Ch. 16\Mod.7 – Distance Vector Routing
Protocols
Part 1 of 2: Distance Vector Routing and
RIP
CCNA 1 version 3.0
RIP routing process
• Request for Comments (RFC) 1058
• RIP has evolved over the years from a Classful Routing Protocol, RIP
Version 1 (RIP v1), to a Classless Routing Protocol, RIP Version 2 (RIP
v2). RIP v2 enhancements include:
– Ability to carry additional packet routing information.
– Authentication mechanism to secure table updates.
– Supports variable length subnet masking (VLSM).
Configuring RIP
Configuring RIP
RIP and IGRP:
• Classful network statements only
• IOS will take subnetted networks but will translate it into
the classful network for the running-config.
Configuring RIP
Clarifications (This is for IGPs only and not EGPs such as BGP):
• The network command does two things:
1. Determines which interfaces will participate in sending and receiving routing
updates, as long as the interface IP address falls in the range of the network
command.
2. Determines which networks this router will announce as being directly
connected to in its routing updates to other routers.
• The network numbers do not necessarily have to be based on the network
class, as it depends on the routing protocol. Network numbers are based on
the network class for RIP, IGRP, and usually EIGRP, but can be more specific
for OSPF, EIGRP and IS-IS.
Triggered Extensions
interface serial 0
ip rip triggered
Triggered Extensions to RIP
• http://www.cisco.com/en/US/products/sw/iosswrel/ps1830/products_feature_gu
ide09186a008008746f.html
• There were two problems using RIP to connect to a WAN:
– Periodic broadcasting by RIP generally prevented WAN circuits from being
closed.
– Even on fixed, point-to-point links, the overhead of periodic RIP
transmissions could seriously interrupt normal data transfer because of the
quantity of information that hits the line every 30 seconds.
• To overcome these limitations, triggered extensions to RIP cause RIP to send
information on the WAN only when there has been an update to the routing
database.
• Periodic update packets are suppressed over the interface on which this
feature is enabled.
Triggered Extensions
interface serial 0
ip rip triggered
•
•
•
RFC 2091, Triggered Extensions to RIP to Support Demand Circuits.
When triggered extensions to RIP are enabled, routing updates are transmitted
on the WAN only if one of the following occurs:
– The router receives a specific request for a routing update. (Full database is
sent.)
– Information from another interface modifies the routing database. (Only
latest changes are sent)
– The interface comes up or goes down. (Partial database is sent.)
– The router is first powered on, to ensure that at least one update is sent.
(Full database is sent.)
You might want to enable this feature if you are using an on-demand circuit and
you are charged for usage time. Fewer routing updates will incur lower usage
costs.
The RIPv1 Protocol
Data Link
Frame
Header
IP Packet
Header
UDP
Segment
Header
RIP Message
Data Link Frame

MAC Source Address

MAC Destination Address = Broadcast
IP Packet

IP Source Address

IP Destination Address = Broadcast: 255.255.255.255

Protocol field = 17 for UDP
UDP Segment

Source Port number field = 520 for RIP Message
RIP Message (Data portion of IP Packet):

Routes: Network IP Address

Hops (metric)
RIP
Message
Data Link
Frame
Header
IP Packet
Header
UDP
Segment
Header
RIP
Message
0
7 8
15 16
23 24
Command = 1 or 2
Version = 1
Must be zero
Address family identifier (2 = IP)
Must be zero
IP Address (Network Address)
Must be zero
Must be zero
Metric (Hops)
31
Multiple Routes, up to a maximum of 25
Address family identifier (2 = IP)
Must be zero
IP Address (Network Address)
Must be zero
Must be zero
Metric (Hops)
•
•
•
•
•
•
Command: 1 signifying a Request or 2 signifying a Reply
Version: 1 for RIP v 1 or 2 for RIP v 2
Address Family Identifier: 2 signifying IP (only exception is for a Request for the Router’s full routing
table, later Semester in RIP v 2)
IP Address: The address of the destination route, which may be a network address, a subnet address
of a host address.
Metric: Hop count between 1 and 16. Note: With RIP the sending router increases the metric before
sending out the RIP message.
Note: The routing table knows the next-hop-ip-address (via) from the source IP address of the packet.
RIP v2 message format
• All the extensions to the original protocol are carried in the unused
•
fields.
The Address Family Identifier (AFI) field is set to two for IP. The only
exception is a request for a full routing table of a router or host, in
which case it will be set to zero.
RIP v2 message format
•
•
•
•
The Route Tag field provides a way to differentiate between internal and
external routes.
External routes are those that have been redistributed into the RIP v2.
The Next Hop field contains the IP address of the next hop listed in the IP
Address field.
Metric indicates how many internetwork hops, between 1 and 15 for a valid
route, or 16 for an unreachable route.
Configuring RIP
RIP must be enabled and the networks specified. The remaining tasks are
optional. Among these optional tasks are:
• Applying offsets to routing metrics (Not commonly used)
• Adjusting timers
• Specifying a RIP version (RIPv1 or RIPv2)
• Enabling RIP authentication
• Configuring route summarization on an interface
• Verifying IP route summarization
• Disabling automatic route summarization (RIPv2)
• Running IGRP and RIP concurrently (Usually, redistributing, not concurrently.)
• Disabling the validation of source IP addresses
• Enabling or disabling split horizon
• Connecting RIP to a WAN
ip classless command
• IP classless only affects the operation of the forwarding processes in
IOS. IP classless does not affect the way the routing table is built.
• This command concerns classless and classful routing behavior,
which is not the same as classless and classful routing protocols
(later).
• To discuss this command, we will use information which is not in the
curriculum.
• For more information:
– The Routing Table: Part 1 or 2 - The Routing Table Structure
(PDF)
– The Routing Table: Part 2 or 2 - The Routing Table Lookup
Process (PDF)
Parent and Child Routes
RouterB#show ip route
R
C
C
C
S
S
S*
172.16.0.0/24 is subnetted, 3 subnets
172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0
172.16.2.0 is directly connected, Serial0
172.16.3.0 is directly connected, FastEthernet0
192.168.1.0/24 is directly connected, Serial1
172.0.0.0/8 is directly connected, Serial1
160.0.0.0/4 is directly connected, Serial1
0.0.0.0/0 is directly connected, Serial1
Parent Route
• Created automatically whenever there is a route with a mask greater
than the classful mask.
• For non-VLSM routes, contains the mask of the child routes.
Child Routes
• Routes with masks greater than the default classful mask.
Lookup what?
RouterB#show ip route
R
C
C
C
S
S
S*
172.16.0.0/24 is subnetted, 3 subnets
172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0
172.16.2.0 is directly connected, Serial0
172.16.3.0 is directly connected, FastEthernet0
192.168.1.0/24 is directly connected, Serial1
172.0.0.0/8 is directly connected, Serial1
160.0.0.0/4 is directly connected, Serial1
0.0.0.0/0 is directly connected, Serial1
Routing Table process matches:
• The routing table process compares the left-most bits in the packet’s
destination IP address with the left-most bits in the route in the routing table,
looking for a longest-bit-match.
• The subnet mask of the route in the routing table specifies the minimum
number of left-most bits that must match.
• Before checking child routes, the classful mask of the parent route is used.
• For child routes the parent route’s mask is used.
