advanced routing reference manual ver. 0.9

8/10/2019 Advanced Routing Reference Manual Ver. 0.9

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eference Manual ver. 1.0 (2012-14)

eated by Paul Nadstoga ([email protected])


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Contents

EIGRP 1

OSPF 27

CONTROLLING ROUTING UPDATES 8

BGP 1

BRANCH OFFICE 1

IPv6 16

APPENDIXES 20


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EIGRP

EIGRP Basics

EIGRP Packets

EIGRP Stuck In Active

EIGRP Timers

EIGRP Metric

EIGRP Tables

EIGRP Over NBMA

EIGRP Configurations

EIGRP Verification and Tshooting


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ADVANCED ROUTING ver. 1.0 CREATED BY PAWEL PAUL N=DSTOGA ([email protected]) 2012-14

EIGRP BASICS

TYPE ALGORITHM INTERNAL AD EXTERNAL AD SUMMARY AD STANDARD PROTOCOLS TRANSPORT AUTHENTICATION MULTICAST IP TIMERS

Distance

VectorDUAL 90 170 5 Cisco

IP

IPX

AppleTalk

RTP:IP:88 MD5 224.0.0.10

HELLO: 5 /

HOLD: 15 /

he following conditions have to be met for two routers to form a neighbor relationship:

Autonomous Systemvalues match

source IP address of a received HELLOis in the same subnetas the primary IP addressconfigured on the receiving interface(subnet mask does not need to be identical)

K valuesmatch

authentication key IDs+ key strings match(if authentication is configured)


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GRP PACKETS

PACKET OVERVIEW COMMENTS

HELLO

initially used to discover and verify neighbors

later used to maintain the relationship (keep-alive mechanism)

sent at interval specified by the HELLO timer

multicasted on 224.0.0.10

unreliable (delivery not acknowledged by the recipient)

the default HELLO timerdepends on the interface bandwid

neighbors learn each others timers through the HELLO

packetsand use that information to forge a relationship

more than one HELLO packetsmay be needed to convey all

routing information to a new neighbor

UPDATE

used to exchange routing information

initially sent when forming a relationship and then only to affected routers

unicasted to a specific router

multicasted to a group of routers

reliable (delivery acknowledged by the recipient)

Contains:

prefix / prefix length

metric components (bandwidth, delay, reliability, load)

non-metric components (MTU, hop count)

sent as multicast initially and when oneACKreceived from

specific router the UPDATEis resent as an unicast

also sent when a topology change is detected - in such case

the router sends a multicast UPDATEto all its neighbors UPDATEsent on an interface does not contain routes that

were learnt through the same interface because of the spli

horizon rule

QUERY

sent when a specific information is required from one / all of its neighbors

normally sent as multicast but can be retransmitted as unicast in certain cases

reliable (delivery acknowledged by the recipient)

if all outstanding QUERIESare not replied within the ACTIVEtimer, the neighbor that failed to

reply is removed from the neighbor table

Also used when a router loses its successor and cant find a feasib

successorfor a route - in such case DUAL places the router in acti

stateand start sending multicasts in s earch for a successor.

REPLY

used to respond to a QUERY

reliable(delivery acknowledged by the recipient)

Always sent as unicast to specifically inform the originator it does

not need to go into active statebecause it an alternative route is

available.

ACK sent to acknowledge UPDATE, QUERYand REPLY

unicast HELLOpackets and contain a nonzero ack. number

GOODBYE

also known as graceful shutdown

send to notify the neighbors when a router is shutting down the EIGRP process or removes a

network statement that included the neighbors in the EIGRP process (e.g. no network 10.0.0.0)

Sent as a HELLOpacket with all K values set to 255.


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GRP STUCK-IN-ACTIVE

a situation that may take place when the successoris lost and a FSdoes not exist

when the successor to a network is lost, QUERIESare sent toall the neighbors asking for an alternative route(note: the inactive link is not queried)

if REPLIESare not received, the route is put into anACTIVEstate

by default, the router will wait 180 sec. to receive replies to queries sentany adjacency that hasnt replied by then will be reset


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EIGRP TIMERS

TIMER OVERVIEW COMMENTS

HELLO

specifies the time interval at which the HELLOpackets are retransmitted

To adjust:

To verify:

Works independently in each directio

neighbors dont need to use the same

HELLOtimer values

HOLD

specifies the time interval during which a router will consider a neighbor alive without receiving a HELLOfrom that neighbor by default equals to 3 x HELLOtimer

To adjust:

To verify:

changing the HELLOtimer does automatically adjust the HOLDt

the HOLDtimer is sent to the

neighbor in the HELLOpacket i.e

router does not use locally

configured timer value be the va

receives from the neighbor in th

HELLOpacket

the IOS does not prevent the use

from setting the HOLDtimer to a

value lesser than HELLO!

ACTIVE

specifies the time interval the router waits after sending a QUERYbefore declaring the route stuck in active(SIA) and

resetting the neighbor relationship

To adjust:

increasing the timer might be us

when troubleshooting EIGRP

timers active-time disabled- dis

time limit for active states

DEFAULT TIMER VALUES

BANDWITDH EXAMPLE LINK DEFAULT HELLO TIMER DEFAULT HOLD TIMER ACTIVE

< 1.544 Mbps Multipoint Frame Relay 60 sec. 180 sec.

180 sec.

> 1.544 Mbps T1, Ethernet 5 sec. 15 sec.


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IGRP METRIC

FULL (ALL K VALUES USED)

( )

DEFAULT(ONLY K1 + K3 USED AND ARE EQUAL TO 1)

bw= 107/ minimum bandwidth in kbps (if the result is not a whole number the value is rounded down)delay= sum of delays of outgoing interfaces in secs / 10

256 = multiplier used for compatibility with IGRP (EIGRP uses 32 bit metric while IGRP uses 24)


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METRIC COMPONENTS

COMPONENT OVERVIEW COMMENTS

BANDWIDTH

the bandwidth of the interface

static value

To modify:

Default values for:

ethernet: 100000 Kbit/sec

serial: 1544 Kbit/sec

DELAY

measure of time it takes for a packet to traverse a route

static value

To modify:

Default value for:

ethernet:100 usec

serial: 20000 usec

To view total delay for a route:

show ip eigrp topology A.A.A.A/MM

LOAD

amount of traffic utilizing the link

dynamic value (0-255)

calculated on a 5 min. basis

1/255 minimally loaded link

255/255 fully saturated link

RELIABILITY a measure of probability that the link will fail i.e. how often the link has experienced errors

calculated on a 5 min. basis

1/255 least reliable link

255/255 fully reliable link

MTU not used anywhere in the metric calculation but sent for prefixes

K VALUES

Defaults:

K1=1, K2=0, K3=1, K4=0, K5=0

To modify:

identical K values are one of the conditions for

routers to become an EIGRP neighbor

TOS was never implemented so the value has t

always set to 0

TSHOOT

show interface (interface)

show ip protocols


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EXAMPLE: DEFAULT METRIC CALCULATION

