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Chapter 9
EIGRP – Part 2 of 2
CIS 82 Routing Protocols and Concepts
Rick Graziani
Cabrillo College
[email protected]
Last Updated: 4/20/2009
Note
 My web site is www.cabrillo.edu/~rgraziani.
 For access to these PowerPoint presentations and other
materials, please email me at [email protected].
 See notes section for additional information.
2
For further information
 This presentation is an
overview of what is
covered in the
curriculum/book.
 For further explanation
and details, please read
the chapter/curriculum.
 Book:
 Routing Protocols
and Concepts
 By Rick Graziani and
Allan Johnson
 ISBN: 1-58713-206-0
 ISBN-13: 978-58713206-3
3
DUAL
 DUAL Concepts
 Successor and Feasible Distance
 Feasible Successors, Feasibility Condition, and Reported Distance
 Topology Table: Successor and Feasible Successor
 Topology Table: No Feasible Successor
 Finite State Machine
DUAL Concepts
 Diffusing Update Algorithm is the algorithm used by EIGRP.
 Determines:
 Best loop-free path
 Loop-free backup paths (which can be used immediately)
 DUAL also provides the following:
 Fast convergence
 Minimum bandwidth usage with bounded updates
 DUAL uses several terms that are discussed in more detail
throughout this section:
 Successor
 Feasible distance
 Feasible successor
 Reported distance or advertised distance
 Feasible condition or feasibility condition
5
10.0.0.0/8
I can get to
10.0.0.0/8 with
a metric of 300.
I can get to
10.0.0.0/8 with
a metric of 100.
RX
R2
RA
R3
R1
RB
I will choose R3
to get to
10.0.0.0/8 which
means I have a
cost of 120. Is R2
a valid back up?
No, because it
comes back
through R1 (loop).
6
10.0.0.0/8
I can get to
10.0.0.0/8 with
a metric of 300.
I can get to
10.0.0.0/8 with
a metric of 100.
RX
RB
R2
RA
R3
R1
I will choose R3
to get to
10.0.0.0/8 which
means I have a
cost of 120. Is R2
a valid back up?
Yes, because it
has its own path
to 10.0.0.0/8. (no
loop)
7
I can only use
R2 as a backup
if it reports a
cost less than
my total cost
through R3.
 EIGRP is a distance vector
routing protocol.
 Does not see any topology map.
 Can’t tell if there is a loop or
not?
 To play it safe, EIGRP only
accepts a backup route if it
meets the Feasibility Condition
(coming).
 R1 will only use R2 if R2’s
metric to 10.0.0.0/8 is less than
R1’s cost through R3.
8
Topology
may not
 Download: cis82-EIGRP-B-student.pkt
 Completed configuration from cis82-EIGRP-A-student.pkt
 EIGRP has been configured on R1, R2 and R3
 All routers have the proper bandwidth commands.
 Do show run
9
Successor and Feasible Distance
R2# show ip route
<code output omitted>
D
IP address of the successor
192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:00:15, S0/0/1
R3 is my successor for
getting to 192.168.1.0/24
Successor
 A successor is a neighboring router that is used for packet
forwarding and is the least-cost route to the destination network.
 What router is the success for R2?
 R3
10
Successor and Feasible Distance
R2# show ip route
<code output omitted>
D
Feasible Distance
192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:00:15, S0/0/1
 Feasible distance (FD) is the lowest calculated metric to reach the
destination network.
 The metric for the route.
11
Feasible Successors, Feasibility Condition, and
Reported Distance
I wonder if R1 could be a
feasible successor for getting
to 192.168.1.0/24?
Feasible
Successor?
Successor
 DUAL fast convergence because it can use backup paths to other
routers known as feasible successors.
 Does not require to recompute DUAL.
12
Feasible Successors, Feasibility Condition, and
Reported Distance
I wonder if R1 could be a
feasible successor for getting
to 192.168.1.0/24?
Feasible
Successor?
Successor
 Is R1 a Feasible Successor?
 Does R2 know if R1 has a loop-free backup path to 192.168.1.0/24?
 Remember, EIGRP is a Distance Vector Routing protocol.
13
Feasible
Successor
 A feasible successor (FS) is a neighbor who has a loop-free
backup path to the same network as the successor by satisfying the
feasibility condition.
 Would R2 consider R1 to be a feasible successor to network
192.168.1.0/24?
 To be a feasible successor, R1 must satisfy the feasibility
condition (FC).
