FRAME-RELAY

ü Rules to remember when configuring point-to-point sub-interfaces are: o No frame-relay map statements can be used with point-to-point sub-interfaces o One and only once DLCI can be ass

Trang 1

FRAME-RELAY

ü A point-to-point subinterface can only accommodate a single DLCI at any given time point sub-interfaces are treated by the IOS like a physical point-to-point interface and do not need either inverse-arp or frame-relay map statements

Point-to-ü Multipoint DLCI’s rely on either inverse-arp or frame-relay map statements for proper operation

ü You must manually clear inverse-arp with a clear frame-inarp command to remove any undesired inverse-arp entries

ü The broadcast parameter is required for protocols such as OSPF

ü If the router is reloaded inverse-arp will be disabled for any DLCI that is used with a frame-relay map statement

ü As a rule when configuring frame-relay map statements make note of the protocol and the DLCI specified if there are any inverse mappings for that same protocol referencing the same DLCI replace the inverse-arp entries with frame-relay map statements

ü Rules to remember when configuring point-to-point sub-interfaces are:

o No frame-relay map statements can be used with point-to-point sub-interfaces

o One and only once DLCI can be associated with a single point-to-point interfaces

ü Without the frame-relay interface DLCI command, all DLCI’s are assigned to the physical interface

ü Split horizon only blocks routing updates in a hub and spoke topology

ü A Cisco IOS remedy to this split horizon problem is to disable split horizon on the hub router in a frame-relay network this can be performed at the interface configuration mode

ü Split horizon is disabled on relay physical IP interfaces split horizon is enabled on relay point-to-point and multi-point IP sub-interfaces

frame-ü OSPF is not affected by the rule of split horizon since it does not apply it

ü A remedy to the problem of “hello mismatches” is using the Cisco IOS interface configuration command “IP OSPF network”:

ü A popular selection for OSPF networks is the point-to-multipoint option

ü When using only physical interfaces in a hub and spoke topology you need to add a frame-relay map statement on the spoke routers to assure spoke to spoke reachability nothing needs to be done

to the hub router

ü If using point-to-point sub-interfaces each sub-interface must be configured as a separate sub net

ü If a physical or multipoint sub interface is being used at the hub remember to disable split horizon

at the hub

Interface configuration: (physical)

encap frame

frame-relay lmi-type {cisco ansi q933a} note: after IOS 11.2 lmi is auto-sensed

ip address { A.B.C.D mask }

frame-relay map ip ip-address dlci

Trang 2

Interface configuration: (sub-interface)

ip address { A.B.C.D mask }

frame-relay interface-dlci dlci note: PtoP can only have 1 dlci, PtoMP can have multiple dlci’s

PHYSICAL INTERFACE AT THE HUB AND PtoP SUBINTERFACES AT THE SPOKES:

frame-relay interface-dlci dlci statements at the spokes

MULTIPOINT SUBINTERFACE AT THE HUB AND PHTSICAL INTERFACES AT THE SPOKES:

Add map statement to spokes note: add map to hub also because of the inverse-arp being disabled

frame-relay interface-dlci dlci statements at the hub ( or frame-map statements )

PtoP SUBINTERFACES AT THE HUB:

Overcomes the problem of split-horizon without having to disable it Note: each subinterface will need its

own subnet

EX PVCs on same subnet

interface serial 0

ip ospf network point-to-multipoint

EX PVCs on different subnets

interface serial 0

ip ospf network broadcast

SHOW and DEBUG:

Show frame-relay pvc

Show frame-relay map

Show frame-relay lmi

Deb ip packet

Deb fram packet

Clear frame-relay-inarp

ISDN AND DDR ROUTING

ü The broadcast parameter allows broadcast traffic to be forwarded and broadcasts will reset the idle timer

ü Just as with frame-relay map statements the dialer-map broadcast parameter is required for proper OSPF operation over a DDR link

ü Note that when the broadcast parameter is added the DDR link can stay up indefinitely due to constant broadcast traffic, to remedy this situation granular dialer-lists must be configured

