autonomous system decides for itself which internal routing protocol (e.g., it can be RIP or OSP) to run within its own autonomous system. However, each autonomous system has one or more routers (r1 and r2 in the figure) that run the inter-autonomous system routing protocol (BGP4) in addition to the internal routing protocol of the system.

The core of the routing protocol is the routing algorithm, that is, what algorithm is needed to obtain the items in the routing table. An ideal routing algorithm should have the following characteristics: (1) The algorithm must be correct and complete.

Here, "correct" means that along the route guided by each routing table, the packet must eventually reach the destination network and destination host. (2) The algorithm should be simple in calculation.

The calculation of the routing should not add too much additional overhead to the network traffic. (3) The algorithm should be able to adapt to changes in traffic volume and network topology, that is, it should be adaptive. When the traffic volume in the network changes, the algorithm can adaptively change the route to balance the load of each link.

When one or some nodes or links fail to work, or are repaired and put into operation, the algorithm can also change the route in time. This adaptability is sometimes referred to as "robustness." 4) The algorithm should be stable.

When the network traffic and network topology are relatively stable, the routing algorithm should converge to an acceptable solution, rather than constantly changing the outgoing route. (5) The algorithm should be fair. The routing algorithm should be equal for all users except for a few with high priority.

For example, if the end-to-end latency of only one pair of users is minimized, but the other users are not considered, this obviously does not meet the requirements of fairness. (6) The algorithm should be optimal. The routing algorithm should be able to find the best route so that the average packet delay is the lowest and the network throughput is maximized.

While we want to get the "best" algorithm, it's not always the most important. For some networks, network reliability is sometimes more important than the minimum packet average latency or maximum throughput. Therefore, the so-called "best" can only be a more reasonable choice relative to a particular requirement.

Routing Information Protocol (RIP) is a standard for exchanging routing information between a gateway and a host.

OSPF (Open Shortest Path First) [1] is an Interior Gateway Protocol (IGP) that is used to make routing decisions within a single autonomous system (AS). In contrast to RIP, OSPF is a link-state routing protocol, while RIP is a distance vector routing protocol. OSPF's protocol management distance (AD) is 110.

In general, the routing protocol in daily life should be a simple RIP protocol.

The OSPF protocol is suitable for companies with large scales, large IP requirements, and many departments.

OSPF runs on IP and RIP runs on UDP, two are not the same concept !!

It's usually ospf, but that kind of router can't be seen (* hee-hee......

Routing protocols such as RIP, IGRP, EIGRP, OSPF, IS-IS, and BGP generate and maintain routing tables.

According to the working principle of the routing protocol, it can be divided into: distance vector routing protocol and link state routing protocol.

According to the scope of work, it can be divided into: internal gateway routing protocol and external gateway routing protocol.

According to whether the subnet mask is carried when the route is updated, it can be divided into: classified routing protocols and non-classified routing protocols.

There are quite a few of them, but the problem is protocol conversion, so you have to have clear conditions, because the route is not only in the network, but also in other connections.

Static routing protocols, dynamic routing protocols (OSPF, BGP, IS-IS, etc.).

RIP is the first widely used protocol in the internal gateway protocol (IGP) [1058[1]] RIP is a distributed routing protocol based on distance vectors, which is a standard protocol on the Internet, and its biggest advantage is that it is simple to implement and has little overhead.

But there are also many disadvantages of RIP.

First, it limits the size of the network, with a maximum distance of 15 (16 means unreachable). Second, the information exchanged by the router is the complete routing table of the router, so as the network scales, the overhead increases. Finally, "bad news spreads slowly", making the update process take too long to converge.

Therefore, for larger networks, the OSPF protocol should be used. However, the majority of smaller networks still use the RIP protocol.

A router is usually needed when two computers that are not directly connected need to communicate over several networks. Routers provide a way to open up a path through a mesh connection. Several paths are marked in Figure R 9 for the Los Angeles and New York offices.

This mesh network provides redundant paths to adjust the traffic load or reverse links, often with one path preferred over the other for reasons such as cost, speed, or avoiding congestion. The task of the routing protocol is to provide routers with the routing information they need to share with each other to establish the best path through the mesh network.