14
Feasibility Condition
I will send R2
my RD to
192.168.1.0/24
of 2,172,416.
Feasibility Condition:
For R1 to be a Feasible
Successor it must tell
me that it’s metric to
reach 192.168.1.0/24 is
less than my metric
through my Successor
R3.
My FD to
192.168.1.0/24
is 2,172,416
(my routing
table).
R1# show ip route
<output omitted>
D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 01:12:26, Serial0/0/1
 The reported distance (advertised distance) - EIGRP neighbor’s FD to the same
destination network.
 The metric that a router reports to a neighbor about its own cost to that
network.
 Feasibility Condition: The FC is met when a neighbor’s reported distance
(RD) to a network is less than the local router’s FD to the same destination
15
network.
Feasibility Condition
Feasible
Successor?
Feasibility Condition: For
R1 to be a Feasible
Successor it must tell me
that it’s metric to reach
192.168.1.0/24 is less than
my metric through my
Successor R3.
Successor
 If R3 is the successor, can the neighbor R1 be a Feasible Successor to this
same 192.161.0/24 network?
 In other words, if the link between R2 and R3 fails, can R1 immediately
be used as a backup path without a recomputation of DUAL?
 R1 can only be an FS (Feasible Successor) if it meets the FC (Feasibility
Condition).
16
Feasibility Condition
I will send R2
my RD to
192.168.1.0/24
of 2,172,416.
My FD to
192.168.1.0/24
is 2,172,416
(my routing
table).
R1# show ip route
<output omitted>
D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 01:12:26, Serial0/0/1
 R1’s FD to 192.168.1.0/24 is 2,172,416.
 R1 reports 2,172,416 to R2 as its RD (Reported Distance)
 R2’s perspective: 2,172,416 is?
 R1’s RD (Reported Distance) to 192.168.1.0/24
 R1’s perspective: 2,172,416 is?
 Its FD (Feasible Distance) to 192.168.1.0/24
17
R2# show ip route
Feasible Distance
<output omitted>
D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:00:15, Serial0/0/1
R1’s RD is less than
R2’s FD, so R1 is the
FS for 192.168.1.0/24
Feasibility Condition: For R1 to
be a Feasible Successor it must
tell me that it’s metric to reach
192.168.1.0/24 (Reported
Distance) is less than my metric
(Feasible Distance) through my
Successor R3.
R1# show ip route
Reported Distance sent to R2
<output omitted>
D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 01:12:26, Serial0/0/1
 Does R1 meet the Feasibility Condition?
 Is the RD of R1, 2,172,416, less than R2’s own FD of 3,014,400?
 Yes, R1 meets the feasibility condition.
 R1 is a FS (Feasible Successor) for R2 to the 192.168.1.0/24 network.
18
R2# show ip route
Feasible Distance
<output omitted>
D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:00:15, Serial0/0/1
If R1 was the successor, the 64
Kbps link is the slowest
bandwidth, plus another delay of
R1’s s0/0/1. This would be a
higher metric (41,026.560) than
3,014,400 via successor R3.
R1# show ip route
Reported Distance sent to R2
<output omitted>
D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 01:12:26, Serial0/0/1
 Why isn’t R1 the successor if its RD is less than R2’s FD to 192.168.1.0/24?
 The 64 Kbps link would be used as the “slowest bandwidth part of the
metric calculation.
 The total cost for R2, its FD to reach 192.168.1.0/24 is greater through R1
41,026.560 than it is through R3 3,014,400.
19
Topology Table: Successor and Feasible Successor
R2# show ip eigrp topology
IP-EIGRP Topology Table for AS(1)/ID(10.1.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
<output omitted>
P 192.168.1.0/24, 1 successors, FD is 3014400
Successor via 192.168.10.10 (3014400/28160), Serial0/0/1
Feasible Successor via 172.16.3.1 (41026560/2172416), Serial0/0/0
P 192.168.10.8/30, 1 successors, FD is 3011840
via Connected, Serial0/1
<output omitted>
 The successor, FD, and any FSs with their RDs are kept by a router
in its EIGRP topology table or topology database.
 Do on R2: show ip eigrp topology
 Can you find the successor and feasible successor for
192.168.1.0/24?
20
Topology Table: Successor and Feasible Successor
 P: This route is in the Passive state.
