Routing Information Protocol (RIP) Sungsu Kim Sungsu Kim March 25, 2008

Contents  Autonomous systems  Interdomain and intradomain routing  RIP Overview, history  Distance vector algorithm  Protocol Specification and Message Format  Potential problems of RIP  Timers  Security considerations in RIP2  What is RIPng advantages and usage  Disadvantages of RIP2 and proposed solutions  Conclusion

Autonomous Systems  An autonomous system (AS) is a region of the Internet that is administered by a single entity and that has a unified routing policy  Each autonomous system is assigned an Autonomous System Number (ASN).  Examples of autonomous regions are:  UofT ’ s campus network  MCI ’ s backbone network  Regional Internet Service Provider  Routing is done differently –within an autonomous system (intradomain routing) and –between autonomous systems (interdomain routing).

Interdomain and Intradomain Routing  Routing protocols for intradomain routing are called interior gateway protocols (IGP)  Routing protocols for interdomain routing are called exterior gateway protocols (EGP)

Interdomain and Intradomain Routing Intradomain Routing  Routing within an AS  Ignores the Internet outside the autonomous system  Protocols for Intradomain routing are also called Interior Gateway Protocols or IGP ’ s.  Popular protocols are –RIP (simple, old) –OSPF (better) Interdomain Routing  Routing between AS ’ s  Assumes that the Internet consists of a collection of interconnected AS ’ s  Protocols for interdomain routing are also called Exterior Gateway Protocols or EGP ’ s.  Routing protocol: –BGP

RIP - History  Late 1960s : Distance Vector protocols were used in the ARPANET  Mid-1970s: XNS (Xerox Network system) routing protocol is the precursor of RIP in IP (and Novell ’ s IPX RIP and Apple ’ s routing protocol)  1982Release of routed for BSD Unix  1988RIPv1 (RFC 1058) - classful routing  1993RIPv2 (RFC 1388) - adds subnet masks with each route entry - allows classless routing  1998Current version of RIPv2 (RFC 2453)

Components of a Routing Algorithm  A procedure for sending and receiving reachability information between neighboring routers  A procedure for calculating optimal routes –Routes are calculated using a shortest path algorithm:  Goal: Given a network were each link is assigned a cost. Find the path with the least cost between two networks.  A procedures for reacting to and advertising topology changes

Approaches to Shortest Path Routing  There are two basic routing algorithms found on the Internet. 1. Distance Vector Routing  Each node knows the distance (=cost) to its directly connected neighbors  A node sends periodically a list of routing updates to its neighbors.  If all nodes update their distances, the routing tables eventually converge  New nodes advertise themselves to their neighbors 2. Link State Routing  Each node knows the distance to its neighbors  The distance information (=link state) is broadcast to all nodes in the network  Each node calculates the routing tables independently

RIP updating algorithm 1.Add on 1 hop to the hop count for each advertised destination 2.Repeat the following steps for each advertised destination 1.If (destination no in the routing table) 1.Add the advertised information to the table 2.Else 1.If (next-hop field is the same) 1.Replace entry in the table with the advertised one 2.Else 1.If (advertised hop count smaller than one in the table) 2.Replace entry in the routing table 3.return

13.2 RIP (routing table)  update periodically by updating algorithm Destination Hop Count Next Hop

N2 N3 N4 N5 N6 N1 A B C N11- N21- N31- ① N21- N41- N51- ① N31- N61- ① N21- N41- N51- ② RIP N11- N21- N31- N42B N52B ③ Hop count Next hop Updating routing table by RIP

RIPv1 Packet Format One RIP message can have up to 25 route entries 1: request 2: response 2: for IP 0…0: request full rou- ting table Address of destination Cost (measured in hops) 1: RIPv1

Operations - Input Processing  Handles the datagram received on RIP port (520).  Do validation ( such as version number etc) – If validation fails log the error  Check command field (Request or Response)  Handling Input Request Message– –Initialization Request -- Send entire routing table. –Specific request -- Send only entries requested. –Send response immediately  Handling Input Response Message- A response can be received for one of several following reasons. –Response to a specific query (direct UDP connection for the router). –Regular update (Unsolicited response). –Triggered update caused by a route change.

