Router ABR sumarizando no propaga la ruta por defecto
Fecha: 16 de marzo del
2023
Escenario
Este escenario originalmente se realizó en Packet
Tracer y era para estudiar la sumarización de rutas con OSPF, pero el
comportamiento
con una ruta por defecto que no era el esperado
hizo que se terminara realizando con equipos reales.
Este lab es casi una continuación del lab #107 de julio del 2014, de hecho, es el mismo pero con
el agregado de una ruta por defecto en un
router que trabajará como ASBR (router limítrofe
del sistema autónomo) y que la inyecta al resto del sistema OSPF. El router ABR
(router
de borde de área) la aprende y la propaga al
router que se encuentra en el área 0, y este la aprende como ruta por defecto.
Hasta aquí venimos bien, pero en el ABR queremos
sumarizar o resumir 7 redes en una sola ruta (para facilitar el caso son todas
contiguas)
y al hacerlo la ruta por defecto “desaparece” en
el router de backbone. Vamos y vemos…
Como en otros escenarios, este es parte de un
escenario real mas complejo y está simplificado para que sea mas “digerible”.
1.- Prueba en Packet
Tracer:
1.1.- Verificación
previa:
1.1.1.- En el router
RT-ABR:
RT-ABR#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 192.168.1.2
to network 0.0.0.0 (ruta por defecto vía RT-ASBR)
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, Vlan1000
C 192.168.1.0/24 is directly connected, Vlan1
C 192.168.2.0/24 is directly connected, Vlan2
C 192.168.3.0/24 is directly connected, Vlan3
C 192.168.4.0/24 is directly connected, Vlan4
C 192.168.5.0/24 is directly connected, Vlan5
C 192.168.6.0/24 is directly connected, Vlan6
C 192.168.7.0/24 is directly connected, Vlan7
O*E2 0.0.0.0/0 [110/1] via
192.168.1.2, 00:10:48, Vlan1
RT-ABR#
1.1.2.- En el router RT-Backbone:
RT-Backbone#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 (ruta por defecto vía RT-ABR)
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected,
FastEthernet0/0
O IA 192.168.1.0/24 [110/2] via
10.0.0.1, 00:00:19, FastEthernet0/0
O IA 192.168.2.0/24 [110/2] via
10.0.0.1, 00:00:19, FastEthernet0/0
O IA 192.168.3.0/24 [110/2] via
10.0.0.1, 00:00:19, FastEthernet0/0
O IA 192.168.4.0/24 [110/2] via
10.0.0.1, 00:00:19, FastEthernet0/0
O IA 192.168.5.0/24 [110/2] via
10.0.0.1, 00:00:19, FastEthernet0/0
O IA 192.168.6.0/24 [110/2] via
10.0.0.1, 00:00:19, FastEthernet0/0
O IA 192.168.7.0/24 [110/2] via
10.0.0.1, 00:00:19, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via
10.0.0.1, 00:00:19, FastEthernet0/0
RT-Backbone#
1.2.- Sumarizamos en RT-ABR:
Para sumarizar utilizamos la máscara /21 que
agrupa los bits en común entre las redes afectadas, en binario el 3er octeto sería:
1
2631
8426 8421 <- peso de bit en 3er octeto,
entonces 128+64+32+16+8=248
| | | |
| | | |
00000000 red 0 (no incluída en el escenario pero
entra en la máscara)
00000001 red 1
00000010 red 2
00000011 red 3
00000100 red 4
00000101 red 5
00000110 red 6
00000111 red 7
00001000 red 8 (queda fuera de la máscara, ver punto 2.7.)
|
| |
17
21 24 <- número de bit en la máscara
Resumiendo, la máscara agrupa a todos los bits en
común: en el 1er octeto forman 192, todos en el 2do octeto forman 168, los bits
en común
del 3ro forman 0, el resto de los bits que no
coinciden quedan fuera de la máscara y se representan con otro 0.
RT-ABR#conf t
Enter
configuration commands, one per line.
End with CNTL/Z.
