Download NetAdmin

EIGRP
Table of Contents
Basics of EIGRP
EIGRP Terminology
EIGRP Operation
EIGRP Configuration
Monitoring EIGRP
Chapter 6 Lab Notes
EIGRP Overview
Enhanced version of Cisco’s proprietary IGRP dramatically
increases operational efficiency because EIGRP…
•
•
•
•
Uses a more granular version of IGRP’s metrics (32 bits v. 24 bits)
Has faster convergence than any other IGP
Is scalable because of VLSM and route summarization
Supports multiple routed protocols through protocol-dependant
modules
• Replaces Novell RIP and Apple’s RTMP
• Is technically an advance distance-vector routing protocol
 Uses partial updates
 Hello packets for neighbor discovery
• Is relatively easy to administer
 However, does not have OSPF’s hierarchical design (no areas)
EIGRP Metrics
EIGRP scales IGRP’s metrics by a factor of 256
•
•
•
•
IGRP metric = 24 bits; EIGRP metric = 32 bits
Bandwidth and Delay are equally weighted
Reliability, Load, and MTU are off by default
Hop count limited to 224 (IGRP’s limit is 255)
To remember the metric components…
•
•
•
•
•
Big
Dogs
Really
Like
Me
=
=
=
=
=
Bandwidth
Delay
Reliability
Load
MTU
EIGRP Tables
Like OSPF, EIGRP maintains three unique tables to
assist in routing traffic.
• Neighbor Table
• Topology Table
• Routing Table
EIGRP maintains one table of each for each routed
protocol configured on the router.
• For example, if a router was configured with IP, IPX and
AppleTalk, EIGRP would maintain…
 3 Neighbor Tables
 3 Topology Tables
 3 Routing Tables
Neighbor Table
Use the show ip eigrp neighbors command
to view the table.
• Similar to OSPF’s Adjacencies database;
 Contains a list of all neighbors discovered through hellos
 Maintains hello and holdtime intervals on each neighbor
 Maintains information required by RTP (discussed later)
 SRTT—Smooth Round-trip Timer; avg. time it takes to send
and then receive a reply from that neighbor
 RTO—Retransmission Timeout; how long to wait without
receiving an acknowledgement to a reliably sent packet
Router#show ip eigrp neighbors
IP-EIGRP neighbors for process 100
H
Address
Interface
0
1
192.168.224.2
192.168.208.2
Se0
Se1
Hold
(sec)
13
11
Uptime
SRTT
(ms)
00:01:28 930
00:02:20
35
RTO
5000
1140
Q
Cnt
0
0
Seq
Num
30
21
Topology Table
Use the show ip eigrp topology [all-links]
command to view the table.
• Similar to OSPF’s Link-State (Topology) database;
 Contains all routes the router has learned about from its neighbors and
all the information necessary to calculate a set of distances and
vectors to all reachable destinations
 FD—Feasible Distance; lowest calculated metric to reach a destination
as opposed to…
 RD—Reported Distance or Advertised Distance; distance to the
destination reported by the neighbor.
Router#show ip eigrp topology
Feasible Distance
Reported Distance
IP-EIGRP Topology Table for process 100
Codes: P – Passive, A – Active, U – Update, Q – Query, R – Reply,
r – Reply status
P 192.150.42.120 255.255.255.248, 1 successors, FD is 2172416
via 192.150.42.9 (2172416/2169856), Fddi0
P 192.150.42.8 255.255.255.248, 1 successors, FD is 28160
via Connected, Fddi0
Routing Table
Use the show ip route command to view table
Like all routing protocols, EIGRP maintains a
routing table with…
• Best routes to destination networks
• Maintains up to four equal-cost routes for each
destination
 Unequal-cost routes can be installed if the variance
command has been configured
• You are already familiar with the routing table. You will
notice that EIGRP routes are designated with a D.
EIGRP Concepts & Terminology
Successor
• The best, least cost route to the destination installed in the routing
table; multiple successors can be installed for load balancing
Feasible Successor
• A next-hop alternative route to the destination kept in the topology
table, ready to be installed if the successor fails; feasible
successors are only in the topology table
Active State
• During route recomputation, routes lost due to a successor’s failure
are said to be in the active state. The active state ends when the
route is restored or removed.