From R3 to 172.30.0.0 /24 through s1/1

,,

,+

256* ( * (6476.6839 = 6476) + * (2500)

256* (6476+ 2500)

256* 8976

2297856

From R3 to 172.30.0.0 /24 through fa0/0

,,

+,+

256* ( * (6476.6839 = 6476) + * (2510)

256* (6476+ 2510)

256* 8986

2300416

*Not a Feasible Successorsince AD equals (needs to be less) than Feasible Distanceof th

current Successor(via s1/1 - 172.1.34.1)


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EIGRP TABLES

TABLE OVERVIEW COMMENTS

NEIGHBOR TABLE list of directly connected routers running E IGRP with which adjacencies are formed

o view the table content:

R1#show ip eigrp neighbors>

H (handle)- an IOS internally used number to track a

neighbor by recording the order in which the neighbours

were learnt

Address- neighbors L3 address

Interface- local interface on which the neighbor can be

reached

Hold (hold time)- maximum time in s econds that the rou

waits to hear from the neighbor before considering the lidown (any EIGRP packet received after the fi rst HELLOfr

that neighbor resets the timer)

Uptime- time that has elapsed since the neighbor was ad

to the table

SRTT (smoothed round-trip time)- the average number o

milliseconds it takes for an EIGRP packet to be sent to thi

neighbor and for the local router to receive anACKfor th

packet - this timer determines the RTO

RTO (retransmission timeout)- the number of millisecon

that the router waits for an ACKbefore retransmitting a

reliable packet from the retransmission quote to the

neighbor. If an UPDATE, QUERYor REPLYpacket is sent, a

copy of packet is queued. If the RTO expires before anAC

received, another copy of the queued packet is sent

Q Cnt (queue count)- number of packets waiting in the q

to be sent out (if constantly higher than 0 a congestion

problem may exist) Seq Num - sequence number of the last UPDATE, QUERY

REPLYpacket that was received from the neighbor (used

detect out-of-order packets)


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TOPOLOGY TABLE list of all routers learnt from each EIGRP neighbor the table is updated when a di rectly connected router /

interface changes or a neighbor reports a route change


Router#show ip eigrp topology (active | all-links | detail-links)>

active- shows only active entries

all-links- shows all links in topology table

detail-links- more detailed version of the above

P(Passive)- correct state for a stable network (network is

available and installation can occur in the routing table

A(Active)- network is currently unavailable, and installat

cannot occur in the routing table (there are outstanding

queries for this network). A route will be put into Active s

when the currentSuccessoris down and Feasible Success

are not available U(Update) - network is being updated (placed in an UPDA

packet); also applies if the router is waiting for anACKfo

UPDATE

Q(Query)- outstanding query packet for this network (als

applies if the router is waiting for anACKfor aQUERY)

R(Reply status) - router is generating a REPLYfor this

network or is waiting for anACKfor the REPLY

S(Stuck-in-active status)- indicates EIGRP convergence

problem for the network with which it is associated

successor - next-hop router with lowest cost and loop fre

path (successors end up in the routing table)

Feasible Successor- a backup router with loop-free path

become one a router has to meet the Feasible Condition)

Feasible Condition- AD of Feasible Successormust be les

than the FD of the current Successor

AD (Advertised Distance)- cost between the next-hop ro

and the destination

FD (Feasible Distance)- cost from a local router to the

destination


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ROUTING TABLE

list of all best routes from EIGRP topology table and other routing processes

the best route to a destination (successor) is chosen by comparing all FDs to that

destination and selecting the route with the lowest FD - which becomes the routers

metric shown in the table


Router#show ip route eigrp>

[90/156160] - EIGRPs AdministrativeDistance (believabilit

[90/156160] - the cost to reach the network (Feasible Dist


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EIGRP OVER NBMA

THINGS TO KEEP IN MIND:

by defaultmulticasts and broadcastsare denied on NBMA networkswhich requires special consideration for protocols such as EIGRP that rely on multicasts to establish and maintai

neighbor relationships

in point-to-multipoint topologies, split horizonenabled on the hub may prevent updates from being propagatedacross all network

pseudo broadcastmust be enabled on the frame-relay interface OREIGRP neighbors need to be statically configured if thepseudo broadcastcannot be used or is not supported

EXAMPLE:


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CONFIGURATIONS COMMENTS

CONFIGURE FR INTERFACES ---> R1(config)#interface s1/0

R1(config-if)#encapsulation frame-relay

R1(config-if)#ip address 172.16.124.1 255.255.255.0

R1(config-if)#no frame-relay inverse-arp

R1(config-if)#no arp frame-relay

R1(config-if)#bandwidth 128

R1(config-if)#ip bandwidth percent eigrp 1 40

R2(config)#interface s1/0



R2(config-if)#no frame-relay inverse-arpR2(config-if)#no arp frame-relay








By default EIGRP uses 50% of the bandwidth specified with th

bandwidthcommand on a frame relay enabled interface.

ip bandwidth-percentdefines how much percentage o

interface bandwidth can be utilized the EIGPR

(*has to be configured on a per (sub)interface basis)

(** for multipoint interfaces the router further divides t

bandwidth according to the number of neighbours out t

interface)

STATICALLY ADD FR MAPS ---> R1(config-if)#frame-relay map ip 172.16.124.2 102 broadcast

R1(config-if)#frame-relay map ip 172.16.124.3 103 broadcast



R4(config-if)#frame-relay map ip 172.16.124.1 301 broadcastR4(config-if)#frame-relay map ip 172.16.124.2 301 broadcast

To confirm:

Router#show frame-relay map

broadcast(aka. pseudo broadcast) emulated broadcas

acts as broadcast but the packets are sent as unicast

messages

ENABLE EIGRP ---> R1(config)#router eigrp 1

R1(config-router)#no auto-summary

R1(config-router)#network 10.0.0.0



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R2(config)#router eigrp 1




R4(config)#router eigrp 1




SUMMARISE UPDATES ---> R1(config)#interface s1/0

R1(config)#ip summary-address eigrp 1 10.1.0.0 255.255.0.0

R2(config)#interface s1/0R2(config)#ip summary-address eigrp 1 10.2.0.0 255.255.0.0


R4(config)#ip summary-address eigrp 1 10.3.0.0 255.255.0.0

DISABLE SPLIT-HORIZON ---> R1(config)#interface s1/0

R1(config-if)#no ip split-horizon eigrp 1

At this stage routes from R2 are not being propagated to R3 a

vice versa because split horizon will prevent R1 to advertise t

10.2.0.0/16 network via the same interface it was received o

Disabling split horizon will generate on the local end:

*Oct 18 21:20:12.041: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neigh

172.16.124.3 (Serial1/0) is resync: split horizon changed

*ENABLE EIGRP NON-BROADCAST MODE ---> R1(config-router)#neighbor 172.16.124.2 s1/0

R1(config-router)#neighbor 172.16.124.3 s1/0



May be used as first solution or when the Frame Relay cloud

not supportpseudo broadcast. Changes the EIGRP packets

propagation mechanism from multicast to unicast.