• For VLSM routes, the mask is contained with the child route.
Parent and Child Routes
RouterB#show ip route
R
C
C
C
S
S
S*
172.16.0.0/24 is subnetted, 3 subnets
172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0
172.16.2.0 is directly connected, Serial0
172.16.3.0 is directly connected, FastEthernet0
192.168.1.0/24 is directly connected, Serial1
172.0.0.0/8 is directly connected, Serial1
160.0.0.0/4 is directly connected, Serial1
0.0.0.0/0 is directly connected, Serial1
DA = 192.168.1.10
• 16 bits of 172.16.0.0 do not match, so child routes are not checked.
• 24 bits of 192.168.1.0/24 do match, so this route is used.
Parent and Child Routes
RouterB#show ip route
R
C
C
C
S
S
S*
172.16.0.0/24 is subnetted, 3 subnets
172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0
172.16.2.0 is directly connected, Serial0
172.16.3.0 is directly connected, FastEthernet0
192.168.1.0/24 is directly connected, Serial1
172.0.0.0/8 is directly connected, Serial1
160.0.0.0/4 is directly connected, Serial1
0.0.0.0/0 is directly connected, Serial1
DA = 172.16.2.1
• 16 bits of 172.16.0.0 do match, so child routes are checked.
• 24 bits of 172.16.1.0 do not match, so continue to next child route.
• 24 bits of 172.16.2.0 do match, so this route is used!
Parent and Child Routes
RouterB#show ip route
R
C
C
C
S
S
S*
172.16.0.0/24 is subnetted, 3 subnets
172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0
172.16.2.0 is directly connected, Serial0
172.16.3.0 is directly connected, FastEthernet0
192.168.1.0/24 is directly connected, Serial1
172.0.0.0/8 is directly connected, Serial1
160.0.0.0/4 is directly connected, Serial1
0.0.0.0/0 is directly connected, Serial1
DA = 32.1.1.10
• 16 bits of 172.16.0.0 do not match, so child routes are not checked.
• 24 bits of 192.168.1.0/24 do not match, so this route is not used.
• 8 bits of 172.0.0.0/8 do not match, so this route is not used.
• 4 bits of 160.0.0.0/4 do not match, so this route is not used.
• 0 bits of 0.0.0.0/0 does match, so this route is used!
Parent and Child Routes
RouterB#show ip route
R
C
C
C
S
S
S*
172.16.0.0/24 is subnetted, 3 subnets
172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0
172.16.2.0 is directly connected, Serial0
172.16.3.0 is directly connected, FastEthernet0
192.168.1.0/24 is directly connected, Serial1
172.0.0.0/8 is directly connected, Serial1
160.0.0.0/4 is directly connected, Serial1
0.0.0.0/0 is directly connected, Serial1
DA = 172.16.4.1
• 16 bits of 172.16.0.0 do match, so child routes are checked.
• 24 bits of 172.16.1.0 do not match, so continue to next child route.
• 24 bits of 172.16.2.0 do not match, so continue to next child route.
• 24 bits of 172.16.3.0 do not match, no more child routes.
Now what??? It depends!
Classful Routing Behavior
RouterB#show ip route
R
C
C
C
S
S
S*
172.16.0.0/24 is subnetted, 3 subnets
172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0
172.16.2.0 is directly connected, Serial0
172.16.3.0 is directly connected, FastEthernet0
192.168.1.0/24 is directly connected, Serial1
172.0.0.0/8 is directly connected, Serial1
160.0.0.0/4 is directly connected, Serial1
0.0.0.0/0 is directly connected, Serial1
DA = 172.16.4.1
Router(config)# no ip classless
• With classful routing behavior, if the child routes are checked but
there are no matches, the routing lookup process ends and the Packet
is dropped. (The packets get in, but they can’t get out!)
• Supernet and default routes are not checked.
• Default with IOS 11.2 and prior
Classless Routing Behavior
RouterB#show ip route
R
C
C
C
S
S
S*
172.16.0.0/24 is subnetted, 3 subnets
172.16.1.0 [120/1] via 172.16.2.1, 00:00:20, Serial0
172.16.2.0 is directly connected, Serial0
172.16.3.0 is directly connected, FastEthernet0
192.168.1.0/24 is directly connected, Serial1
172.0.0.0/8 is directly connected, Serial1
160.0.0.0/4 is directly connected, Serial1
0.0.0.0/0 is directly connected, Serial1
DA = 172.16.4.1
Router(config)# ip classless
• With classless routing behavior, if the child routes are checked but
there are no matches, the routing lookup process continues with other
routes in the routing table, including supernet and default routes.
• 8 bits of 172.0.0.0/8 do match, so this route is used!
• Default with IOS 11.3 and later
Common RIP Configuration Issues
Split Horizon
• The following command is used to disable split horizon:
GAD(config-if)#no ip split-horizon
• The following command is used to enable (default) split horizon:
GAD(config-if)#ip split-horizon
Common RIP Configuration Issues
Holddown Timer
• The ideal setting would be to set the timer just longer that the longest
possible update time for the internetwork.
• To change the holddown timer:
Router(config-router)#timers basic update invalid
holddown flush [sleeptime]
Common RIP Configuration Issues
Update Timer
• The default RIP update interval in Cisco IOS is 30 seconds. This can
be configured for longer intervals to conserve bandwidth, or for shorter
intervals to decrease convergence time.
• To change the update internal:
GAD(config-router)#update-timer seconds
Common RIP Configuration Issues
router rip
passive-interface fastethernet 0/0
For RIP and IGRP, the passive interface command stops the router from
sending updates to a particular neighbor, but the router continues to
listen and use routing updates from that neighbor. (More later.)
• Also used when there are no routers on that interface, such as stub
LANs.
Router(config-router)# passive-interface interface
Common RIP Configuration Issues
• Because RIP is a broadcast protocol, the network administrator may
•
•
have to configure RIP to exchange routing information in a nonbroadcast network such as Frame Relay.
In this type of network, RIP needs to be told of other neighboring RIP
routers.
To do this use the router rip command:
Router(config-router)# neighbor ip address
Common RIP Configuration Issues
• By default, the Cisco IOS software receives RIP Version 1 and Version
•
2 packets, but sends only Version 1 packets.
The network administrator can configure the router to only receive and
send Version 1 packets or the administrator can configure the router to
send only Version 2 packets.
Compatibility with RIP v1
NewYork
interface fastethernet0/0
ip address 192.168.50.129 255.255.255.192
ip rip send version 1
ip rip receive version 1
RIPv2
interface fastethernet0/1
ip address 172.25.150.193 255.255.255.240
ip rip send version 1 2
•
•
•
Interface FastEthernet0/0 is
configured to send and receive
RIP v1 updates.
FastEthernet0/1 is configured
to send both version 1 and 2
updates.
FastEthernet0/2 has no special
configuration and therefore
sends and receives version 2
by default.
interface fastethernet0/2
ip address 172.25.150.225 225.255.255.240
router rip
version 2
network 172.25.0.0
network 192.168.50.0
Verifying RIP configuration
Verifying RIP configuration
• Also: show running-config
Troubleshooting RIP update issues
Troubleshooting RIP update issues
Other commands to troubleshoot RIP:
• show ip rip database
• show ip protocols {summary}
• show ip route
• debug ip rip {events}
• show ip interface brief
Load balancing with RIP
• RIP is capable of load balancing over as many as six equal-cost paths,
•
with four paths being default. RIP performs what is referred to as
“round robin” load balancing.
