Routing Protocols and Concepts: Chapter 7 potx

Chapter 7
RIP version 2
Routing Protocols and Concepts
2
Topics
 RIPv1 Limitations
 RIPv1: Topology Limitations
 RIPv1: Discontiguous
Networks
 RIPv1: No VLSM Support
 RIPv1: No CIDR Support
 Configuring RIPv2
 Enabling and Verifying RIPv2
 Auto-Summary and RIPv2
 Disabling Auto-Summary in
RIPv2
 Verifying RIPv2 Updates
 VLSM and CIDR
 RIPv2 and VLSM
 RIPv2 and CIDR
 Verifying and Troubleshooting
RIPv2
 Verification and
Troubleshooting Commands
 Common RIPv2 Issues
 Authentication
RIPv1 Limitations
 RIPv1: Topology Limitations
 RIPv1: Discontiguous Networks
 RIPv1: No VLSM Support
 RIPv1: No CIDR Support

4
Note on Classful Routing Protocols, RIPv1 limitations
 The first part of this presentation discusses the limitations of classful
routing protocols such as RIPv1.
 RIPv1 is used as an example, so we can see how RIPv2 a classless
routing protocol does not have these same limitations.
 Classful routing protocols have three major limitations:
 Does not support discontiguous networks.
 Does not support VLSM
 Does not support CIDR
 Instead of just “memorizing” these facts, we will demonstrate and
“understand” why a classful routing protocol has these limitations.
5
RIPv1: Distance Vector, Classess Routing Protocol
 RIP Version 2 (RIPv2) is defined in RFC 1723.
 RIPv2 is the first classless routing protocol discussed in this book.
 RIPv2 has lost popularity when compared to other routing protocols
such as EIGRP, OSPF and IS-IS.
 RIPv2, it is ideal for explaining the differences between a classful
routing protocol (RIPv1) and a classless routing protocol (RIPv2).
6
RIPv1 and RIPv2
 RIPv2 is actually an enhancement of RIPv1’s features and extensions
rather than an entirely new protocol.
 Next-hop addresses included in the routing updates
 Use of multicast addresses in sending updates
 Authentication option available
 Both versions of RIP share the following features and limitations:
 Use of hold-down and other timers to help prevent routing loops
 Use of split horizon and split horizon with poison reverse to also

help prevent routing loops
 Use of triggered updates when there is a change in the topology for
faster convergence
 Maximum hop count of 15 hops, with the hop count of 16 signifying
an unreachable network
7
 In a discontiguous network, a classful major network address, such as
172.30.0.0/16, is separated by one or more other major networks.
 172.30.0.0/16 is divided by the networks:
 209.165.200.228/30
 209.165.200.232/30
 Classful routing protocols do not include enough routing information to
route properly for discontiguous networks.
RIPv1 Limitations
172.30.0.0
/16
172.30.0.0
/16
8
 R2: static summary route to the 192.168.0.0/16 network.
 Redistribution - Inject static route(s) into routing protocol updates.
 For now, this summary route will cause problems with RIPv1 because:
 192.168.0.0/16 is not a major classful address (192.168.0.0/24)
 Includes all the /24 versions of 192.168.0.0/16
Summary Route
172.30.0.0/16
172.30.0.0
/16
R2(config)# ip route 192.168.0.0 255.255.0.0 null0
9

 R1 and R3 contain VLSM networks.
 Both R1 and R3 are configured with /24 subnets of the 172.30.0.0/16
network.
 R3: 172.30.200.0/24 subnetted again, using the first 4 bits for subnets and
the last 4 for hosts.
 172.30.200.16/28 and 172.30.200.32/28
VLSM
172.30.0.0/16
172.30.0.0
/16
10
VLSM
 R3: 172.30.200.0/24 subnetted again, using the first 4 bits for
subnets and the last 4 for hosts.
 172.30.200.16/28 and 172.30.200.32/28
11
 We use RFC 1918 and Cisco Example addresses for all topologies.
Private Addresses and Cisco Example Addresses
RFC 1918 Private Addresses
Cisco Example Addresses
12
 Loopback interface
 Software-only interface
 Used to emulate an interface.
 Can be assigned an IP address.
 Specific purposes with some routing protocols such as OSPF (later)
 A loopback interface can be:
 pinged
 subnet advertised in routing updates.
 Ideal for simulating multiple networks attached to the same router.

