Pruebas de elección de ruta por defecto
en OSPF
Fecha: 1 y 2 de septiembre del 2016
Escenario
En caso de tener un router de borde con dos ISP y dos rutas por defecto, se puede decidir (o forzar) el OSPF
de alguna manera, para que se pueda elegir una ruta por defecto en particular y la otra esté en failover ?
Verificación inicial
Gateway#sh
ip route
Codes: C - connected, S - static, I - IGRP, R -
RIP, M - mobile, B - BGP
D
- EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1
- OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
*
- candidate default, U - per-user static route, o - ODR
P
- periodic downloaded static route
Gateway of last resort is 10.0.0.1 to network 0.0.0.0
10.0.0.0/30 is subnetted, 2 subnets
C
10.0.0.0 is directly connected, Ethernet0/0/0
C
10.0.0.4 is directly connected, Ethernet0/1/0
C
192.168.1.0/24 is directly connected, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via 10.0.0.1, 00:02:04, Ethernet0/0/0
[110/1] via 10.0.0.5, 00:02:04, Ethernet0/1/0
Gateway#
Pero si ISP_2 levantara (o levantase) antes que ISP_1…
Gateway#sh
ip route
Codes: C - connected, S - static, I - IGRP, R -
RIP, M - mobile, B - BGP
D
- EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1
- OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
*
- candidate default, U - per-user static route, o - ODR
P -
periodic downloaded static route
Gateway of last resort is 10.0.0.5 to network 0.0.0.0
10.0.0.0/30 is subnetted, 2 subnets
C
10.0.0.0 is directly connected, Ethernet0/0/0
C
10.0.0.4 is directly connected, Ethernet0/1/0
C
192.168.1.0/24 is directly connected, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via 10.0.0.5, 00:06:29, Ethernet0/1/0
[110/1] via 10.0.0.1, 00:02:20, Ethernet0/0/0
Gateway#
Primer prueba: modificamos la AD de la ruta por defecto con un valor mayor (20).
ISP_1(config)#ip route 0.0.0.0 0.0.0.0
200.45.0.1 20
Verifcación:
ISP_1#sh
ip route
Codes: L - local, C - connected, S - static, R
- RIP, M - mobile, B - BGP
D
- EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1
- OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
*
- candidate default, U - per-user static route, o - ODR
P
- periodic downloaded static route
Gateway of last resort is 200.45.0.1 to network
0.0.0.0
10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C
10.0.0.0/30 is directly connected, GigabitEthernet0/0
L 10.0.0.1/32 is directly connected,
GigabitEthernet0/0
O 10.0.0.4/30 [110/11] via 10.0.0.2, 00:03:40, GigabitEthernet0/0
O 192.168.1.0/24 [110/2] via 10.0.0.2, 00:03:40, GigabitEthernet0/0
200.45.0.0/24 is variably subnetted, 2 subnets, 2 masks
C 200.45.0.0/29 is directly connected,
GigabitEthernet0/1
L
200.45.0.6/32 is directly connected, GigabitEthernet0/1
S* 0.0.0.0/0 [20/0] via 200.45.0.1
ISP_1#
Gateway#clear ip ospf process (se
reinicia OSPF para que ambas rutas se aprendan al mismo tiempo)
Reset ALL OSPF processes? [no]: yes
00:04:07: %OSPF-5-ADJCHG: Process 1, Nbr
10.0.0.1 on Ethernet0/0/0 from FULL to DOWN, Neighbor Down: Adjacency forced to
reset
00:04:07: %OSPF-5-ADJCHG: Process 1, Nbr
10.0.0.1 on Ethernet0/0/0 from FULL to DOWN, Neighbor Down: Interface down or
detached
00:04:07: %OSPF-5-ADJCHG: Process 1, Nbr
10.0.0.5 on Ethernet0/1/0 from FULL to DOWN, Neighbor Down: Adjacency forced to
reset
00:04:07: %OSPF-5-ADJCHG: Process 1, Nbr
10.0.0.5 on Ethernet0/1/0 from FULL to DOWN, Neighbor Down: Interface down or
detached
00:04:15: %OSPF-5-ADJCHG: Process 1, Nbr
10.0.0.1 on Ethernet0/0/0 from LOADING to FULL, Loading Done
00:04:15: %OSPF-5-ADJCHG: Process 1, Nbr
10.0.0.5 on Ethernet0/1/0 from LOADING to FULL, Loading Done
Gateway#sh
ip route
Codes: C - connected, S - static, I - IGRP, R -
RIP, M - mobile, B - BGP
D
- EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1
- OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
*
- candidate default, U - per-user static route, o - ODR
P
- periodic downloaded static route
Gateway of last resort is 10.0.0.1 to network
0.0.0.0
10.0.0.0/30 is subnetted, 2 subnets
C
10.0.0.0 is directly connected, Ethernet0/0/0
C
10.0.0.4 is directly connected, Ethernet0/1/0
C
192.168.1.0/24 is directly connected, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via 10.0.0.1, 00:03:08, Ethernet0/0/0 (la AD no cambió a 20)
[110/1] via 10.0.0.5, 00:03:08, Ethernet0/1/0
Gateway#
Las rutas externas se incluyen en dos categorías, tipo externo 1 y tipo externo 2. La diferencia entre ellas es la forma en que se calcula
el costo (métrica) de la ruta.
