Nov 04, 2004CS573: Network Protocols and Standards1 IP Routing: GGP and RIP Network Protocols and Standards Autumn

Nov 04, 2004CS573: Network Protocols and Standards2 IP Routing Protocols Autonomous System Interior Gateway Protocols GGP RIP OSPF Exterior Gateway Protocols BGP EGP IP Multicast Routing MPLS

Nov 04, 2004CS573: Network Protocols and Standards3 IP Routing Protocols Autonomous Systems

Nov 04, 2004CS573: Network Protocols and Standards4 Routing in the Internet Routing Algorithms Bellman-Ford Dijkstra Routing Protocols Distance Vector Link State Routing Hierarchy Interior Gateway Protocols (RIP, OSPF, IGRP) Exterior Gateway Protocols (EGP, BGP, CIDR, Policy Routing) Multicasting (IGMP)

Nov 04, 2004CS573: Network Protocols and Standards5 Internet from the start First, there was ARPANET Routers had complete information about all the possible destinations – core routers GGP (gateway-to-gateway) protocol was used for routing – a distance vector protocol RR R R H H H

Nov 04, 2004CS573: Network Protocols and Standards6 Internet from the start Then, LANs were connected to ARPANET R RR ARPANET LAN Core Routers

Nov 04, 2004CS573: Network Protocols and Standards7 Internet from the start Problems with above configuration: Routing overhead increased with the number of connected routers Number of routes increased with the number of connected segments Frequency of routing exchanges increased Higher likelihood that something went wrong somewhere requiring updates Number of different types of routers increased Slow deployment of new versions of routing algorithms

Nov 04, 2004CS573: Network Protocols and Standards8 Internet from the start Backbone Network R1R1 Local Network Core Router R2R2 R3R3 Local Network R4R4

Nov 04, 2004CS573: Network Protocols and Standards9 Autonomous System R RR Backbone Network AS Core Routers AS: Autonomous System

Nov 04, 2004CS573: Network Protocols and Standards10 Autonomous System What is an autonomous system? A set of routers and networks under the same administration. Examples: A single router directly connecting one local network to the Internet A corporate network linking several local networks through a corporate backbone A set of client networks served by a single ISP NOTE: From a routing point of view, all parts of an AS must remain connected

Nov 04, 2004CS573: Network Protocols and Standards11 Autonomous System Internal connectivity within the AS means: All routers must be connected Parts of network connected through core AS (yes, core is an AS!) cannot form an AS All routers must exchange routing information in order to maintain the connectivity (normally achieved by using a single routing protocol) Routers inside an AS are called “interior gateway” and the protocol they use is called Interior Gateway Protocol (IGP)

Nov 04, 2004CS573: Network Protocols and Standards12 Autonomous System In 1982, the IGP of choice was GGP IGPs in use today are: RIP OSPF IGRP Each AS is identified by a 16-bit number Number is assigned by the numbering authorities

Nov 04, 2004CS573: Network Protocols and Standards13 Autonomous System: Benefits Routing overhead is lower Network management becomes easy Easier computation of new routes Distribution of new software versions is easier Failing elements can be isolated easily AS use an Exterior Gateway Protocol to exchange information about reachability

Nov 04, 2004CS573: Network Protocols and Standards14 IP Routing Protocols Gateway-to-Gateway Protocol GGP

Nov 04, 2004CS573: Network Protocols and Standards15 GGP The “old” ARPANET routing protocol Defined in RFC 823 A distance-vector routing protocol Only core routers participate in GGP GGP messages travel in IP datagrams with protocol type = 3 GGP measures distance in router hops. i.e., the number of hops along a path refers to the number of routers

Nov 04, 2004CS573: Network Protocols and Standards16 GGP Message Types 4 types of GGP messages GGP Routing Update message (type 12) GGP Acknowledgment message (type 2/10) GGP Echo Request or Reply (type 0 or 8)

Nov 04, 2004CS573: Network Protocols and Standards17 GGP Routing Update A router sends this message to advertise the destination networks it knows how to reach To keep the size of message small, networks are grouped by distance In the message “Distance” is followed by a list of “Net” addresses that are at this distance Contains a field that tells how many distance groups are being reported (3 in case below) D1 – Net1, Net5, Net11 D2 – Net4, Net2, Net7, Net16 D3 – Net6, Net9

Nov 04, 2004CS573: Network Protocols and Standards18 IP Routing Protocols Routing Information Protocol RIP

Nov 04, 2004CS573: Network Protocols and Standards19 Routing Information Protocol A distance vector based IGP Similar to GGP Designed at UC Berkeley Based on Xerox XNS Distributed with 4BSD UNIX (routed) First RFC was 1058, current RFC is 2453 Started off in small networks and then extended to larger networks See Huitema, Chapter 5

Nov 04, 2004CS573: Network Protocols and Standards20 RIP Details Routers are active machines Advertise their routes (IP NET, distance) to others Hosts are passive machines They listen and update their routes but do not advertise RIP uses hop count metric RIP messages are transmitted using UDP at port 520