Loopback Interfaces
172.30.0.0/16
172.30.0.0
/16
13
RIPv1 Topology Limitations
 RIPv1 configuration for all three routers
R1(config)# router rip
R1(config-router)# network 172.30.0.0
R1(config-router)# network 209.165.200.0
R2(config)# ip route 192.168.0.0 255.255.0.0 null0
R2(config)# router rip
R2(config-router)# redistribute static
R2(config-router)# network 10.0.0.0
R2(config-router)# network 209.165.200.0
R3(config)# router rip
R3(config-router)# network 172.30.0.0
R3(config-router)# network 209.165.200.0
14
Static Routes and
Null Interfaces
 CIDR allows route aggregation.
 A single high-level route entry with a subnet mask less than the classful
mask can be used to represent many lowerlevel routes.
 This results in fewer entries in the routing table.
 The static route on R2 is using a /16 mask to summarize all 256 networks
ranging from 192.168.0.0/24 to 192.168.255.0/24.
 For Lab purposes:
 The static summary route 192.168.0.0/16 does not actually exist.
 To simulate this static route, we will use a null interface as the exit

interface.
 You do not need to enter commands to create or configure the null
interface.
 It is always up but does not forward or receive traffic.
 Traffic sent to the null interface is discarded.
R2(config)# ip route 192.168.0.0 255.255.0.0 Null0
15
Route Redistribution
 Redistribution involves taking the routes from one routing source and
sending those routes to another routing source.
 Routes can only be redistributed into a dynamic routing protocol.
 Dynamic routing protocol to a different dynamic routing protocol.
 Static routes to a dynamic routing protocol.
 Directly connected networks to a dynamic routing protocol.
 Want R2 to redistribute our static route (192.168.0.0/16) by importing the
route into RIPv1 and then sending it to R1 and R3 using the RIPv1 process.
 We will see whether this is indeed happening, and if not, why not.
R2(config)# ip route 192.168.0.0
255.255.0.0 null0
R2(config)# router rip
R2(config-router)# redistribute static
Is static route being sent via RIPv1 with other RIPv1 routes?
16
Verifying and Testing
Connectivity
 Whenever R2 pings any of the 172.30.0.0 subnets on R1 or R3, only
about 50 percent of the pings are successful.
R2# ping 172.30.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.30.1.1, timeout is 2 seconds:

!U!.!
Success rate is 60 percent (3/5), round-trip min/avg/max = 28/29/32 ms
R2# ping 172.30.100.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.30.100.1, timeout is 2 seconds:
!U!.!
Success rate is 60 percent (3/5), round-trip min/avg/max = 28/28/28 ms
R2#
17
Verifying and Testing
Connectivity
 R1 is able to ping 10.1.0.1 but is unsuccessful when attempting to
ping the 172.30.100.1 interface on R3.
R1# ping 10.1.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5),round-trip min/avg/max = 28/28/28 ms
R1# ping 172.30.100.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.30.100.1, timeout is 2 seconds:

Success rate is 0 percent (0/5)
R1#
X
18
Verifying and Testing
Connectivity
 R3 is able to ping 10.1.0.1 but is unsuccessful when attempting to
ping the 172.30.1.1 interface on R1.