This means that RIP takes turns forwarding packets over the parallel
paths.
• This is only part of the story…
Fast Switching and Process Switching
The following information is taken from Routing TCP/IP Volume I by Jeff Doyle.
• Load sharing or Load balancing allows routers to take advantage of
•
•
•
multiple paths to the same destination.
Equal-cost load balancing:
– Distributes packets equally among multiple paths with equal metrics
– RIP, IGRP, EIGRP, OSPF, IS-IS and BGP
Unequal-cost load balancing:
– Distributes packets among multiple paths with different metrics,
inversely proportional to the cost of the routes.
– EIGRP
Load sharing can be either:
– Per Destination (Fast Switching)
– Per Packet ( Process Switching)
Fast Switching
– Per Destination Load Balancing
Router(config-if)# ip route-cache
ping 10.0.0.2
•
•
•
•
•
ping 10.0.0.1
The default for most interfaces is Fast Switching.
Load balancing is distributed according to the destination IP address.
Given two paths to the same network, all packets for one destination IP
address will travel over the first path, all packets for a second destination will
travel over the second path, all packets for the third destination will again travel
over the first path, and so on.
To enable fast switching:
Router(config-if)# ip route-cache
To enable distributed or process switching:
Router(config-if)# no ip route-cache
Fast Switching
– Per Destination Load Balancing
Router(config-if)# ip route-cache
ping 10.0.0.2
ping 10.0.0.1
Fast Switching
1. Router switches first packet to a particular destination, a routing table lookup
is performed and an exit interface is selected.
2. The necessary data-link information to frame the packet for the selected
interface is retrieved including any ARP cache information.
3. The route and data-link information is stored in fast switching cache.
4. The router uses the cache to look up subsequent packets.
5. All other packets to the same destination are immediately switched out the
same interface without the router performing another routing table lookup,
including any recursive lookups. (Also no ARP cache lookup).
Process Switching
– Per Packet Load Balancing
Router(config-if)#no ip route-cache
ping 10.0.0.2
ping 10.0.0.1
Process Switching
• Given equal cost paths, per packet load sharing means that one packet to a
destination is sent over one link, the next packet to the same destination is
sent over the next link, and so on.
• If the paths are unequal cost, the load balancing may be one packet over the
higher-cost link for every three packets over the lower-cost link, or similar
ratio.
• With process switching, for every packet, the router performs a route table
lookup and selects an interface, and looks up the data-link information.
• To enable distributed or process switching:
Router(config-if)# no ip route-cache
Which one?
Fast Switching
ping 10.0.0.2
ping 10.0.0.1
Router(config-if)# ip route-cache
Process Switching
ping 10.0.0.2
ping 10.0.0.1
Router(config-if)#no ip route-cache
Fast Switching or Process Switching
• Process switching (per packet load balancing) has a price, load
balancing may be distributed more evenly but the lower switching time
and processor utilization of fast switching are lost.
Using debug ip packet with
Fast Switching and Process Switching
Router# debug ip packet
IP: s=192.168.3.2 (FastEthernet0),
g=192.168.1.2, forward
IP: s=192.168.3.2 (FastEthernet0),
g=192.168.2.2, forward
IP: s=192.168.3.2 (FastEthernet0),
g=192.168.1.2, forward
IP: s=192.168.3.2 (FastEthernet0),
g=192.168.2.2, forward
•
•
d=10.0.0.1 (Serial0/0),
d=10.0.0.1 (Serial0/1),
d=10.0.0.1 (Serial0/0),
d=10.0.0.1 (Serial0/1),
debug ip packet can be used to observe packets sent
and received and the interfaces that are involved.
IMPORTANT: The debug ip packet command allows
only process switched packets to be observed. Fast switch
packets are not displayed (except for the first packet in the
flow).
Load balancing across multiple paths
• Note: The example used in this section of the online curriculum is really
•
•
•
•
for IGRP/EIGRP and does not fit well in this section of RIP.
By default, most IP routing protocols install a maximum of four parallel
routes in a routing table.
Static routes always install six routes.
The exception is BGP, which by default allows only one path to a
destination.
The range of maximum paths is one to six paths. To change the
maximum number of parallel paths allowed, use the following
command in router configuration mode:
Router(config-router)#maximum-paths [number]
RIP and Administrative Distance
RIP and Floating Static Routes
X
172.16.0.0/16
router rip
network 192.168.14.0
ip route 172.16.0.0 255.255.0.0 bri0/1 130
• Floating static routes are static routes which are used as backup
•
•
routes.
They are only injected into the routing table when a route with a lower
administrative distance (dynamic or another static route) goes down.
Should the route with the lower administrative distance come back up
then the floating static route is removed from the routing table.
Redistribute Static
172.16.0.0/16
RIP
•
•
•
RouterA
ip route 172.16.0.0 255.255.0.0 eth 0
Router rip
redistribute static
network ….
Redistributes static routes into the dynamic routing domain.
172.16.0.0/16 will be seen by other RIP routers as a
dynamic route learned via RIP.
The default metric is 0, so B and D will have a hop count of
1, where C will have a hop count of 2.
RIPv1 Labs – 3 Scenarios
•
•
•
Read the following lab.
In groups review the configurations and the outputs.
Afterwards, we will discuss the this lab together, paying
particular attention to the Reflection sections.
RIPv1 Labs – 3 Scenarios
Objective
• In this lab, you will configure RIP routing in three different scenarios.
• At the end of each scenario, all hosts and all routers should be able to reach
(ping) each other.
Scenario
There are five separate classful networks. After configuring RIP, we want to view
the RIP update messages being sent and received by each router.
•
•
•
Scenario 1: Running RIPv1 on classful networks
Scenario 2: Running RIPv1 on subnets and between classful networks
Scenario 3: Running RIPv1 on a stub network
These three scenarios can be done in sequence or separately.
RIPv1 Labs – 3 Scenarios
Setup
• Use the 8 Steps to Success to help you configure the routers.
• Be sure your cabling is correct, as this causes more troubleshooting issues
than anything else.
• If the routers have a startup-config already on them, erase it and reboot the
routers.
• Configure the routers to include hostnames and the proper interface
commands including IP addresses, subnet masks, etc.
• Each router should be able to ping the interface of the adjacent (neighboring)
router and the host on its LAN (Ethernet) interface.
• Test and troubleshoot as necessary.
Basic Configurations
• There is a Basic Configuration included for each scenario, but it does not
include clock rate, no shutdown and some other necessary commands.
• Note: Even though some of the networks are in numerical order, obviously this
does not need to be the case. We only did this to make it easier to remember
where the networks originated from.
RIPv1 Labs – 3 Scenarios
Optional: Keeping outputs from interrupting our inputs
Before we begin to configure RIP, lets configure the console 0 port to keep debug and other
output messages from interrupting our input. Use the following command on each router
to keep the debug out from interfering with you command-line input:
Router(config)# line console 0
Router(config-line)# logging synchronous
Optional: Changing the default timeout
After 10 minutes, by default, if there is no input via the console, the user will be logged off.
