RIP (routing information protocol) as a distance-vector protocol, from development to now has been in use ever since, although now relatively small. But the more the RIP or small business use, its configuration is simple, easy to manage and so on.
Features RIP
distance vector routing protocol; number of hops to calculate the best path; maximum of 15 hops, not jump up to 16; 30 seconds periodically new; but at the same time to prevent the update package is too large, and therefore, Cisco routers updated ranging from 25-35S. Default four, up to six equivalent load balancing; RIPV1: not support VLSM (update does not include Netmask), while routing update the UDP port (520) transmits a broadcast packet to update the port, this version does not support authentication. RIPV2: Updates using UDP port (520) port sends multicast address 224.0.0.9 update, this version supports certification.
Operating mechanism of RIP
distance vector routing protocol is based on Bellman - Ford algorithm. For distance vector routing protocol, the neighbor who is not important. Distance vector routing algorithm will complete routing table to pass adjacent router, then the router table then receive an option to add their own table to complete the entire routing table, this is called routing by rumor (hearsay); because this route is from adjacent routers update rather than passively accept their own initiative to detect changes in the network.
Update mechanism
will view the router broadcasts the updated received update, and the current information from its routing table comparing; a route to a new network or to the network are known and better route metric will be installed in the routing table; then continues outwardly broadcasts its routing table has been updated. Concern the destination network distance vector routing protocols and distance vector (the direction of the source routing). Before sending updates, each router will add its own distance value to measure the router. When the router receives an update, the network interfaces associated with the received learned it up. The router then use this interface to reach the respective destinations.
Anti-loop mechanism
Split Horizon (horizontal split)
an interface in the routing information can not be received reverse longer transmitted from this interface. This method reduces the routing information incorrectness and equipment load is greatly reduced.
Drug suppression reversed
once the drug suppression B receives the route, took this route is marked as possibly down state. When the routing updates to the B time after, put the poison reverse route sent to tell C C I already know to ensure that connected devices knows drug suppression uplink message routing, to ensure accuracy. routing toxic levels beyond suppression split That level of segmentation has no effect on drug inhibition routes.
Holddown Timers (holddown)
inhibition was directly triggered by the timing update settings. If a route entry is invalid, connected to the router will send triggered updates, the update contains trigger suppression time is the failure of this route.
Principle: a route entry fails, a period of time in the inhibition of the route, i.e. not received within a specific time period on any routing update the route in the following cases, however, inhibit the release time:
1. inhibition timer expires.
2. receives a better route metric value updated (smaller than the original measure).
3. refresh time to time.
Set to infinity
such as RIP agreed 16 jump is infinite value. Once the distance to reach this value, this road, but not immediately cleared by the mark as possible down state from the routing table, because the refresh time not arrived, this time if there is a data stream then still be looped back until the brush
new time to time. so, now it is difficult to see the figure of distance vector routing protocol, unless the network is relatively simple.
Route Poisoning (drug suppression routing)
counting to infinity can not avoid routing loops fundamentally because C does not clearly specify 10.4.0.0 route becomes unavailable, therefore, also take some time to reach 16 jump or refresh time, obviously not good the route is in the C drug suppression advertising routes this damage, clearly tell the neighbors that route has been broken, do not need to count to infinity, to speed up the convergence of time.
Triggered Updates (triggered updates)
trigger an update and normal RIP updates are not the same; when the routing table changes, the updated information immediately broadcast to neighboring routers, and then spread, without having to wait for 30 seconds cycle Similarly, when a router has just started RIP, it broadcasts (request packet), the message received from the neighbor router response immediately update a message, without having to wait until the next update cycle. in this way, topology changes will soon spread to all RIP network, greatly reducing the convergence time.