Routers are no more than two, one route choice, and second, data forwarding. Forward data relatively easy, the difficulty is how to determine the best path to the destination network. Therefore, path selection router becomes the most important work.
Many routing protocols to complete the path choice, in common with RIP, OSPF, IGRP, and EIGRP protocol and so on. These algorithms, we can not simply say who's good and who bad, because the algorithm based on the merits of using the environment to be judged. Such as RIP protocol, it is sometimes not an accurate selection of the optimal path, the convergence time slightly lengthy, Dan for small-scale, without professional maintained network Laishui, it is the preferred routing protocol, Women's fancy is its simplicity.
If you do is have a small network project, let us arrange a program, 30 minutes reading this article (first reading), 20 minutes to look over the order referred to herein and the operation method (Second Reading), 30 minutes to configure the network with all routers (small network, routers can be equipped with not a few), the final 20 minutes, check the network works properly. Well, 100 minutes, your RIP network up and running. It's that simple, do not believe, continue to look down.
1, RIP What
RIP (Routing Information Protocols, Routing Information Protocol) is the most widely used distance vector protocol, it is a Xerox (Xerox) developed in 70 years. At that time, RIP is the XNS (Xerox Network Service, Xerox Network Service) protocol as part of clusters. TCP / IP version of the RIP protocol is an improved version of Xerox. RIP biggest feature is the realization principle, whether or configuration are very simple.
Measurement
RIP metric is based on the number of hops (hops count), each through a router, the path hop count plus one. Thus, the more hops, the longer the path, RIP algorithm will give priority to the path less hops. RIP to support the maximum number of hops is 15, a network of 16 hops is considered unreachable.
Routing update
RIP routing updates are achieved through the regular broadcast. By default, the router every 30 seconds and it is connected to the network broadcast its own routing table, the router will receive the broadcast information received to add to its own routing table. Each router that broadcasts all of the routers on the network eventually will learn all the routing information. Under normal circumstances, every 30 seconds the router received a routing information can be confirmed, if after 180 seconds, or 6 update cycle, a route entry have not been confirmed, the router that it has been ineffective. If after 240 seconds, or 8 update cycle, the routing entry is still not confirmed, it will be removed from the routing table. Above 30 seconds, 180 seconds and 240 seconds of delay are controlled by a timer, which are updated timer (Update Timer), invalid timer (Invalid Timer) and the refresh timer (Flush Timer).
Routing loop
Distance vector type routing algorithms prone to cycle, RIP is a distance vector algorithm, so it is no exception. If you have a routing loop network, information is circulating transfer, will never get there. To avoid this problem, RIP equal distance vector algorithm has the following four mechanisms.
Level split (split horizon). Level of segmentation to ensure the router to remember the source of each routing information, and do not receive this information send it again at the port. This is to ensure that does not produce the most basic measures routing loop.
Toxicity reversal (poison reverse). When a path information becomes invalid, the router does not immediately remove it from the routing table, but by 16, that does not measure up to the broadcast it out. Although this increase in the size of the routing table, but helps to eliminate the routing loop, it can immediately remove any loop between adjacent routers.
Trigger update (trigger update). When the routing table changes, the update packet immediately broadcast to all neighboring routers, instead of waiting 30 seconds of the update cycle. Similarly, when a RIP router just started, it broadcasts a request packet. Adjacent routers receive this broadcast an update packet immediately answer, without having to wait until the next update cycle. Thus, changes in network topology will be the fastest spreading in the network, reducing the possibility of routing loop generated.
Inhibition time (holddown timer). After an invalid routing information, over time, this road are in the suppression by the state, that is not received within a certain period of time on the same destination address of routing updates. If, on the router from a network segment that a path failure, then immediately in another segment that this route effective. The effective information often is not correct, inhibition of time to avoid this problem, and, when a link frequent starts and stops, the inhibition reduces the routing time of floating, increased network stability.
Even with the above 4 methods, the routing loop problem can not be fully resolved only by the maximum degree of reduction. Once the routing loop is really there, routing entries count measure appears to infinity (Count to Infinity) situation. This is because the routing information is passed loop, each pass through a router to add a measure has been added to the 16, the path becomes unreachable for a. RIP choose 16 as not up to the measure is very clever, both large enough to guarantee the normal operation of most networks, but also small enough to allow counting to infinity takes the shortest time.
Neighbor
Some networks are NBMA (Non-Broadcast MultiAccess, non-broadcast multiple access), that does not allow broadcast networks to transmit data. For this network, RIP can not rely on radio transmission routing table. There are many solutions, the simplest is to specify the neighbor (neighbor), which specifies the routing table to send to a specific router platform.
RIP defect
RIP Although simple and proven, but there are some important deficiencies, mainly the following:
Too simple to jump based on the number of calculated measures, often come to non-optimal routing;
Measure the extent of 16, not suitable for large networks;
Poor security, to accept routing updates from any device;
No classes do not support IP address and VLSM (Variable Length Subnet Mask, variable-length subnet mask);
Convergence is slow, time often greater than 5 minutes;
The bandwidth consumed large.
