RIP Routing Information Protocol Routing is the method

RIP Routing Information Protocol 指導老師：梁德昭老師 簡報者：方佳娣

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

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

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”.

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

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

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)

Distance Vector algorithms Preventing instability. . the slow convergence problem… D: directly connected, metric 1 B: route via D, metric 2 1 A 1 1 C: route via B, metric 3 B C 1 A: route via B, metric 3 10 D: 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 D 1 Target netwrok

Distance Vector algorithms Preventing instability. . the slow convergence problem… Network 1 R 1 R 2 R 3

Distance Vector algorithms Solutions w Split horizon Simple split horizon n Split horizon with poisoned reverse n w Hold down w Triggered updates

Routing Information protocol Specifications for RIP Message Format 0 8 16 Command(1) Version(1) 24 must be zero(2) address family identifier(2) IP address (4) must be zero (4) metric (4) must be zero(2) 31 …

Routing Information protocol Problems… n Addressing consideration RIP 1 does not know the subnet mask, so evaluation of an address may be ambiguous. Consider the subnet mask 255. 128… n AS and IGP/EGP interactions

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 Command(1) Version(1) 24 Must be zero (2) address family identifier(2) IP address (4) subnet mask (4) Next hop (4) metric (4) RIP tag (2) 31 …

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.

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

Routing Information protocol Disadvantages of RIP n n n 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.