(*the exit interface still has to be advertised with the networ

command)

(** the mechanism change will only affect the interface via w

the routers communicated the EIGRP neighbor)

(*** both ends have to use the same mode)

Changing the mode will generate the following on the local e

*Oct 18 21:39:23.961: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1: Neigh

172.16.124.2 (Serial1/0) is down: Static peer configured


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EIGRP CONFIGURATIONS

ACTIVATION

STEP # COMMANDS COMMENTS

START EIGRP PROCESS

AS allows to start separate EIGRP processes on the same route

(the value has to be the same for all the routers within the sam

processes).

AUTOMATIC

SUMMARIZATION

auto-summarywhen enabled, EIGRP automatically

summarize network updates to their classful boundaries

HARDCODE ROUTER ID

To verify:

Mainly used in external routes as a loop prevention mechanis

external routes are tagged with the RID and in case the advert

router receives them back with its own RID they are dropped.

Unique for each AS.

1. use the configured value: eigrp router-id

2.

use the highest IPv4 address on an UP|UPloopback

3.

use the highest IPv4 address on an UP|UPnon-loopba

ADD NETWORKS

To add all networks:

To add individual networks:


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PASSIVE INTERFACES

To verify:

passive-interface- no HELLOs are sent on the interface

(hence no relationship can be formed) but the network i

advertised

passive-interfacedefault- sets all interfaces as passive

A passive interface is still part of the EIGRP process and the

network advertised but no HELLOs are sent to that interface.

PROPAGATE DEFAULT

GATEWAY

network 0.0.0.0- can also be used to include any static

in the updates

ip default-network- sets and redistributes given netwo

default (has to be classful and has to be reachable by th

router)


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LOAD BALANCING

Equal load balancing:

Unequal load balancing:

To verify:

Load balancing is the ability to forward traffic over all its netw

ports that are the same metric from the destination address.

When a packet is process-switched, equal load balancing occu

aper-packetbasis. When packets are packet-switched, load

balancing occurs on aper-destinationbasis.

maximum-paths - installs routes with a metric equal to t

minimum metric in the routing table (the default is 4; se

1 to disable load balancing)

variance- a multiplier that is applied to a successors me

any path with a metric that fits within the range can be

unequal balanced over (default is 1 meaning only equal

balancing is enabled)

The command affects which routes end up in the routing

table but does not affect the r outes roles i.e. successor,

feasible successoretc.

STUB ROUTING

To verify local settings:


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MANUAL

SUMMARIZATION

theASspecifies that summarization will only be sent ou

neighbors in within that AS

while summarizing it has to be remembered that routes

always prefer more specific routes

the summary route will use a metric equal to the lowest

metricof a subordinate route

advertising a summary will take down and bring up all

neighbor relationships established via that interface

summarization should be avoided if the priority is for th

routes to always take the shortest paths

The following will be generated on the local end:

*Oct 18 21:03:05.482: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1

Neighbor 172.16.124.1 (Serial1/0) is resync: summary config

The following will be generated on the far end:

*Oct 18 21:03:15.810: %DUAL-5-NBRCHANGE: EIGRP-IPv4 1

Neighbor 172.16.124.2 (Serial1/0) is resync: peer graceful-re


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AUTHENTICATION


DEFINE KEYS

*


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REDISTRIBUTION

o set a default-metric (NOTE: this command does not affect the metric of directly connected networks)

Router(config-router)#default-metric (bandwidth kb; 1-4294967295) (delay10-microsec; 0-255) (reliability;0-255) (load;0-255) (MTU;1-65535)>

ROUTING PROTOCOLS

PULL ROUTES FROM: COMMANDS COMMENTS

RIP

default-metric- overridden by the

redistribute metriccommand

metric- redistribute router with the spec

metric (by default it is set to infinite

(unreachable) for all redistributed protoc

except for EIGRP with different AS - in su

case the it takes the metric from the sou

of the routing information)

matchinternal- redistribute the OSPF

internal routes

match external - redistribute OSPF exte

Type 1/2 routes

match nssa-external- redistribute OSPF

external routes

route-map- applies a route mapto

redistributed routes

EIGRP was designed to automatically redistribu

IGRP route from the same AS.

Good practice to make redistributed routes ap

as links e.g. 100Mb:

#default-metric 100000 10 255 1 1500

OSPF

Example:

BGP


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EIGRP VERIFICATION AND TSHOOTING

show ip eigrp neighbors

show ip eigrp topology (all-links)

show ip eigrp interface

show ip eigrp interface detail

show ip eigrp traffic

show ip route eigrp

show ip protocols

debug ip eigrp neighbors

debug ip eigrp packet

clear ip eigrp neighbors

COMMAND VERIFIES / DISPLAYS EXAMPLE

show ip eigrp neighbors

EIGRP neighbors for a given process

neighborsIP addresses

the local interface the neighbors are reachable through

HOLDtimers

how long the adjacency have been active

show ip eigrp neighbors detail

detailed information about neighbors


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show ip eigrp topology

EIGRP router-id

successors, feasible distances, feasible successors, advertised distances

networks states

show ip eigrp interfaces

interfaces participating in a given EIGRP process

number of peers on a given interfaces

does not display information aboutpassive-interfaces

show ip eigrp interface detail

detailed information about interfaces enabled for EIGRP does not includepassive interfaces


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show ip eigrp traffic

Displays EIGRP traffic statistics

show ip route eigrpDisplays routing tables entry learnt via EIGRP


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show ip protocols

Displays IP routing protocol process parameters and statistics

debug ip eigrp neighbors Displays events associated with EIGRP neighbors

debug ip eigrp packet Displays events associated with EIGRP packets

clear ip eigrp neighbors Purges EIGRP neighbor table


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OSPF

OSPF Basics

OSPF Routers

OSPF Packets

OSPF Tables

OSPF Metric

OSPF Areas OSPF Virtual Links

OSPF Timers

OSPF Routers ID

OSPF Link ID

OSPF DR / BDR

OSPF Adjacencies States

OSPF Networks

OSPF Over NMBA

OSPF Configurations

OSPF Verification and Tshooting


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ADVANCED ROUTING ver. 1.0 CREATED BY PAWEL PAUL NADSTOGA ([email protected]) 2012-14

SPF BASICS

TYPE ALGORITHM AD STANDARD PROTOCOLS TRANSPORT AUTHENTICATION DROHTERS DR/BDR TIM

Link State Dijkstra 110 RFC 2328

RFC 2740IP IP:89

plain text

MD5224.0.0.5 224.0.0.6

10/

30/

The following conditions have to be met for two routers to form a neighbor relationship:

Area IDmatch on both ends

stub flagmatch (on/off)

route-IDsare unique

primary IP addressesof the routers must be on the same subnet

hello timermatch on both ends

hold timermatch on both ends

authentication modes andpasswords match(if authentication is configured)


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SPF ROUTERS

o view a router type:

show ip protocols

ROUTER OVERVIEW COMMENTS

INTERNAL routers that have all their interfaces in the same area and have identical LSDBs