 DUAL is not performing its diffusing computations to determine a path for a
network
 The route is in a stable mode
 Active state - DUAL is recalculating or searching for a new path
 192.168.1.0/24: This is the destination network that is also found in the routing
table.
 How many successors are there? What does it mean?
 1 successors: This shows the number of successors for this network.
 If there are multiple equal-cost paths to this network, there will be multiple
successors.
 FD is 3014400: This is the FD, the EIGRP metric to reach the destination network.21
Successor Information
 via 192.168.10.10: This is the next-hop address of the successor, R3.
 This address is shown in the routing table.
 3,014,400: This is the FD to 192.168.1.0/24.
 It is the metric shown in the routing table.
 28,160: This is the RD of the successor
 R3’s cost to reach this network.
 Serial0/0/1: This is the outbound interface used to reach this network.
 Also shown in the routing table.
22
Feasible Successor Information
 via 172.16.3.1: This is the next-hop address of the FS, R1.
 41,026,560: This would be R2’s new FD to 192.168.1.0/24 if R1 became the
new successor.
 2,172,416: This is the RD of the FS or R1’s metric to reach this network.
 This value, RD, must be less than the current FD of 3,014,400 to meet
the FC.
 Serial0/0/0: This is the outbound interface used to reach the FC, if this
router becomes the successor.
23
Show eigrp topology [network]
R2# show ip eigrp topology 192.168.1.0
IP-EIGRP topology entry for 192.168.1.0/24
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 3014400
Routing Descriptor Blocks:
192.168.10.10 (Serial0/0/1), from 192.168.10.10, Send flag is 0x0
Successor
Composite metric is (3014400/28160), Route is Internal
Vector metric:
Minimum bandwidth is 1024 Kbit
Default metrics calculations
Total delay is 20100 microseconds
Reliability is 255/255
Optional metrics
Load is 1/255
Other information passed in routing update (not
Minimum MTU is 1500
Hop count is 1
part of composite metric)
172.16.3.1 (Serial0/0/0), from 172.16.3.1, Send flag is 0x0
Feasible
Composite metric is (41026560/2172416), Route is Internal
Successor
Vector metric:
Minimum bandwidth is 64 Kbit
Reported Distance of R1 to R2 for
Total delay is 40100 microseconds
192.168.1.0
Reliability is 255/255
Load is 1/255
Feasible Distance for to 192.168.1.0 if
Minimum MTU is 1500
R3 was the successor. This is the
Hop count is 2
metric that would be if R2’s routing
table if R3 was the successor.
24
R2#
R2#
show
show
ipip
route
route
Feasible Distance
<output
<output
omitted>
omitted>
D D
192.168.1.0/24
192.168.1.0/24
[90/41026560]
[90/3014400] via
via 192.168.10.10,
192.168.10.10, 00:00:15,
00:00:15, Serial0/0/1
Serial0/0/1
X
Feasible Successor
Successor
Successor
 What if the link between R2 and R3 failed?
25
Topology Table: No Feasible Successor
R1# show ip route
D
C
D
D
C
D
C
D
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
192.168.10.0/24 is a summary, 00:45:09, Null0
192.168.10.4/30 is directly connected, Serial0/0/1
192.168.10.8/30 [90/3523840] via 192.168.10.6, 00:44:56, S0/0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks
172.16.0.0/16 is a summary, 00:46:10, Null0
Successor
172.16.1.0/24 is directly connected, FastEthernet0/0
172.16.2.0/24 [90/40514560] via 172.16.3.2, 00:45:09, S0/0/0
172.16.3.0/30 is directly connected, Serial0/0/0
192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:44:55, S0/0/1
 Route to 192.168.1.0/24:
 What router is the Successor for 192.168.10.6?
 R3
 What is R1’s FD?
 2,172,416
26
Topology Table:
No Feasible
Successor
Feasible
Successor?
R1# show ip route
D
192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:44:55, S0/0/1
 Is R2 a Feasible Successor?
 If current path to 192.168.1.0/24 fails will R1 (DUAL) automatically use R2 as
a backup route?
 Is the path to 192.168.1.0/24 via R2 a guaranteed loop-free path? (more later)
 Does R2 meet the Feasibility Condition?
27
Topology Table:
No Feasible
Successor
Feasible
Successor?
R1# show ip eigrp topology
<output omitted>
P 192.168.1.0/24, 1 successors, FD is 2172416
via 192.168.10.6 (2172416/28160), Serial0/0/1
 Does the topology table only any Feasible Successors?
