Tài liệu CIS 185 CCNP ROUTEEIGRP Part 1 pdf

EIGRP Packet Types – Hello Packet  What are Hello packets used for by EIGRP to:  Discover neighbors sometimes called neighborships  Form adjacencies with those neighbors  What is t

CIS 185 CCNP ROUTE

EIGRP Part 1

Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: Fall 2012

Materials

 Implementing Cisco IP Routing

(ROUTE) Foundation Learning

Guide: Foundation learning for the

Review

What do we remember about EIGRP?

 What type of protocol is EIGRP?

 Distance Vector

 What are the default metrics used by EIGRP?

 Bandwidth (slowest) and Delay (cumulative)

 What are the optional metrics?

 Reliability and Load

 Note: Book also state MTU but it is not a metric.

 What algorithm is used to determine best path?

 DUAL (Diffusing Update Algorithm)

Review of EIGRP from CCNA

 Enhanced Interior Gateway Routing Protocol (EIGRP)

 Released in 1992 with Cisco IOS Software Release 9.21.

 Enhancement of Cisco’s:

 Interior Gateway Routing Protocol (IGRP)

 Both are Cisco proprietary, operate only on:

 Cisco routers

RTP and EIGRP

Packet Types

 What transport layer protocol does EIGRP use?

 Reliable Transport Protocol (RTP)

Protocol-Dependent

Modules

 EIGRP uses protocol-dependent modules (PDM) to route

different protocols, including:

 Internetwork Packet Exchange (IPX)

 AppleTalk

EIGRP Header MessageEIGRP

On a LAN, the EIGRP

The destination IP address is

set to the multicast 224.0.0.10

and the EIGRP protocol field

is 88.

The EIGRP header identifies the type of EIGRP packet and

autonomous system number.

The EIGRP message consists of the Type / Length / Value (TLV).

EIGRP Header

EIGRP Packet

EIGRP Packet

Types – Hello

Packet

 What are Hello packets used for by EIGRP to:

 Discover neighbors (sometimes called neighborships)

 Form adjacencies with those neighbors

 What is the multicast address? Hint: 224.0.0.?

 224.0.0.10

 Are these sent as reliable or unreliable deliver?

 Unreliable delivery – No ACKs returned

Hello Protocol

NBMA Link that are

All other serial interfaces and

LANs

Hello Protocol

 Default hold time - 3 times the hello interval

 If the hold time expires:

 EIGRP declares the route as down

 DUAL searches for a new path in the topology table or by

sending out queries.

 It is NOT automatically adjusted if Hello Interval is modified.

NBMA Link that are

All other serial interfaces and

LANs

 Update Packets – Reliable Delivery

 Acknowledgment (ACK) Packets – Unreliable Delivery

 Sent when reliable delivery is used (update, query, and reply

 Queries and replies use reliable delivery (Ack returned)

 Used by DUAL when searching for networks and other tasks.

DUAL: An Introduction

J J Garcia-Luna-Aceves

Summary - RTP Packet Types

 Hellos – Identifies neighbors

 Used by the neighbor discovery and recovery process

 Multicast

 Unreliable delivery

 Acknowledgements (ACK) – Acknowledges receipt

 Hello packets with no data

 Unicast

 Unreliable delivery

 Updates – Advertises routes

 Transmitted only when necessary

 Unicast when sent to a specific router

 Multicast when sent to multiple routers

Administrative Distance

 We will discuss Administrative Distance in more detail in a later chapter.

 Later in this chapter, you learn how to configure EIGRP summary routes.

Routes manually summarized.

Routes redistributed into EIGRP.

Neighbor Adjacencies and

EIGRP Reliability

21

Configuring Hello Intervals and Hold Times

 Configurable on a per-interface basis, NOT per neighbor (LANs)

 Does not have to match with other EIGRP routers to establish

adjacencies.

Router(config-if)# ip hello-interval eigrp as-number seconds

Router(config-if)# ip hold-time eigrp as-number seconds

Neighbor Table Contents

23

R1# show ip eigrp neighbors

IP-EIGRP neighbors for process 100

H Address Interface Hold Uptime SRTT RTO Q Seq

Seconds remaining before declaring neighbor down.

The current hold time and is reset to the maximum hold time whenever a Hello packet

congestion on the link.

The sequence number of the last update, query, or reply packet that was received from this neighbor.

Amount of time since this neighbor was added to the neighbor table.

Neighbor Table Contents

 Smooth Round Trip Timer (SRTT)—The

average number of milliseconds it takes for an

EIGRP packet to be sent to this neighbor and

for the local router to receive an

acknowledgment of that packet

 Used to determine the retransmit interval,

a.k.a retransmit timeout (RTO).

