1
CCNA3
–
module 3 EIGRP
2
EIGRP
Cisco proprietary, released in 1994
Based on IGRP
EIGRP is an
advanced distance
-
vector
routing protocol that relies on features
commonly associated with link
-
state
protocols. (sometimes called a
hybrid
routing protocol
)
Supports VLSM and CIDR
Allows for multiple routed protocols
3
EIGRP
Uses Hello protocols to create and maintain neighbor
relationships and to determine when a link is down.
(Like link
-
state)
Every 5 seconds, with a hold timer of 15 seconds
Links less than T1 speed, Hellos are every 60
seconds, hold timer of 180 seconds
Partial routing updates in response to topology
changes
When a change in topology occurs, EIGRP does not
flood updates like link
-
state protocols, but
immediately
sends those changes to its neighbors.
Has speed and efficiency of routing updates like a
link
-
state protocol, along with a topology database.
4
EIGRP Benefits
Rapid Convergence
–
DUAL routing algorithm
Efficient use of bandwidth
partial, bounded updates
–
only sent to routers
that need the information & not entire routing
table
small “Hello” packets to keep in touch with other
routers
–
minimal use of bandwidth
Supports VLSM and CIDR
Multiple network
-
layer support (multiprotocol)
IP, IPX, and AppleTalk
5
EIGRP and IGRP
Automatically
redistributes when using same AS
number.
Topology example….
6
Metric calculation: IGRP/EIGRP
(with the following default constant values):
Constant Value
K1
1
K2
0
K3 1
K4
0
K5
0
Notes
k2
metric effects
LOAD
k4
and
k5
effects
RELIABILITY
metric
= [K1 *
bandwidth
+ ((K2 *
bandwidth
) / (256 *
load
)) +
(K3 *
delay
)] * [K5/(
reliability
+ K4)]
7
Metric Calculation
Simplify the previous equation by
applying the default constants
…
8
The metrics used by EIGRP in making routing
decisions are (
lower the metric the better
):
bandwidth
delay
load
reliability
By default, EIGRP uses only:
Bandwidth (carrying capacity)
Delay (end
-
to
-
end travel time)
Metric Calculation
9
If these are the default:
bandwidth (default)
delay (default)
When are these used?
load
reliability
Use
show interface
command to view the
metrics used on a specific interface that is
routing EIGRP.
Metric Calculation
10
Metric Calculation
–
show interfaces
Router> show interfaces s1/0
Serial1/0 is up, line protocol is up
Hardware is QUICC Serial
Description: Out to VERIO
Internet address is 207.21.113.186/30
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
rely 255/255, load 246/255
Encapsulation PPP, loopback not set
Keepalive set (10 sec)
<output omitted>
11
Bandwidth
Expressed in
kilobits
(
show interface
)
This is a
static number
and used for metric
calculations only.
Does not necessarily reflect the actual bandwidth of
the link.
You can adjust the bandwidth metric on an interface
using what command?
What command restores the interface bandwidth to
the original default?
The default values:
What is the default bandwidth of serial interfaces on
CISCO routers?
Metric Calculation
–
Bandwidth
12
Delay
Like bandwidth, delay it is a
static number
.
Expressed in
microseconds
,
millionths of a
second
(Uses the Greek letter mu with an S,
S, NOT “ms”
which is millisecond or
thousandths of a second
)
The default values:
What is the default delay of a Cisco serial interface?
IGRP/EIGRP metric uses the
sum of all of the
delays
of all of the outbound interfaces to the
destination network.