Passive State
• Installed routes that are not in the process of being recomputed
are said to be in the passive state.
EIGRP Concepts & Terminology
Diffusing Update Algorithm (DUAL)
• EIGRP’s route computation engine; guarantees a loop-free
topology; calculates EIGRP’s metric and installs successors in the
routing table & feasible successors in the topology table
Route Evaluation
• Occurs when the topology changes; DUAL evaluates the topology
table, searching for feasible successors and immediately installing
them, if found; no recomputation is necessary
Route Recomputation
• DUAL begins recomputing if no feasible successors are found;
queries neighbors for alternative routes; process ends when all
neighbors have replied and DUAL either installs successor or
removes route from the topology and routing tables.
Protocol Dependant Modules (PDM)
• EIGRP’s scalable and adaptable feature because of its modularity;
theoretically, EIGRP does not have to be completely rewritten to
route IPv6—just add a PDM.
EIGRP Packet Types
Hello Packets
• Unreliable multicast to 224.0.0.10 to discover and maintain
neighbors; contains the router’s neighbor table
• Default hello interval depends on the bandwidth
≤ 1.544 Mbps = 60 sec. hello interval (180 holdtime)
> 1.544 Mbps = 5 sec. hello interval (15 holdtime)
Update Packets
• Sent reliably, there are 2 types
 Unicast to new neighbor discover; contains routing table
 Multicast to all neighbors when topology changes
Query & Reply Packets
• Queries are multicast reliably during route recomputation, querying
neighbors for a new successor to a lost route
• Neighbors unicast a reply to the query whether or not they have a
route.
Acknowledgement Packets
• “Dataless” packet that acknowledges the receipt of a packet sent
reliably
Reliable Transport Protocol
RTP is EIGRP’s flexible protocol used to transport
message types through a network
• Since EIGRP is protocol independent, it has to have its
own connection-oriented and connectionless services
• RTP allows unicasting and multicasting reliable and
unreliable packets to peers simultaneously
• RTP maintains a transmission list in the neighbor table
with sequence numbers to determine when a required
acknowledgement has been received.
 Works much like TCP’s Positive Acknowledgement with
Retransmission
The EIGRP Process
EIGRP operation is completed in five stages:
•
•
•
•
•
Building neighbor relationships
Discovering routes
Choosing the best routes
Maintaining routes
Removing routes
These stages do not necessarily occur sequentially
• Building relationships and discovering routes occur
together as do choosing and maintaining routers
Note: The following EIGRP Operation discussion is adapted from CCNP
Routing Exam Prep: Exam 640-503 (© 2000) by Robert Larson, et al.
Building Neighbor Relationships
Neighbor relationships are established through the
use of Hello packets
• A new router configured with EIGRP will multicast hello
packets to directly connected routers
• The receiving routers will reply if the new router is…
 Configured with EIGRP
 In same AS
 Using the same metric weights
• EIGRP routers, unlike OSPF, do not have to have the
same hello intervals
 Defaults, however, are 5 sec. for > T1 and 60 sec. for ≤ T1.
Discovering Routes
While neighbor relationships are established, the
following steps occur:
• The new router multicast hellos to 224.0.0.10
• Directly connected routers respond with a unicast
update packet containing all the routes in their routing
table
• The new router replies to all neighbors with a unicast
Ack packet and places the contents of the updates in its
topology table
• The new router then unicast update packets to all
neighbors with the contents of its topology table (this is
how its neighbors learn about the router’s uniquely
configured networks such as a new LAN)
• Neighbors reply to the new router’s update with an Ack
packet.
Building/Discovering Example
1.
C comes online and multicasts
hellos to A & B.
2.
A & B unicast an update packet
containing routing table contents
3.
C replies to unicast updates with
Ack packet and builds topology
table
4.
C unicasts updates to A & B with
contents of topology table
(includes C’s new LAN)
5.
A & B reply with an Ack packet.
C
A
B
Choosing the Best Routes
After a new router has received all the updates
from directly connected neighbors, it can calculate
its DUAL.
• First, the metric for each route in the topology table is
calculated using the following formula:
Metric = 256[(10,000,000/min. bandwidth) + sum of delays]
• Then, the route with the lowest cost is designated the
successor and is installed (up to 4 with equal costs) in
the routing table.