 No, only the successor.
 Why do you think R2 is not a Feasible Successor?
 R2 is not an FS because it does not meet the FC.
 Topology shows that R2 has a backup route
 EIGRP does not have a map of the network topology.
 EIGRP is a distance vector routing protocol
28
Topology Table: No Feasible Successor
R1# show ip eigrp topology all-links
<output omitted>
R1’s FD
P 192.168.1.0/24, 1 successors, FD is 2172416, serno 5
Successor via 192.168.10.6 (2172416/28160), Serial0/0/1
Feasible Successor? (No) via 172.16.3.2 (41026560/3014400), Serial0/0/0
<output omitted>
R2’s RD
 You can view all possible links whether they satisfy the feasible condition or
not by adding the [all-links] option.
 Even those routes that are not FSs.
 Is R2 a Feasible Successor?
 Does R2 meet the Feasibility Condition?
 Is R2’s RD less than R1’s FD?
29
Topology Table:
No Feasible
Successor
R2 does not meet FC!
R2’s RD 3,014,400
> R1’s FD 2,172,416
Feasible
Successor?
My FD is
3,014,400. I will
send this as my RD
to R1.
R1# show ip eigrp topology all-links
<output omitted>
R1’s FD
P 192.168.1.0/24, 1 successors, FD is 2172416, serno 5
via 192.168.10.6 (2172416/28160), Serial0/0/1
via 172.16.3.2 (41026560/3014400), Serial0/0/0
<output omitted>
R2’s RD
 Even though R2 looks like a viable backup path to
192.168.1.0/24, R1 has no idea that its path is not a potential
loop back through itself.
30
Topology Table:
No Feasible
Successor
Feasible
Successor?
R2 does not meet FC!
R2’s RD 3,014,400
> R1’s FD 2,172,416
My FD is
3,014,400. I will
send this as my RD
to R1.
R1# show ip eigrp topology all-links
<output omitted>
P 192.168.1.0/24, 1 successors, FD is 2172416, serno 5
via 192.168.10.6 (2172416/28160), Serial0/0/1
via 172.16.3.2 (41026560/3014400), Serial0/0/0
<output omitted>
 Does this mean R2 cannot be used if the successor fails?
 R2 can be used, but there will be a longer delay before adding it
to the routing table.
 Before this can happen, DUAL will need to do some further
processing, which is explained in the next topic.
31
Finite State Machine
 The centerpiece of EIGRP is DUAL (EIGRP route-calculation engine).
 DUAL Finite State Machine (FSM)
 This FSM contains all the logic used to calculate and compare routes in an
EIGRP network.
32
DUAL FSM
 FSMs defines:
 The set of possible states that something can go through
 What events cause those states
 What events result from those states
 Beyond the scope of this course.
33
FSM Example
HUNGRY
(START)
NO FOOD
FOR 5
HOURS
FOOD IS
INEDIBLE
GET FOOD
EAT MORE
FOOD
FULL
EATING
NOT ENOUGH
FOOD
EAT ENOUGH
FOOD
34
DUAL FSM
R2# show ip eigrp topology
<partial output>
P 192.168.1.0/24, 1 successors, FD is 3014400
Successor via 192.168.10.10 (3014400/28160), Serial0/0/1
Feasible
via 172.16.3.1 (41026560/2172416), Serial0/0/0
Successor
35
DUAL FSM
X
R2# debug eigrp fsm
R2# conf t
R2(config)# int s0/0/1
R2(config-if)# shutdown
<some debug output omitted>
DUAL: Find FS for dest 192.168.1.0/24. FD is 3014400, RD is 3014400
DUAL: 192.168.10.10 metric 4294967295/4294967295
DUAL: 172.16.3.1 metric 41026560/2172416 found Dmin is 41026560
DUAL: Removing dest 192.168.1.0/24, nexthop 192.168.10.10
DUAL: RT installed 192.168.1.0/24 via 172.16.3.1
 shutdown command simulates a failure of the link between R2 and R3.
36
DUAL FSM
Previous topology table
R2# show ip route
<some output omitted>
D
192.168.1.0/24 [90/41026560] via 172.16.3.1, 00:08:58, Serial0/0
R2# show ip eigrp topology
<partial output>
P 192.168.1.0/24, 1 successors, FD is 3014400
via 172.16.3.1 (41026560/2172416), Serial0/0
Successor
 R1 now becomes the successor
 There are no new feasible successors.
