RIP

RIPv1 Distance Vector Routing Protocol, classful Distribution of Routing Tables via broadcast to adjacent routers Only one kind of metric: Number of Hops Connections with different bandwidth can not be weighted Routing loops can occur -> bad convergence in case of a failure Count to infinity problem (infinity = 16) Maximum network size is limited by the number of hops Fig. 59 Properties of RIPv1 (TI1332EU02TI_0004 The Network Layer, 81)

RIP Characteristics

RIP-1 permits only a Single Subnet Mask Port 1 130.24.13.1/24 130.24.13.0/24 RIP-1: 130.24.36.0 RIP-1: 130.24.36.0 RIP-1: 130.24.0.0 Router A 130.24.25.0/24 Port 2 200.14.13.2/24 200.14.13.0/24 130.24.36.0/24 Fig. 60 RIP-1 permits only a single subnet mask (TI1332EU02TI_0004 The Network Layer, 83)

Router Configuration The router command starts a routing process. The network command is required because it enables the routing process to determine which interfaces participate in the sending and receiving of routing updates. An example of a routing configuration is: GAD(config)#router rip GAD(config-router)#network 172.16.0.0 The network numbers are based on the network class addresses, not subnet addresses or individual host addresses.

Configuring RIP Example

Verifying RIP Configuration

The debug ip rip Command Most of the RIP configuration errors involve an incorrect network statement, discontiguous subnets, or split horizons. One highly effective command for finding RIP update issues is the debug ip rip command. The debug ip rip command displays RIP routing updates as they are sent and received.

Problem: Routing Loops Routing loops can occur when inconsistent routing tables are not updated due to slow convergence in a changing network.

Problem: Counting to Infinity

Solution: Define a Maximum

Solution: Split Horizon

Route Poisoning Route poisoning is used by various distance vector protocols in order to overcome large routing loops and offer explicit information when a subnet or network is not accessible. This is usually accomplished by setting the hop count to one more than the maximum.

Triggered Updates New routing tables are sent to neighboring routers on a regular basis. For example, RIP updates occur every 30 seconds. However a triggered update is sent immediately in response to some change in the routing table. The router that detects a topology change immediately sends an update message to adjacent routers that, in turn, generate triggered updates notifying their adjacent neighbors of the change. When a route fails, an update is sent immediately rather than waiting on the update timer to expire. Triggered updates, used in conjunction with route poisoning, ensure that all routers know of failed routes before any holddown timers can expire.

Triggered Updates Graphic

Solution: Holddown Timers

RIP Timers RIP uses numerous timers to regulate its performance. These include a routing-update timer, a route timeout timer, and a route-flush timer. The routing-update timer clocks the interval between periodic routing updates. Generally, it is set to 30 seconds, with a small random amount of time added whenever the timer is reset. This is done to help prevent congestion, which could result from all routers simultaneously attempting to update their neighbors. Each routing table entry has a route-timeout timer associated with it. When the route-timeout timer expires, the route is marked invalid but is retained in the table until the route-flush timer expires.

RIP v1: Packet Format • Command—Indicates whether the packet is a request or a response. The request asks that a router send all or part of its routing table. The response can be an unsolicited regular routing update or a reply to a request. Responses contain routing table entries. Multiple RIP packets are used to convey information from large routing tables. • Version number—Specifies the RIP version used. This field can signal different potentially incompatible versions. • Zero—This field is not actually used by RFC 1058 RIP; it was added solely to provide backward compatibility with prestandard varieties of RIP. Its name comes from its defaulted value: zero.

RIP v1: Packet Format Address-family identifier (AFI)—Specifies the address family used. RIP is designed to carry routing information for several different protocols. Each entry has an address-family identifier to indicate the type of address being specified. The AFI for IP is 2. Address—Specifies the IP address for the entry. Metric—Indicates how many internetwork hops (routers) have been traversed in the trip to the destination. This value is between 1 and 15 for a valid route, or 16 for an unreachable route.

RIP v2: Packet Format The RIP 2 specification (described in RFC 1723) allows more information to be included in RIP packets and provides a simple authentication mechanism that is not supported by RIP. Subnet Masks & secure table updates

1. Command—Indicates whether the packet is a request or a response 1. Command—Indicates whether the packet is a request or a response. The request asks that a router send all or a part of its routing table. The response can be an unsolicited regular routing update or a reply to a request. Responses contain routing table entries. Multiple RIP packets are used to convey information from large routing tables. 2. Version—Specifies the RIP version used. In a RIP packet implementing any of the RIP 2 fields or using authentication, this value is set to 2. 3. Unused—Has a value set to zero. 4. Address-family identifier (AFI)—Specifies the address family used. RIPv2's AFI field functions identically to RFC 1058 RIP's AFI field, with one exception: If the AFI for the first entry in the message is 0xFFFF, the remainder of the entry contains authentication information. Currently, the only authentication type is simple password.

5. Route tag—Provides a method for distinguishing between internal routes (learned by RIP) and external routes (learned from other protocols). 6. IP address—Specifies the IP address for the entry. 7. Subnet mask—Contains the subnet mask for the entry. If this field is zero, no subnet mask has been specified for the entry. 8. Next hop—Indicates the IP address of the next hop to which packets for the entry should be forwarded. 9. Metric—Indicates how many internetwork hops (routers) have been traversed in the trip to the destination. This value is between 1 and 15 for a valid route, or 16 for an unreachable route.