Trang 3

ü A physical interface can be associated with multiple dialer pools A logical dialer interface can be associated with only one dialer pool

ü In order to configure PPP chap authentication with dialer profiles enter the PPP authentication chap statement at both the physical interface and the logical dialer interface

ü The dialer remote name statement is critical for the called party it must match the calling party host name or the name specified in the calling parties PPP chap host name statement

Configuring Legacy ISDN :

Global configuration:

isdn switch-type ?

basic-1tr6 1TR6 switch type for Germany

basic-5ess Lucent 5ESS switch type for the U.S

basic-dms100 Northern Telecom DMS-100 switch type for the U.S

basic-net3 NET3 switch type for UK, Europe, Asia and Australia

basic-ni National ISDN switch type for the U.S

basic-qsig QSIG switch type

basic-ts013 TS013 switch type for Australia (obsolete)

ntt NTT switch type for Japan

vn3 VN3 and VN4 switch types for France

dialer-list list-number protocol protocol-name permit/deny

username Remote-router-name password password ( only if using PPP encap/auth )

Interface configuration: (minimal using dialer string… very inefficient use of B channels both sides

REQUIRE dialer strings)

ip address ip-address mask

dialer string dialer-string-numer

dialer-group dialer-group-number

Interface configuration: (minimal using dialer map)

ip address ip-address mask

encap ppp

ppp authentication chap | pap

dialer map ip A.B.C.D ?

WORD Dialer string

broadcast Broadcasts should be forwarded to this address

class dialer map class

modem-script Specify regular expression to select modem dialing script

name Map to a host

spc Semi Permanent Connections

speed Set dialer speed

system-script Specify regular expression to select system dialing script

Trang 4

3 steps:

Configure the physical interface: (all legacy statements must be removed)

Dialer pool-member dialer-pool-number

Encap ppp

ppp auth chap

Configure the logical dialer interface: (minimal)

ip address A.B.C.D mask

encap ppp

Dialer remote-name remote-router-name

dialer string dialer-string-number

dialer pool number

dialer-group number

ppp auth chap

Routing issues over ISDN:

ü Use static routes and dialer-lists that filter routing updates ( no broadcast parameter on map statement)

ü SNAPSHOT routing for DV protocols

ü OSPF Demand circuit- Cisco has a solution to limit OSPF hello traffic over and ISDN link: IP OSPF DEMAND–CIRCUIT By entering this interface configuration command on one side of a bri connection, OSPF adjacencies will be formed and ongoing OSPF hellos will be suppressed

SHOW and DEBUG:

sh int bri0 (shows D channel)

sh int bri0 1 or bri0 2 (shows B channels)

deb isdn q921

deb isdn q31

ISDN – Snapshot routing

ü All snap shot routing configuration is performed at the interface configuration mode Typically the snap shot client is a branch office and the snap shot server is the headquarters or hub office

Configuring the Snapshot client:

Interface commands:

Dialer map snapshot sequence-number dial-string

Snapshot client active-period quiet-period suppress-statechange-updates dialer

Configuring the Snapshot server:

Interface commands:

snapshot server active-period dialer

Note: ALL PERIODS ARE IN MINUTES

SHOW and DEBUG:

sho snapshot

clear snapshot

deb snapshot

Trang 5

deb dialer packet

deb dialer events

Dial Backup

ü You can use dial backup to backup an individual frame-relay DLCI by placing the DLCI under a point-to-point subinterface If the DLCI becomes inactive the point-to-point sub-interfaces line protocol attains a state of down and the designated back up interface will become active

ü When applying a dial backup to a legacy ISDN\DDR configuration the physical interface is placed

in standby mode When an interface is in standby mode no other traffic can pass over it With dialer profiles the logical dialer interface is in standby mode and the physical interfaces are free to

be used for other services

Apply two interface configuration commands to the primary interface:

For primary link failure:

Backup interface {bri0 | dialer}

Backup delay { XXX YYY }

• XXX = time in seconds to wait before activating the backup interface

• YYY = time in seconds to wait before putting backup interface in standby after primary is up

