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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