Although a good idea in production environment, in a lab environment this can be
somewhat annoying. To turn-off the automatic timeout feature, we use the command:
exec-timeout minutes [seconds], setting both the minutes and seconds to 0.
Router(config)# line console 0
Router(config-line)# exec-timeout 0 0
Scenario 1: Running RIPv1 on classful networks
SanJose2
hostname SanJose2
interface ethernet 0
ip add 192.168.1.1 255.255.255.0
interface serial 0
ip add 192.168.2.1 255.255.255.0
SanJose1
hostname SanJose1
interface ethernet 0
ip add 192.168.3.1 255.255.255.0
interface serial 0
ip add 192.168.2.2 255.255.255.0
interface serial 1
ip add 192.168.4.2 255.255.255.0
Baypointe
hostname Baypointe
interface ethernet 0
ip add 192.168.5.1 255.255.255.0
interface serial 0
ip add 192.168.4.1 255.255.255.0
Scenario 1: Running RIPv1 on classful networks
Objective: Running RIPv1 on classful networks
This scenario is the same one we used in the network discovery lab, with the same
configurations and the same outputs. The concepts specific to this scenario will become
more clear when we view the differences between this scenario and Scenario 2: Running
RIPv1 on subnets and between classful networks.
Step 1 – Configuring RIP
First, lets enable RIP on each router.
From global configuration you will enter the command (the default is RIPv1):
Router(config)#router rip
Once you are in the Router RIP configuration sub-mode, all you need to do is enter the
classful network address for each directly connected network, using the network
command.
Router(config-router)#network directly-connected-classful-networkaddress
Scenario 1: Running RIPv1 on classful networks
Here are the commands for each router:
SanJose2#configure terminal
Enter configuration commands, one per line.
SanJose2(config)#router rip
SanJose2(config-router)#network 192.168.1.0
SanJose2(config-router)#network 192.168.2.0
End with CNTL/Z.
Baypointe#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Baypointe(config)#router rip
Baypointe(config-router)#network 192.168.4.0
Baypointe(config-router)#network 192.168.5.0
SanJose1#configure terminal
Enter configuration commands, one per line.
SanJose1(config)#router rip
SanJose1(config-router)#network 192.168.2.0
SanJose1(config-router)#network 192.168.3.0
SanJose1(config-router)#network 192.168.4.0
End with CNTL/Z.
Step 2 – Understanding the network command
SENDING RIP MESSAGES
Each router will begin to send RIP update message out each interface belonging to one of the network
statements.
SanJose2(config)#router rip
SanJose2(config-router)#network 192.168.1.0
SanJose2(config-router)#network 192.168.2.0
For example, SanJose2 to will send out RIP update messages on Ethernet 0 because that interface has an
IP address that belong to the network 192.168.1.0, and on Serial 0 because that interface has an IP
address that belongs to the network 192.168.2.0.
Just because a router has a directly connected network does not mean it will automatically include that
network in its routing updates to neighboring routers. The network command also tells the RIP to
include these networks in its updates to adjacent neighbors.
To view the RIP messages being sent and received use the debug ip rip command.
SanJose2# debug ip rip
RIP protocol debugging is on
SanJose2
01:03:27: RIP: sending v1 update to
01:03:27:
network 192.168.2.0,
01:03:27: RIP: sending v1 update to
01:03:27:
network 192.168.1.0,
255.255.255.255 via Ethernet0 (192.168.1.1)
metric 1
255.255.255.255 via Serial0 (192.168.2.1)
metric 1
Scenario 1: Running RIPv1 on classful networks
LISTENING FOR RIP MESSAGES
Routers will also listen for RIP messages on each interface belonging to one of the
network statements.
For example, SanJose2 to will listen for RIP update messages on Ethernet 0
because that interface has an IP address that belong to the network
192.168.1.0, and also listen for RIP update messages on Serial 0 because that
interface has an IP address that belongs to the network 192.168.2.0.
As RIP messages are received router, will add those networks in the messages to
their routing tables:
If the RIP message contains a network not currently in the routing table.
If the RIP message contains a network with a better metric (fewer hops) than an
entry currently in the routing table.
SanJose2
01:10:56: RIP: received v1 update from 192.168.2.2 on Serial0
01:10:56:
192.168.4.0 in 1 hops
01:10:56:
192.168.3.0 in 1 hops
Scenario 1: Running RIPv1 on classful networks
Step 3 – Viewing the debug ip rip output and the routing tables
Remember that SanJose1 will learn routes to networks from SanJose2. It
will then send that information to Baypointe, telling Baypointe that it is
the next hop to get to those networks, and incrementing the metric (hop
count) by one.
After convergence, each router will continue to send its RIP update
messages out the appropriate interfaces every 30 seconds.
Lets look at the debug messages and the routing table for each router:
SanJose2
01:30:45: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (192.168.1.1)
01:30:45:
network 192.168.4.0, metric 2
01:30:45:
network 192.168.5.0, metric 3
01:30:45:
network 192.168.2.0, metric 1
01:30:45:
network 192.168.3.0, metric 2
01:30:45: RIP: sending v1 update to 255.255.255.255 via Serial0 (192.168.2.1)
01:30:45:
network 192.168.1.0, metric 1
SanJose2#
01:30:50: RIP: received v1 update from 192.168.2.2 on Serial0
01:30:50:
192.168.4.0 in 1 hops
01:30:50:
192.168.5.0 in 2 hops
01:30:50:
192.168.3.0 in 1 hops
SanJose2#
SanJose2#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<omitted>
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
R
192.168.4.0/24
R
192.168.5.0/24
C
192.168.1.0/24
C
192.168.2.0/24
R
192.168.3.0/24
SanJose2#
[120/1] via
[120/2] via
is directly
is directly
[120/1] via
192.168.2.2, 00:00:10, Serial0
192.168.2.2, 00:00:10, Serial0
connected, Ethernet0
connected, Serial0
192.168.2.2, 00:00:10, Serial0
SanJose1
01:33:05:
01:33:05:
SanJose1#
01:33:07:
01:33:07:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
01:33:08:
RIP: received v1 update from 192.168.4.1 on Serial1
192.168.5.0 in 1 hops
RIP: received v1 update from 192.168.2.1 on Serial0
192.168.1.0 in 1 hops
RIP: sending v1 update to 255.255.255.255 via Ethernet0 (192.168.3.1)
network 192.168.4.0, metric 1
network 192.168.5.0, metric 2
network 192.168.1.0, metric 2
network 192.168.2.0, metric 1
RIP: sending v1 update to 255.255.255.255 via Serial0 (192.168.2.2)
network 192.168.4.0, metric 1
network 192.168.5.0, metric 2
network 192.168.3.0, metric 1
RIP: sending v1 update to 255.255.255.255 via Serial1 (192.168.4.2)
network 192.168.1.0, metric 2
network 192.168.2.0, metric 1
network 192.168.3.0, metric 1
SanJose1#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<omitted>
Gateway of last resort is not set
C
192.168.4.0/24 is directly connected, Serial1
R
192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:12, Serial1
R
192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:10, Serial0
C
192.168.2.0/24 is directly connected, Serial0
C
192.168.3.0/24 is directly connected, Ethernet0
Baypointe
01:34:53: RIP:
01:34:53:
01:34:53:
01:34:53:
01:34:53:
01:34:53: RIP:
01:34:53:
Baypointe#
01:34:56: RIP:
01:34:56:
01:34:56:
01:34:56:
sending
network
network
network
network
sending
network
v1 update to
192.168.4.0,
192.168.1.0,
192.168.2.0,
192.168.3.0,
v1 update to
192.168.5.0,
received v1
192.168.1.0
192.168.2.0
192.168.3.0
255.255.255.255 via Ethernet0 (192.168.5.1)
metric 1
metric 3
metric 2
metric 2
255.255.255.255 via Serial0 (192.168.4.1)
metric 1
update from 192.168.4.2 on Serial0
in 2 hops
in 1 hops
in 1 hops
Baypointe#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
C
C
R
R
R
192.168.4.0/24
192.168.5.0/24
192.168.1.0/24
192.168.2.0/24
192.168.3.0/24
is directly
is directly
[120/2] via
[120/1] via
[120/1] via
connected, Serial0
connected, Ethernet0
192.168.4.2, 00:00:23, Serial0
192.168.4.2, 00:00:23, Serial0
192.168.4.2, 00:00:23, Serial0
Scenario 1: Running RIPv1 on classful networks
NOTE: At this point all routers should be able to ping all networks. We will discuss RIP much
more in the chapter on Routing Protocols (RIP).
