Tài liệu CCIE_CRAMsheet docx

FRAME-RELAY

9 A point-to-point subinterface can only accommodate a single DLCI at any given time. Point-to￾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.

9 Multipoint DLCI’s rely on either inverse-arp or frame-relay map statements for proper operation.

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

inverse-arp entries.

9 The broadcast parameter is required for protocols such as OSPF

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

map statement.

9 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.

9 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

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

interface

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

9 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.

9 Split horizon is disabled on frame-relay physical IP interfaces split horizon is enabled on frame￾relay point-to-point and multi-point IP sub-interfaces.

9 OSPF is not affected by the rule of split horizon since it does not apply it.

9 A remedy to the problem of “hello mismatches” is using the Cisco IOS interface configuration

command “IP OSPF network”:

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

9 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.

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

9 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

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

FR scenarios:

ALL PHYSICAL:

Add map statement to spokes (to other spokes). NOTHING needs to be done at Hub.

ALL SUB-INTERFACES:

Frame-relay interface-dlci statements on hub (PtoMP) and spokes (PtoP) note: distance vector protocols

will be affected because of split horizon. Disable split-horizon a the hub. OSPF will have network type

mismatches.

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

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

timer.

9 Just as with frame-relay map statements the dialer-map broadcast parameter is required for proper

OSPF operation over a DDR link

9 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.