BACKBONE

routers that sit on the perimeter of the backbone areaand have at least one interface connected to

Area 0

maintain OSPF routing information using the same algorithms and rules as the internalrouters

ABR

Area Border Router

routers that have interfaces attached to multiple areas maintain separate LSDBs for each area they are connected to

serve as exit points for the area (routing information destined to another area can get there only via

the ABR of the local area)

to identify itself as an ABR, the router sends Type 1

with a border bit(b bit) set ABR containing a NSSA area will also become an AS

CISCO recommends no more than 2 areas per ABR

addition toArea 0)

ASBR

Autonomous System Border Router

routers that have at least one interface attached to an external internetwork (another AS) e.g. a

non-OSPF network

capable of importing non-OSPF network information to the OSPF network and vice-versa (route

redistribution)

to identify itself as an ASBR, the router sends Type

LSAwith an external bit(e bit) set

any form of redistributionenabled on a router will m

it as an ASBR (it doesnt even have to be working i.e

redistributing RIP when its not activated)


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SPF PACKETS

all OSPF packet types are encapsulated directly into an IP payload

a protocol ID of 89 defines all OSPF packets

PACKET OVERVIEW COMMENTS

HELLO

sent to discover neighbors and form adjacencies with them Sent to:

DROTHER - 224.0.0.5

DR/BDR - 224.0.0.6

DBD

Database Description

contains LSA headers only and describes the content of the entire link-state database

each DBD has a sequence number which can be incremented only by the master (which in turn is

explicitly acknowledged by the slave)

Exchanged during EXTSTART + EXCHANGEadjacency

establishment phases.

LSR Link-State Request

requests specific link-state records from a router

LSU

Link-State Update

sends specifically requested link-state records

all LSUs are acknowledged

LSAck Link-State Acknowledgement

send to acknowledge the receipt of the other packets

LSA

Link-State Advertisement

11 types

all have 20-byte headers

the LSA includes a link ID field that identifies (by network number and mask) the object that this linkconnects to

sequence number

each router link is defined as an LSA type

Each LSAhas their own age timerand waits 30 minbe

requiring an update.

Sequence numbersif the seq. in the update is:

same as localignore the update

higher than localaccept and propagate

lower than localignore the update, send back


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SAs

TYPE 1: Router LSAs

advertised by every router in the area

flooded within its area only (does not cross ABR)

includes list of directly attached links

contains (O) intra-area routes

each link is identified by IP prefix assign

to link and link type

TYPE 2: Network LSAs

advertised by the DR

generated for every transit broadcast and NBMA network within the area (intra-area)

flooded to all routers within the transit network area (does not cross ABR)

lists each of the attached routers that make up the transit network (including the DR itself +

subnet mask used on the link)

contains (O) intra-area routes

the link-state IDfor a network LSA is th

address of the advertising DR interface

TYPE 3: Summary LSA

advertised by the ABR

used to flood network information outside the originating area (inter-area)

describes network number and subnet mask of the link

flooded throughout a single area only but are regenerated by ABRs to flood into other areas

contains (IA) intra-area routes

it is advised to perform manualsummarization at the ABR (by default T

3 LSA is advertised into the backbone a

for every subnet defined in the originat

area)

TYPE 4: Summary LSA

advertised by the ABR(but only when ASBR exist within an area)

used to advertise an ASBR to all other routers in the AS (router ID and route to it)

flooded throughout a single area only but are regenerated by ABRs to flood into other areas

TYPE 5: External LSA

advertised by the originating ASBR

used to advertise networks from outside the OSPF AS

flooded to the entire AS

advertising router ID (ABSR) remains unchanged throughout the AS

contains (E1/E2) external routes

Type 4 LSAis needed to find the ASBR

TYPE 6: Group Summary NOT SUPPORTED BY CISCO ROUTERS

TYPE 7: NSSA External Link LSA

originated by the ASBR within NSSAs

flooded only within the NSSA in which they originated

contains (E1/E2) external routes

converted into Type 5 LSAby the ABR w

leaving the area

TYPE 9, 10, 11: Opaque DESIGNED FOR FUTURE USE


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SPF TABLES

TABLE OVERVIEW COMMENTS

NEIGHBOUR TABLE

also known as adjacency database

list of directly connected routers running OSPF with which adjacencies are

formed


R1#show ip ospf neighbors ((type | number) (neighbor-id) detail))>

type- interface type (FastEthernet, Serial etc.)

number - interface number

neighbor-id- neighbors router ID

detail- displays all neighbors given in detail

Neighbor ID - neighbors router ID Pri- priority of the neighbors interface on which adjacency is

formed

State- adjacency state

Dead Time- if the router doesnt receive a HELLOpacket from t

neighbor before the timer expires, the adjacency is considered

Address- IP address of the neighbors interface on which adjace

is formed

Interface- local interface on which adjacency is formed


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TOPOLOGY TABLE

typically referred to as LSDB (Link State Database)

contains all routers and their attached links in the area or network

all routers within an area have an identical LSDB


1#show ip ospf database>

Link ID- name given to the entity on the links far end (see page

ADV Router - advertising router ID

Age - the time that has passed since the last link update

Seq# - link-state sequence number (detects old/duplicate LSAs)

Checksum - fletcher checksum of the complete contents of the

Link count- number of interfaces detected for router


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ROUTING TABLE also known asforwarding database

contains list of best paths to destinations


Router#show ip route ospf>

[110/65] - OSPFs Administrative Distance (believability)

O- OSPF intra-area route (from within the area)

IA - OSPF inter-area route (from outside the area but from loca

N1- OSPF NSSA external type 1 route

N2- OSPF NSSA external type 2 route

E1- OSPF external type 1 route (from outside of local AS)

E2- OSPF external type 2 route (from outside of local AS)

For the same prefix/prefix length, OSPF always prefers routes in the

following order:

O

IA

E1

E2


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SPF METRIC

()

reference bandwidth(default)= 100 Mbps

COST

OSPF term for metric

routes metric is the sum of all costs along the path

the lower the metric the more preferred the route is

To hardcode cost on an interface:

ip ospf cost- the command hardcodes the cost and over

the value that normally would be calculated using the

formula

The COSTis advertised in the LSAa that are advertised within aOSPF area. When the COSTis calculated to a destination then

based on the exit interface of each router in the path to the

destination. Not consistent values along the path can lead to

asymmetric routing and the path one way may not be the sam

the return path.

REFERENCE BANDWIDTH

defaults to 100Mbps

To modify:

To verify:

100Mbps = 100,000Kbps = 100,000,000bps

Cisco recommends keeping the value constant throughout the

entire OSPF AS to avoid sub-optimal routing decisions.