Step 4 – Turning-off debug
Don’t forget to turn-off debug when you are done collecting the output.
Router# undebug all
or
Baypointe# undebug ip rip
Step 5 – Reflections
• For each router compare the RIP received messages with its routing table. Now you see
how the information is entered into the routing table.
• Cisco IOS uses split horizon with poison reverse, however this information is not
displayed with debug ip rip command.
• You will notice that the routers send RIP messages out their stub Ethernet interfaces,
even though there are no routers out there to receive those messages. This does take up
unnecessary bandwidth on the link; so later we will see how to keep those RIP messages
from going out those interfaces.
Scenario 2: Running RIPv1 on subnets and between
classful networks
Note: This lab has some
important information regarding
RIP and boundary routers!
SanJose2
hostname SanJose2
interface ethernet 0
ip add 172.30.1.1 255.255.255.0
interface serial 0
ip add 172.30.2.1 255.255.255.0
SanJose1
hostname SanJose1
interface ethernet 0
ip add 172.30.3.1 255.255.255.0
interface serial 0
ip add 172.30.2.2 255.255.255.0
interface serial 1
ip add 192.168.4.9 255.255.255.252
Baypointe
hostname Baypointe
interface ethernet 0
ip add 192.168.5.1 255.255.255.0
interface serial 0
ip add 192.168.4.10 255.255.255.252
Scenario 2: Running RIPv1 on subnets and between
classful networks
Objective: Running RIPv1 on subnets and between classful networks
In this scenario we will see how subnetted routes are distributed with the same classful
network. We will also see how RIPv1 automatically summarizes between classful
network boundaries. You will notice that SanJose1 and SanJose2 have subnets
belonging to the 172.30.0.0 network, but Baypointe does not.
Making changes between Scenario 1 and Scenario 2
Be sure to change the IP addressing as displayed in the diagram and Basic Configuration
section for Scenario 2. Sometimes when changing the IP address on a serial
interface, you may need to reset that interface by doing a shutdown, wait for the
LINK-5-CHANGED message, then follow it with a no shutdown command.
If you have just completed Scenario 1, lets remove RIP by issuing the following command
on each router:
Router(config)# no router rip
Scenario 2: Running RIPv1 on subnets and between
classful networks
Step 1 – Configuring RIP
Once again, lets enable RIP on each router.
Once you are in the Router RIP configuration sub-mode, all you need to do
is enter the classful network address for each directly connected
network, using the network command. If a router has multiple
interfaces on the same classful network, you will only need to enter a
single command enabling RIP on all interfaces for that network.
Router(config-router)#network directly-connectedclassful-network-address
Here are the commands for each router:
SanJose2#configure terminal
Enter configuration commands, one per line.
SanJose2(config)#router rip
SanJose2(config-router)#network 172.30.0.0
End with CNTL/Z.
Notice we only used a single network statement for SanJose2, which includes both interfaces, on different
subnets, of the 172.30.0.0 major network.
SanJose1#configure terminal
Enter configuration commands, one per line.
SanJose1(config)#router rip
SanJose1(config-router)#network 172.30.0.0
SanJose1(config-router)#network 192.168.4.0
End with CNTL/Z.
Again, notice that we only used a single network statement for SanJose1, which includes both interfaces, on
different subnets, of the 172.30.0.0 major network.
Baypointe#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Baypointe(config)#router rip
Baypointe(config-router)#network 192.168.4.0
Baypointe(config-router)#network 192.168.5.0
Scenario 2: Running RIPv1 on subnets and between
classful networks
Question: What would happen if you entered a network statement that
was a subnet? For example:
SanJose2(config)#router rip
SanJose2(config-router)#network 172.30.1.0
Answer: The IOS would automatically convert it to a classful network
statement:
SanJose2#show running-config
router rip
network 172.30.0.0
Step 2 – Viewing the debug ip rip output and the routing tables
SanJose2
SanJose2# debug ip rip
00:14:10: RIP: received v1 update from 172.30.2.2 on Serial0
00:14:10:
172.30.3.0 in 1 hops
00:14:10:
192.168.4.0 in 1 hops
00:14:10:
192.168.5.0 in 2 hops
SanJose2#
00:14:29: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.30.1.1)
00:14:29:
subnet 172.30.2.0, metric 1
00:14:29:
subnet 172.30.3.0, metric 2
00:14:29:
network 192.168.4.0, metric 2
00:14:29:
network 192.168.5.0, metric 3
00:14:29: RIP: sending v1 update to 255.255.255.255 via Serial0 (172.30.2.1)
00:14:29:
subnet 172.30.1.0, metric 1
SanJose2#
00:14:39: RIP: received v1 update from 172.30.2.2 on Serial0
00:14:39:
172.30.3.0 in 1 hops
00:14:39:
192.168.4.0 in 1 hops
00:14:39:
192.168.5.0 in 2 hops
SanJose2# undebug all
SanJose2#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<omitted>
Gateway of last resort is not set
172.30.0.0/24 is subnetted, 3 subnets
C
172.30.2.0 is directly connected, Serial0
R
172.30.3.0 [120/1] via 172.30.2.2, 00:00:08, Serial0
C
172.30.1.0 is directly connected, Ethernet0
R
192.168.4.0/24 [120/1] via 172.30.2.2, 00:00:08, Serial0
R
192.168.5.0/24 [120/2] via 172.30.2.2, 00:00:08, Serial0
Scenario 2: Running RIPv1 on subnets and between
classful networks
Reflections
• IMPORTANT INFORMATION: RIPv1 is a classful routing protocol. Classful routing
protocols do not send the subnet mask with network in routing updates, ie. 172.30.1.0 is
sent by SanJose1 to SanJose2 without any subnet mask information.
• QUESTION: Notice that SanJose2 is receiving the subnet 172.30.3.0 from SanJose1,
which is put in the routing table under the parent network (classful network) of 172.30.0.0
with the /24 subnet mask (172.30.0.0/24 is subnetted, 3 subnets). Also notice that the
RIP message received from SanJose1 was “172.30.3.0 in 1 hops” but did not include a
subnet mask for the subnet. How does SanJose2 know that this subnet has a /24
(255.255.255.0) subnet mask?