RT-ABR(config)#router ospf 1
RT-ABR(config-router)#area 1 range 192.168.0.0 255.255.248.0
RT-ABR(config-router)#end
RT-ABR#
1.3.- Verificación posterior:
RT-Backbone#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 not
set (ya no hay mas ruta por
defecto)
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/0
O IA 192.168.0.0/21 [110/2] via
10.0.0.1, 00:00:31, FastEthernet0/0
RT-Backbone#
1.4.- Realizamos un debug
para verificar:
RT-Backbone#debug ip routing
IP routing
debugging is on
RT-Backbone#
RT: del
192.168.1.0 via 10.0.0.1, ospf metric [110/2]
RT: delete
network route to 192.168.1.0
RT: NET-RED 192.168.1.0/24
RT: del 192.168.2.0 via 10.0.0.1, ospf metric
[110/2]
RT: delete
network route to 192.168.2.0
RT: NET-RED 192.168.2.0/24
RT: del 192.168.3.0 via 10.0.0.1, ospf metric
[110/2]
RT: delete
network route to 192.168.3.0
RT: NET-RED 192.168.3.0/24
RT: del 192.168.4.0 via 10.0.0.1, ospf metric
[110/2]
RT: delete
network route to 192.168.4.0
RT: NET-RED 192.168.4.0/24
RT: del 192.168.5.0 via 10.0.0.1, ospf metric
[110/2]
RT: delete
network route to 192.168.5.0
RT: NET-RED 192.168.5.0/24
RT: del 192.168.6.0 via 10.0.0.1, ospf metric
[110/2]
RT: delete
network route to 192.168.6.0
RT: NET-RED 192.168.6.0/24
RT: del 192.168.7.0 via 10.0.0.1, ospf metric
[110/2]
RT: delete
network route to 192.168.7.0
RT: NET-RED 192.168.7.0/24
RT: del 0.0.0.0 via 10.0.0.1, ospf metric [110/1]
(aquí decide borrar la ruta por defecto)
RT: delete
network route to 0.0.0.0
RT: NET-RED
0.0.0.0/0
RT:
SET_LAST_RDB for 192.168.0.0/21
NEW rdb: via 10.0.0.1
RT: add 192.168.0.0/21 via 10.0.0.1, ospf
metric [110/2] (agrega la ruta sumarizada)
RT: NET-RED
192.168.0.0/21
RT-Backbone#
Al no comportarse de la manera esperada, ya que
la sumarización solo debería afectar a las 192.168.x.x y no a la ruta por
default,
decidimos realizar el escenario con equipos
reales para conpararlo con el Packet Tracer.
2.- Prueba con equipos
reales:
Armamos el escenario de la manera mas similar
posible, reemplazamos los switches intermedios por switches embebidos en los
Cisco 881
y capturamos en Wireshark los LSU (Link State
Updates) que el router ABR genere al momento de sumarizar.
2.1.- Verificación
previa:
2.1.1.- En el router ABR:
RT-ABR#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
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, H - NHRP, l - LISP
+ - replicated route, % - next hop
override
Gateway of
last resort is 192.168.1.2 to network 0.0.0.0
O*E2 0.0.0.0/0 [110/1] via 192.168.1.2, 19:16:23, Vlan1 (ruta por defecto aprendida del
ASBR)
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.0.0.0/24 is directly connected,
Vlan1000
L 10.0.0.1/32 is directly connected,
Vlan1000
192.168.1.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.1.0/24 is directly connected,
Vlan1
L 192.168.1.1/32 is directly connected,
Vlan1
192.168.2.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.2.0/24 is directly connected,
Vlan2
L 192.168.2.1/32 is directly connected,
Vlan2
192.168.3.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.3.0/24 is directly connected,
Vlan3
L 192.168.3.1/32 is directly connected,
Vlan3
192.168.4.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.4.0/24 is directly connected,
Vlan4
L 192.168.4.1/32 is directly connected,
Vlan4
192.168.5.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.5.0/24 is directly connected,
Vlan5
L 192.168.5.1/32 is directly connected,
Vlan5
192.168.6.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.6.0/24 is directly connected,
Vlan6
L 192.168.6.1/32 is directly connected,
Vlan6
192.168.7.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.7.0/24 is directly connected,
Vlan7
L 192.168.7.1/32 is directly connected,
Vlan7
RT-ABR#
2.1.2.-
En el router Backbone:
RT-Backbone#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
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, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is 10.0.0.1
to network 0.0.0.0 (ruta por defecto aprendida del ABR)
O*E2
0.0.0.0/0 [110/1] via 10.0.0.1, 00:02:00, Vlan1000
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.0.0.0/24 is directly connected,
Vlan1000
L 10.0.0.2/32 is directly connected,
Vlan1000
O IA 192.168.1.0/24 [110/2] via 10.0.0.1, 00:02:00, Vlan1000 (todas
las rutas a sumarizar)
O IA 192.168.2.0/24 [110/2] via 10.0.0.1, 00:02:00, Vlan1000
O IA 192.168.3.0/24 [110/2] via 10.0.0.1, 00:02:00, Vlan1000
O IA 192.168.4.0/24 [110/2] via 10.0.0.1, 00:02:00, Vlan1000
O IA 192.168.5.0/24 [110/2] via 10.0.0.1, 00:02:00, Vlan1000
O IA 192.168.6.0/24 [110/2] via 10.0.0.1, 00:02:00, Vlan1000
O IA 192.168.7.0/24 [110/2] via 10.0.0.1, 00:02:00, Vlan1000
RT-Backbone#
2.2.-
Activamos debug:
RT-ABR#debug ip ospf 1 events
OSPF events debugging is on for
process 1
RT-ABR#debug ip ospf 1 flood
OSPF flooding debugging is on for
process 1
RT-ABR#debug ip ospf 1 lsa
RT-ABR#debug ip ospf 1
lsa-generation
OSPF LSA generation debugging is on
for process 1
RT-ABR#
2.3.- Sumarizamos:
RT-ABR#conf t
Enter configuration commands, one per
line. End with CNTL/Z.