Metric Calculation
–
Delay
13
Changing the delay informational parameter:
The delay can be changed using:
Router(config
-
if)#
delay
tens
-
of
-
S
(microseconds)
Example of changing the delay on a serial interface to
30,000 microseconds
:
Router(config
-
if)#
delay
3000
To restore the 20,000 microsecond default value:
Router(config
-
if)#
no delay
Metric Calculation
–
Delay
14
IGRP vs EIGRP Metric Calculation
The difference
:
IGRP metric is 24 bits long
EIGRP metric is 32 bits long
EIGRP metric is 256 times greater for the
same route
EIGRP allows for finer comparison of
potential routes
15
IGRP vs EIGRP Metric Calculation
IGRP
bandwidth = (10,000,000
÷
bandwidth
)
delay =
delay
÷
10
EIGRP
bandwidth = (10,000,000
÷
bandwidth
) * 256
delay = (
delay
÷
10) * 256
Note: The reference
-
bandwidth
For both IGRP and EIGRP: 10
7
,
(10,000,000/bandwidth), whereas
with OSPF it
was 10
8
(100,000,000/bandwidth)
16
Metrics
–
HOP COUNT
EIGRP also imposes a maximum hop count
of 224
IGRP maximum hop count of 255
RIP maximum hop count of 15
17
EIGRP Configuration
RTA(config)#
router eigrp
AS
RTA(config
-
router)#
network
network
RTA(config
-
router)#
eigrp
log
-
neighbor
-
changes
RTA(config
-
if)#
bandwidth
kilobits
AS must be the same on
all routers in the AS
If AS’s are identical on a
router running both IGRP
and EIGRP, routing
tables are redistributed
automatically.
Enables logging of neighbor adjacency
changes to monitor stability & help
detect problems
CISCO recommends this command.
EIGRP assumes default if not set.
If the link is slower, router might not
converge, routing updates may be lost,
or suboptimal path selection may result.
18
EIGRP tables
Neighbor
Topology
Routing
19
EIGRP Neighbor tables
Lists adjacent routers
One table for each routed protocol that
EIGRP supports
RTX#
show ip eigrp neighbors
IP
-
EIGRP neighbors for process 1
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 10.2.0.2 Se1 12 00:27:39 333 1998 0 10
0 10.1.0.1 Se0 14 01:17:14 40 240 0 27
20
EIGRP Neighbor tables
Fields in neighbor table:
Neighbor address (Address)
Hold time (Hold Uptime)
Smooth round
-
trip timer (SRTT)
Queue count (Q Cnt)
Sequence number (Seq No)
21
DUAL
–
calculating best paths
When the hold time expires, DUAL is informed of
the topology change and must recalculate the
new topology.
DUAL (Diffusing Update Algorithm)
–
allows
routers involved in a topology change to
synchronize at the same time, while not
involving routers that are unaffected by the
change (distance
-
vector algorithm)
22
EIGRP Topology tables
Contains all of the EIGRP routing tables in the
autonomous system
DUAL combines information supplied by
neighbor and topology tables and calculates
the lowest cost routes to each destination.
EIGRP routers track changes and switch to
alternate routes when necessary
DUAL places this primary route, or
successor
route
, information in the routing table
23
EIGRP Topology tables
Topology tables includes:
Feasible distance (FD)
–
lowest calculated metric to
each destination.
Route source (via xxx.xxx.xxx.xxx)
–
ID of router that
originally advertised route
Reported distance (RD)
–
distance that an adjacent
neighbor reports to specific destination
Interface information
–
interface through which the
destination is reachable
Route status
–
passive (P)
–
route is stable and ready for use
Active (A)
–
route is in the process of being recomputed by
DUAL
24
EIGRP Topology tables
RTX#
show ip eigrp topology
IP
-
EIGRP Topology Table for process 100
Codes: P
-
Passive, A
-
Active, U
-
Update, Q
-
Query, R
-
Reply, r
-
Reply status
P 200.10.3.0/24, 1 successors, FD is 2169856
via Connected, Serial1
via Redistributed (2169856/
0
)
P 200.10.4.0/24, 1 successors, FD is 2169856
via Connected, Serial0
RD
25
EIGRP Topology tables
Successor
–
route that is selected as the primary
route to use to reach a destination.
DUAL identifies and places route in routing table
There can be up to
four
successor routes for any
particular route.
Copy of successor is also placed in topology table
EIGRP sorts the topology table so that the
successor routes are at the top, followed by the
feasible successors. Bottom of list may include
routes that DUAL believes to be loops.
26
EIGRP Topology tables
Feasible Successor
–
backup route
Identified at same time as successor but kept only
in the topology table
May have multiple feasible successors but not
mandatory to have any
They are neighbors that are downstream (closer
to the destination)
Must have lower advertised cost (RD) than
existing successor’s FD
If feasible successor not identified,
active status
placed on route and query packets sent to all
neighbors to recompute topology.
27
Successor & Feasible Successor
28
Recomputation of Routes
If route becomes unavailable and DUAL
cannot find feasible successor.
Neighbor routers are compelled to answer
query for a loop
-
free path.