 RTO—The amount of time, in milliseconds, that

the router waits for an acknowledgment before

retransmitting a reliable packet from the

retransmission queue to a neighbor.

24

Start Stop

Start Stop

No ACK Returned

EIGRP Reliability

 RTO—The amount of time, in milliseconds, that the

router waits for an acknowledgment before

retransmitting a reliable packet from the

retransmission queue to a neighbor.

 Updates, queries and replies are sent reliably.

 A sequence number is assigned and an explicit ACK

is returned for each sequence number.

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Start Stop

 When a neighbor is declared down:

 The adjacency is removed

 All networks reached through that neighbor are removed from the routing table.

 180 second hold time on low-speed NBMA links can be a long time to wait.

 Retransmission occurs after each RTO timer expires.

 After 16 attempts the neighbor is declared down.

 This is less time than waiting for the hold time to expire.

16 x RTO < Hold Timer

EIGRP Reliability

26

 Potential problem on multiaccess (Frame Relay, Ethernet) media where

multiple neighbors reside.

 The next reliable multicast packet cannot be sent until all peers have

Acknowledged the previous multicast packet.

 If one or more neighbors are slow to respond it adversely affects all peers.

 When a neighbor is slow to respond to multicasts or does not acknowledge the

multicast, the router will retransmit the packet as a unicast.

 This allows reliable multicasts to continue and speeds up convergence without waiting for peers on lower speed links.

 Multicast flow timer - Determines how long a router should wait for an ACK to

be received before switching from multicast to unicast.

 Calculation is based on RTO and SRTT (Cisco proprietary)

R3# show ip eigrp interfaces

IP-EIGRP interfaces for process 1

Xmit Queue Mean Pacing Time Multicast Pending

Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes

Se0/1 1 0/0 60 0/15 299 0

Se0/0 1 0/0 607 0/15 3031 0

R3#

Upda te101

Neighbor Table Contents

 The show ip eigrp interfaces detail command displays a router's

EIGRP Hello timer setting for each enabled interface

R3# show ip eigrp neighbors detail

IP-EIGRP neighbors for process 1

H Address Interface Hold Uptime SRTT RTO Q Seq Type

Initial Route Discovery

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Hello, I am Router A Is anyone there?

Hello, I am Router B

Here is all my routing information.

I’m using split horizon.

Thanks for the information!

That is very nice of you.

Here is all my routing information.

I’m also using split horizon.

Thanks for the information!

We’ve reached convergence.

EIGRP

Neighbor

Table

EIGRP Neighbor Table

EIGRP

Topology

Table

EIGRP Topology Table

IP

Routing

Table

IP Routing Table

Example: EIGRP Tables

Router C’s tables:

3 Highest active IP address of any of its physical interfaces.

Router(config)# router eigrp as

Router(config-router)# router-id ip-address

Forming Neighbor Adjacencies

 The following are the most common causes of problems with EIGRP

 Access list denying multicast packets

 Manual change (summary router, metric change, route filter)

 Does NOT prevent neighbor relationships

 Hello and Hold timer setting mismatch

 Duplicate router IDs

The Metric

EIGRP Message

EIGRP Message - TLVs

TLV 0x0001 - EIGRP Parameters

• K values are used to calculate the EIGRP metric.

• The Hold Time advertised by a neighbor is the maximum

time a router should wait for any valid EIGRP message sent

by that neighbor before declaring it dead.

TLV 0x0002 - Internal IP Routes

• Delay: Sum of delays in units of 10

microseconds from source to

destination

• Bandwidth: Lowest configured

bandwidth on any interface along the

route

• Prefix length: Specifies the number

of network bits in the subnet mask

• Destination: The destination address

of the route

TLV 0x0003 - External IP Routes

 IP external routes are routes which are imported into EIGRP through redistribution of a default route or other routing protocols.

• Fields used to track

external source of route.

• Same fields contained in

the Internal IP route TLV (0x0002).

Metric

 By default, K1 and K3 are set to 1, and K2, K4, and K5 are set to 0

 The result is that only the bandwidth and delay values are used in

the computation of the default composite metric.

Metric

 The K values on R1 are set to the default

 Changing these values to other than the default is not

recommended unless the network administrator has a very good

reason to do so.

 Cisco recommends that these values are not modified.

R1# show ip protocols

Routing Protocol is “eigrp 1”

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

<output omitted>

Metric: Displaying Interface Values

SanJose2> show interface s0/0

Serial0/0 is up, line protocol is up

Hardware is QUICC Serial

Description: Out to Westasman

Internet address is 192.168.64.5/30

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

rely 255/255, load 246/255

<output omitted>

 EIGRP bandwidth uses the minimum bandwidth link represented in

107 divided by the kilobits per second.

 Show interfaces displays bandwidth in kilobits per second.