For primary link load overload:

Backup interface {bri0 | dialer}

Backup load { XXX YYY }

• XXX = amount of load to be exceeded to trigger backup intf

• YYY = amount of load to be attained to deactivate backup intf

To backup a FR individual dlci, place the dlci under a PtoP subinterface

Floating static routes can also be used for backup

SHOW and DEBUG:

sho interface

RIP

ü Rip routes have a default administrative distance of 120

ü A hop count is the number of routers a rip update has transited

ü When the static default route 0.0.0.0 0.0.0.0 is configured on a rip speaking router, rip

automatically redistributes the 0.0.0.0 entry into the rip domain

ü Another method of advertising a default route with rip is to use the default information originate statement under the router rip configuration mode By entering this statement 0.0.0.0 route will be advertised into the rip domain, even if there is no 0.0.0.0 route on the router that is the source of the default route

ü In a rip domain, all subnets must be contiguous The contiguous subnet requirement can be overcome by using a combination of default routes and the ip classless command

Trang 6

ü A default route allows a rip speaking router to forward all class full network prefixes that are not listed in a given routers routing table However, a default route does not automatically allow a rip speaking router to forward all subnets that are not listed in a given routers routing table

ü By enabling ip classless, you override the contiguous subnet rule and allow the router to look for the longest match beyond the listed subnets If a subnet is not listed on a router with ip classless enabled, it will eventually match the 0.0.0.0 entry ( the default route)

ü If you adjust the timers on one router in a rip domain, adjust the timers on all routers to the exact same settings

ü The most useful debugging tool for rip routing is debug ip rip

ü RIP V1 and IGRP will advertise routes having a different subnet mask than the interface if the route is in a different major network RIP will assume a classful mask

Router Commands - RIP

*auto-summary Enable automatic network number summarization default Set a command to its defaults

**default-information Control distribution of default information

**default-metric Set metric of redistributed routes

**distance Define an administrative distance

***distribute-list Filter networks in routing updates exit Exit from routing protocol configuration mode

*flash-update-threshold Specify flash update threshold in second help Description of the interactive help

system

*input-queue Specify input queue depth

*maximum-paths Forward packets over multiple paths

**neighbor Specify a neighbor router

**network Enable routing on an IP network

no Negate a command or set its defaults

*offset-list Add or subtract offset from IGRP or RIP metrics

output-delay Interpacket delay for RIP updates

*passive-interface Suppress routing updates on an interface

***redistribute Redistribute information from another routing protocol

*timers Adjust routing timers

*traffic-share Algorithm for computing traffic share for alternate routes

*validate-update-source Perform sanity checks against source address of routing updates

**version Set routing protocol version

Interface Commands - RIP

Rtr(config-if)#ip rip ?

**Authentication Authentication control

**receive advertisement reception

**send advertisement transmission

(Importance - ***High **Medium *Low)

IGRP

ü Rip has a maximum hop count of 15 IGRP has a max hop count of 100

ü IGRP routes have a default administrative distance of 100

ü Bandwidth is the smallest of all bandwidths on outbound ports in a given path Delay is the sum

of all delays of outbound ports in a path

Trang 7

ü As with rip, if you adjust timers on one you must adjust on all

ü IGRP does not advertise the 0.0.0.0 network to downstream IGRP neighbors Rip and EIGRP do

ü With IGRP, you must use the “ ip default–network” global configuration command When using this statement, it is recommended that you assign a class full address If you use a subnet, with “ip default -network” a static route will be created in your running configuration

Router Commands - IGRP

default Set a command to its defaults

***distribute-list Filter networks in routing updates

exit Exit from routing protocol configuration mode

help Description of the interactive help system

*input-queue Specify input queue depth

*metric Modify IGRP routing metrics and parameters

*validate-update-source Perform sanity checks against source address of routing updates

*variance Control load balancing variance

EIGRP

ü The feasible distance is the metric used by a given router to reach a specific destination network