Interface Type Bandwidth COST

Loopback 8,000,000,000 1

Serial 56,000 1785

T1 1,544,000 64

Ethernet 10,000,000 10

Fast Ethernet 100,000,000 1

Gigabit Ethernet 1,000,000,000 1


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SPF AREAS

an area is a logical collection of OSPF networks, routers, and links that share area ID

a router within a given areamaintains a topological database only for the area to which it belongs

an router does not have detailed information about network topology beyond of the area it belongs to

OSPF uses 2-layer hierarchy: transitand regular(the underlying physical connectivity must map to the two-layer area structure with all non-backbone areas directly attaching toArea 0

the purpose of dividing networks into sub-domains is to restrict the propagation of routesand reduce the amount of resources required by each router to maintain i ts link database

recommended maximum number of routers in an OSPF area: 50

AREA OVERVIEW COMMENTS

BACKBONE (AREA 0)

a standard area that has been designated to as the central point to which all areas connect

all traffic moving from one area to another area must traverse the backbone

all characteristics of the STANDARDarea apply also to AREA 0

STANDARD

contains LSA Types: 1/2, 3, 4, 5

contains route types: O, IA, E1/2

STUBBY

contains LSA Types: 1/2, 3

contains route types: O, IA

E1/2external routes are not allowed

a default route (Type 3 LSA) is injected by the ABR (0.0.0.0/0 via ABR)

To create:

for an area to become STUBBY, all routers belongto it must be configured to operate as such

area cannot be converted to STUBBY if it contains

virtual link

STUB routers and non-STUB routers will not form

adjacencies!


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TOTALLY STUBBY

contains LSA Type: 1/2and 3(LSA Type 3is only used to advertise 0.0.0.0/0)

contains route types: O

E1/2external routes are not allowed

a default route (via Type 3 LSA) is injected by the ABR (0.0.0.0/0 via ABR)

because LSA Type 4 and 5are not permitted, STUBBYand TOTALLY STUBBYareas cannot

contain ASBR

only the ABR configuration needs to be modified to transform STUBBYto TOTALLY STUBBYarea

To create (on ABR only):

STUBBYand TOTALLY STUBBYareas can be used t

reduce the resource utilization of routers in portio

the network not requiring full routing knowledge

area cannot be converted to TOTALLY STUBBY if it

contains a virtual link

NOT SO STUBBY

contains LSA Types: 1/2, 3, 7

contains route types: O,IA,N1/2

implements STUBBYor TOTALLY STUBBYfunctionality yet contains an ASBR

allows LSA Type 7(originated by ASBR) to advertise N1/2 external routes

the ABR converts it into LSA Type 5before flooding them to the rest of OSPF domain (if there

are multiple ABRs in an NSSA, the ABR with the highest router IDperforms the translation)

LSA Type 3will pass into and out of the area

ABR will not inject a default route into an NSSA unless explicitly configured to do so

To create NSSA (allows N1/2 external routes + allows IA inter-area routes):

To create NSSA with stubfunctionality (allows N1/2 external routes + allows IA inter-area routes +

injects default route (Type 7 LSAwith 0.0.0.0/0 via ABR):

To create NSSA with totally stubfunctionality (allows N1/2 external routes + injects default route

(Type 3 LSAwith 0.0.0.0/0 via ABR):

*default-information originate- ensures that AB

injects a default route into a STUBBY NSSA (by de

it doesnt but does in TOTALLY STUBBY NSSAarea

area cannot be converted to a NSSAif it contains

virtual link

while all routers in the NSSA have to be configure

such, additional functions (default-information, n

summary) need to be only configured on the ABR


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CENARIO 2: TOTALLY STUBBY AREA

AREA 23 is a TOTALLY STUBBY area

E1/E2routes (Type 5 LSA) are not accepted from ASBR (R3)

IAroutes (Type 3 LSA) are not advertised by ABR (R2) into AREA 23

ABR injects default route: Type 3 LSAwith 0.0.0.0/0 via ABR into AREA 23

R1(config-router)#router ospf 1>

(O) INTRA-AREA ROUTES (IA) INTER-AREA ROUTES (E1/2) EXTERNAL ROUTES (N1/2) NSSA EXTERNAL ROUTES DEFAULT ROUTE Type LSAs ACCEPTED

R1 n/a n/a 1/2, 3, 4, 5

R2: AREA 0n/a n/a 1/2, 3, 4, 5

R2: AREA 23 X X n/a n/a 1/2, *3 (only for default)

R3 X X n/a 0.0.0.0/0 via ABR 1/2, *3 (only for default)


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CENARIO 5: NOT SO STUBBY AREA (TOTALLY STUB FUNCTIONALITY)

AREA 23 is a NOT SO STUBBY area with TOTALLY STUB functionality

all characteristics of a NSSA plus:

o IAroutes (Type 3 LSA) are not propagated by ABR (R2) into AREA 23

o ABR (R2) injects default route: Type 3 LSAwith 0.0.0.0/0 via ABR

R1(config-router)#router ospf 1>

(O) INTRA-AREA ROUTES (IA) INTER-AREA ROUTES (E1/2) EXTERNAL ROUTES (N1/2) NSSA EXTERNAL ROUTES DEFAULT ROUTE Type LSAs ACCEPTED

R1 X n/a 1/2, 3, 4, 5

R2: AREA 0 X n/a 1/2, 3, 4, 5

R2: AREA 23 X n/a 1/2,*3 (only for default),7

R3 X X 0.0.0.0/0 via ABR 1/2,*3 (only for default),7


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SPF VIRTUAL LINKS

used when an area cannot be directly connected to the backbone

act as a tunnelformed tojoin two areas across an intermediate area

both end routers must share a common area

at least one endmust reside in Area 0

HELLOs are sent every 10 sec. by default

LSAs learnt through a virtual link have the DoNotAge(DNA) option set so that they do not age out (required to avoid excessive flooding over the virtual link)

cannot traverse stubareas


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IRTUAL LINKS CONFIGURATION

COMMANDS COMMENTS

Router(config-router)#area (transit area ID) virtual-link (router ID of the far end router) (*hello-interval (sec.)) (*dead-interval (sec.))>

o verify:

Router#show ip ospf virtual-links>

both ends of a virtual links need to be

configured

hello-interval- specifies the time betw

the HELLOpackets that are sent on the

interface

dead-interval- specifies the time that m

pass without HELLOpackets being seen

before the neighbor declares the route

down

AMPLE:


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SPF TIMERS

TIMER OVERVIEW COMMENTS

HELLO

specifies the time interval at which the HELLOpackets are retransmitted

To adjust:

To verify:

Matching timer value is a condition of forming an

adjacency.

