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RIP Routing Information Protocol

RIP Routing Information Protocol. 指導老師:梁德昭 老師 簡報者:方佳娣. Routing. Routing is the method by which the host or router decides where to send the data gram. IGP. IGP. EGP. AS. AS. Routing. EGP--- External gateway protocol IGP--- Internal gateway protocol

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RIP Routing Information Protocol

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  1. RIPRouting Information Protocol 指導老師:梁德昭老師 簡報者:方佳娣

  2. Routing • Routing is the method by which the host or router decides where to send the data gram. IGP IGP EGP AS AS

  3. Routing • EGP--- External gateway protocol • IGP--- Internal gateway protocol  Most used IGPs include RIP, Hello, OSPF, IS-IS…..

  4. Routing Information protocol • RIP, version 1 and version 2, is the most commonly used interior protocol. • RIP is one of a class of algorithms known as “distance vector algorithms”.

  5. Distance Vector algorithms • Each entity keeps a routing database with one entry for every possible destination in the system. • Address • Router • Interface • Metric • Timer This database would be updated by the messages sent by the neighboring routers.

  6. Distance Vector algorithms • When a routing update arrives from a neighbor, add the cost associated with the network that is shared with it. And compare the resulting distance with the current routing table entries. D(i,i)=0 , all i D(i,j)=min[d(I,k)+D(k,j)], otherwise  D(i,j) represents the metric of the best rout  d(i,j) represents the cost of individual steps

  7. Distance Vector algorithms • Periodically( in RIP, 30 sec. is used ), send a routing update to every neighbor. • Wait for 180 sec. before timing out a route. • A specific metric value is chosen to indicate an unreachable destination.(in RIP, 16 is used)

  8. 1 A B 1 1 C 1 10 D 1 Target netwrok Distance Vector algorithms • Preventing instability ..the slow convergence problem… D: directly connected, metric 1 B: route via D, metric 2 C: route via B, metric 3 A: route via B, metric 3 D: dir,1 dir,1 dir,1 dir,1 dir,1 dir,1 B: UNR C,4 C,5 C,6 C,11 C,12 C: B,3 A,4 A,5 A,6 …… A,11 D,11 A: B,3 C,4 C,5 C,6 C,11 C,12

  9. Distance Vector algorithms Preventing instability ..the slow convergence problem… Network 1 R1 R2 R3 Network 1 R1 R2 R3

  10. Distance Vector algorithms • Solutions • Split horizon • Simple split horizon • Split horizon with poisoned reverse • Hold down • Triggered updates

  11. Specifications for RIP Routing Information protocol Message Format 0 8 16 24 31 …

  12. Routing Information protocol Problems… • Addressing consideration RIP 1 does not know the subnet mask, so evaluation of an address may be ambiguous. Consider the subnet mask 255.255.255.128… • AS and IGP/EGP interactions

  13. RIP 2 Extensions To expand the amount of useful information carried in RIP messages and to add a measure of security. Message Format for RIP 2 : 0 8 16 24 31 …

  14. RIP 2 Extensions • Using Route tag to provide a method of separating “internal” RIP from “external” RIP routes, which may have been imported from an EGP or another IGP. • The Subnet Mask field contains the subnet mask which is applied to the IP address to yield the non-host portion of the address.

  15. Routing Information protocol Advantages of RIP • In small network, RIP has little overhead of bandwidth used and configuration and management time. • Easily to implement.

  16. Routing Information protocol Disadvantages of RIP • Inappropriate for larger networks. • Depends on “counting to infinity” ,which may consume a large amount of network bandwidth. • Uses fixed “metrics” to compare alternative routes. It’s not appropriate for parameters such like measured delay, reliability, or load.

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