37
No Feasible
Successor
NOT Feasible
Successor
Successor
 What if the path to the successor fails and there are no FSs?
 R1 to 192.168.1.0/24
 R3 is the Successor
 No Feasible Successors
38
No Feasible
Successor
NOT Feasible
Successor
X
Successor
R1# show ip eigrp topology
<output omitted>
P 192.168.1.0/24, 1 successors, FD is 2172416
via 192.168.10.6 (2172416/28160), Serial0/0/1
<output omitted>
 Simulate a failure of the link between R1 and R3 with a shutdown on R1’s
S0/0/1 interface.
39
No Feasible Successor
R1# debug eigrp fsm
R1# conf t
R1(config)# int s0/0/1
R1(config-if)# shutdown
<some debug output omitted>
DUAL: Find FS for dest 192.168.1.0/24. FD is 2172416, RD is 2172416
DUAL: 192.168.10.6 metric 4294967295/4294967295
DUAL: 172.16.3.2 metric 41026560/3014400 not found Dmin is 41026560
DUAL: Dest 192.168.1.0/24 entering active state.
DUAL: rcvreply: 192.168.1.0/24 via 172.16.3.2 metric 41026560/3014400
DUAL: Find FS for dest 192.168.1.0/24. FD is 4294967295, RD is
4294967295 found
DUAL: Removing dest 192.168.1.0/24, nexthop 192.168.10.6
DUAL: RT installed 192.168.1.0/24 via 172.16.3.2
 192.168.1.0/24 network put into the active state and shows that EIGRP
queries are sent to other neighbors.
 R2 replies with a path to this network
 This becomes the new successor
 Installed into the routing table.
40
No Feasible Successor
1. R1 puts 192.168.1.0/24
into Active State.
2. Query from R1 for
192.168.1.0/24
3. R2 forwards the Query
for 192.168.1.0/24
4. R3 replies to R2 –
Yes I have a route to
192.168.1.0/24
5. R2 forwards the
reply to R1
6. R1 puts route to 192.168.1.0/24 via R2
into Routing Table.
Successor
X
Successor
This process takes longer than if
R1 had R2 as Feasible Successor
in it’s topology table.
R1# show ip route
<some output omitted>
D
192.168.1.0/24 [90/41026560] via 172.16.3.2, 00:00:17, Serial0/0/0
41
No Feasible
Successor
Successor
X
R1# show ip eigrp topology
<parital output>
P 192.168.1.0/24, 1 successors, FD is 41026560
via 172.16.3.2 (41026560/3014400), Serial0/0/0
Successor
 The topology table for R1 now shows R2 as the successor and
shows that there are no new feasible successors.
42
More EIGRP Configurations
 The Null0 Summary Route
 Disabling Automatic Summarization
 Manual Summarization
 EIGRP Default Route
 Fine-Tuning EIGRP
The Null0 Summary Route
R1# show ip route
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
D
192.168.10.0/24 is a summary, 00:45:09, Null0
C
192.168.10.4/30 is directly connected, Serial0/0/1
D
192.168.10.8/30 [90/3523840] via 192.168.10.6, 00:44:56, S0/0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks
D
172.16.0.0/16 is a summary, 00:46:10, Null0
C
172.16.1.0/24 is directly connected, FastEthernet0/0
D
172.16.2.0/24 [90/40514560] via 172.16.3.2, 00:45:09, S0/0/0
C
172.16.3.0/30 is directly connected, Serial0/0/0
D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:44:55, Serial0/0/1
 EIGRP automatically includes a Null0 summary route as a child
route whenever both of the following conditions exist:
 There is at least one subnet that was learned via EIGRP.
 Automatic summarization is enabled. (By default with EIGRP)
 What if R1 received a packet: 172.16.4.10
 It would be discarded – never looking for a supernet or default route
 Regardless of ip classless or no ip classless command
44
Disabling
Automatic
Summarization
172.16.0.0/16
R3# show ip route
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
D
192.168.10.0/24 is a summary, 01:08:35, Null0
C
192.168.10.4/30 is directly connected, Serial0/0/0
C
192.168.10.8/30 is directly connected, Serial0/0/1
D
172.16.0.0/16 [90/2172416] via 192.168.10.5, 01:08:30, Serial0/0/0
C
192.168.1.0/24 is directly connected, FastEthernet0/0
 Like RIP, EIGRP automatically summarizes at major network
boundaries using the default auto-summary command.