DEAD

specifies the time interval during which a router will consider a neighbour alive without receiving a

HELLOfrom that neighbour

by default equals to 4 x HELLOtimer

To adjust:

To verify:

Matching timer value is a condition of forming an

adjacency

ip ospf dead-interval minimal hello-multiplier

sets the dead intervalto 1 sec. with HELLOs se

the rate of multiplier per second


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SPF ROUTER ID

routers name in the OSPF process

duplicate router-idswill prevent two routers from becoming neighbors!

determined in the following order:

1. ID hardcoded using the command

2. highestIP of an UP|UP local loopback interface

3.

highestIP of an UP|UP physical local physical interface(doesnt have to be OSPF enabled)

if the router-idcannot be determined (no IP addresses assigned to interfaces) the OSPF process will not start (router-id= 0.0.0.0) and the following error will be generated:

the ID doesnt change unless:

o the router is rebooted

o the OSPF process is cleared e.g. with #clear ip ospf process

flood war- an error message generated when a router in a different area has the same router ID as the one the message is displayed on and is advertising a network that the local route

isnt advertising

SPF LINK ID

Link ID is a name given to the entity that is on the other end of the link

LINK TYPE DESCRIPTION LINK ID

1 Point-to-point Neighbor Router ID

2 Link to transit network Interface address of the DR

3 Link to stub area IP network number

4 Virtual link Neighbor Router ID

view Link ID:

show ip ospf database


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SPF DR / BDR

on a Multipoint Broadcast networks routers form adjacencies with DR(Designated Routers) and BDR(Backup Designated Router)

a router that is neitherDR nor BDR is called DROTHER

DROTHERsonly form FULLadjacencies with DR and BDR

DROTHERS form 2-WAYadjacencies with themselves

adjacencies have synchronized LSDBs

BDR does not perform any DR functions when the DR is operating

BDR receives all information, but it is the DR that performs LSA forwarding and LSDB synchronization

a router can have interface belonging to different networks behaving as both DR and BDR

DROTHERS listen on 224.0.0.5

DR & BDR listen on 224.0.0.6

the DR/BDR improve network functionality by reducing routing update traffic

R / BDR ELECTION PROCESS COMMENTS

routers view the OSPF priority value of the other routers during HELLOexchange

the router with the highest priority becomes theDR

the router with the second highest priority becomes theBDR

router ID acts as atie breaker

the only time DR/BDR changeis when one of them is out of service

adding routers with higher prioritythan current BD/BDR does not preemptcurrent selection

BDR uses the wait timer to determine whether the DR is out of service (if the DR is not confirmed to be forwarding LSAs

before the timer expires it is consider down)

should the DR failthe BDR becomes the new DRand new BDR is elected

o modify interface priority:

Router(config-if)#ip ospf priority (0-255)>

o view interface priority:

Router#show ip ospf neighbor>

Router#show ip ospf neighbor detail>

o view current DB/BDB:

Router#show ip ospf neighbor>


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SPF ADJACENCIES STATES

when an adjacencies are formed the routers go through several state changes before they become fully adjacent

STATE OVERVIEW COMMENTS

DOWN

HELLOpackets have been sent but none have been received Events that can cause this state:

starting an OSPF process on a router

RouterDeadInterval he expiration

KillNbr

InactivityTimer

LLDown

ATTEMPTThe router sends unicast HELLO packetsevery poll interval to the neighbor from which HELLOpacketshave

not been received within the DEADinterval

This state is only valid for manually configured neigh

in an NBMA environment.

INIT

the router has received HELLO packetfrom its neighbor, but the receiving routers ID was not included in

the incoming HELLOpacket

one-way HELLO

When a router receives a HELLO from a neighbor, it

should be able to find own router-id in the content

which acknowledges that the packet came as a repl

locally generated HELLO.

2-WAY

a bi-directional communication has been established between two routers (each router has seen the

other routers HELLO packet)

at this stage it is decided whether two routers should become neighbors (based on whether the required

conditions have been met)

on broadcast and non-broadcast multi-access networks DROTHERS form only 2-WAY relationship with

each other and FULL relationship with DR/BDR

At the end of this stage DR/BDR election occurs for

broadcast and non-broadcast multi-access network

EXSTART

routers and their DR/BDR establish a master/slave relationship and choose the initial sequence number

for adjacency formation the router with the highest router IDbecomes the master and starts the exchange (it al so is the only

router that can increment the sequence number)

master/slave election takes place on a per-neighbor basis

EXCHANGE

routers exchange DBD (Database Description) packets in this state

each DBD packet has a sequence number which can be only incremented by master (slave explicitly

acknowledges it)


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LOADING

the actual exchange of link-state information occurs

based on the information received in DBD routers send link-state request packets (which are provided in

LSUs)

FULL

routers are fully synchronized with each other (all the router and network LSAs are exchanged and the

routers databases are fully synced)

ready to run SPF (Shortest Path First) algorithm and individually figure out the best routes to networks

from their own perspective

Considered a normal state for an OSPF router (i f rou

are stuck in other states it may indicate problems w

forming adjacencies - with the exception of 2-WAY

which is a desired state between DROTHERS).


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SPF NETWORKS

NETWORK OVERVIEW COMMENTS

MULTI-ACCESS BROADCAST

a multi-access broadcast network e.g. Ethernet

DB/DBD election for each segment

1 x mode of operation

The DR/BDR concept is at the link level i.e. router can have different inte

belonging to different areas acting as DR, BDR or DROTHER

POINT-TO-POINT

a network that joins a single pair of routers e.g. PPP, HDLC

mode auto-detected by OSPF

OSPF packets are sent using multicast 224.0.0.5

no DB/DBD election

default timers: 10 HELLO / 40 DEAD

1 x mode of operation may also be a sub-interface running FR or ATM

the IP source address of a packet is set to the address of the outgoi

interface

NON-BROADCAST MULTI-

ACCESS

a network that interconnects more than two routers but has no

broadcast capabilities e.g. FR, X.25

5 x modes of operation

LOOPBACK

the default OSPF network type for a loopback interface, causing theOSPF to advertise host routers instead of actual network masks

the LOOPBACK network type is a CISCO proprietary extension that is not

configurable but present on a loopback interface by default

ip ospf network point-to-point- on an loopback interfaces ensures the whole subnet is advertised (the interface is treated as a stub ho

VIRTUAL LINK act as a tunnel formed to join two areas across an intermediate area


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NON-BROADCAST

RFC compliant mode

HELLO / DEAD = 30/120 sec.

DR/BDR elected

single subnet

neighbors are statically configured

acts like a LAN environment with broadcast disabled

preferred topology: full mesh

default OSPF mode for all NBMA networks

CONFIGURATIONS:

Setting network type:

Adding neighbors:

In hub and spoketopology, DR must be manually hardcoded on th

hubso that the spokescan form full adjacencies with it

Also, the spokes should never become BDR because they have no

connectivity with the rest of the networks

Infull meshits acceptable for the DR/BDR election to automatica

elect DR/BDR

neighbor A.A.A.A- manually hardcodes the OSPF neighbor

priority- hardcodes the priority of the neighbor (good pract

configure priority value on both ends to avoid errors)

cost- hardcodes the costto reach the neighbor

In hub and spoketopologies the neighbors only need to be hardco

on the hub (reason: it is the hub that initiates the HELLOexchange

process; the spokesonly respond to it) - however it is still a good

practice to hardcode all neighbors

POINT-TO-MULTIPOINT

BROADCAST

RFC compliant mode


DR/BDR not elected

single subnet

neighbors are automatically formed

treats the cloud like a series of point-to-point links

preferred topology: partial | star

CONFIGURATIONS:


in this mode OSPF advertises host routes (not networks)

can be mixed with point-to-point mode on the far ends as lo

timers are adjusted


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POINT-TO-MULTIPOINT

NONBROADCAST

CISCO extension


DR/BDR not elected

single subnet


used when multi / broadcastsare not allowed on the virtual circuits


CONFIGURATIONS:


acts likepoint-to-multipointmode with broadcast disable

can be mixed with point-to-point mode on the far ends a

long as timers are adjusted

POINT-TO-POINT

CISCO proprietary


DR/BDR not elected

one subnet for each point-to-point link



CONFIGURATIONS:



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XAMPLES: OSPF OVER NBMA CONFIGURATION

NSIDERATIONS:

choosing appropriate OSPF mode over NBMA will depend on particular circumstances such as:

o support for broadcasts / multicasts

o topology used (fully meshed,partially meshed, hub-and-spoke (star))

o IP addresses availability

DR/BDR have to have full connectivity with the rest of the nodes (unless the network is fully meshedthis process cannot be automatic)

for automatic neighbordiscovery use broadcastparameter with FR mapping

for static neighborhardcoding use neighborcommand under OSPR process sub-configuration mode

there is no one right way to configure OSPF over NBMA - technically each mode can be configured over every topology

the aim is to achieve fully network connectivity over the cloudas efficiently as possible - if a mode is working over a suboptimal topology then tuning is essential


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CENARIO 1: BROADCAST MODE

MAIN CHARACTERISTICS:

HELLO/DEAD = 10/40 sec.

DR/BDR elected

single subnet

neighbors are automatically discovered

broadcasts / multicasts are allowed over the cloud


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R1(config-if)#no shutdown













frame-relay inverse arp - maps a known L2 address (DLC

an unknown L3 address (IP)

arp frame-relay - allows the router to answer to remote

routers ARP query

Since broadcastcapabilities have to be enabled while statically

adding FR mapping automatic FR neighbor discovery should be

disabled.




R2(config-if)#frame-relay map ip 10.1.123.3 201



To confirm FR mappings:


broadcast - enables pseudo broadcast (forwards broadca

style unicast packets to the specified node)


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HARDCODE OSPF PRIORITIES ---> R1(config)#interface s1/0

R1(config)#ip ospf priority 255





On fully meshed networks it is fine to let the routers automat

elect the DR/BDR.

Because the network is not fully meshed, letting the DR/BDR

automatically elected can lead to connectivity issues - the

DR/BDR/DROTHER assignment will take place on a link basis

(R1 R2, R1 R4) and not a segment basis.

Both DR/BDR rely on full connectivity with all the nodes on th

segment to work properly. Since only the hub (R1) meets this

requirement it has be hardcoded as DR. R1 and R4 only have d

connection to R1 and not to each other. Therefore neither can

become BDR and none will be elected. Both routers need to b

hardcoded as DROTHERS.

HARDCODE OSPF MODES R1(config-if)#ip ospf network broadcast

R2(config-if)#ip ospf network broadcast

R4(config-if)#ip ospf network broadcast

To confirm OSPF mode:

Router#show ip ospf interface

ENABLE OSPF ---> R1(config)#router ospf 1

R1(config-router)#router-id 1.1.1.1

R1(config-router)#network 10.1.123.1 0.0.0.0 area 0


R1(config)#router ospf 1








At this stage the adjacencies will be formed and OSPF will be

operational.


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CENARIO 2: NON-BROADCAST MODE



DR/BDR elected

single subnet


broadcasts / multicasts are not allowed over the cloud


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routers ARP query

Since broadcastsare not allowed over the FR cloud, building t

map should rely on static entries with the dynamic mapping

disabled.

STATICALLY ADD FR MAPS ---> R1(config-if)#frame-relay map ip 10.1.123.2 102








It is necessary to add maps in a way that both spokes can reac

other - otherwise the spoke wont be able to reach networks

advertised by the other spoke.

Since the topology is not fully meshed the route to remote sp

should be mapped through the hub.





DR/BDR election will occur during establishing adjacencies.

Because the network is not fully meshed, letting the DR/BDR b



(R1 R2, R1 R4) and not a segment basis.


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R4(config)#ip ospf priority 0Both DR/BDR rely on full connectivity with all the nodes on the






HARDCODE OSPF MODES ---> R1(config-if)#ip ospf network non-broadcast

R2(config-if)#ip ospf network non-broadcast

R4(config-if)#ip ospf network non-broadcast















At this stage the adjacencies will not form since OSPF is workin

non-broadcastmode and will not multicast HELLOs.

Neighbors need to be statically configured under the OSPF

process.

MANUALLY ADD OSPF NEIGHBORS ---> R1(config)#router ospf 1

R1(config-router)#neighbor 10.1.123.2 priority 0






Technically, the neighbors only need to be hardcoded on the h

it is the hub that initiates the HELLO exchange process; the spo

only respond to it - however it is still a good practice to hardcoall neighbors.

Same case withpriority- its already configured on each route

the FR interface but its a good practice to hardcode it again un

the neighborstatement.

No need for the spokes to become neighbors since all the traff

has to go through the hubanyways.

The neighbor command causes the HELLOsto be unicasted in

of multicasted.


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CENARIO 3: POINT-TO-MULTIPOINT BROADCAST



DR/BDR not elected

single subnet



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routers ARP query

Since broadcastcapabilities have to be enabled while statically

adding FR mapping automatic FR neighbor discovery should be

disabled.









HARDCODE OSPF MODES ---> R1(config-if)#ip ospf network point-to-multipoint

R2(config-if)#ip ospf network point-to-multipoint

R4(config-if)#ip ospf network point-to-multipoint




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At this stage the adjacencies will be formed and OSPF will be

operational.

(*note: take notice of how host routes are advertised not the

whole networks)


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CENARIO 4: POINT-TO-MULTIPOINT NON-BROADCAST



DR/BDR not elected

single subnet



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routers ARP query

Since broadcastsare not allowed over the FR cloud, building t

map should rely on static entries with the dynamic mapping

disabled.

STATICALLY ADD FR MAPS ---> R1(config-if)#frame-relay map ip 10.1.123.2 102








It is necessary to add maps in a way that both spokes can reac

other - otherwise the spoke wont be able to reach networks

advertised by the other spoke.

Since the topology is not fully meshed the route to remote sp

should be mapped through the hub.







DR/BDR election will occur during establishing adjacencies.

Because the network is not fully meshed, letting the DR/BDR



R2, R1 R4) and not a segment basis.

Both DR/BDR rely on full connectivity with all the nodes on the



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HARDCODE OSPF MODES ---> R1(config-if)#ip ospf network point-to-multipoint non-broadcast

R2(config-if)#ip ospf network point-to-multipoint non-broadcast

R4(config-if)#ip ospf network point-to-multipoint non-broadcast




R1(config-router)#router-id 1.1.1.1R1(config-router)#network 10.1.123.1 0.0.0.0 area 0










At this stage the adjacencies will not form since OSPF is worki

non-broadcastmode and will not multicast HELLOs.Neighbors need to be statically configured under the OSPF

process.

