DYNAMIC ROUTING PROTOCOLS

Enabling RIP

RIP• RIP exists in two versions – RIP v1, RIP v2• RIP was designed for smaller networks (Max Hop Count - 15)• Although it lacks the capabilities of many of its successors, its

simplicity and widespread use• Operates from UDP port 520• encapsulated in a UDP (User Datagram Protocol) segment

with both the Source and Destination Port fields set to that value.

RIP version 1 RIP Version 2

Classful Routing Classless Routing

No Support for IPv6, Multicast Supports IPv6, Multicast

Does not advertise Subnet Mask Advertise Subnet Mask, Next Hop

No Summarization Support Supports Summarization

No VLSM VLSM

RIP Operation• RIP defines two message types:

– Request messages - Used to ask neighboring routers to send an update– Response messages - Carries the update.

• Metric – Hop Count– 1: Directly Connected Network– 16: Un-reachable Network

• RIP Process –– On startup, RIP broadcasts a packet carrying a Request message out

each RIP-enabled interface– RIP process then enters a loop, listening for RIP Request or Response

messages from other routers– Neighbors receiving the Request send a Response containing their

route table If they have RIP Enabled on that Interface

• Destination address of the update is the all-hosts broadcast 255.255.255.255

RIP Timers and Stability Features• Update Timer – 30 Sec

– Router's full route table with the exception of entries suppressed by the split horizon rule

• Invalid Timer 180 Sec– use to limit the amount of time a route can stay in a route table

without being updated• Flush Timer – 240 Sec

– Route will be advertised with the unreachable metric until the flush timer expires, at which time the route will be removed from the route table

• Holddown Timer – 180 Sec– Update with a hop count higher than the metric recorded in the route

table will cause the route to go into holddown for 180 seconds • Router(config)#Router rip• Router(config-router)#timers basic update invalid holddown flush• Timing of all the routers in the RIP domain must be changed

RIP Operation• Administrative Distance – 120• Case Study 1 - Classful Routing: Directly Connected Subnets

– Classful route lookups

• Case Study 2 - Summarization at Boundary Routers

• Router configuration– Select routing protocols.– Specify networks or interfaces.

IP Routing Configuration Tasks

– Defines an IP routing protocol

Router(config)#router protocol [keyword]

• Mandatory configuration command for each IP routing process

• Identifies the physically connected network that routing updates are forwarded to

Router(config-router)#network network-number

Dynamic Routing Configuration

– Starts the RIP routing process

Router(config)#router rip

Router(config-router)#network network-number

• Selects participating attached networks

• Requires a major classful network number

RIP Configuration

RIP Configuration Example

Verifying the RIP Configuration

Displaying the IP Routing Table

debug ip rip Command

Case Study 1 – Configuring RIP• Enable RIP with the command router rip• Specify each major network on which to run RIP with the

network command• debug ip rip – Observe network summarization and split

horizon

Case Study 2 – Passive Interfaces• Floyd (Don’t Include network 192.168.12.0)

– Router rip• Network 192.168.100.0

• Will the above method work for Andy Router??• To block RIP broadcasts on an interface connected to a subnet of a RIP-

enabled network. – Makes a router a silent host on the data link specified– Add the passive-interface interface# command to the RIP process

Case Study 3 – Configuring Unicast Updates• No RIP updates should be exchanged between Andy and

Floyd, but both should exchange updates with Bea• Addition of a neighbor command under the RIP processes of

Andy enables RIP to send a Unicast advertisement to Bea's interface

• passive-interface command continues to prevent broadcast updates on the link

Case Study 3 – Configuring Unicast Updates• Bea’s Rip Configurations• router rip • network 192.168.12.0 • network 192.168.200.0• Andy’s Rip Configuration• router rip • passive-interface Ethernet0 • network 172.17.0.0 • network 192.168.12.0 • network 192.168.83.0 • neighbor 192.168.12.67• Floyd RIP Configurations• router rip • passive-interface Ethernet0 • network 192.168.12.0 • network 192.168.100.0 • neighbor 192.168.12.67

Case Study 3 – Debug Ip RIP• Andy#debug ip rip events• RIP event debugging is on • Andy#• RIP: received v1 update from 192.168.12.67 on Ethernet0 • RIP: Update contains 1 routes • RIP: sending v1 update to 255.255.255.255 via Ethernet1 (192.168.83.1) • RIP: Update contains 4 routes• RIP: Update queued• RIP: Update sent via Ethernet1 • RIP: sending v1 update to 255.255.255.255 via Ethernet2 (192.168.12.195) • RIP: Update contains 6 routes • RIP: Update queued • RIP: Update sent via Ethernet2 • RIP: sending v1 update to 255.255.255.255 via Serial0 (172.17.1.1) • RIP: Update contains 7 routes • RIP: Update queued

Case Study 3 – Debug Ip RIP• RIP: Update sent via Serial0 • RIP: sending v1 update to 255.255.255.255 via Serial1 (172.17.2.1) • RIP: Update contains 7 routes • RIP: Update queued • RIP: Update sent via Serial1 • RIP: sending v1 update to 192.168.12.67 via Ethernet0 (192.168.12.65) • RIP: Update contains 4 routes • RIP: Update queued • RIP: Update sent via Ethernet0 • RIP: received v1 update from 172.17.1.2 on Serial0 • RIP: Update contains 1 routes • RIP: received v1 update from 172.17.2.2 on Serial1 • RIP: Update contains 1 routes • RIP: received v1 update from 192.168.12.67 on Ethernet0 • RIP: Update contains 1 routes

