Tudo sobre Inverse-ARP !!!

Senhora e Senhores,

Inspirado no Post anterior do Sandro, traduzi este Post de um site com um nome bem sugestivo:
CCIE - The Beginning --> http://cciethebeginning.wordpress.com/tag/inverse-arp/

Espero que gostem !!!

Abs,

Frame-Relay é um dos principais itens da prova prática do CCIE , por isso antes de passar para quaisquer outros recursos avançados, é crucial compreender perfeitamente todos os tópicos relacionados com a sua aplicação: ponto-a-ponto, multiponto, sub-interfaces, habilitar ou desabilitar o Inverse-ARP.
Neste post duas principais topologias serão tratadas: a primeira com interfaces ponto-a-ponto e sub-interfaces e a segunda com interfaces multi-ponto e sub-interfaces Para cada caso o Inverse-ARP será ativado e desativado.

Vamos organizar assim:
1) Ponto-a-ponto
Ia) Sem Inverse-ARP
• Interface
• Sub-interface
• Checar Conectividade
Ib) Com Inverse-ARP
• Interface
• Sub-interface
2) Ponto-multiponto
II-a) Sem Inverse-ARP
• Interface
• Sub-interface
II-b) Com Inverse ARP
• Interface
• Sub-interface

Primeiro vamos começar por uma breve revisão de "LMI" e "inverse ARP":

LMI (Local Management Interface): Gerencia o link entre o Roteador Frame-Relay e o Switch do Provedor e mantém o status entre os dois dispositivos
O roteador envia solicitações a cada 10 segundos e o Switch FR responde com uma mensagem de KeepAlive.

O LMI também faz o roteador disparar a mensagem de Inverse-ARP (router IP sobre o VC).

Inverse ARP: permite que um roteador FR reaja a uma mensagem LMI recebida  "PVC UP" e anuncia o seu endereço IP para a outra extremidade do PVC, isso é particularmente útil quando o endereço IP do outro lado do PVC não é conhecido ou quando uma interface/sub-interface FR do roteador termina em mais de um PVC.

I-Ponto-a-Ponto

Ia) SEM Inverse-ARP
Interface
- Quando usar uma "interface física" para terminar um PVC ponto-a-ponto com uma "sub-interface" no outro lado, um mapeamento estático é necessário para mapear o DLCI local para o próximo salto IP.

SpokeA:

interface Serial0/0
ip address 172.16.0.18 255.255.255.240
encapsulation frame-relay
ip ospf network point-to-point
frame-relay map ip 172.16.0.17 110 broadcast
frame-relay interface-dlci 110
no frame-relay inverse-arp

SpokeB:

interface Serial0/0
ip address 172.16.0.34 255.255.255.240
encapsulation frame-relay
ip ospf network point-to-point
frame-relay map ip 172.16.0.33 201 broadcast
frame-relay interface-dlci 201
no frame-relay inverse-arp

Sub-interface
- Só interface DLCI local.
- Não há necessidade de mapeamento estático para o outro lado, porque é um ponto-a-ponto "sub-interface" e há apenas um DLCI no outro lado.

HUB:

interface Serial0/0
no ip address
encapsulation frame-relay
no frame-relay inverse-arp
!
interface Serial0/0.101 point-to-point
ip address 172.16.0.17 255.255.255.240
ip ospf network point-to-point
frame-relay interface-dlci 101
!
interface Serial0/0.102 point-to-point
ip address 172.16.0.33 255.255.255.240
ip ospf network point-to-point
frame-relay interface-dlci 102
!
interface Serial0/0.103 point-to-point
ip address 172.16.0.49 255.255.255.240
ip ospf network point-to-point
frame-relay interface-dlci 103

SpokeC:

interface Serial0/0
no ip address
encapsulation frame-relay
no frame-relay inverse-arp
!
interface Serial0/0.301 point-to-point
ip address 172.16.0.50 255.255.255.240
ip ospf network point-to-point
frame-relay interface-dlci 301
!! it doesn’t matter whether inverse ARP is configured or not
!!no frame-relay inverse-arp

Checar Conectividade

HUB:
HUB#ping 172.16.0.18
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.0.18, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/55/96 ms
HUB#ping 172.16.0.34
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.0.34, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 52/70/112 ms
HUB#ping 172.16.0.50
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.0.50, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/84/168 ms
HUB#

Ib) COM Inverse-ARP

Interface
- Quando usar uma "interface física" para terminar um ponto-a-ponto em PVC, com uma "sub-interface" no outro lado, e Inverse-ARP ativado, não há necessidade de um mapeamento estático.
Sub-interface
- Só interface DLCI local está configurado.
- Não há necessidade de mapeamento estático para o outro lado, porque é uma "sub-interface" ponto-a-ponto e há apenas um DLCI no outro lado.