El costo de una ruta tipo 2 es siempre el costo externo, independientemente del costo interno para alcanzar dicha ruta.
A menos que se indique lo contrario, el tipo externo predeterminado que se especifica para las rutas externas es el tipo 2.
Fuente: http://www.cisco.com/cisco/web/support/LA/7/73/73214_1.html#t33
Segunda prueba: modificamos el costo OSPF en la inteface Gi0/0 de ISP_1.
ISP_1(config)#interface GigabitEthernet0/0
ISP_1(config-if)#ip ospf cost 10
ISP_1(config-if)#
Tercer prueba (con equipos reales):
Un costo tipo 1 es la suma del costo externo y del costo interno que se utilizó para alcanzar dicha ruta. Una ruta tipo 1 siempre es preferible
sobre una ruta tipo 2 para el mismo destino.
Fuente: http://www.cisco.com/cisco/web/support/LA/7/73/73214_1.html#t33
La configuración es similar a ISP_1 salvo el siguiente comando no soportado por Packet Tracer.
ISP_1(config-router)#default-information originate metric-type 1 (por default sería tipo 2 (como vimos no agrega costos OSPF))
ISP_1(config-router)#
Verificamos cuando falla ISP_2:
Gateway#sh
ip route
Codes: C - connected, S - static, R - RIP, M -
mobile, B - BGP
D
- EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1
- OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1
- OSPF external type 1, E2 - OSPF external type 2
i
- IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate
default, U - per-user static route
o
- ODR, P - periodic downloaded static route
Gateway of last resort is 10.0.0.1 to network
0.0.0.0
10.0.0.0/30 is subnetted, 1 subnets
C
10.0.0.0 is directly connected, FastEthernet0/1
C
192.168.1.0/24 is directly connected, FastEthernet0/0
O*E1 0.0.0.0/0 [110/2] via 10.0.0.1, 00:00:12,
FastEthernet0/1 (costo=1 de la ruta estática + costo=1 de la interface
local)
Gateway#
Cuarta prueba (la mas compleja, por lo tanto la preferida):
Eliminamos ISP_1 del proceso 1 de OSPF y lo agregamos en un nuevo proceso pero con distancia administrativa 120
(este número se utilizó sólo porque es mayor a 110, nada que ver con RIP).
Gateway(config)#router ospf 1
Gateway(config-router)#distance 120 (modificamos
mayor a 110)
Gateway(config-router)#no network 10.0.0.4 0.0.0.3 area 0 (eliminamos ISP_2 del proceso)
00:01:58: %OSPF-5-ADJCHG: Process 1, Nbr
10.0.0.5 on Ethernet0/1/0 from FULL to DOWN, Neighbor Down: Interface down or
detached
Gateway(config-router)#exit
Gateway(config)#router ospf 2
Gateway(config-router)#net 10.0.0.4 0.0.0.3 area 0
Gateway(config-router)#net 192.168.1.0 0.0.0.255 area 0
00:02:21: %OSPF-5-ADJCHG: Process 2, Nbr
10.0.0.5 on Ethernet0/1/0 from LOADING to FULL, Loading Done
Gateway(config-router)#end
Gateway#clear
ip ospf process
Reset ALL OSPF processes? [no]: yes
00:02:31: %OSPF-5-ADJCHG: Process 1, Nbr
10.0.0.1 on Ethernet0/0/0 from FULL to DOWN, Neighbor Down: Adjacency forced to
reset
00:02:31: %OSPF-5-ADJCHG: Process 1, Nbr
10.0.0.1 on Ethernet0/0/0 from FULL to DOWN, Neighbor Down: Interface down or
detached
00:02:31: %OSPF-5-ADJCHG: Process 2, Nbr
10.0.0.5 on Ethernet0/1/0 from FULL to DOWN, Neighbor Down: Adjacency forced to
reset
00:02:31: %OSPF-5-ADJCHG: Process 2, Nbr
10.0.0.5 on Ethernet0/1/0 from FULL to DOWN, Neighbor Down: Interface down or
detached
00:02:40: %OSPF-5-ADJCHG: Process 2, Nbr 10.0.0.5 on Ethernet0/1/0 from LOADING to FULL, Loading Done
00:02:45: %OSPF-5-ADJCHG: Process 1, Nbr 10.0.0.1 on Ethernet0/0/0 from LOADING to FULL, Loading Done
Verificación:
Gateway#sh
ip route
Codes: C - connected, S - static, I - IGRP, R -
RIP, M - mobile, B - BGP
D
- EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1
- OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
*
- candidate default, U - per-user static route, o - ODR
P
- periodic downloaded static route