• DUAL then looks for feasible successors. A feasible
successor must have a lower feasible distance to the
destination than the installed route’s feasible distance.
• All feasible successors are maintained in the topology
table so DUAL can install them immediately if the
successor fails.
Maintaining Routes
As new routers come online and old routes fail,
EIGRP quickly and efficiently handles these
situations with little or no downtime.
• As new routers come online, their hello packets and the
ensuing update process has a “domino effect” on the
network.
• All routers in the AS almost instantaneously converge
on the router’s new networks.
Maintaining routes also means informing directly
connected neighbors when another neighbor stops
sending hello packets at the required interval.
Removing Routes
When a route fails (a directly connected neighbor is no
longer sending hellos), the detecting router’s DUAL…
• Enters the route evaluation phase.
 Is there a feasible successor in the topology table? If so, immediately
install it, begin routing to the alternative path, and update neighbors
about the alternative.
 If no feasible successor exists, enter route recomputation
• If necessary, enter the route recomputation phase.
 Query neighbors for a alternative route
– If neighbor has a feasible successor, it will send it to the router
– If it does not have one, it will query all its directly connected neighbors,
thus flooding the AS with the query until an alternate route is or is not
found.
 Once the router has received replies from all queried neighbors, it can
then recalculate the best route.
– If a new alternative is found, it will be installed in the routing table.
– If no new alternative is found, the old route is removed.
EIGRP Convergence Summary
1. Router detects link failure; enters route evaluation
 Feasible successors are promoted to successors
 Successors are installed in the routing table immediately
 All neighbors are updated about the new alternate route
2. If no feasible successors, router enters route recomputation
 Queries are flooded throughout the AS in search of an alternate
 All routers reply whether they have an alternative or not
 Originating router waits for all replies before either
–
–
Removing the queried network for its topology and routing tables or
Adding an alternative path for the queried network in its tables
 If a query receives no response, the route becomes “stuck-in-active”
3. The router has now converged and will now work to converge the entire
internetwork by…
 Generating an update and multicasting it out all interfaces
–
Update contains info. on what paths the router has added/removed from its
topology and routing tables
 Each receiving router will replay with an Ack packet and modify tables
accordingly
–
The EIGRP internetwork has now converged.
Basic Configuration
Similar to IGRP, EIGRP is started with the following
commands:
Router(config)#router eigrp [AS_number]
Router(config-router)#network network-number
• A router running both IGRP and EIGRP with the same AS number
will automatically redistribute from one routing process into the
other
 EIGRP routes redistributed into IGRP are denoted with an “I” in the
routing table.
 IGRP routes redistributed into EIGRP are denoted with an “D EX” in
the routing table.
For interfaces whose actual bandwidth is different than
EIGRP’s defaults, use the following command.
Router(config-if)#bandwidth kilobits
• For example, a serial link defaults to T1 speeds or 1544 kbps. If
the contracted speed is ½ a T1 or 768 kbps…
Router(config-if)#bandwidth 768
Route Summarization
EIGRP recognizes two types of summary routing:
• Automatic route summarization
• Manual route summarization
Automatic Summarization (on by default in EIGRP)
• Works the same as IGRP and RIP
 Summarizes routes on the classful boundary; does not advertise
subnets; subnets must be contiguous.
 For example;
– Subnets 172.16.16.0/20, 172.16.32.0/20, and 172.16.48.0/20 would be
automatically summarized as 172.16.0.0/16
 Automatic summarization has its benefits
– Conserves resources across classful boundaries in networks with proper IP
addressing design.
Manual Summarization
• EIGRP can summarize routes at classless boundaries on any router
interface on the network
 This capability is an advantage over OSPF, which can only summarize
on ABRs and ASBRs
Manual Summarization
Automatic summarization must be turned off.
• in the routing process for EIGRP…
Router(config-router)#no auto-summary
To configure a classless summary route…
• Subnets must be contiguous!!