II) O Ponto-Multiponto

IIa)SEM InverseARP

Interface
Com inverse ARP desabilitado deve-se definir o local de mapeamento estático DLCI (PVC) para o próximo salto de endereços IP, pois a interface termina mais de um PVC.

SpokeB:
interface Serial0 / 0
ip address 172.16.0.34 255.255.255.240
encapsulamento frame-relay
ip OSPF rede ponto-a-multiponto
frame-relay map ip 172.16.0.33 201 broadcast
frame-relay map ip 172.16.0.35 203 broadcast
não frame-relay-inverse arp

Sub-interface
Tal como acontece com as interfaces físicas, nas sub-interfaces você precisa definir mapeamento estático de interface local DLCI para IP remoto porque a sub-interface termina mais de um PVC.

HUB:
interface Serial0/0
no ip address
encapsulation frame-relay
no frame-relay inverse-arp
!
interface Serial0/0.102 multipoint
ip address 172.16.0.33 255.255.255.240
ip ospf network point-to-multipoint
frame-relay map ip 172.16.0.34 102 broadcast
frame-relay map ip 172.16.0.35 103 broadcast

SpokeC:
interface Serial0/0
no ip address
encapsulation frame-relay
no frame-relay inverse-arp
!
interface Serial0/0.300 multipoint
ip address 172.16.0.35 255.255.255.240
ip ospf network point-to-multipoint
frame-relay map ip 172.16.0.33 301 broadcast
frame-relay map ip 172.16.0.34 302 broadcast

Checar Conectividade

HUB:
HUB#sh frame map
Serial0/0.102 (up): ip 172.16.0.34 dlci 102(0×66,0×1860), static,
broadcast,
CISCO, status defined, active
Serial0/0.102 (up): ip 172.16.0.35 dlci 103(0×67,0×1870), static,
broadcast,
CISCO, status defined, active
Serial0/0.101 (up): point-to-point dlci, dlci 101(0×65,0×1850), broadcast
status defined, active
HUB#

HUB#sh ip route
…
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.16.0.32/28 is directly connected, Serial0/0.102
O 172.16.0.34/32 [110/64] via 172.16.0.34, 00:19:49, Serial0/0.102
O 172.16.0.35/32 [110/64] via 172.16.0.35, 00:19:49, Serial0/0.102
C 172.16.0.16/28 is directly connected, Serial0/0.101
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
O IA 10.10.0.1/32 [110/65] via 172.16.0.18, 00:19:49, Serial0/0.101
C 10.0.1.0/24 is directly connected, Loopback0
O IA 10.30.0.1/32 [110/65] via 172.16.0.35, 00:19:49, Serial0/0.102
O IA 10.20.0.1/32 [110/65] via 172.16.0.34, 00:19:49, Serial0/0.102
HUB#

HUB#ping 172.16.0.34
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.0.34, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 28/84/132 ms
HUB#ping 172.16.0.35
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.0.35, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 24/110/168 ms
HUB#ping
Protocol [ip]:
Target IP address: 10.20.0.1
Repeat count [5]:
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: 10.0.1.1
Type of service [0]:
Set DF bit in IP header? [no]:
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.20.0.1, timeout is 2 seconds:
Packet sent with a source address of 10.0.1.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/72/96 ms
HUB#

IIb)COM InverseARP

Interface
Quer se trate de uma sub-interface ou uma interface física com Inverse-ARP ativado com o Ponto-Multiponto, não é necessário mapear estaticamente locais DLCI's para os próximos saltos:
SpokeB:
interface Serial0/0
ip address 172.16.0.34 255.255.255.240
encapsulation frame-relay
ip ospf network point-to-multipoint
ip ospf priority 0
serial restart-delay 0
no dce-terminal-timing-enable
frame-relay interface-dlci 201
frame-relay interface-dlci 203

Sub-interface
- Inverse ARP irá descobrir que DLCI usar para atingir um determinado endereço IP adjacente, para isso aciona as mensagens LMI para enviar mensagens Inverse-ARP.
- Recomenda-se deasativar o Inverse-ARP no exame CCIE Lab, caso contrário, os roteadores não serão ligados conforme a topologia do exame. Em geral, dê uma particular atenção a configuração padrão e os parâmetros.