• ANSWER: SanJose2 received this information on an interface belonging to the same
classful network as the incoming 172.30.3.0 update. The IP address that SanJose1
received the “172.30.3.0 in 1 hops” message was on (Serial 0) with an IP address of
172.30.2.1 and a subnet mask of 255.255.255.0. SanJose2 uses its own subnet mask
and applies it to this and all other 172.30.0.0 subnets it receives on this interface. The
172.30.3.0 network is placed with the other 172.30.0.0 /24 subnets in the routing table.
• Routers running RIPv1 are limited to using the same subnet mask for all subnets with the
same classful network. Classless routing protocols like RIPv2 allow the same major
(classful) network to use different subnet masks on different subnets. This is known as
VLSM (Variable Length Subnet Masks) and is discussed later (Cabrillo’s CCNA Sem 2
course and the CCNP Advanced Routing).
SanJose1
SanJose1#debug ip rip
RIP protocol debugging is on
SanJose1#
00:17:52: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.30.3.1)
00:17:52:
subnet 172.30.2.0, metric 1
00:17:52:
subnet 172.30.1.0, metric 2
00:17:52:
network 192.168.4.0, metric 1
00:17:52:
network 192.168.5.0, metric 2
00:17:52: RIP: sending v1 update to 255.255.255.255 via Serial0 (172.30.2.2)
00:17:52:
subnet 172.30.3.0, metric 1
00:17:52:
network 192.168.4.0, metric 1
00:17:52:
network 192.168.5.0, metric 2
00:17:52: RIP: sending v1 update to 255.255.255.255 via Serial1 (192.168.4.9)
00:17:52:
network 172.30.0.0, metric 1
SanJose1#
00:18:10: RIP: received v1 update from 172.30.2.1 on Serial0
00:18:10:
172.30.1.0 in 1 hops
SanJose1#
00:18:12: RIP: received v1 update from 192.168.4.10 on Serial1
00:18:12:
192.168.5.0 in 1 hops
SanJose1# undebug all
SanJose1#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<omitted>
Gateway of last resort is not set
172.30.0.0/24 is subnetted, 3 subnets
C
172.30.2.0 is directly connected, Serial0
C
172.30.3.0 is directly connected, Ethernet0
R
172.30.1.0 [120/1] via 172.30.2.1, 00:00:14, Serial0
192.168.4.0/30 is subnetted, 1 subnets
C
192.168.4.8 is directly connected, Serial1
R
192.168.5.0/24 [120/1] via 192.168.4.10, 00:00:10, Serial1
Scenario 2: Running RIPv1 on subnets and between
classful networks
Reflections
• The same subnet route information applies with routes sent from
SanJose2 to SanJose1 (see Reflections for SanJose2).
• SanJose1 knows that the 172.30.1.0 update has a subnet mask of /24
because it received it on an interface with a /24 subnet mask (Serial 0,
172.30.3.2 255.255.255.0).
SanJose1#debug ip rip
RIP protocol debugging is on
SanJose1#
00:17:52: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.30.3.1)
00:17:52:
subnet 172.30.2.0, metric 1
00:17:52:
subnet 172.30.1.0, metric 2
00:17:52:
network 192.168.4.0, metric 1
00:17:52:
network 192.168.5.0, metric 2
00:17:52: RIP: sending v1 update to 255.255.255.255 via Serial0 (172.30.2.2)
00:17:52:
subnet 172.30.3.0, metric 1
00:17:52:
network 192.168.4.0, metric 1
00:17:52:
network 192.168.5.0, metric 2
00:17:52: RIP: sending v1 update to 255.255.255.255 via Serial1 (192.168.4.9)
00:17:52:
network 172.30.0.0, metric 1
SanJose1#
00:18:10: RIP: received v1 update from 172.30.2.1 on Serial0
00:18:10:
172.30.1.0 in 1 hops
SanJose1#
00:18:12: RIP: received v1 update from 192.168.4.10 on Serial1
00:18:12:
192.168.5.0 in 1 hops
SanJose1# undebug all
SanJose1#show ip route
Codes: <omitted>
Gateway of last resort is not set
172.30.0.0/24 is subnetted, 3 subnets
C
172.30.2.0 is directly connected, Serial0
C
172.30.3.0 is directly connected, Ethernet0
R
172.30.1.0 [120/1] via 172.30.2.1, 00:00:14, Serial0
192.168.4.0/30 is subnetted, 1 subnets
C
192.168.4.8 is directly connected, Serial1
R
192.168.5.0/24 [120/1] via 192.168.4.10, 00:00:10, Serial1
Scenario 2: Running RIPv1 on subnets and between
classful networks
More Reflections
• IMPORTANT INFORMATION: Notice the RIP update being sent out Serial 1:
RIP: sending v1 update to 255.255.255.255 via Serial1 (192.168.4.9)
network 172.30.0.0, metric 1
•
Compare that to the same information for the 172.30.0.0 network being sent out
Serial 0 & Ethernet 0:
RIP: sending v1 update to 255.255.255.255 via Serial0 (172.30.2.2)
subnet 172.30.3.0, metric 1
•
•
•
Notice that the 172.30.0.0 subnets are being summarized to their classful
network address of 172.30.0.0 when sent out Serial 1 to Baypointe.
RIP automatically summarizes RIP updates between classful networks.
Because the 172.30.0.0 update is being sent out an interface (Serial 1) on a
different classful network (192.168.4.0), RIP sends out only a single update for
the entire classful network instead of all of the different subnets. This is similar
to what we did with summarizing several static routes into a single static route.
A router like SanJose1, which has an interface in more than one classful
network is sometimes called a “boundary router” in RIP. Boundary routers
automatically summarize RIP subnets from one classful network to the other.
Scenario 2: Running RIPv1 on subnets and between
classful networks
More Reflections (continued)
• How is this an advantage? Fewer updates sent and received, resulting in less
bandwidth used for routing updates between SanJose1 and Baypointe. Just as
importantly, Baypointe will now only have a single route for the 172.30.0.0/16
network, no matter how many subnets there are or how it is subnetted. This will
result in faster lookup process in the routing table for Baypointe.
• What do you expect to see in Baypointe’s received RIP messages and its
routing table? That’s right, only a single 172.30.0.0 network via SanJose1.
• Are there any disadvantages? Yes, discontinguous networks. We will see
this later, but the idea here is what if Baypointe had another connection via
Serial 1 to another router, SantaCruz1 on 192.168.4.12/30 subnet, which also
has other 172.30.0.0/24 subnets (172.30.4.0/24, 172.30.5.0/24, etc.).
Baypointe would also receive the same 172.30.0.0 network from SantaCruz1 as
well. Baypointe would not know how to reach the specific subnet, and
mistakenly load-balance the packets between the two routers. We will see an
example of this later this semester.