45
Disabling
Automatic
Summarization
172.16.0.0/16
172.16.0.0/16
R3# show ip route
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
D
192.168.10.0/24 is a summary, 01:08:35, Null0
C
192.168.10.4/30 is directly connected, Serial0/0/0
C
192.168.10.8/30 is directly connected, Serial0/0/1
D
172.16.0.0/16 [90/2172416] via 192.168.10.5, 01:08:30, Serial0/0/0
C
192.168.1.0/24 is directly connected, FastEthernet0/0
 Both R1 and R2 automatically summarizing.
 R1 is the successor because of the difference in bandwidth.
46
Disabling
Automatic
Summarization
172.16.0.0/16
R3# show ip route
<output omitted>
D
172.16.0.0/16 [90/2172416] via 192.168.10.5, 01:08:30, Serial0/0/0
 Is this the best route for all 172.16.0.0 subnets?
 No
 R3 will route all packets destined for 172.16.2.0 through R1.
 Solution?
 Need R1 and R2 to send individual subnets.
 R1 and R2 must stop automatically summarizing 172.16.0.0/16.
47
Disabling Automatic Summarization
R1(config)# router eigrp 1
R1(config-router)# no auto-summary
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.3.2 (Serial0/0/0) is
resync: summary configured
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.3.2 (Serial0/0/0) is
down: peer restarted
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.3.2 (Serial0/0/0) is
up: new adjacency
<output omitted>
R2(config)# router eigrp 1
R2(config-router)# no auto-summary
R3(config)# router eigrp 1
R3(config-router)# no auto-summary
 Automatic summarization can be disabled with the no auto-summary.
 The router configuration command eigrp log-neighborchanges is on by
default on some IOS implementations. .
48
Disabling Automatic Summarization
R1# show ip route
C
D
C
D
C
D
192.168.10.0/30 is subnetted, 2 subnets
192.168.10.4 is directly connected, Serial0/0/1
192.168.10.8 [90/3523840] via 192.168.10.6, 00:16:55, S0/0/1
172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
172.16.1.0/24 is directly connected, FastEthernet0/0
172.16.2.0/24 [90/3526400] via 192.168.10.6, 00:16:53, S0/0/1
172.16.3.0/30 is directly connected, Serial0/0/0
192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:16:52, Serial0/0/1
 R1 no more Null0 summary routes:
D
192.168.10.0/24 is a summary, 00:45:09, Null0
D
172.16.0.0/16 is a summary, 00:46:10, Null0
 What does this mean?
 This mean any packets for their parent networks that do not match a
child route, the routing table will check supernet and default routes.
 Unless no ip classess is used
49
Disabling Automatic Summarization
R2# show ip route
D
C
D
C
C
C
D
192.168.10.0/30 is subnetted, 2 subnets
192.168.10.4 [90/3523840] via 192.168.10.10, 00:15:44, S0/0/1
192.168.10.8 is directly connected, Serial0/0/1
172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
172.16.1.0/24 [90/3526400] via 192.168.10.10, 00:15:44, S0/0/1
172.16.2.0/24 is directly connected, FastEthernet0/0
172.16.3.0/30 is directly connected, Serial0/0/0
10.0.0.0/30 is subnetted, 1 subnets
10.1.1.0 is directly connected, Loopback1
192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:15:44, S0/0/1
 R2 no more Null0 summary routes :
D
192.168.10.0/24 is a summary, 00:00:15, Null0
D
172.16.0.0/16 is a summary, 00:00:15, Null0
50
172.16.0.0/16
R3# show ip route
172.16.0.0/16
C
C
D
D
D
C
192.168.10.0/30 is subnetted, 2 subnets
192.168.10.4 is directly connected, Serial0/0/0
192.168.10.8 is directly connected, Serial0/0/1
172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
172.16.1.0/24 [90/2172416] via 192.168.10.5, 00:00:11, S0/0/0
172.16.2.0/24 [90/3014400] via 192.168.10.9, 00:00:12, S0/0/1
172.16.3.0/30 [90/41024000] via 192.168.10.5, 00:00:12, S0/0/0
[90/41024000] via 192.168.10.9, 00:00:12, S0/0/1
192.168.1.0/24 is directly connected, FastEthernet0/0
 Why does R3’s routing table now have two equal-cost paths to
172.16.3.0/24?
