Exchange "vs" Routes "(2) Author: Systems Engineer Published: 2002/08/12 03:10 am An important function of the switch is to avoid exchange cycle, which involves the STP (Spanning Tree Protocol, branching tree protocol). The function of the branch tree protocol is to avoid cyclic transmission in the network composed of the data frame. As shown in the figure, if there is a redundant link in the network, the STP protocol is set out of the root switch (Route Bridge), then determine each The path between the non-root switches to the root switch, finally, all links on this path are set to the forward state, and the remaining switches are the redundant link, which is set to the block state. Another important feature of the switch is that there are three advantages of VLAN (Virtual LAN, virtual LAN). There are three advantages: port separation. Even on the same switch, the port in different VLANs cannot be communicated. Such a physical switch can When used as multiple logical switches. The security of the network. Different VLANs cannot communicate directly, eliminate the unsafeness of broadcast information. Flexible management. Change the network to the network does not have to change port and connect, only the software configuration can The VLAN can be divided by port or MAC address. Sometimes we need to maintain the consistency of the VLAN on the network composed of the switch. This requires the switch to communicate with VLANs according to VTP (VLAN TRUNK Protocol, VLAN Backbone Agreement) Information .vtp protocol only runs on the port between the backbone port, that is, the port between the switches. Routing router is the connection device between the network, one of its important work is the path selection. This function is the core of the router smart, it is Implemented by the administrator's configuration and a series of routing algorithms. Routing algorithms are moving quiet, static routing is a special route, which is manually set by the administrator. Hand-configured all routes can make the network normal Operation, but will also bring some limitations. After the network topology changes, the static route does not automatically change, and there must be a network administrator's intervention. The default route is one of the static routes, and is also set by the administrator. When the routing entry for the target network is found, the router sends information to the default router. The dynamic algorithm, as the name suggests, the route automatically calculated by the router, often said RIP, OSPF, etc. It is a typical representative of a dynamic algorithm. It is also possible to divide the routing algorithm into two .dv (Distance, distance vector) algorithm to transfer the routing information of the current router to adjacent routers, adjacent routers add this information to their own Routing table. And LS (Link S Tate, link status) Algorithm transmits link status information to all routers in the domain, receives the router to build network topology maps using this information, and use the shortest path priority algorithm in the chart to determine the route. In contrast, the distance vector algorithm is relatively simple, and the link status algorithm is more complicated, and more CPUs and memory occupied. However, since the link state algorithm is used as its own calculation result, it is not easy to generate a routing cycle. RIP is a typical representative of the DV class algorithm, and OSPF is a representative protocol of LS. The four most common routing protocols are RIP, IGRP, OSPF, and EIGRP.
RIP (Routing Information Protocols, Routing Information Protocol) is the most wide range of distance vector protocols, which is developed by Xerox in the 1970s. At that time, RIP was part of the XNS (Xerox Network Service, Xerox Network Services) protocol cluster. The TCP / IP version of RIP is an improvement version of the Xerox Agreement. The biggest feature of RIP is that regardless of the principle or configuration method, it is very simple. RIP is based on hop calculation routing and sends update messages to neighbor routers. IGRP is a proprietary protocol proprietary and implemented in a Cisco router. It also belongs to the distance vector type, so there is a common point in many places, such as broadcast updates, and more. Its and RIP's largest differences are aspects of metrics, load balancing. IGRP supports weight load balancing on multiple paths, so that the bandwidth of the network can be utilized more reasonable. In addition, with the RIP only uses the number of hops as the measurement, IGRP uses a variety of parameters, constitutes a composite metric, which may include: bandwidth, delay, load, reliability, and MTU (maximum transmission unit), etc. Wait. The OSPF protocol was developed in the 1980s. In the 1990s, it became an industrial standard, which is a typical link state protocol. The main features of OSPF include: supporting VLSM (shielding long subnet), fast convergence, low bandwidth usage, and the like. The OSPF protocol exchanges link status information between neighbors so that the router establishes a link state database (LSD). After that, the router uses SPF (Shortest Path First, shortest path priority) algorithm based on the information in the database, and selects the route. The main basis is bandwidth. EIGRP is the enhanced version of IGRP, which is also a Cisco proprietary routing protocol. EIGRP uses a Diffusion Update (DUAL) algorithm, to some extent, it is similar to the distance vector algorithm, but has a shorter convergence time and better operability. As an extension of IGRP, EIGRP supports a variety of roudably protocols such as IP, IPX, and AppleTalk, and more. When running in an IP environment, EIGRP can also be smoothly connected to IGRP because their metric is consistent. The above four routing protocols are domain internal routing protocols, which are usually used inside the autonomous system. When the connection between the autonomous system is often used, a domain routing protocol such as BGP (Border Gateway Protocols, boundary routing protocol) and EGP (External Gateway Protocols, external routing protocol) is often employed. The domain routing protocol currently used on the Internet is the fourth edition of BGP. Convergence is an important issue encountered when the routing algorithm is selected. The convergence time refers to the change from the topology of the network to all related routers on the network to know this change, and the time required to change accordingly. The shorter this time, the smaller the interference of the network changes to the whole network. The convergence time is too long, resulting in the emergence of routing cycles. In the above-mentioned various domain, the convergence time of RIP and IGRP is relatively long. It is a minute order; OSPF is short, and it can converge in dozens of seconds; the minimum of EIGRP, the network topology changes, a few seconds The convergence state can be reached. The online network of all-exchange parks is a structure of a router plus switch. As shown in the figure below, the switch is responsible for the transmission within the network, dividing the VLAN to ensure the security and flexibility of the second layer, and the router completes the addressing and data forwarding of the network.