RIP Request  When a router is powered on  Used for diagnostic purposes

Operations – Output Processing  Describes the processing used to create response and request messages.  The out put processing is triggered by the following ways. –By input processing –By regular routing update ( broadcast/multi cast at every 30 secs) –By the triggered updates ( When a route changes)  Generating Request Message –Can send one Request –Request for entire routing table.  Generating Response Messages –Response to Request  Sent to only one destination –Regular updates  Send the entire routing table –Triggered Updates  Create Response messages to neighbors.

RIP Response  Response to request, deliver routing information every 30 seconds

Example of RIP massage

Timer RIP message  periodic timer : controlling the sending of messages  expiration timer : governing the validity of a route  garbage collection : advertising the failure of a route

Potential Problems and Solutions Potential Problems: –Count to infinity problem –Routing loops SOLUTION: Triggered Updates/Split Horizon for Preventing Two-hop Loops Split Horizon: "Split horizon" is a scheme for avoiding problems caused by including routes in updates sent to the router from which they were learned. –Simple - The information about destination routed on the link is omitted –With poisonous reverse -The corresponding distance is set to infinity if the destination is routed on the link Triggered updates: –Split horizon with poisoned reverse will prevent any routing loops that involve only two routers. However, it is possible to end up with patterns in which three routers are engaged in mutual deception. –A timer is associated with each entry in the routing table - much longer than the period of transmission of information –Triggered updates request nodes to send messages as soon as they notice a change in the routing table

Count to infinity problem  Limit hop count as 16  If hop count is 16, then destination is unreachable

Disadvantages of RIP  Slow convergence – –meaning that a change somewhere in the Internet propagates very slowly through the rest of the internet. – –For example, suppose there is a change in network 1.   since each router sends its periodic update every 30 seconds, it means an average of 15 seconds (range of 0 to 30 sec)

Instability  Happening when a packet could go from one router to another in a loop

For the stability of RIP  Triggered update  If there are no changes, updates are sent at 30sec interval  If there is change, router immediately sends out the its new table-update in less time than 15sec  Spilt horizons –Utilizes selectivity in sending of routing message –Router must distinguish between different interfaces –If a router has received route updating info from an interface, then this same updated info must not be sent back through this interface

Poison Reverse  Variation of split horizons  Information received by the router is used to update the RT and then passed out to all interfaces  But, a table entry that has come through one interface is set to a metric of 16 as it goes out throughout the same

Advantages of RIP and Disadvantages of RIP1  Advantages of RIP: –RIP is very useful in a small network, where it has very little overhead in terms of bandwidth used and configuration and management time. –Easy to implement than newer IGP’s –Many implementations are available in the RIP field.  Disadvantages of RIP1: –minimal amount of information for router to route the packet and also very large amount of unused space. –Subnet support : Supports subnet routes only within the subnet network –Not secure; anyone can act as a router just by sending RIP-1 messages –RIP1 was developed for an AS that originally included less than a 100 routers

RIP2  Latest version of RIP, RFC: 2453,Build in 1990  Advantages: –An AS can include several hundred routers with RIP-2 protocol. –Compatible upgrade of RIPv1 including subnet routing, authentication, CIDR aggregation, route tags and multicast transmission –Subnet Support : uses more convenient partitioning using variable-length subnets – –An end system can run RIP in passive mode to listen for routing information without supplying any. – –Low requirement in memory and processing at the node  RIP and RIP2 are for the IPv4 network while the RIPng is designed for the IPv6 network. RIPng

Practical use in Yahoo Chat IM  Routing information protocol: gives command, version ip domain and address information.