 Shouldn’t the best path only be through R1 with the 1544-Mbps link?
51
Disabling
Automatic
Summarization
172.16.0.0/16
172.16.0.0/16
R3# show ip route
<output omitted>
D
172.16.3.0/30 [90/41024000] via 192.168.10.5, 00:00:12, S0/0/0
[90/41024000] via 192.168.10.9, 00:00:12, S0/0/1
 The slowest link is the 64-Kbps link
52
Manual Summarization
 EIGRP can be configured to summarize routes, whether or not
automatic summarization (auto-summary) is enabled.
 Modified topology.
53
Manual
Summarization
R3(config)# interface loopback 2
R3(config-if)# ip address 192.168.2.1 255.255.255.0
R3(config-if)# interface loopback 3
R3(config-if)# ip address 192.168.3.1 255.255.255.0
R3(config-if)# router eigrp 1
R3(config-router)# network 192.168.2.0
R3(config-router)# network 192.168.3.0
 Add two more networks to R3.
 Configure EIGRP network statements.
54
Manual
Summarization
192.168.1.0/24,
192.168.2.0/24,
192.168.3.0/24
192.168.1.0/24,
192.168.2.0/24,
192.168.3.0/24
Only pertinent routes shown
R1#
D
D
D
show ip route
192.168.1.0/24 [90/2172416] via 192.168.10.6, 02:07:38, S0/0/1
192.168.2.0/24 [90/2297856] via 192.168.10.6, 00:00:34, S0/0/1
192.168.3.0/24 [90/2297856] via 192.168.10.6, 00:00:18, S0/0/1
R2#
D
D
D
show ip route
192.168.1.0/24 [90/3014400] via 192.168.10.10, 02:08:50, S0/0/1
192.168.2.0/24 [90/3139840] via 192.168.10.10, 00:01:46, S0/0/1
192.168.3.0/24 [90/3139840] via 192.168.10.10, 00:01:30, S0/0/1
 Instead of sending three separate networks, R3 can summarize the
192.168.1.0/24, 192.168.2.0/24, and 192.168.3.0/24 networks as a single route.
55
Determining the Summary EIGRP Route
1. Write out the networks that you want to summarize in binary.
2. Find the matching bits.
 Count the number of leftmost matching bits, which in this example is 22.
 This number becomes your subnet mask for the summarized route: /22
or 255.255.252.0.
3. To find the network address for summarization, copy the matching 22 bits
and add all 0 bits to the end to make 32 bits.
The result is the summary network address and mask for 192.168.0.0/22
56
Configure EIGRP
Manual
Summarization
192.168.0.0/22
192.168.0.0/22
Router(config-if)# ip summary-address eigrp as-number network-address
subnet-mask
R3(config)# interface serial 0/0/0
R3(config-if)# ip summary-address eigrp 1 192.168.0.0 255.255.252.0
R3(config)# interface serial 0/0/1
R3(config-if)# ip summary-address eigrp 1 192.168.0.0 255.255.252.0
 Because R3 has two EIGRP neighbors, the EIGRP manual summarization
in configured on both Serial 0/0/0 and Serial 0/0/1.
57
Verify EIGRP
Manual
Summarization
192.168.0.0/22
192.168.0.0/22
R1# show ip route
<output omitted>
D 192.168.0.0/22 [90/2172416] via 192.168.10.6, 00:01:11, Serial0/0/1
R2# show ip route
<output omitted>
D 192.168.0.0/22 [90/3014400] via 192.168.10.10, 00:00:23, Serial0/0/1
 Fewer number of total routes in routing tables
 Faster routing table lookup process more efficient.
 Summary routes also require less bandwidth
 Single route can be sent rather than multiple individual routes.
58
EIGRP Default
Route
Default Route
Redistribute
default static
route in
EIGRP
updates
The ISP router in our topology does
not physically exist. By using a
loopback interface, we can simulate
a connection to another router.
R2(config)# ip route 0.0.0.0 0.0.0.0 loopback 1
R2(config)# router eigrp 1
R2(config-router)# redistribute static
59
EIGRP Default
Route
Default Route
Redistribute
default static
route in
EIGRP
updates
Only static default route shown,
other output omitted.
