RIP and IGRP
RIP and IGRP have many similarities in their general
logic but several differences in the details of their implementation.
Feature
|
RIP (Default)
|
IGRP (Default)
|
Update Timer
|
30 sec
|
90 sec
|
Metric
|
Hop Count
|
|
Hold-down Timer
|
180 sec
|
280 sec
|
Flash (Triggered) Updates
|
Yes
|
Yes
|
Mask Sent in Update
|
No
|
No
|
Infinite-Metric Value
|
16
|
4 294 967 295
|
The IGRP metric provides a better measurement of how
good a route is, as compared with RIP’s metric. IGRP’s metric is calculated
using the bandwidth and delay settings on the interface on which the update was
received. When bandwidth and delay are used, the metric is more meaningful than
hop count; longer hop routes that go over faster links are considered better
routes by IGRP.
RIP uses hop count as its metric. When an update is
received, the metric for each subnet in the update signifies the number of routers
between the router receiving the update and each subnet. Before sending an
update, a router increments by 1 its metric for routes to each subnet.
Finally, the issue of whether the mask is sent is
particularly important if variable-length subnet masks (VLSMs) in the same
network are desired. Neither RIP or IGRP support VLSM.
The key to configuring RIP and IGRP is to master the
use of the network command. Other than that, configuration is relatively easy.
You should also know the more-popular show and debug commands, which help you
examine and troubleshoot routing protocols.
The following table summarize the more popular
commands used for RIP and IGRP configuration and verification.
Fig - 28
Command
|
Configuration Mode
|
router rip
|
Global
|
router igrp as-number
|
Global
|
network net-number
|
Router subcommand
|
passive-interface [default] {interface-type
interface-number}
|
Router subcommand
|
maximum-paths number-paths
|
Router subcommand
|
variance multiplier
|
Router subcommand
|
traffic-share {balanced | min}
|
Router subcommand
|
show ip route [ip-address [mask]
[longer- prefixes]]| [protocol [process-id]]
|
Shows the entire routing table, or a subset if
parameters are entered.
|
show ip protocols
|
Shows routing protocol parameters and current
timer values.
|
debug ip rip
|
Issues log messages for each RIP update.
|
debug ip igrp transactions [ip-address]
|
Issues log messages with details of the IGRP
updates.
|
debug ip igrp events [ip-address]
|
Issues log messages for each IGRP packet.
|
ping [protocol | tag] {host-name | system-address}
|
Sends and receives ICMP echo messages to verify
connectivity.
|
Each network
command enables RIP or IGRP on a set of interfaces. This command “matches” one
or more interfaces on a router. For each interface, the network command causes
the router to do three things:
_The router
broadcasts or multicasts routing updates out an interface.
_The router
listens for incoming updates on that same interface.
_The
router, when sending an update, includes the subnet off that interface in the
routing update.
The router
matches interfaces with the network command by asking this simple question:
"Which
of my interfaces have IP addresses with the same network number referenced in
this network subcommand?"
For all
interfaces that match the network command, the router does the three things
just listed.
Here are
the examples of configuring RIP and IGRP on the routers, shown on the following
known picture:
RIP Configuration
Router R1:
...!router
ripnetwork
10.0.0.0!...R1#sh ip
routeCodes: C
- connected, S - static, 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 i
- IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia
- IS-IS inter area, * - candidate default, U - per-user static route o
- ODR, P - periodic downloaded static routeGateway
of last resort is not set 10.0.0.0/24
is subnetted, 4 subnetsC 10.10.1.0
is directly connected, FastEthernet0/0R 10.10.2.0
[120/1] via 10.10.1.2, 00:00:19, FastEthernet0/0R 10.10.3.0
[120/2] via 10.10.1.2, 00:00:19, FastEthernet0/0R 10.10.10.0
[120/2] via 10.10.1.2, 00:00:19, FastEthernet0/0R1#R1#ping
10.10.3.3Type
escape sequence to abort.Sending
5, 100-byte ICMP Echos to 10.10.3.3, timeout is 2 seconds:!!!!!Success
rate is 100 percent (5/5), round-trip min/avg/max = 108/159/264 msR1#
Router R2:
...!router
ripnetwork
10.0.0.0!...R2#sh ip
routeCodes: C
- connected, S - static, 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 i
- IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia
- IS-IS inter area, * - candidate default, U - per-user static route o
- ODR, P - periodic downloaded static routeGateway
of last resort is not set 10.0.0.0/24
is subnetted, 4 subnetsC 10.10.1.0
is directly connected, FastEthernet0/0C 10.10.2.0