If neighbor has no route, it responds so.
Excess computation = network instability
To prevent convergence problems, DUAL
always tries to find a feasible successor before
resorting to recomputation
29
Recomputation of Routes
Stuck in Active
routers
–
one or more routers don’t respond to query
(180 seconds) then routes placed in stuck in
active state
EIGRP then clears its table of neighbors
that did not respond
30
Route Tagging
Routing Table
–
Internal routes
routes originating
within
the EIGRP AS
External routes
routes originating
outside
the EIGRP AS
31
Routing Table & Tagging
RouterB#
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, 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
Gateway of last resort is not set
C 10.1.1.0 is directly connected, Serial0
D
172.16.0.0 [90/2681856] via 10.1.1.0, Serial0
D EX
192.168.1.0 [170/2681856] via 10.1.1.1, 00:00:04, Serial0
External EIGRP routes are redistributed from IGRP networks
32
RTA#
show ip route
<output omitted>
C 10.1.1.0 is directly connected, Serial0
D
172.16.0.0 [90/2681856] via 10.1.1.0, Serial0
D EX
192.168.1.0 [170/2681856] via 10.1.1.1, 00:00:04, Serial0
External EIGRP routes are redistributed from IGRP networks
RTC#
show ip route
<output omitted>
C 192.168.1.0 is directly connected, Serial0
I
10.1.0.0 [100/10476] via 192.168.1.1, 00:00:04, Serial0
I
172.16.0.0 [100/10476] via 192.168.1.1, 00:00:04, Serial0
RTC only sees
IGRP routes
192.168.1.0
was redistributed
from IGRP
33
Hellos & RTP
Hello Packets
Sent every 5 seconds (high
-
bandwidth links)
and every 60 seconds by default (low
-
bandwidth links)
As long as routers receive hello packets
–
route in
passive
state
Reliable Transport Protocol (RTP)
Layer 4 protocol
Guarantees delivery of packets
Allows EIGRP to multicast and unicast to
different peers simultaneously
34
DUAL FSM
DUAL Finite
-
State Machine (DUAL FSM)
Full name of DUAL technology
Tracks routes advertised by neighbors and
uses composite metric to compare them
Guarantees each path is loop
-
free
Inserts lowest
-
cost paths (successor routes)
into routing table
Neighbor & Topology tables supply DUAL with
route information to make decisions quickly
35
DUAL FSM
FD is not mandatory
2 < 3
36
EIGRP Packets
•
Hello Packets
•
5 second updates (T1/Point
-
to
-
Point link)
•
Multicast on IP address
224.0.0.10
•
Hold Time =
3 times the Hello interval
(15 seconds)
•
Neighbor routers hello and dead intervals
do not
need to match with EIGRP (unlike
OSPF)
37
EIGRP Packets
•
Acknowledgement
•
Used by RTP to signal reliable exchange of information
•
Hello packet without data; unicast to specific host
•
Update
•
Discovery of new neighbor
•
EIGRP router sends unicast to neighbor so that it can
add to its topology table
•
EIGRP router send multicast to all neighbors if topology
change occurs
38
EIGRP Packets
•
Query & Reply
•
Query
-
Used to obtain specific information from one or
all of its neighbors (multicast or unicast)
•
Reply
–
response to query (unicast)
•
Used, for example, if DUAL places a route in active
state and multicasts neighbors, searching for successor
39
EIGRP Route Summarization
EIGRP automatically summarizes routes at the
classful
boundary
This may not be preferable, especially if using
VLSM
To disable auto
-
summarization:
Router(config
-
router)#
no auto
-
summary
Manual Summarization command:
Router(config
-
if)#
ip summary
-
address
eigrp
AS ip
-
address subnet
-
mask
administrative distance
(configured on a per-interface basis)
40
EIGRP Route Summarization
41
Verifying EIGRP
Show ip eigrp neighbors
Show ip eigrp interfaces
Show ip eigrp topology
Show ip eigrp topology all
-
links
Show ip eigrp traffic
AS
Debug eigrp fsm
Debug eigrp packets
42
RIP, IGRP, & OSPF
Troubleshooting
Show & debug commands
Debug ip rip
Debug ip igrp events
Debug ip igrp transactions
Debug ip ospf events
Show ip route
Show running
-
config
Show ip protocols
show ip ospf neighbor
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