Gateway of last resort is 10.0.0.5 to network 0.0.0.0
10.0.0.0/30 is subnetted, 2 subnets
C
10.0.0.0 is directly connected, Ethernet0/0/0
C
10.0.0.4 is directly connected, Ethernet0/1/0
C
192.168.1.0/24 is directly connected, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via 10.0.0.5, 00:01:53, Ethernet0/1/0
Gateway#
Verificamos cuando falla ISP_2:
Gateway#sh
ip route
Codes: C - connected, S - static, I - IGRP, R -
RIP, M - mobile, B - BGP
D
- EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1
- OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
*
- candidate default, U - per-user static route, o - ODR
P
- periodic downloaded static route
Gateway of last resort is 10.0.0.1 to network 0.0.0.0
10.0.0.0/30 is subnetted, 2 subnets
C
10.0.0.0 is directly connected, Ethernet0/0/0
C
10.0.0.4 is directly connected, Ethernet0/1/0
C
192.168.1.0/24 is directly connected, FastEthernet0/0
O*E2 0.0.0.0/0 [120/1] via 10.0.0.1, 00:03:09, Ethernet0/0/0
Gateway#
Se recupera ISP_2:
Gateway#sh
ip route
Codes: C - connected, S - static, I - IGRP, R -
RIP, M - mobile, B - BGP
D -
EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1
- OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
*
- candidate default, U - per-user static route, o - ODR
P
- periodic downloaded static route
Gateway of last resort is 10.0.0.5 to network 0.0.0.0
10.0.0.0/30 is subnetted, 2 subnets
C
10.0.0.0 is directly connected, Ethernet0/0/0
C
10.0.0.4 is directly connected, Ethernet0/1/0
C
192.168.1.0/24 is directly connected, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via 10.0.0.5, 00:00:06, Ethernet0/1/0
Gateway#
Configuración de equipos (con prueba 4):
Internet#sh runn (sólo lo relevante al escenario)
Building configuration...
!
hostname Internet
!
interface FastEthernet0/0
ip
address 200.0.0.6 255.255.255.248
!
interface Ethernet0/0/0
ip
address 200.45.0.1 255.255.255.248
!
interface Ethernet0/1/0
ip
address 190.0.0.1 255.255.255.248
!
end
Internet#
ISP_1# sh runn (sólo lo
relevante al escenario)
Building configuration...
!
hostname ISP_1
!
interface GigabitEthernet0/0
ip
address 10.0.0.1 255.255.255.252
ip nat
inside
!
interface GigabitEthernet0/1
ip
address 200.45.0.6 255.255.255.248
ip nat
outside
!
router ospf 1
router-id 10.0.0.1
log-adjacency-changes
network
10.0.0.0 0.0.0.3 area 0
default-information originate
!
ip nat inside source list 10 interface
GigabitEthernet0/1 overload
ip classless
ip route 0.0.0.0 0.0.0.0 200.45.0.1
!
access-list 10 permit 192.168.1.0 0.0.0.255
!
end
ISP_1#
ISP_2# sh runn (sólo lo relevante al escenario)
Building configuration...
!
hostname ISP_2
!
interface GigabitEthernet0/0
ip
address 10.0.0.5 255.255.255.252
ip nat
inside
!
interface GigabitEthernet0/1
ip
address 190.0.0.6 255.255.255.248
ip nat
outside
!
router ospf 1
router-id 10.0.0.5
log-adjacency-changes
network
10.0.0.0 0.0.0.3 area 0
network
10.0.0.4 0.0.0.3 area 0
default-information
originate
!
ip nat inside source list 10 interface
GigabitEthernet0/1 overload
ip classless
ip route 0.0.0.0 0.0.0.0 190.0.0.1
!
access-list 10 permit 192.168.1.0 0.0.0.255
!
end
ISP_2#
Gateway# sh runn (sólo lo relevante al escenario)
Building configuration...
!
hostname Gateway
!
interface FastEthernet0/0
ip
address 192.168.1.1 255.255.255.0
!
interface Ethernet0/0/0
ip
address 10.0.0.2 255.255.255.252
!
interface Ethernet0/1/0
ip
address 10.0.0.6 255.255.255.252
!
router ospf 1
log-adjacency-changes
network
10.0.0.0 0.0.0.3 area 0
network
192.168.1.0 0.0.0.255 area 0
distance
120
!
router ospf 2
log-adjacency-changes
network
10.0.0.4 0.0.0.3 area 0
network
192.168.1.0 0.0.0.255 area 0
!
ip classless
!
end
Gateway#
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