R1# show ip route
Gateway of last resort is 192.168.10.6 to network 0.0.0.0
D*EX
0.0.0.0/0 [170/3651840] via 192.168.10.6, 00:02:14, S0/0/1
R2# show ip route
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
S*
0.0.0.0/0 is directly connected, Loopback1
R3# show ip route
Gateway of last resort is 192.168.10.9 to network 0.0.0.0
D*EX
0.0.0.0/0 [170/3139840] via 192.168.10.9, 00:01:25, S0/0/1
60
EIGRP Default
Route
Default Route
Redistribute
default static
route in
EIGRP
updates
Only static default route shown,
other output omitted.
R1# show ip route
Gateway of last resort is 192.168.10.6 to network 0.0.0.0
D*EX
0.0.0.0/0 [170/3651840] via 192.168.10.6, 00:02:14, S0/0/1
 D: This static route was learned from an EIGRP routing update.
 *: The route is a candidate for a default route.
 EX: The route is an external EIGRP route, in this case a static route outside
of the EIGRP routing domain.
 170: This is the AD of an external EIGRP route.
61
EIGRP Default Route
Default Route
Redistribute
default static
route in
EIGRP
updates
 There is another method to propagate a default route in EIGRP, using the
ip default-network command.
 More information on this command can be found at this site:
 http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a
0080094374.shtml.
62
Fine-Tuning EIGRP: EIGRP Bandwidth Utilization
EIGRP updates use no
more than 50% of the
link’s bandwidth by
default.
Router(config-if)# ip bandwidth-percent eigrp as-number percent
 By default, EIGRP uses only up to 50 percent of the bandwidth of
an interface for EIGRP information.
 Prevents the EIGRP process from overutilizing a link.
 Can be modified with ip bandwidth-percent eigrp
63
EIGRP Bandwidth
Utilization
R1(config)# interface serial 0/0/0
R1(config-if)# bandwidth 64
R1(config-if)# ip bandwidth-percent eigrp 1 25
R2(config)# interface serial 0/0/0
R2(config-if)# bandwidth 64
R2(config-if)# ip bandwidth-percent eigrp 1 25
 Limit EIGRP to no more than 25 percent of the link’s bandwidth.
 EIGRP will never use more the 18 Kbps of the link’s bandwidth for
EIGRP packet traffic.
64
Configuring Hello Intervals and Hold Times
Router(config-if)# ip hello-interval eigrp as-number seconds
Router(config-if)# ip hold-time eigrp as-number seconds
 Hello intervals and hold times do not have to match with other
EIGRP routers to establish adjacencies.
 We will see later, OSPF’s Hello and other timers do need to
match.
 Range from 1 to 65,535
 If you change the hello interval, make sure that you also change the
hold time to a value greater than the hello interval.
 Otherwise, neighbor adjacency will go down after the hold time
expires and before the next hello interval.
65
Configuring
Hello Intervals
and Hold Times
R1(config)# int s0/0/0
R1(config-if)# ip hello-interval eigrp 1 60
R1(config-if)# ip hold-time eigrp 1 180
R2(config)# int s0/0/0
R2(config-if)# ip hello-interval eigrp 1 60
R2(config-if)# ip hold-time eigrp 1 180
 The no form can be used on both of these commands to restore the
default values.
66
Topics
 Introduction to EIGRP
 EIGRP: An Enhanced Distance
Vector Routing Protocol
 EIGRP Message Format
 Protocol-Dependent Modules
 RTP and EIGRP Packet Types
 Hello Protocol
 EIGRP Bounded Updates
 DUAL: An Introduction
 Administrative Distance
 Authentication
 Basic EIGRP Configuration
 EIGRP Network Topology
 Autonomous Systems and
Process IDs
 The router eigrp Command
 The network Command
 Verifying EIGRP
 Examining the Routing Table
 EIGRP Metric Calculation
 EIGRP Composite Metric and the K
Values
 EIGRP Metrics
 Using the bandwidth Command
 Calculating the EIGRP Metric
 DUAL
 DUAL Concepts
 Successor and Feasible Distance
 Feasible Successors, Feasibility
Condition, and Reported Distance
 Topology Table: Successor and
Feasible Successor
 Topology Table: No Feasible
Successor
 Finite State Machine
 More EIGRP Configurations
 The Null0 Summary Route
 Disabling Automatic Summarization
 Manual Summarization
 EIGRP Default Route
 Fine-Tuning EIGRP
67
Chapter 9
EIGRP
CIS 82 Routing Protocols and Concepts
Rick Graziani
Cabrillo College
[email protected]
Last Updated: 4/28/2008