is directly connected, Serial1/0R 10.10.3.0
[120/1] via 10.10.2.1, 00:00:14, Serial1/0R 10.10.10.0
[120/1] via 10.10.2.1, 00:00:14, Serial1/0R2#
Router R3:
...!router
ripnetwork
10.0.0.0!...R3#sh ip
routeCodes: C
- connected, S - static, 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 i
- IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia
- IS-IS inter area, * - candidate default, U - per-user static route o
- ODR, P - periodic downloaded static routeGateway
of last resort is not set 10.0.0.0/24
is subnetted, 4 subnetsR 10.10.1.0
[120/2] via 10.10.3.1, 00:00:10, Serial1/0R 10.10.2.0
[120/1] via 10.10.3.1, 00:00:10, Serial1/0C 10.10.3.0
is directly connected, Serial1/0R 10.10.10.0
[120/1] via 10.10.3.1, 00:00:10, Serial1/0R3#
Router R:
...!router
ripnetwork
10.0.0.0!...R#sh ip
routeCodes: C
- connected, S - static, 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 i
- IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia
- IS-IS inter area, * - candidate default, U - per-user static route o
- ODR, P - periodic downloaded static routeGateway
of last resort is not set 10.0.0.0/24
is subnetted, 4 subnetsR 10.10.1.0
[120/1] via 10.10.2.2, 00:00:01, Serial1/0C 10.10.2.0
is directly connected, Serial1/0C 10.10.3.0
is directly connected, Serial1/1C 10.10.10.0
is directly connected, FastEthernet0/1R#
IGRP Configuration
You configure IGRP just like RIP, except that the
router igrp command has an additional parameter-the autonomous system (AS)
number. The term autonomous system refers to a network that is within the
control of a single company or organization. The term AS number refers to a
number assigned to a single company or organization when it registers its
connection to the Internet. However, for IGRP, you do not need a registered AS
number. All that is needed for IGRP to work is for all the routers to use the
same AS number.
IGRP configuration begins with the router igrp 1
global configuration command. Then four consecutive network commands match all
the interfaces on the router so that IGRP is fully enabled. In fact, these
network commands are identical to the network commands in the complete RIP
configuration.
IGRP uses a composite metric. This metric is
calculated as a function of bandwidth, delay, load, and reliability. By
default, only bandwidth and delay are considered; the other parameters are
considered only if they are enabled via configuration. Delay and bandwidth are
not measured values but are set via the delay and bandwidth interface
subcommands. (The same formula is used to calculate the metric for EIGRP, but
with a scaling factor so that the actual metric values are larger, allowing
more granularity in the metric.)
Administrative Distance
Many companies and organizations use a single
routing protocol. However, in some cases, a company needs to use multiple
routing protocols. For instance, if two companies connect their networks so
that they can exchange information, they need to exchange some routing
information. If one company uses RIP, and the other uses IGRP, on at least one
router, both RIP and IGRP must be used. This is just one example, but it is not
that unusual to need to run more than one routing protocol in a single router.
Depending on the network topology, two routing
protocols might learn routes to the same subnets. When a single routing
protocol learns multiple routes to the same subnet, the metric tells it which
route is best. However, because different routing protocols use different
metrics, the IOS cannot compare the metrics. For instance, RIP might learn a
route to subnet 10.1.1.0 with metric 1, and IGRP might learn a route to
10.1.1.0 with metric 8729. There is no basis for comparison between the two
metrics.
To decide which route to use, IOS uses a concept
called administrative distance. Administrative distance is a number that
denotes how believable an entire routing protocol is on a single router. The
lower the number, the better, or more believable, the routing protocol. For
instance, RIP has a default administrative distance of 120, and IGRP defaults
to 100, making IGRP more believable than RIP. So, when both routing protocols
learn routes to the same subnet, the router adds only the IGRP route to the
routing table.
The administrative distance values are configured on
a single router as follows and are not exchanged with other routers.
Router
Type |
Administrative Distance (AD)
|
Connected |
0 |
Static
|
1 |
EIGRP summary route
|
5 |
eBGP
|
20 |
EIGRP (internal)
|
90 |
IGRP
|
100 |
OSPF
|
110 |
IS-IS
|
115 |
EIRP (external)
|
170 |
iBGP (external)
|
200 |
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