• Use the following command on the interface that will
advertise the summary:
Router(config-if)#ip summary-address eigrp AS-number ip-address mask
Manual Summarization Example
On Router B, you would summarize routes
advertised to A as follows:
!Start the routing process & disable automatic summarization
RTB(config)#router eigrp 100
RTB(config-router)#network 190.1.1.0
RTB(config-router)#network 190.1.2.0
RTB(config-router)#network 190.1.3.0
RTB(config-router)#no auto-summary
!Then on the interface, summarize the subnets advertised to A
RTB(config-router)#interface e0
RTB(config-if)#ip address 10.2.50.1 255.255.255.0
RTB(config-if)#ip summary-address eigrp 100 190.1.0.0 255.255.252.0
A
10.2.50.0/24
e0
e2
B
190.1.1.0/24
C
e1
190.1.0.0/22
Advertised to A
10.2.10.0/24
D
190.1.3.0/24
190.1.2.0/24
Manual Summarization Example
Router B’s topology table would show all the
specific routes as well as the summary:
RTB#show ip eigrp topology
IP-EIGRP Topology Table for process 1
(output omitted)
P 190.1.1.0/24, 1 successors, FD is 10511872
via Connected, Serial1
P 190.1.0.0/22, 1 successors, FD is 10511872
via Summary (10511872/0), Null0
P 190.1.3.0/24, 1 successors, FD is 10639872
via 190.1.1.1 (10639872/128256), Serial1
P 190.1.2.0/24, 1 successors, FD is 10537472
via 190.1.1.1 (10639872/128256), Serail1
A
10.2.50.0/24
e0
s1
B
190.1.1.0/24
C
e1
190.1.0.0/22
Advertised to A
10.2.10.0/24
D
190.1.3.0/24
Null0 means there’s
no specific interface
for 190.1.1.0/22; more
specific routes exist.
190.1.2.0/24
Manual Summarization Example
Router A’s topology table would show only the
summary route:
• Any packet destined for a network that is part of the
190.1.0.0/22 summary would be sent to Router B.
RTA#show ip eigrp topology
IP-EIGRP Topology Table for process 1
(output omitted)
P 190.1.0.0/22, 1 successors, FD is 11023872
via 10.2.50.1 (11023872/10511872), Serial0
A
10.2.50.0/24
e0
s1
B
190.1.1.0/24
C
e1
190.1.0.0/22
Advertised to A
10.2.10.0/24
D
190.1.3.0/24
190.1.2.0/24
Bandwidth Optimization
By default, EIGRP will only consume up to 50% of a link’s
configured bandwidth.
• If a link in 256Kbps, then EIGRP traffic will use up to 128Kbps
Why would you want to change the default setting?
• May be necessary when network apps require certain amounts of
bandwidth at all times.
• Sometimes, EIGRP traffic will require a certain level of bandwidth
availability.
Note: Changing EIGRP’s bandwidth percentage has no
effect on user traffic.
Two commands to configure EIGRP traffic percentage.
• bandwidth
• ip bandwidth-percent eigrp
bandwidth Configuration
The bandwidth command
Router(config-if)#bandwidth bandwidth
• Configured on the interface where you want to adjust
EIGRP traffic.
• Whatever value is specified with the bandwidth
command, EIGRP always takes 50% of it (by default).
• Remember: The bandwidth command is only used by
routing protocols—it has no effect on user traffic when
the protocol is EIGRP. The router does not use this
command for any other purpose.
• For example, you have a 128kbps link and you only
want EIGRP to use 16kbps.
Router(config-if)bandwidth 32
 EIGRP will use, at most, 50% of the configured bandwidth
 User traffic will still be allowed to use at least 112kbps (128-16)
bandwidth-percent Configuration
The second way to modify how much bandwidth
EIGRP uses is to use the following command:
Router(config-if)#ip bandwidth-percent eigrp AS-number percent
Use this command when you want to specify a
different percentage than 50% of the configured
bandwidth.
• For example, you have a 64kbps link and the bandwidth
has been set to 32kbps for metric calculation purposes.
• However, you want EIGRP to be able to use an entire
32kbps of the link’s 64kbps speed, if needed.
Router(config)#int s0
AS #
Router(config-if)#bandwidth 32
Router(config-if)#ip bandwidth-percent eigrp 123 100
NBMA Configurations
NBMA Configuration
Guidelines
• EIGRP should not exceed
the CIR of the hub’s serial
line (also called the access
line).
 To do so is called
“oversubscribing” the link
• Aggregate traffic of all links
to the hub should no exceed
the hub’s access line speed.