ü If a directly connected neighbors metric to a given destination network is less than your own metric, you cannot create a routing loop by selecting a shorter path to a given destination network

ü EIGRP internal routes have an administrative distance of 90

ü External EIGRP routes have an administrative distance of 170

ü The only difference between an IGRP metric and an EIGRP metric is that the EIGRP metric is represented by a value that is larger than the IGRP metric by a factor of 256

ü If you have a discontiguous subnet, you will want to disable the automatic summarization feature

of EIGRP

ü EIGRP propagates a route to network 0.0.0.0, but the static route must be redistributed into EIGRP RIP and OSPF behave as described when using the ip default-network command

Router Commands - EIGRP

*auto-summary Enable automatic network number summarization

Trang 8

***distribute-list Filter networks in routing updates

*eigrp EIGRP specific commands

exit Exit from routing protocol configuration mode

help Description of the interactive help system

metric Modify IGRP routing metrics and parameters

*variance Control load balancing variance

Interface Commands - EIGRP

Rtr(config-if)#ip hello-interval eigrp 1 ?

<1-65535> Seconds between hello transmissions

Rtr(config-if)#ip hold-time eigrp 1 ?

<1-65535> Seconds before neighbor is considered down

Rtr(config-if)#ip split-horizon eigrp ?

<1-65535> Autonomous system number

OSPF

ü OSPF routers on broadcast networks will elect a DR and BDR

ü OSPF routers on NBMA networks will elect a DR and BDR and all OSPF packets are unicast

ü PtoMP networks are a special configuration of NBMA networks in which the networks are treated

as a collection of PtoP links Routers DONOT elect a DR and BDR and OSPF packets are multicast

ü Loopback interfaces are considered stub networks and advertised as host routes Adding the interface command ip ospf network point-to-point can alter this default behavior

ü The cost of a route is the sum of the costs of all outgoing interfaces to a destination Default OSPF cost is 10^8/BW (configured BW of the interface)

ü Best practice dictates that a non-backbone area’s addresses should be summarized INTO the backbone area by its own ABR, as opposed to having all other ABRs summarize the area into their areas

ü Recall from EIGRP that when a summary route is configured, a route to the null interface is created and automatically entered into the route table to prevent routing loops and black holes THEREFORE, whenever you are configuring summary routes within an OSPF domain, be sure to add a static route for the summary address pointing to a null interface

ü By default, redistributed routes have external metric type 2 Type 2 routes have a cost which consists of the external cost only Type 1 routes include the cost of traversing the OSPF domain

OSPF Authentication:

ü When authentication is configured, it must be configured for an entire area

Configuring Type 1 authentication:

On each interface in the area:

Trang 9

ip ospf authentication-key password (note: the passwords DON’T need to be the same throughout the

area, but MUST be the same between neighbors.)

Router mode configuration:

area X authentication

Configuring Type 2 authentication:

On each interface in the area:

ip ospf message-digest-key md5 password (note: the passwords DON’T need to be the same throughout

the area, but MUST be the same between neighbors.)

Router mode configuration:

area X authentication message-digest

Manage Authentication Keys:

key chain name-of-chain

key number

key-string

accept-lifetime start-time {infinite | end-time | duration seconds}

send-lifetime start-time {infinite | end-time | duration seconds}

LSA Types-

Router LSAs (Type 1) are produced by every router Lists all of a router’s links, or interfaces, along with

the state and outgoing cost of each link These LSAs are flooded only within the area in which they are originated

Use command: show ip ospf database router

Network LSAs (Type 2) are produced by the DR on every multi-access network Lists all attached routers

including the DR itself Like Type 1’s network LSAs are flooded only within the originating area

Use command: show ip ospf database network

Network Summary LSAs (Type 3) are originated by ABRs They are sent into a single area to advertise

destinations outside that area An ABR also advertises the destinations within its attached areas into the backbone with Network Summary LSAs Default routes external to the area but internal to the OSPF AS are also advertised as Network Summary LSAs

Use command: show ip ospf database summary

ASBR Summary LSAs (Type 4) are also originated by ABRs ASBR Summary LSAs are identical to

network Summary LSAs except that the destination they advertise is an ASBR, not a network

Use command: show ip ospf database asbr-summary

Autonomous System External LSAs (Type 5) are originated by ASBRs and advertise either a destination

external to the OSPF AS, or a default route external to the OSPF AS

Use command: show ip ospf database external

NSSA External LSAs (Type 7) are originated by ASBRs within NSSAs Unlike Autonomous System

External LSAs which are flooded throughout an OSPF AS, NSSA External LSAs are only flooded within the originating NSSA

Use command: show ip ospf database nssa-external

Area Types-

Trang 10

Stub Area – an area into which Autonomous System External LSAs (Type 5) are not flooded Type 4s also blocked ABRs at the edge of the stub network will use Network Summary LSAs (Type 3) to advertise

a single default route (destination 0.0.0.0) into the area

To configure: ALL routers in stub area must have area X stub in their router mode configuration

Totally Stubby Area – use a default route to reach ALL destinations outside its area The ABR of a totally

stubby area will block not only Autonomous System External LSAs (Type 5) but also all Network

Summary LSAs (Type 3) with the exception of a single type 3 LSA to advertise the default route

To configure: ALL routers in stub area must have area X stub in their router mode configuration, and the

ABR must have area X stub no-summary

Not-So-Stubby Area – allow external routes to be advertised into the OSPF AS while retaining the

characteristics of a stub area to the rest of the AS These type 7 LSAs are flooded throughout the NSSA but are blocked at the ABR (translated to type 5 LSAs and flood it throughout the other areas

To configure: ABR router in stub area must have area X nssa in its router mode configuration, and the

ASBR must have area X nssa also

The way that OSPF generates default routes (0.0.0.0) varies depending on the type of area the default route is being injected into

Normal Areas

By default, in normal areas routers don't generate default routes To have an OSPF router generate a default route, use the default-information originate [always] [metric metric-value] [metric-type type-value] [route-map map-name] command This generates an external type-2 link with link-state ID 0.0.0.0 and network mask 0.0.0.0, which makes the router an autonomous system boundary router (ASBR)

There are two ways to inject a default route into a normal area If the ASBR already has the default route, you can advertise 0.0.0.0 into the area If the ASBR doesn't have the route, you can add the keyword always to the default-information originate command, and then advertise 0.0.0.0

Stub and Totally Stubby Areas

For stub and totally stubby areas, the area border router (ABR) to the stub area generates a summary state advertisement (LSA) with the link-state ID 0.0.0.0 This is true even if the ABR doesn't have a default route In this scenario, you don't need to use the default-information originate command

link-Not-So-Stubby Areas

The ABR for the NSSA generates the default route, but not by default To force the ABR to generate the default route, use the area <x> nssa default-information originate command The ABR generates a type 7 LSA with the link-state ID 0.0.0.0

Router Commands - OSPF

Rtr(config)#router ospf 1

***area OSPF area parameters

**auto-cost Calculate OSPF interface cost according to bandwidth

*default-information Control distribution of default information

*default-metric Set metric of redistributed routes

*distance Define an administrative distance

*distribute-list Filter networks in routing updates

*ignore Do not complain about specific event

Trang 11

*log-adjacency-changes Log changes in adjacency state

***network Enable routing on an IP network

*no Negate a command or set its defaults

*router-id router-id for this OSPF process

***summary-address Configure IP address summaries

*traffic-share Algorithm for computing traffic share for alternate

OSPF intertace commands

Rtr(config-if)#ip ospf ?

***authentication-key Authentication password (key)

**cost Interface cost

*database-filter Filter OSPF LSA during synchronization and flooding

*dead-interval Interval after which a neighbor is declared dead

***demand-circuit OSPF demand circuit

*hello-interval Time between HELLO packets

***message-digest-key Message digest authentication password (key)

***network Network type

***priority Router priority

*retransmit-interval Time between retransmitting lost link state advertisements

*transmit-delay Link state transmit delay

Area

Rtr(config-router)#area ?