 As you can see, there is an obvious problem when trying to
communicate with the 172.30.0.0 discontiguous subnets.
R3# ping 10.1.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5),round-trip min/avg/max = 28/28/28 ms
R3# ping 172.30.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.30.1.1, timeout is 2 seconds:

Success rate is 0 percent (0/5)
R3#
X
19
RIPv1: Discontiguous Networks
 Because the subnet mask is not included in the update, RIPv1 and
other classful routing protocols must summarize networks at major
network boundaries.
20
 RIPv1 on both Routers R1 and R3 will summarize their 172.30.0.0
subnets to the classful major network address of 172.30.0.0 when
sending routing updates to R2.
RIPv1:
Discontiguous
Networks
21
Examining the Routing Tables
 R2 has two equal-cost routes to the 172.30.0.0/16 network.
 R1 and R3 are sending R2 a RIPv1 update for the 172.30.0.0 network

with a metric of 1 hop.
 R2’s routing table only contains the major classful network address of
172.30.0.0 and adds the Class B subnet mask of /16.
R2# show ip route
R 172.30.0.0/16 [120/1] via 209.165.200.230, 00:00:09, Serial0/0/0
[120/1] via 209.165.200.234, 00:00:11, Serial0/0/1
209.165.200.0/30 is subnetted, 2 subnets
C 209.165.200.232 is directly connected, Serial0/0/1
C 209.165.200.228 is directly connected, Serial0/0/0
10.0.0.0/16 is subnetted, 1 subnets
C 10.1.0.0 is directly connected, FastEthernet0/0
S 192.168.0.0/16 is directly connected, Null0
22
debug ip rip
 R2 is receiving two 172.30.0.0 equal-cost routes with a metric of 1 hop:
 one route on Serial 0/0/0 from R1 and
 the other route on Serial 0/0/1 from R3.
 Also notice that the subnet mask is not included with the network
address in the update.
R2# debug ip rip
RIP: received v1 update from 209.165.200.230 on Serial0/0/0
172.30.0.0 in 1 hops
RIP: received v1 update from 209.165.200.234 on Serial0/0/1
172.30.0.0 in 1 hops
RIP: sending v1 update to 255.255.255.255 via Serial0/0/0
(209.165.200.229)
RIP: build update entries
network 10.0.0.0 metric 1
subnet 209.165.200.232 metric 1
RIP: sending v1 update to 255.255.255.255 via Serial0/0/1

(209.165.200.233)
RIP: build update entries
network 10.0.0.0 metric 1
subnet 209.165.200.228 metric 1
23
show ip route
 R1 has its own 172.30.0.0 routes:
 172.30.2.0/24
 172.30.1.0/24.
 R1 does not send R2 those subnets.
 R1 and R3 are boundary routers only sending the summarized 172.30.0.0
 Result, R2 only knows about the 172.30.0.0/16 classful network and is
unaware of any 172.30.0.0 subnets.
R1# show ip route
172.30.0.0/24 is subnetted, 2 subnets
C 172.30.2.0 is directly connected, Loopback0
C 172.30.1.0 is directly connected, FastEthernet0/0
209.165.200.0/30 is subnetted, 2 subnets
R 209.165.200.232 [120/1] via 209.165.200.229, 00:00:16,Serial0/0/0
C 209.165.200.228 is directly connected, Serial0/0/0
R 10.0.0.0/8 [120/1] via 209.165.200.229, 00:00:16, Serial0/0/0
R1#
24
Determining the mask and network address
 Receiving an Update: Determining subnet mask for routing table
 What is the major classful network address of the receiving interface?
 What is the major classful network address of the network in the routing
update?
 Are they the same major classful network address?
 Yes: Apply subnet mask of the receiving interface for this network

address in the routing table.
 No: Apply classful subnet mask for this network address in the
routing table.
 Sending an Update: Determining whether or not to summarize route sent
 What is the major classful network address of the sending interface?
 What is the major classful network address of the network in the routing
update?
 Are they the same major classful network address?
 Yes: Send subnet network address
 No: Send summary address – the classful network address
25
Example 1
172.16.0.0/1610.0.0.0/8 192.168.1.0/24
.1 .1 .1.2