Baypointe
Baypointe#debug ip rip
RIP protocol debugging is on
Baypointe#
00:20:09: RIP: received v1 update from 192.168.4.9 on Serial0
00:20:09:
172.30.0.0 in 1 hops
Baypointe#
00:20:24: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (192.168.5.1)
00:20:24:
network 172.30.0.0, metric 2
00:20:24:
network 192.168.4.0, metric 1
00:20:24: RIP: sending v1 update to 255.255.255.255 via Serial0 (192.168.4.10)
00:20:24:
network 192.168.5.0, metric 1
Baypointe#
Baypointe#undebug all
Baypointe#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<omitted>
Gateway of last resort is not set
R
C
C
172.30.0.0/16 [120/1] via 192.168.4.9, 00:00:11, Serial0
192.168.4.0/30 is subnetted, 1 subnets
192.168.4.8 is directly connected, Serial0
192.168.5.0/24 is directly connected, Ethernet0
Scenario 2: Running RIPv1 on subnets and between
classful networks
Reflections
• Notice that Baypointe is only receiving the classful summary of the 172.30.0.0
subnets:
RIP: received v1 update from 192.168.4.9 on Serial0
172.30.0.0 in 1 hops
•
•
•
R
SanJose1 automatically summarized the subnets into a single classful update.
This keeps Baypointe’s routing table smaller, resulting in faster routing table
lookups.
This also isolates any changes in the 172.30.0.0 network on SanJose1 and
SanJose2 from affecting Baypointe. In other words, SanJose1 and SanJose2
can add and delete 172.30.0.0/24 subnets without affecting Baypointe’s routing
table, as Baypointe doesn’t care. Baypointe will send all packets destined for
the 172.30.0.0/16 network to SanJose1. Baypointe’s routing table:
172.30.0.0/16 [120/1] via 192.168.4.9, 00:00:11, Serial0
Also, the subnet mask scheme could be changed (i.e. to /27) on the 172.30.0.0
network without affecting Baypointe’s routing table or the RIP update sent to
Baypointe by SanJose1.
Scenario 3: Running RIPv1 on a stub network
SanJose2
hostname SanJose2
interface ethernet 0
ip add 172.30.1.1 255.255.255.0
interface serial 0
ip add 172.30.2.1 255.255.255.0
SanJose1
hostname SanJose1
interface ethernet 0
ip add 172.30.3.1 255.255.255.0
interface serial 0
ip add 172.30.2.2 255.255.255.0
interface serial 1
ip add 192.168.4.9 255.255.255.252
Baypointe
hostname Baypointe
interface ethernet 0
ip add 192.168.5.1 255.255.255.0
interface serial 0
ip add 192.168.4.10 255.255.255.252
Objective: Running RIPv1 on a stub network
In this scenario we will modify Scenario 2 to only run RIP between SanJose1 and SanJose2. Scenario 3 is a
very common situation for many companies. It is very common that a company will want to run a
dynamic routing protocol (RIPv1 in our case) within their own network, but find in unnecessary to run a
dynamic routing protocol between their company and their ISP.
For Scenario 3 let us assume that Baypointe is the ISP for our Company XYZ, which consists of the
SanJose1 and SanJose2 routers using the 172.30.0.0/16 major network, subnetted with a /24 mask.
Company XYZ is a stub network, meaning there is only one way in and out of the 172.30.0.0/16 network, in
via SanJose1 (a.k.a. the entrance router) and out via Baypointe (the ISP). It is doesn’t make sense for
SanJose1 to send Baypointe the RIP update of 172.30.0.0 every 30 seconds, because Baypointe has no
other way to get there. RIP update message from SanJose1 to Baypointe, if RIP were configured:
RIP: received v1 update from 192.168.4.9 on Serial0
172.30.0.0 in 1 hops
Instead, it makes more sense for Baypointe to have a static route configured for the 172.30.0.0/16 network via
SanJose1.
Well, how about traffic from Company XYZ towards the Internet? It makes no sense for Baypointe to send
more than the 120,000 summarized Internet routes to SanJose1. All SanJose1 needs to know is that if it
is not in the 172.30.0.0 network then send it to the ISP, Baypointe. This is the same for all other
Company XYZ routers (only SanJose2 in our case), that they would send all traffic with destination IP
addresses other than 172.30.0.0 to SanJose1 who would forward them on to Baypointe. Let’s see how
to configure this.
Making changes between Scenario 2 and Scenario 3
Be sure to change the IP addressing as displayed in the diagram and Basic
Configuration section for Scenario 3. Sometimes when changing the IP address
on a serial interface, you may need to reset that interface by doing a shutdown,
wait for the LINK-5-CHANGED message, then follow it with a no shutdown
command.
If you have just completed Scenario 2, lets remove RIP by issuing the following
command on each router:
Router(config)# no router rip
Step 1 – Configuring RIP on SanJose1 and SanJose2
Here are the commands for each router:
SanJose2#configure terminal
Enter configuration commands, one per line.
SanJose2(config)#router rip
SanJose2(config-router)#network 172.30.0.0
SanJose1#configure terminal
Enter configuration commands, one per line.
SanJose1(config)#router rip
SanJose1(config-router)#network 172.30.0.0
End with CNTL/Z.
End with CNTL/Z.
Notice that we are only including the 172.30.0.0 interfaces, networks, for SanJose1.
We will not be exchanging RIP updates with Baypointe via the 192.168.4.0/30
network.
Step 2 - Configuring the default static route on SanJose1
On SanJose1, let’s configure a static default route, sending all default traffic, packets with
destination IP addresses which do not match a specific route in the routing table, to
Baypointe.
SanJose1(config)# ip route 0.0.0.0 0.0.0.0 serial 1
Notice, since the exit interface is a point-to-point serial interface we chose to use the exitinterface instead of a intermediate-address (next-hop-ip address), saving the router from
having to do a recursive lookup. However, using an intermediate-address (next-hop-ipaddress) would have worked also.
Previous to IOS version 12.1, SanJose1 would propagate, send, this default route
automatically via RIP with its RIP updates to all other routers (in this case SanJose2).
SanJose2 and all other routers will receive this default route via RIP and forward to all
other routers in the RIP routing domain.
However, with IOS 12.1 and later, we need to enter the default-information originate
command on Baypointe, the router with the static default route. This will tell SanJose1 to
include the static default route with its RIP updates to SanJose2.
SanJose1(config)#router rip
SanJose1(config-router)#default-information originate
Step 3 - Configuring the static route on Baypointe for the 172.30.0.0/16 network
Since Baypointe and SanJose1 are not exchanging RIP updates, we need to configure a static
route on Baypointe for the 172.30.0.0/16 network. This will send all 172.30.0.0/16 traffic,
packets with destination IP addresses of 172.30.x.x, to SanJose1.
Baypointe(config)# ip route 172.30.0.0 255.255.0.0 serial 0
Once again, notice, since the exit interface is a point-to-point serial interface we chose to use
the exit-interface instead of a intermediate-address (next-hop-ip address), saving the
router from having to do a recursive lookup. However, using an intermediate-address
(next-hop-ip-address) would have worked also.