 EIGRP delay value is the sum of delays in tens of microseconds

multiplied by 256.

 Show interfaces displays delay in microseconds.

Metric Calculation

 For a review and examples of how the EIGRP metric is calculate

read Chapter 2 EIGRP, “EIGRP Metric Calculation” or review my

CIS 82 PowerPoint presentations on EIGRP.

41

DUAL

EIGRP Operations  EIGRP selects primary (successor)

and backup (feasible successor) routes and injects those into the topology table

 The primary (successor) routes are then moved to the routing table

IP EIGRP Neighbor Table

Neighbor IP Address Local router exit

interface to neighbor

IP EIGRP Topology Table

Destination 1 FD / AD via each neighbor

IP Routing Table

Destination 1 Best route

List of directly connected adjacent EIGRP neighbor routers and the local interface to exit

to reach it

List of all routes learned from each EIGRP neighbor and identifies successor routes and feasible successor routes

List of the best (successor) routes from the EIGRP topology table and other routing processes

Example: EIGRP Tables

 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:

 Feasible condition or feasibility condition

Feasible distance (FD) is the minimum distance (metric) along a path to a

destination network.

Reported distance (RD or AD) is the distance (metric) towards a destination as

advertised by an upstream neighbor Reported distance is the distance reported

in the queries, the replies and the updates.

A neighbor meets the feasible condition (FC) if the reported distance by the

neighbor is less than the current feasible distance (FD) of this router "If a

neighbors metric is less than mine, then I know the neighbor doesn't have a loop going through me."

A feasible successor is a neighbor whose reported distance (RD) is less than the

current feasible distance (FD) Feasible successor is one who meets the feasible condition (FC).

Your route (metric) to the network (RD to me) must be LESS than my current route (my total metric) to that same network If your route (metric) to the network (RD to me) is LESS than my current route (my total metric), I will include you as a

FEASIBLE SUCCESSOR.

If your route (metric) to the network (RD to me) is MORE than my current route (my

total metric), I will NOT include you as a FEASIBLE SUCCESSOR.

Successors and Feasible Successors

 FD = RD + additional Delay of serial link between R1 and neighbor

(This could also be due the slowest bandwidth.)

Which router is the successor?

 RD of R2 is greater than FD through R3.

 Does not meet FC.

Successor

NOT a Feasible Successor

RX

RD = 6,000,000

RD = 3,000,000

Network X

 Or maybe R2’s does have a valid path to Network X.

 But R1 can’t tell because the distance vector update only gives it

distance and direction.

Successor

NOT a Feasible Successor

RX

 FD = RD + additional Delay of serial link between R1 and neighbor

(This could also be due the slowest bandwidth.)

Successor Feasible

Successor?

 RD of R2 is less than (or equal to) the FD through R3.

 Meets FC, there is no loop back through R1.

 Is a FS.

Successor Feasible

Successor

 If there are no Feasible Successors, the router must ask neighbors for help in hope of

finding a new, loop-free path to the destination

 Neighbor routers are compelled to reply to this query

 If a neighbor has a route, it will reply with information about the successor(s)

 If not, the neighbor notifies the sender that it doesn’t have a route to the destination

either

Looking for new route

Query and Reply Packets

Step 1

 Successor

 Feasible Successor (AD is less than FD)

Step 2

X

 Router D: Sets the metric to network 10.1.1.0/24 as unreachable (–1 is unreachable).

 No FS (Feasible Successor) in the topology table, so the route changes from the passive

state to the Active state

 Active state: Router sends out queries to neighboring routers looking for a new successor.

 Sends a query to Routers C and E for an alternative path to network 10.1.1.0/24

 Marks Routers C and E as having a query pending (q)

 Router E: DUAL marks the path to network 10.1.1.0/24 through Router D as Unusable.

 Router C: DUAL marks the path to network 10.1.1.0/24 through Router D as Unusable. 57

 Router D: DUAL receives a reply from Router C indicating no change to the path to 10.1.1.0/24

 DUAL removes the query pending flag from Router C.

 DUAL stays Active on network 10.1.1.0/24, awaiting a reply from Router E to its query (q).

 Router E: there is no FS to network 10.1.1.0/24, because the AD from Router C (3) is not less

than the original FD (also 3)

 DUAL generates a query to Router C.

 DUAL marks Router C as query pending (q).

 Router C: DUAL marks the path to network 10.1.1.0/24 through Router E as Unusable. 58

Step 4

R Q

Step 5

 Router D: DUAL stays active on network 10.1.1.0/24, awaiting a reply from Router E (q).

 Router E: DUAL receives a reply from Router C indicating no change.

 It removes the query flag from Router C.

 It calculates a new FD and installs a new successor route in the topology table.

 It changes the route to network 10.1.1.0/24 from Active to Passive (converged).