HUB:
interface Serial0/0
no ip address
encapsulation frame-relay
!
interface Serial0/0.102 multipoint
ip address 172.16.0.33 255.255.255.240
ip ospf network point-to-multipoint
frame-relay interface-dlci 102
frame-relay interface-dlci 103

SpokeC:
interface Serial0/0
no ip address
encapsulation frame-relay
!
interface Serial0/0.300 multipoint
ip address 172.16.0.35 255.255.255.240
ip ospf network point-to-multipoint
frame-relay interface-dlci 301
frame-relay interface-dlci 302

Checar Conectividade

HUB:
HUB(config-subif)#do sh frame map
Serial0/0.102 (up): ip 172.16.0.34 dlci 102(0×66,0×1860), dynamic,
broadcast,
CISCO, status defined, active
Serial0/0.102 (up): ip 172.16.0.35 dlci 103(0×67,0×1870), dynamic,
broadcast,
CISCO, status defined, active
Serial0/0.101 (up): point-to-point dlci, dlci 101(0×65,0×1850), broadcast
status defined, active
HUB(config-subif)#
HUB(config-subif)#do ping
Protocol [ip]:
Target IP address: 10.20.0.1
Repeat count [5]:
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: 10.0.1.1
Type of service [0]:
Set DF bit in IP header? [no]:
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.20.0.1, timeout is 2 seconds:
Packet sent with a source address of 10.0.1.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 44/80/156 ms
HUB(config-subif)#

SpokeB:
SpokeB(config-if)#do sh frame map
Serial0/0 (up): ip 172.16.0.33 dlci 201(0xC9,0×3090), dynamic,
broadcast,
CISCO, status defined, active
Serial0/0 (up): ip 172.16.0.35 dlci 203(0xCB,0×30B0), dynamic,
broadcast,, status defined, active
SpokeB(config-if)#

SpokeC:
SpokeC(config-subif)#do sh frame map
Serial0/0.300 (up): ip 172.16.0.33 dlci 301(0×12D,0×48D0), dynamic,
broadcast,
CISCO, status defined, active
Serial0/0.300 (up): ip 172.16.0.34 dlci 302(0×12E,0×48E0), dynamic,
broadcast,
CISCO, status defined, active
SpokeC(config-subif)#

Debugando o LMI:
HUB#
*Mar 1 08:55:48.173: Serial0/0(out): StEnq, myseq 152, yourseen 20, DTE up
*Mar 1 08:55:48.173: datagramstart = 0×7B6D434, datagramsize = 13
*Mar 1 08:55:48.177: FR encap = 0xFCF10309
*Mar 1 08:55:48.177: 00 75 01 01 01 03 02 98 14
*Mar 1 08:55:48.201:
*Mar 1 08:55:48.205: Serial0/0(in): Status, myseq 152, pak size 13
*Mar 1 08:55:48.205: RT IE 1, length 1, type 1
*Mar 1 08:55:48.209: KA IE 3, length 2, yourseq 21, myseq 152
*Mar 1 08:55:58.173: Serial0/0(out): StEnq, myseq 153, yourseen 21, DTE up
*Mar 1 08:55:58.173: datagramstart = 0×7B6D2F4, datagramsize = 13
*Mar 1 08:55:58.177: FR encap = 0xFCF10309
*Mar 1 08:55:58.177: 00 75 01 01 01 03 02 99 15
*Mar 1 08:55:58.185:
*Mar 1 08:55:58.213: Serial0/0(in): Status, myseq 153, pak size 13
*Mar 1 08:55:58.217: RT IE 1, length 1, type 1
*Mar 1 08:55:58.217: KA IE 3, length 2, yourseq 22, myseq 153
*Mar 1 08:56:08.173: Serial0/0(out): StEnq, myseq 154, yourseen 22, DTE up
*Mar 1 08:56:08.177: datagramstart = 0×7B6CDF4, datagramsize = 13
*Mar 1 08:56:08.177: FR encap = 0xFCF10309
*Mar 1 08:56:08.177: 00 75 01 01 01 03 02 9A 16
*Mar 1 08:56:08.185:
*Mar 1 08:56:08.221: Serial0/0(in): Status, myseq 154, pak size 37
*Mar 1 08:56:08.221: RT IE 1, length 1, type 0
*Mar 1 08:56:08.225: KA IE 3, length 2, yourseq 23, myseq 154
*Mar 1 08:56:08.225: PVC IE 0×7 , length 0×6 , dlci 101, status 0×2 , bw 0
*Mar 1 08:56:08.229: PVC IE 0×7 , length 0×6 , dlci 102, status 0×0 , bw 0
*Mar 1 08:56:08.229: PVC IE 0×7 , length 0×6 , dlci 103, status 0×2 , bw 0
*Mar 1 08:56:18.173: Serial0/0(out): StEnq, myseq 155, yourseen 23, DTE up
*Mar 1 08:56:18.173: datagramstart = 0×7B6D6B4, datagramsize = 13
*Mar 1 08:56:18.177: FR encap = 0xFCF10309
*Mar 1 08:56:18.177: 00 75 01 01 01 03 02 9B 17
*Mar 1 08:56:18.185: