1. Understanding RIP, IGRP andStatic RouteConfiguration
ip route[address][subnet mask][next hop IP]
Routers can only forward packets to subnets in its routing table
ip route[address][subnet mask][next hop IP]
the new routes can be verified with
ip route [address][subnet mask][interface]
showip route (displays all of router’s ip routes)
-> Disadvantage to doing this is that static routing works one-way
(add route on Router A to Router B, but Router B still doesn’t have route to Router A)
Extended Ping Command: Simulates a ping from ethernet host, but actually comes
from router itself. When a ping from a router works, but a ping from a host does not,
the extended ping could help you re-create the problem without needing to work
with the end user on the phone.
1. ping
2. Target Address (IP)
3. Extended Commands = y
4. Source Address (IP)
Distance Vector Concepts
Advertise entire routing table (subnet number and metric) to directly connected
neighbors.
Key Points:
 Updates are sent to all neighboring routers through active interfaces, once
every so many seconds.
 If a router learns multiple routes to the same subnet, it chooses the best
route based on the metric (number of hops).
 Failure to receive updates after x amount of time results in removal of that
route
 Routers add directly connected subnets to their routing tables, even without
a routing protocol
Distance Vector Loop Avoidance Features eliminate roundabout "ghost" routes to
failed or cyclically-linked routers.
Route Poisoning: Router notices link is down, continues to advertise the route, but
with very large metric (view as infinite and invalid). Other routers remove their
routes to the downed subnet.
RIP uses 16 as the infinite metric
Split Horizon: If 2 routers advertise tables at about the same time, with one link
down, they would continually exchange incorrect routing metrics (counting to
infinity). Split horizon doesn't allow this because all routes with outgoing interface x
are not included in updates sent out that same interface x.
In other words, if route to subnet comes in through interface 1, don’t send update of

2. the same route out interface 1
Ex) Router A’s Ethernet goes down, set metric to 16 and send to neighbor. At the
same time, Router B sends update to Router A, using the old metric that the cost is 2.
Now Router A = 2, Router B = 16. After x amount of time, the two routers exchange
routing table and in turn switch the metrics. This process would repeat indefinitely.
*Split Horizon with Poison Reverse (or Poison Reverse):Cisco’s proprietary distance
vector routing protocols use this (used by default). Spit horizon used when network
links up, but when link fails, allows broadcast of infinite metric (including previously
blocked port from Split Horizon).
*Hold-Down Timer: Defeats the counting-to-infinity problem when
multiple/redundant links exist between routers. Routers must wait the duration of
the hold-down timer before believing any "good" information about that route.
Triggered/Flash Updates: Sends new update as soon as route fails.
Summary
Issue Solution
Either use the first route learned or put
Multiple routes to the same subnet
multiple routes to the same subnet in the
have equal metrics
routing table.
Split horizon—The routing protocol
advertises routes out an
interface only if they were not learned from
updates entering
that interface.
Routing loops occur due to updates Split horizon with poison reverse—The
passing each other over a single link routing protocol uses
split-horizon rules unless a route fails. In that
case, the route is
advertised out all interfaces, including the
interface in which
the route was learned, but with an
infinite-distance metric.
Route poisoning—When a route to a subnet
Routing loops occur because routing fails, the subnet is
information loops advertised with an infinite-distance metric.
through alternative paths This term
specifically applies to routes that are

3. advertised when the
route is valid. Poison reverse refers to routes
that normally are
not advertised because of split horizon but
that are advertised
with an infinite metric when the route fails.
Hold-down timer—After finding out that a
route to a subnet
has failed, a router waits a certain period of
time before
believing any other routing information
about that subnet.
Triggered updates—When a route fails, an
Counting to infinity
update is sent
immediately rather than waiting on the
update timer to expire.
Used in conjunction with route poisoning,
this ensures that all
routers know of failed routes before any
hold-down timers
can expire.
Comparing RIP and IGRP
Feature RIP IGRP
Update Timer 30 seconds 90 seconds
Metric Hop count Bandwidth/delay (also, reliability, MTU, and load)
Hold-Down Timer 180 280
Flash Updates Yes Yes
VLSM No No
Infinite-Metric Value 16 4,294,967,295
Configuring RIP and IGRP
Configurati
Command
on Mode
router rip Global
router igrp [as number] Global

4. enable IGRP for the
router igrp [as AS and enter
Global
number] (config-router)
mode.
advertise to other
Router
network [net routers that this
subcomma
number] router has a path to
nd
the given network.
passive-interface[default&a Router don't send routing
mp;#93; subcomma updates out through
{interface type interface number} nd the given interface.
keep at
Router most number'''differ
maximum-pathsnumber subcomma ent routes to the
nd same destination in
the routing table.
Router
traffic-share {balanced | min} subcomma
nd
share traffic
between routes,
Router either
traffic-share {balanced | min} subcomma proportionally or
nd just between those
of the minimum
metric value.
EXEC Commands
Command Description
Shows the entire routing table, or a
show ip route
subset if parameters are entered.
Shows routing protocol parameters and
show ip protocols
current timer values.
Issues log messages for each RIP
debug ip rip
update.
debug ipigrp transactions [ip Issues log messages with details of the
address] IGRP updates.
debug ipigrp Issues log messages with details of the

5. transactions [ip IGRP updates.
address]
debug ipigrp events [ip Issues log messages for each IGRP
address] packet.
Sends a series of ICMP echoes with
trace increasing TTL values to verify the
current route to a host.
RIP Configuration
router rip
network [network address1] -> Use network number
(address w/ normal class address)
network [network address2]
IGRP ConfigurationIGRP Configuration
routerigrp [as number] -> Note: All routers should use
the same AS number
network [network address1]
network [network address2]
show running-config -> I = address found by IGRP, C = directly connected
Example
I 10.1.4.0 [100/8539] via 10.1.2.14, 00:00:50,
Ethernet0
-> The [100/8359] can be broken into two separate
parts:
 100 = administrative distance
 8539 = metric (function of bandwidth and delay)
 The higher the bandwidth, the lower the metric
 The lower the cumulative delay, the lower the metric
Bandwidth Defaults
LAN Interfaces = default reflects the correct bandwidth
Serial Interfaces = defaults to 1544 kbps (T1 speed)
-> Configure using the bandwidth [kbps] interface
command
To migrate from RIP to IGRP (Commands)
 no router rip
 router igrp[as number]
 network [network ID]
Debug/show commands include
 debug ip rip

6.  show ip route
 debug ipigrp transactions (detailed info on updates)
 debug ipigrp events (summary that states updates received)
 show ip protocol (Update timer, elapsed time since update received)
Additional Notes
- If multiple route exist, router chooses best metric route
- If routes tie, keep the first/pre-existing route
Command: maximum-paths 1 (default is maximum-paths 4)
- When RIP places multiple routes, router balances traffic
Command to use lowest-cost: traffic-share min
Variance allows metrics to be considered equal, since IGRP/EIGRP metrics are
calculated through formula and often won’t be exactly the same.
Example: metric = 100, variance = 2, If value > (lowest metric *
variance), add route
Administrative Distance: In order to compare metrics between different routing
protocols, use administrative distance to denote how believable an entire routing
protocol is on a single router.
-> The lower the number, the better
Default Administrative Distances
Route Type Administrative Distance
Connected 0
Static 1
EIGRP summary route 5
EBGP 20
EIGRP (internal) 90
IGRP 100
OSPF 110
IS-IS 115
RIP 120
EIGRP (external) 170
iBGP (external) 200
---Reference from

7. http://www.proprofs.com/mwiki/index.php/RIP%2C_IGRP%2C_and_Static_Route_Co
ncepts_and_Configuration
More Related Tips:
How to Configure IGRP (Interior Gateway Routing Protocol)?
Routing Information Protocol & RIP Configuration