Nov 04, 2004CS573: Network Protocols and Standards21 RIP Route Computation There is a cost associated with each link Typically cost =1 i.e., number of hops Each router receives route advertisements from its neighbors Advertisements show distances to all destinations in the network For each destination in the network: The router takes each received advertisement and adds to it the cost to reach that neighbor who sent this advertisement; this gives the distance to the destination The router selects lowest of these as path/cost to that destination

Nov 04, 2004CS573: Network Protocols and Standards22 Algorithm Properties Convergence is guaranteed in a finite time given that topology remains static Starting value of distance estimates to each destination can be any non-negative number No assumption is made as to when the updates are sent or when the distances are computed Each router can work based on its own clock and send its updates asynchronously If the network changes, routes converge to a new equilibrium point

Nov 04, 2004CS573: Network Protocols and Standards23 Example Router Advertisement: Distance to A is 2 Distance to B is 3 Distance to C is 5 Advertisement: Distance to A is 1 Distance to B is 4 Distance to C is 1 Advertisement: Distance to A is 2 Distance to B is 1 Distance to C is 3 Cost = 2 Cost = 3Cost = 1 P1 P2 P3 Distance toThrough DestinationPort P1Port P2Port P3 A344 B437 C654

Nov 04, 2004CS573: Network Protocols and Standards24 Counting to Infinity Routes to Target: A: route via B, distance 3 B: route via D, distance 2 C: route via B, distance 3 D: direct, distance 1 Assume that B to D link goes down, and B notices. A DB C Target di D C C Via Dist diD BC xB BA ViaFrom Dist di A C C Via di A C C Via Dist di A C C Via Dist … 1 11 Dist di A C C Via x = destination unreachable; di = directly connected What if the link from C to D also goes down? Counting to Infinity!!! To reach target …

Nov 04, 2004CS573: Network Protocols and Standards25 Some Solutions Split Horizon If A reaches a destination through B, it makes no sense for B to reach the same destination through A Instead of broadcasting the same distance vector on all links, send different versions on each outgoing link by removing the entries for the destinations that are reachable through that link Split Horizon with Poisonous Reverse Include all the destinations in advertisements; even those which were missing in split horizon, but… Set those vector distances to infinity that were missing in the simple version of split horizon

Nov 04, 2004CS573: Network Protocols and Standards26 Triggered Updates Split Horizon can work in loops with two gateways, but not with three or more See example in book by Huitema Another solution to deal with “count to Infinity” problem is triggered updates A gateway is required to send an immediate update when any route changes. This reduces the occurrence of loops Flood of triggered updates resolves loops faster when these happen

Nov 04, 2004CS573: Network Protocols and Standards27 RIPv2 Message Format MUST BE ZERO AS NUMBER AUTHENTICATION TYPE NEXT HOP DISTANCE TO NET VERSION (2)COMMAND (1-5) FFFF FAMILY OF NET 1 ADDRESS OF NET 1 MASK AUTHENTICATION HEADER 31 … …

Nov 04, 2004CS573: Network Protocols and Standards28 Message Format CommandMeaning 1Request for partial or full routing information 2Response containing network-distance pairs from sender’s routing table 3Turn on trace mode (obsolete) 4Turn off trace mode (obsolete) 5Reserved for Sun Microsystems Internal Use

Nov 04, 2004CS573: Network Protocols and Standards29 RIPv2 Message Format Address format is not limited to TCP/IP RIP can be used with multiple network protocol suites Family of net i: Identifies the protocol family under which the network address should be interpreted IP addresses are assigned value 2 Next hop The sending router can specify another router’s IP address as next hop for the network Set to for sender itself Solves similar problem (extra hop) as ICMP redirect

Nov 04, 2004CS573: Network Protocols and Standards30 RIP Metrics and Updates By default, RIP uses hop count as the distance metric Integers 1 through denotes infinity Packets are normally sent every 30sec If a route is not refreshed within 180 seconds, distance is set to infinity and later entry is removed

Nov 04, 2004CS573: Network Protocols and Standards31 Input Processing How to process incoming RIP packets? Examine entries one by one Validation check Address is valid class A, B, or C Network number is not 127 Host port is not a “broadcast” address Metric is not larger than infinity (16) Incorrect entries are ignored And should be reported as errors

Nov 04, 2004CS573: Network Protocols and Standards32 Input Processing Metric for entry is increased by link cost Routing table is searched for an entry corresponding to the destination If the entry is not present, it is added If the entry is present but with a larger metric Entry is updated and timer restarted Entry is present and next hop router is sender of response message Metric is updated and timer restarted For all other cases, entry is ignored

Nov 04, 2004CS573: Network Protocols and Standards33 RIP Responses A separate response is prepared for all connected interfaces/ports Information sent on different ports may vary due to Split Horizon processing Subnet summarization For triggered updates: may include only those entries that have been updated since last transmission Maximum message size: 512 bytes (up to 25 entries) Multiple messages have to be sent if more than 512 bytes Source IP address is that of the interface on which the message is sent Destination IP address is the broadcast address