<0-4294967295> OSPF area ID as a decimal value

A.B.C.D OSPF area ID in IP address format

Rtr(config-router)#area 1 ?

**Authentication Enable authentication

*default-cost Set the summary default-cost of a NSSA/stub area

*nssa Specify a NSSA area

***range Summarize routes matching address/mask (border routers only)

*stub Specify a stub area

***virtual-link Define a virtual link and its parameters

The auto-cost command is used to change the default of 100,000,000 Changing the default affects the cost

of every OSPF interface on the router

Rtr(config-router)#auto-cost reference-bandwidth ?

<1-4294967> The reference bandwidth in terms of Mbits per second

Trang 12

SHOW and DEBUG:

show ip ospf ?

*** <1-4294967295> Process ID number

border-routers Border and Boundary Router Information

database Database summary

flood-list Link state flood list

**interface Interface information

***neighbor Neighbor list

request-list Link state request list

retransmission-list Link state retransmission list

summary-address Summary-address redistribution Information

***virtual-links Virtual link information

Neighbor A.B.C.D remote-as AS-number

Neighbor A.B.C.D update-source loopback is required source router when using a loopback interface

Neighbor A.B.C.D EBGP multihop – used when an EBGP connection is to a non-connected interface

(Loopback) Because the peer is not directly connected, you must use a static route or an IGP for reach ability

Neighbor A.B.C.D next hop self – used when the next hop address on the outgoing update (particularly

across NBMA network) is not reachable to the EBGP peer

ü Within an AS, bgp peers do not need to be directly connected

ü For routers that run ebgp, neighbors are usually directly connected

ü ALL bgp speakers within an AS MUST establish a peer relationship unless you use Route

ü You can disable synchronization if one of the following is true:

1 Your AS does not pass traffic from one AS to another

2 ALL the transit routers in your AS run BGP

ü The only difference between advertising a static and a default route, is that when you redistribute a static, BGP sets the origin attribute of updates to incomplete

ü Redistributing a static route is the best way to advertise a supernet because it stops the route from flapping

ü To ensure a loop free inter-domain topology, BGP does not accept updates that originated from its own AS

Trang 13

ü Origin attribute- will be “i” when injected with network command in router configuration mode,

“e” when learned through EGP, “?” incomplete when a route is redistributed into bgp

ü BGP specifies that the next hop of EBGP learned routes remain unchanged into and through IBGP

The weight attribute is a special CISCO attribute that is used in the path selection when there is more than

one route to the destination The weight attribute is local to the router on which it is assigned and is NOT propagated in routing updates (higher more preferred)

3 ways to set weight:

ü Access-list

ü Route-map

ü Neighbor weight command

The local preference attribute indicates the preferred path when there is multiple paths (higher=better)

Unlike the weight attribute, the local preference IS carried with route updates and exchanged with routers

in the same AS

2 ways to set local preference:

ü use the bgp default local-preference command

ü route-maps

The MED attribute is a hint to EBGP peers about the preferred path into an AS when there are multiple

(lower=better) Unlike local preference, the MED is exchanged between AS’s, but a MED that comes into

an AS does not leave the AS

The community attribute provides a way of grouping destinations to which routing decisions can be

applied To send the attribute you MUST use the neighbor send-community router config command

Other topics:

BGP Route Reflectors- eliminates full mesh requiremnt

BGP Confederations- makes “mini- AS’s” inside of an AS

BGP Peer groups – a group of neighbors that share the same update policies

Summary of the BGP Path Selection Process:

BGP selects only one path as the best path When the path is selected, BGP puts the selected path in its routing table and propagates the path to its neighbors BGP uses the following criteria, in the order presented, to select a path for a destination:

1 If the path specifies a next hop that is inaccessible, drop the update

2 Prefer the path with the largest weight

3 If the weights are the same, prefer the path with the largest local preference

4 If the local preferences are the same, prefer the path that was originated by BGP running on this router

5 If no route was originated, prefer the route that has the shortest AS_path

Định dạng
Số trang	27
Dung lượng	217 KB