Routers are no more than two, one route choice, and second, data forwarding. Forward data relatively easy, the difficulty is how to determine the best path to the destination network. Therefore, path selection router becomes the most important work.
Many routing protocols to complete the path choice, in common with RIP, OSPF, IGRP, and EIGRP protocol and so on. These algorithms, we can not simply say who's good and who bad, because the algorithm based on the merits of using the environment to be judged. Such as RIP protocol, it is sometimes not an accurate selection of the optimal path, the convergence time slightly lengthy, Dan for small-scale, without professional maintained network Laishui, it is the preferred routing protocol, Women's fancy is its simplicity.
If you do is have a small network project, let us arrange a program, 30 minutes reading this article (first reading), 20 minutes to look over the order referred to herein and the operation method (Second Reading), 30 minutes to configure the network with all routers (small network, routers can be equipped with not a few), the final 20 minutes, check the network works properly. Well, 100 minutes, your RIP network up and running. It's that simple, do not believe, continue to look down.
1, RIP What
RIP (Routing Information Protocols, Routing Information Protocol) is the most widely used distance vector protocol, it is a Xerox (Xerox) developed in 70 years. At that time, RIP is the XNS (Xerox Network Service, Xerox Network Service) protocol as part of clusters. TCP / IP version of the RIP protocol is an improved version of Xerox. RIP biggest feature is the realization principle, whether or configuration are very simple.
Measurement
RIP metric is based on the number of hops (hops count), each through a router, the path hop count plus one. Thus, the more hops, the longer the path, RIP algorithm will give priority to the path less hops. RIP to support the maximum number of hops is 15, a network of 16 hops is considered unreachable.
Routing update
RIP routing updates are achieved through the regular broadcast. By default, the router every 30 seconds and it is connected to the network broadcast its own routing table, the router will receive the broadcast information received to add to its own routing table. Each router that broadcasts all of the routers on the network eventually will learn all the routing information. Under normal circumstances, every 30 seconds the router received a routing information can be confirmed, if after 180 seconds, or 6 update cycle, a route entry have not been confirmed, the router that it has been ineffective. If after 240 seconds, or 8 update cycle, the routing entry is still not confirmed, it will be removed from the routing table. Above 30 seconds, 180 seconds and 240 seconds of delay are controlled by a timer, which are updated timer (Update Timer), invalid timer (Invalid Timer) and the refresh timer (Flush Timer).
Routing loop
Distance vector type routing algorithms prone to cycle, RIP is a distance vector algorithm, so it is no exception. If you have a routing loop network, information is circulating transfer, will never get there. To avoid this problem, RIP equal distance vector algorithm has the following four mechanisms.
Level split (split horizon). Level of segmentation to ensure the router to remember the source of each routing information, and do not receive this information send it again at the port. This is to ensure that does not produce the most basic measures routing loop.
Toxicity reversal (poison reverse). When a path information becomes invalid, the router does not immediately remove it from the routing table, but by 16, that does not measure up to the broadcast it out. Although this increase in the size of the routing table, but helps to eliminate the routing loop, it can immediately remove any loop between adjacent routers.
Trigger update (trigger update). When the routing table changes, the update packet immediately broadcast to all neighboring routers, instead of waiting 30 seconds of the update cycle. Similarly, when a RIP router just started, it broadcasts a request packet. Adjacent routers receive this broadcast an update packet immediately answer, without having to wait until the next update cycle. Thus, changes in network topology will be the fastest spreading in the network, reducing the possibility of routing loop generated.
Inhibition time (holddown timer). After an invalid routing information, over time, this road are in the suppression by the state, that is not received within a certain period of time on the same destination address of routing updates. If, on the router from a network segment that a path failure, then immediately in another segment that this route effective. The effective information often is not correct, inhibition of time to avoid this problem, and, when a link frequent starts and stops, the inhibition reduces the routing time of floating, increased network stability.
Even with the above 4 methods, the routing loop problem can not be fully resolved only by the maximum degree of reduction. Once the routing loop is really there, routing entries count measure appears to infinity (Count to Infinity) situation. This is because the routing information is passed loop, each pass through a router to add a measure has been added to the 16, the path becomes unreachable for a. RIP choose 16 as not up to the measure is very clever, both large enough to guarantee the normal operation of most networks, but also small enough to allow counting to infinity takes the shortest time.
Neighbor
Some networks are NBMA (Non-Broadcast MultiAccess, non-broadcast multiple access), that does not allow broadcast networks to transmit data. For this network, RIP can not rely on radio transmission routing table. There are many solutions, the simplest is to specify the neighbor (neighbor), which specifies the routing table to send to a specific router platform.
RIP defect
RIP Although simple and proven, but there are some important deficiencies, mainly the following:
Too simple to jump based on the number of calculated measures, often come to non-optimal routing;
Measure the extent of 16, not suitable for large networks;
Poor security, to accept routing updates from any device;
No classes do not support IP address and VLSM (Variable Length Subnet Mask, variable-length subnet mask);
Convergence is slow, time often greater than 5 minutes;
The bandwidth consumed large.
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