The primary chapter of the RIP protocol

I. Basic overview

RIP (Routing information Protocol, routing Information Protocol) is the first generation of dynamic routing protocol, belonging to the distance vector protocol, based on the hop number to make the path selection (maximum support 16 hops). RIP currently has: IPV4-based version Ripv1,ripv2 and RIPng version based on IPV6

Two. Features

1.OSI hierarchy: Application-layer protocol, UDP-based port 520

2. Algorithm features: Distance vector protocol

3. There are classes and no classes: RIPV1 is a class, RIPv2 is no class

4. Operating range: IGP (internal Gateway Protocol)

5. Best path: Manage distance 120, measure----hop count

Three. RIP routing groupings

1.Request Pack

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Role: Request grouping, which points to the router Neighbor request routing entry when initializing

2.Response Pack

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Role: RIP reply grouping for updating/sending local routing information

Four. RIP timer

1. Update Timer---30s

Update timer, for RIP protocol cycle outbound broadcast routing

2. Failure timer----180s

Invaild timer, when RIP routing (update) exceeds 180s, this route is declared invalid (possible down)

3. Suppression Timer----180s

Hold-down timers for anti-ring, indicating that no other route is received within this time range

4. Refresh Timer----240s

Flushed timers, when RIP routing (update) exceeds 240s, this route entry is removed from the local routing table

Five. RIP Routing algorithm introduction

RIP routing algorithm is the Bellman algorithm (Behrman algorithm).

Bellman algorithm:

① if a neighbor-given route is received, it is received if there is no local.

② If you receive a neighbor-given route, if there is a local, according to the measure of comparison, merit, the inferior is discarded.

③ if received the neighbor to the route, if inferior, but from the original neighbor learned, also input.

For ③: If the R1---->R2 has two paths ① and ②, before the failure, R2 route table is the shortest path ①, when the path ①down, R1 will choose the path ② send packets to R2, so R2 received R1 packets only after not the optimal path ② packets, At this point, because there is no comparison of measures, it can only be received, update the routing table, remove the original routing table.

Six. RIP routing anti-Ring

1. Routing Anti-Ring overview

Because the RIP routing protocol has the feature of "bad Message Propagation slow" (RIP update cycle 30s, failure time 180s), each router cannot simultaneously or nearly simultaneously complete the routing table update, so it is possible to generate a "routing loop"

2.RIP---5 kinds of anti-ring mechanism

① Horizontal Split

Definition: A route entry received from this interface can no longer be sent from this interface. (You can't give him the same gift when someone gives you a gift.)

② Max 16 Jump

Definition: If the route entry hop count of Rip reaches 16 hops, then this route fails and is discarded

③ Route Poisoning

Definition: If a RIP routing entry fails, the route is marked as 16 hops and sent to the neighbor informing the neighbor that there is a problem with the route and deleting the route entry as soon as possible.

④ toxicity Reversal

Definition: If a RIP routing entry fails, the route is marked as 16 hops and sent to the neighbor, informing the neighbor that there is a problem with the route, deleting the route entry as soon as possible, and the neighbor returning a 16-hop route poisoning to achieve confirmation.

⑤ Suppression Timer

Definition: When a failed route is received, the default is to delete the fault route, and if you receive this route from afar, it is possible to create a loop again; To solve this problem, set the suppression timer, and after you receive the failed route, keep 180s before you delete the route entry.

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The primary chapter of the RIP protocol