Distance Vector Protocol  Compatible upgrade of RIPv1 including subnet routing, authentication, CIDR aggregation, route tags and multicast transmission  Subnet support: RIPv1 supports subnet routes only within the subnet network while RIPv2 includes subnet mask in the messages. This allows for subnet knowledge outside subnet. More convenient partitioning using variable length subnet.  RIPv2 is a distance vector based routing protocol. RIP2 supports variable-length subnet masks (VLSM).  Distance vector routing protocols: Distance-based vector routing protocols base the optimal route on the number of hops (i.e., devices) a packet must pass through to reach a destination.  Neighboring nodes send information in regular time intervals  Install routes directly in tables, lowest cost wins  The information sent (the distance vectors) are all routes from the table  The shortest path tree is contained in the routing table  Calculations are based on the Bellman-Ford algorithm

RIP 2 Packet Format  Command -- The command field is used to specify the purpose of the datagram.  Version -- The RIP version number. The current version is 2.  Address family identifier -- Indicates what type of address is specified in this particular entry.  Route tag -- Attribute assigned to a route which must be preserved and readvertised with a route. The route tag provides a method of separating internal RIP routes from external RIP routes, which may have been imported from an EGP or another IGP.  IP address -- The destination IP address.  Subnet mask -- Value applied to the IP address to yield the non-host portion of the address. If zero, then no subnet mask has been included for this entry.  Next hop -- Immediate next hop IP address to which packets to the destination specified by this route entry should be forwarded.  Metric -- Represents the total cost of getting a datagram from the host to that destination. Protocol Structure - RIP & and RIP2: Routing Information Protocol Max pkt size 512

RIPv2 Packet Format (With/Without Authentication Header)  RIPv2 packet with no Authentication  RIPv2 packet with Authentication header  Authentication type (2) is password

Example and Routing Table Structure  IP Routing table for Router R1 Included in RIP routing table -Address of (net/subnet/host) destination -Metric associated with destination -Address of next hop router -Recently updated flag -Several timers

RIP2 Extensions  authentication  routing per subnet  support of multiple metrics  routing domains  multicasting

Addressing Consideration  IP address field in RIP2 message (Request/ Response ) format can be networks, hosts, or a special code used to indicate a default address - example –128.6 Network Address – Host address – Default address  Subnet addresses must not be sent outside the network of which the subnet is a part.  is used to describe a default route.

Initialization  Initialization –This is done when host first comes online. –Determine who the neighbors are. –Set command field to 1 –Send request for entire routing table from neighbors.

Interaction between RIPV1 and RIPV2  Limiting Networks  Disable Auto-Summarization  Single Subnetmask

Security Considerations  Authentication 1. Plaintext Authentication Algorithm 2.Cryptographic Authentication 1.Keyed Message Digest 5 2.HMAC-SHA1  Peer Security  Router Filters

RIPng  IPv6 compatible version of RIP  complete new protocol  Uses distance vector algorithm  Uses standard port nuber 521 and runs over UDP  Installs the best route in the RIPng routing table

RIPng v/s RIP-2 RIPng RIPng RIP-2 RIP-2 Learns IPv6 route information Learns IPv4 route information Uses port number 521. Uses port number 520 Requires no authentication for RIPng protocol packets. Requires authentication for RIP protocol packets No support for multiple instances of RIPng. Support for multiple instances of RIP-2

RIP2 - Disadvantages   RIP-2 supports generic notion of authentication, but only “password” is defined so far. Still not very secure.   RIP2 packet size increases as the number of networks increases hence it is not suitable for large networks.   RIP2 generates more protocol traffic than OSPF, because it propagates routing information by periodically transmitting the entire routing table to neighbor routers   RIP2 may be slow to adjust for link failures.

Solution:OSPF within an AS  Can support fine-grained metrics (vs. RIP)  Multiple metrics –Throughput, Delay, Cost, Reliability  Can compute a different routing table for each metric.  OSPFv2 supports an extension that allows the metric to be used specified in the packet.

Conclusion   RIP2 offers many substantial features used to increase the efficiency of RIP1   RIP2 have one negative feature of RIP1 - the path between two subnets is based on the fewest number of router hops   RIPng is a complete new protocol designed for Ipv6. It uses the same operations as that of RIP1 and RIP2

References               troductionToRIP2.pdfhttp:// troductionToRIP2.pdf  SID=c2a79111d168faf SID=c2a79111d168faf SID=c2a79111d168faf  rdsandVersions.htm rdsandVersions.htm rdsandVersions.htm  os121/121cgcr/ip_c/ipcprt2/1cdrip.htm os121/121cgcr/ip_c/ipcprt2/1cdrip.htm os121/121cgcr/ip_c/ipcprt2/1cdrip.htm 

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