MANUALLY ADD OSPF NEIGHBORS ---> R1(config)#router ospf 1







Technically, the neighbors only need to be hardcoded on the

it is the hub that initiates the HELLO exchange process; the sp

only respond to it - however it is still a good practice to hardco

all neighbors.

Same case withpriority- its already configured on each route

the FR interface but its a good practice to hardcode it again u

the neighborstatement.

No need for the spokes to become neighbors since all the traff

has to go through the hubanyways.

The neighbor command causes the HELLOsto be unicasted in

of multicasted.


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R1(config-if)#interface s0/0.102 point-to-point


R1(config-if)#frame-relay interface-dlci 102

R1(config-if)#interface s1/0.103 point-to-point

R1(config-if)#ip add 10.1.1.5 255.255.255.252





R2(config-if)#interface s1/0.201






R4(config-if)#interface s1/0.301






routers ARP query

Auto discovery can be left on - since there is only one node at

end there is no risk of mapping to undesired / unknown netwo

When configuring FR sub-interfaces, the FR encapsulation and

parameters (LMI type etc.) only need to be configured on the m

interface.

Only the main interface needs to be turned on (no shutdown)






R2(config-router)#router-id 2.2.2.2R2(config-router)#network 10.1.1.2 0.0.0.0 area 0






No need to hardcode OSPF mode on the interfaces - the point

point mode is default for point-to-point interfaces.

At this state the adjacencies will be formed and OSPF will be

operational.


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SPF CONFIGURATIONS

CTIVATION


START OSPF PROCESS process ID- a locally significant number t

does not affect the OSPF operation

HARDCODE ROUTER ID

ADD INTERFACES TO OSPF

PROCESS

Alternatively:

To add every interface:

To manually add neighbor:

network - specifies what interfaces to ad

the OSPF process (added interface will se

receive HELLO packets and advertise thenetworks to which they belong)

The wildcard mask is used for matching prefix

The prefix-length is not matched.

A network command with the most specific

wildcard is revised first.

If a statement ends with subnet mask it will be

converted into appropriate wildcard mask and

saved in the running config. in this format

PASSIVE INTERFACES

To verify:

passive-interface- no HELLOs are sent o

interface (hence no relationship can be

formed) but the network is still advertise

passive-interfacedefault- sets all interfa

as passive

A passive interface is still part of the OSPF procand the network advertised but no HELLOs are

to that interface.

HARDCODE AREA TYPE


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VIRTUAL LINK

hello-interval- specifies the HELLOtime

dead-interval- specifies the time that m

pass without HELLOpackets being seen

before the neighbor declares the router

down

PROPAGATE DEFAULT

GATEWAY


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UNING

FEATURE COMMANDS COMMENTS

ADJUST AD

Globally:

Per routes:

ADJUST TIMERS

o HELLO To verify:

o HOLD

ADJUST RETRANSMIT

INTERVAL

ip ospf retransmit-intervalcontrols the tim

interval between advertisement retransmissi

the previous packet was not acknowledged

ADJUST REFERENCE

BANDWIDTH

To verify:

ADJUST I-FACE COST

ADJUST I-FACE PRIORITY Default = 1

HARDCODE NETWORK TYPE

To verify:


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UTHENTICATION

TYPE COMMANDS COMMENTS

PLAIN TEXT

authentication Type 1 (default = 0, disab

ip ospf authentication- enables plain tex

authentication

ip ospf authentication-key- OSPF passw

MD5

For the entire area:

For an interface:

authentication Type 2

ip ospf authenticationmessage-digest-

enables md5 authentication

ip ospf message-digest-key (1-255) md5

MD5 OSPF password

Routers must use the same key IDto authentic

each other.

The router uses the most recently added key f

authenticating sent packages.

UMMARIZATION

by default, the metric of the summary routeis equal to the highest (worst) metric of the component subnet

TYPE COMMANDS COMMENTS

INTERNAL ROUTES

Configured on and performed by an ABR.

The ABR advertises only the summary route if

least one subordinate subnets exists as an (IA)

inter-area route.

Also creates a summary route pointing toward

Null0for the same range - (behavior known as

sending unknown traffic to bit bucket- if the r

advertising the summary route receives a pack

destined for something covered by the summa

route but not in the routing table, it drops it)

EXTERNAL ROUTES Configured on and performed by an ASBR.


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DISTRIBUTION

UTING PROTOCOLS

o set a default-metric (NOTE: this command does not affect the metric of directly connectednetworks):

Router(config-router)#default-metric (1-16777214)>

PULL ROUTES FROM: COMMANDS COMMENTS

RIP

metric- redistribute router with the spec

metric (by default it is set to 20) (overrid

by a route-mapif used)

metric-type- External Type 1 (increment

seed metric by adding the internal cost) o

Type 2 (do not increment metric)

nssa-only- redistribute only NSSA extern

routes

route-map - apply a route mapfor filteri

redistributed routes

subnets- prevents automatic summariza

of the redistributed routes

Defaults:

when redistributing BGP the metric = 1

when redistributing another OSPF proces

take the source routes metric

when redistributing all other sources, use

default metric = 20

creates a Type 5 LSA for each redistribut

route if not inside an NSSA area

creates a Type 7 LSAfor each redistribute

route if inside an NSSA area

uses External Type 2 metric

redistribute only classful networks (ignor

subnets)

EIGRP

Example:

BGP


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IRECTLY CONNECTED NETWORKS

COMMANDS COMMENTS

outer(config-router)#redistribute connected (*metric (0-16777214)) (*metric-type (1-2)) (*nssa-only) (*route-map (route map name)) (*subnets)>

TATIC ROUTES

COMMANDS COMMENTS

Router(config-router)#redistribute static (*metric (0-16777214)) (*metric-type (1-2)) (*nssa-only) (*route-map (route map name)) (*subnets)>


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SPF VERIFICATION AND TSHOOTING

show ip ospf neighbors

show ip ospf neighbors detail

show ip ospf interface

show ip ospf interface brief

show ip ospf


show ip ospf border-routers

show ip route ospf

show ip protocols

debug ip ospf adjacencies

clear ip ospf process

COMMAND VERIFIES EXAMPLE

show ip ospf neighbor

neighbor ID

neighbor priority

adjacency state

neighbor IP address

local interface through which the neighbor is accessible

show ip ospf neighbor detail

detailed neighbor related information


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show ip ospf interface (*interface)

local interface(s) that participate in OSPF processes

show ip ospf interface brief

local interface(s) that participate in OSPF processes

the areas the interface belongs to

interface IP address

interface COST

interface network type

the number of neighbors


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show ip ospf

OSPF processes

router ID

OSPF areas


various LSAs in the OSPF database organized by area and type


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show ip ospf border-routers

lists boundary routers information

show ip route ospf

network in the routing table learnt via OSPF processes

show ip protocols

router ID

networks OSPF is routing for

reference bandwidth

administrative distance

show ip ospf virtual-link

Information about virtual linkscreated on the local router


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debug ip ospf adj

Debugs OSPF adjacency events

clear ip ospf process Restarts OSPF processes


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1. THE ROUTERS D

advanced routing reference manual ver. 0.9

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