• Bandwidth on virtual circuits
must be the same in both
directions.
Hub
Router
Point-to-Point NBMA
Example of point-to-point
Frame Relay with EIGRP
• Each spoke router has a
virtual circuit to the hub with
a CIR of 256kbps.
• This is an oversubscribed
situation.
 Why would you want to
oversubscribe the spoke
routers?
 To allow up to 256kbps
across each spoke when
traffic from other spokes is
light.
• Configure the 10 subifs with
bandwith of 154kbps so
EIGRP will only use 50% of
the subif when the NBMA is
saturated with user traffic.
Access Line
1.544 Mbps
256k
256k
256k
256k
256k
256k
256k
256k
256k
256k
Point-to-Point Configurations
Hub_Router(config)#interface serial 0
Hub_Router(config-if)#encapsulation frame-relay
Hub_Router(config-if)#int serial0.1 point-to-point
Hub_Router(config-subif)#bandwidth 154
Hub_Router(config-subif)#int serial0.2 point-to-point
Hub_Router(config-subif)#bandwidth 154
. . .
Hub_Router(config-subif)#int serial0.10 point-to-point
Hub_Router(config-subif)#bandwidth 154
The above configuration
insures EIGRP never
uses more than 77kbps
for EIGRP traffic
Access Line
1.544 Mbps
Each Spoke Router must
also be configured with
the same bandwidth as
the Hub Router.
256k
256k
256k
256k
256k
256k
256k
256k
256k
256k
Multipoint EIGRP
In point-to-multipoint configurations...
• If the CIR of each Spoke Router is the same, set the
access line’s bandwidth to the sum of the CIRs
• If the CIR of the Spoke Routers are different, which is
the usual case, either...
 Take the lowest CIR and multiply it by the number of virtual
circuits. This causes higher bandwidth links to be underutilized.
 Preferred Hybrid Solution: Use subinterfaces and configure like
bandwidth virtual circuits on the same subinterface.
EIGRP & IPX Networks
EIGRP can optimizes IPX updates.
• By default, IPX RIP and EIGRP routes are redistributed
into each process.
• If IPX RIP and EIGRP have the same hop count, the IPX
RIP route is believed unless both routes came from the
same router.
 This ensure the router always believes an IPX server over a
Cisco router.
• If EIGRP IPX is running on two neighbor routers, by
default on...
 Serial links, SAP updates are only sent when a change occurs
 LAN links, SAP updates are sent periodically (60 sec)
– You can configure incremental updates if...
» all nodes out the interface are EIGRP peers and
» the LAN link is not directly connected to an IPX server
EIGRP IPX Configurations
EIGRP and IPX basic routing configurations
Router(config)#ipx routing
Router(config)#ipx router eigrp AS
To disable IPX RIP updates for a particular
network
• Since IPX RIP is on by default (no additional
configurations are needed), to disable updates for a
specific network...
Router(config)#ipx router rip
Router(config-ipx-router)#no network network-number
To configure incremental SAP updates on LANs...
Router(config-if)#ipx sap-incremental eigrp AS [rsup-only]
 rsup-only means IPX RIP routing is used. EIGRP is only used for
SAP updates. EIGRP routes are ignored.
Monitoring EIGRP
Monitoring Command
Description
show ip eigrp neighbors [ type
number ][details]
displays the neighbor table; can specify interface; details
expands the output
show ip eigrp interfaces [ type
number ][AS ][details]
displays info about each EIGRP interface; options can specify the
interface, AS, and expand the output
show ip eigrp topology [ AS |[ipdisplays the topology table; extra options can fine tune the output;
address ][mask ]]
for example:
- specify the AS and/or a specific ip address
show ip eigrp topology
- show only routes in the active state, pending convergence, or
[active|pending|zero-successors] routes with no successors
- show all routes, not just feasible successors, with the allshow ip eigrp topology all-links links option
show ip eigrp traffic [ AS ]
displays the number of EIGRP packets sent and received sent
the last time the counter was cleared; use to view excessive
EIGRP routing updates
debug eigrp fsm
Observe the feasible successor activity and determine if routes
are being installed and deleted by the EIGRP routing process
debug eigrp packet
Observe the transmission and receipt of EIGRP packets
including hellos, queries, updates, etc. Sequence numbers are
also displayed.