SanJose1
SanJose1#debug ip rip
RIP protocol debugging is on
SanJose1#
02:09:10: RIP: received v1 update from 172.30.2.1 on Serial0
02:09:10:
172.30.1.0 in 1 hops
SanJose1#
02:09:29: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.30.3.1)
02:09:29:
subnet 172.30.2.0, metric 1
02:09:29:
subnet 172.30.1.0, metric 2
02:09:29:
default, metric 1
02:09:29: RIP: sending v1 update to 255.255.255.255 via Serial0 (172.30.2.2)
02:09:29:
subnet 172.30.3.0, metric 1
02:09:29:
default, metric 1
SanJose1#
SanJose1#undebug all
SanJose1#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<omitted>
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
C
C
R
C
S*
172.30.0.0/24 is subnetted, 3 subnets
172.30.2.0 is directly connected, Serial0
172.30.3.0 is directly connected, Ethernet0
172.30.1.0 [120/1] via 172.30.2.1, 00:00:13, Serial0
192.168.4.0/30 is subnetted, 1 subnets
192.168.4.8 is directly connected, Serial1
0.0.0.0/0 is directly connected, Serial1
Scenario 3: Running RIPv1 on a stub network
Reflections
• Notice that the static default route is being propagated by SanJose1 to
other routers (SanJose2) via RIP.
• Notice the static route in the routing table and the “Gateway of last
resort.”
SanJose2
SanJose2#debug ip rip
RIP protocol debugging is on
SanJose2#
02:07:06: RIP: received v1 update from 172.30.2.2 on Serial0
02:07:06:
172.30.3.0 in 1 hops
02:07:07:
0.0.0.0 in 1 hops
SanJose2#
02:07:23: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.30.1.1)
02:07:23:
subnet 172.30.2.0, metric 1
02:07:23:
subnet 172.30.3.0, metric 2
02:07:23:
default, metric 2
02:07:23: RIP: sending v1 update to 255.255.255.255 via Serial0 (172.30.2.1)
02:07:23:
subnet 172.30.1.0, metric 1
SanJose2#
SanJose2#undebug all
SanJose2#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<omitted>
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is 172.30.2.2 to network 0.0.0.0
172.30.0.0/24 is subnetted, 3 subnets
C
172.30.2.0 is directly connected, Serial0
R
172.30.3.0 [120/1] via 172.30.2.2, 00:00:22, Serial0
C
172.30.1.0 is directly connected, Ethernet0
R*
0.0.0.0/0 [120/1] via 172.30.2.2, 00:00:22, Serial0
Scenario 3: Running RIPv1 on a stub network
Reflections
• Notice that SanJose2 is receiving the default route from SanJose1.
• SanJose2 forwards that default route out Ethernet 0, a RIP enabled
interface, although there are no other routers on that segment.
• Notice the default route in the routing table and that it was learned via
RIP.
• Notice the “Gateway of last resort”
Baypointe
No RIP messages, as we are not running RIP.
Baypointe#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
Gateway of last resort is not set
S
C
C
172.30.0.0/16 is directly connected, Serial0
192.168.4.0/30 is subnetted, 1 subnets
192.168.4.8 is directly connected, Serial0
192.168.5.0/24 is directly connected, Ethernet0
Reflections
• Notice that RIP is not being used on Baypointe. The only routes that are
not directly-connected is the static route.
Scenario 3: Running RIPv1 on a stub network
show ip protocols command
SanJose2 router from Scenario 3.
SanJose2#show ip protocols
Routing Protocol is "rip"
Sending updates every 30 seconds, next due in 11 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Outgoing update filter list for all interfaces is
Incoming update filter list for all interfaces is
Redistributing: rip
Default version control: send version 1, receive any version
Interface
Send Recv
Key-chain
Ethernet0
1
1 2
Serial0
1
1 2
Routing for Networks:
172.30.0.0
Routing Information Sources:
Gateway
Distance
Last Update
172.30.2.2
120
00:00:04
Distance: (default is 120)
SanJose2#
Be sure to understand this command. We will examine it again when we take a closer look at RIPv1,
RIPv2 and IGRP. Take a look at the items in bold and make sure you understand them.
A Few Final Notes
RIP uses broadcasts
• Notice that RIPv1 sends out its RIP updates via an IP broadcast.
02:07:23: RIP: sending v1 update to 255.255.255.255 via Ethernet0
(172.30.1.1)
All devices on the segment will see these RIP updates.
The passive-interface command
• How can you keep a RIP update from being sent out an interface which does not have any
other routers? (i.e The Ethernet interfaces in our network.)
• Because the network statement includes all interfaces which have an IP address on that
classful network, by default RIP will send out updates out each one of those interfaces.
• Do keep RIP from sending updates out an interface which does not have any other routers,
you can use the passive-interface command.
• The passive-interface command allows the interface to receive RIP updates on the
interface, but does not send RIP updates out that interface.
• For example, to keep SanJose2 from sending out RIP updates out Ethernet 0, you can do
the following:
SanJose2(config)#router rip
SanJose2(config-router)#network 172.30.0.0
SanJose2(config-router)#passive-interface Ethernet 0
What is with the /30 network?
• /30 or 255.255.255.252 subnet masks are quite common on serial links.
• A /30 subnet mask helps maximize the hosts addresses, which is perfect for a point-topoint serial link, allowing the following for each subnet:
– 1 network address
– 2 host addresses
– 1 broadcast address
IP Class:
C
IP Address:
192.168.4.0
Mask Bits:
6
Subnet Mask:
255.255.255.252
Subnets:
62+1
IP Major Net:
192.168.4.0
Hosts/Subnet:
2
Major Net Bcast: 192.168.4.255
Subnets for Fixed Length Subnet Masking
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
No.
Subnet
Hosts
Hosts
Broadcast
Address
To
Address
0 192.168.4.0
192.168.4.1
192.168.4.2
192.168.4.3
1 192.168.4.4
192.168.4.5
192.168.4.6
192.168.4.7
2 192.168.4.8
192.168.4.9
192.168.4.10
192.168.4.11
3 192.168.4.12
192.168.4.13
192.168.4.14
192.168.4.15
4 192.168.4.16
192.168.4.17
192.168.4.18
192.168.4.19
5 192.168.4.20
192.168.4.21
192.168.4.22
192.168.4.23
6 192.168.4.24
192.168.4.25
192.168.4.26
192.168.4.27
7 192.168.4.28
192.168.4.29
192.168.4.30
192.168.4.31
8 192.168.4.32
192.168.4.33
192.168.4.34
192.168.4.35
9 192.168.4.36
192.168.4.37
192.168.4.38
192.168.4.39
<omitted>
61 192.168.4.244
192.168.4.245
192.168.4.246
192.168.4.247
62 192.168.4.248
192.168.4.249
192.168.4.250
192.168.4.251
63 192.168.4.252
192.168.4.253
192.168.4.254
192.168.4.255
From
How can I remove a single network from RIP?
Instead of using the following command to remove all networks from RIP:
Router(config)# no router rip
You can specify just the network you wish to remove by using the no network command, for
example:
Router(config)#router rip
Router(config-router)#no network 172.30.0.0
Debug ip routing - FYI

If you wish to see what is happening in the router’s routing table process, you can use
the debug ip routing command:
SanJose2#debug ip routing
IP routing debugging is on
SanJose2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
SanJose2(config)#router rip
SanJose2(config-router)#network 172.30.0.0
SanJose2(config-router)#
00:15:03: RT: add 172.30.3.0/24 via 172.30.2.2, rip metric [120/1]
00:15:03: RT: add 0.0.0.0/0 via 172.30.2.2, rip metric [120/1]
00:15:03: RT: default path is now 0.0.0.0 via 172.30.2.2
00:15:03: RT: new default network 0.0.0.0
End of Part I
• End of Part I
• See Part II for IGRP