Case Study 4: Discontiguous Subnets• Classful protocols such as RIP and IGRP cannot route a

topology in which the subnets of network 10.0.0.0 are separated by different networks– Result is Andy will be "fooled into thinking" that it has two equal-cost

paths to the same network– Andy will load share on the links to Barney and Ernest_T– There is now only a 50-50 chance that packets to network 10.0.0.0 will

reach the correct subnet

Case Study 4: Secondary Addresses• Barney Configuration

– interface e0 – ip address 10.33.55.1 255.255.240.0 secondary

• Andy’s Configuration– interface e1 – ip address 10.33.55.2 255.255.240.0 secondary – interface e2 – ip address 10.33.75.1 255.255.240.0 secondary – router rip – network 10.0.0.0

• Ernest Configurations– interface e0 – ip address 10.33.75.2 255.255.240.0 secondary

•

Case Study 4: Secondary Addresses• Secondary addresses are used to connect the subnets of

network 10.0.0.0 across the same links on which other network addresses exist

• The routing process in this router sees the subnets 192.168.12.192/27 and 10.33.64.0/20 as separate data links, although they reside on the same physical interface– Check with Show ip route

Case Study 5: Manipulating RIP Metrics• RIP metrics must be manipulated so that the two-hop Ethernet route will

be preferred over the one-hop serial route.• Serial Link as a Back Up Link• The route metrics can be manipulated with the offset-list command• Offset-list {access-list-number | name} { in | out} offset [type number]

Case Study 5: Manipulating RIP Metrics• Ernest_T's RIP configuration with an inbound offset list• access-list 1 permit 10.33.0.0 0.0.0.0 • router rip

– network 192.168.12.0 – network 10.0.0.0 – offset-list 1 in 2 Serial0

• Barney's RIP configuration with an inbound offset list• router rip

– offset-list 5 in 2 Serial0 – network 10.0.0.0 – network 192.168.83.0

• access-list 5 permit 10.33.32.0 0.0.0.0

• Examine RIP advertisements incoming from interface S0. For route entries matching the addresses specified in access list 1, add 2 hops to the metric

•

Troubleshooting RIP• Most difficulties with classful protocols such as RIP involve• misconfigured subnet masks or • discontiguous subnets. • If a route table contains inaccurate or missing routes, check

all subnets for contiguity and all subnet masks for consistency• When a high-speed router is sending multiple RIP messages to

a low-speed router. In such a case, the low-speed router might not be able to process updates as quickly as they are received, and routing information might be lost.

• output-delay delay can be used under the RIP command to set an inter-packet gap of between 8 and 50 milliseconds

Review Questions• What port does RIP use?• What metric does RIP use? How is the metric used to indicate an

unreachable network?• What is the update period for RIP?• How many updates must be missed before a route entry will be marked as

unreachable?• What is the purpose of the garbage collection timer?• Why is a random timer associated with triggered updates? What is the

range of this timer?• What is the difference between a RIP Request message and a RIP

Response message?• Which two types of Request messages does RIP use?• Under what circumstances will a RIP response be sent?• Why does RIP hide subnets at major network boundaries?

Configuration Examples• Write configurations for six routers in Figure to route to all subnets via RIP

• Change the configurations of Configuration Exercise 1 so that RIP updates are unicast between RTC and RTD, instead of broadcast.

• The bandwidth of the serial link between RTC and RTD in Figure is very limited. Configure RIP to send updates across this link every two minutes. Carefully consider what timers must be changed and on what routers the timers must be changed.

Configuration Examples• A policy has been established that dictates that network 192.168.4.0

should be unreachable from RTA and that network 192.168.5.0 should be unreachable from RTB. Use one or more offset lists to implement this policy.

• Subnet masks within a major, class-level network must be consistent. The section does not, however, say that subnet masks within a major, class-level network must be identical. The RIP configuration for both routers in Figure follows:

– router rip network 192.168.20.0

• Will packets be routed correctly in this small network? Explain why or why not.

RIP Version 2• Subnet masks carried with each route entry• Authentication of routing updates• Next-hop addresses carried with each route entry• External route tags - Tagging external routes or routes that

have been redistributed into the RIPv2 process• Multicast route updates• RIPv2 multicasts updates to other RIPv2-speaking routers,

using the reserved class D address 224.0.0.9.

Case Study 1: Compatibility with RIPv1• router rip

– version 2 - send and receive version 2

• router rip – version 1

• interface Ethernet0 – ip address 192.168.50.129 255.255.255.192 – ip rip send version 1 – ip rip receive version 1

• interface Ethernet1 – ip address 172.25.150.193 255.255.255.240 – ip rip send version 1 2

• interface Ethernet2 – ip address 172.25.150.225 255.255.255.240

• router rip – version 2

RIP V1

RIP V2

Summary– RIP is a distance vector routing protocol that uses hop count as

the metric for route selection and broadcasts routing updates every 30 seconds.

– To enable a dynamic routing protocol, you will select the routing protocol and then assign IP network numbers.

– The router rip command specifies RIP as the routing protocol. The network command identifies a participating attached network.

– The show ip commands display information about routing protocols and the routing table.

– Use the debug ip rip command to display information on RIP routing transactions.