RT-ABR(config)#router ospf 1
RT-ABR(config-router)#area 1 range
192.168.0.0 255.255.248.0
RT-ABR(config-router)#end
RT-ABR#
2.4.- Verificamos en logs en RT-ABR:
Aquí se genera el
que será el paquete #3 en la captura de Wireshark:
Mar 17 08:17:55.584: OSPF-1 EVENT: Area
config: 'area 1 range 192.168.0.0 255.255.248.0'
Mar 17 08:17:55.584: OSPF-1 LSGEN:
Originate sum LSA 192.168.0.0 mask 255.255.248.0 into area 1 from range
Mar 17 08:17:55.584: OSPF-1 LSGEN: Build
sum 192.168.0.0, mask 255.255.248.0, type 3, age 0, seq 0x80000001
to area 0
Mar 17 08:17:55.584: OSPF-1 LSGEN:
MTID Metric Origin Topology Name
Mar 17
08:17:55.584: OSPF-1 LSGEN: 0
1 intra-area Base (ver las métricas en las capturas de Wireshark)
Mar 17 08:17:55.584: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.0.0 Adv rtr 192.168.7.1 Seq 80000001 to
10.0.0.2 retransmission list
Mar 17 08:17:55.584: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.0.0 Adv rtr 192.168.7.1 Seq 80000001 to flood
list
Mar 17 08:17:55.584: OSPF-1 FLOOD
Vl1000: Flooding update to 224.0.0.5 Area 0
Mar 17 08:17:55.584: OSPF-1 FLOOD
Vl1000: Send Type 3, LSID 192.168.0.0, Adv rtr 192.168.7.1, age 1, seq
0x80000001 (0)
Mar 17 08:17:55.584: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.0.0 Adv rtr 192.168.7.1 Seq 80000001 flood
list
Mar 17 08:17:55.584: OSPF-1 FLOOD
Vl1000: Stop flood timer
Aquí se genera el
que será el paquete #4 en la captura de Wireshark:
Mar 17 08:17:55.584: OSPF-1 LSGEN: Build
sum 192.168.7.0, mask 255.255.255.0, type 3, age 3600, seq 0x80000002 to
area 0
Mar 17 08:17:55.584: OSPF-1 LSGEN:
MTID Metric Origin Topology Name
Mar 17
08:17:55.584: OSPF-1 LSGEN: 0
16777215 Base (ver las métricas en las capturas de Wireshark)
Mar 17 08:17:55.584: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.7.0 Adv rtr 192.168.7.1 Seq 80000002 to
10.0.0.2 retransmission list
Mar 17 08:17:55.584: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.7.0 Adv rtr 192.168.7.1 Seq 80000002 to flood
list
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Start pacing timer 30 ms
Mar 17 08:17:55.587: OSPF-1 LSGEN: Build
sum 192.168.6.0, mask 255.255.255.0, type 3, age 3600, seq 0x80000002 to
area 0
Mar 17 08:17:55.587: OSPF-1 LSGEN:
MTID Metric Origin Topology Name
Mar 17 08:17:55.587: OSPF-1 LSGEN:
0 16777215 Base
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.6.0 Adv rtr 192.168.7.1 Seq 80000002 to
10.0.0.2 retransmission list
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.6.0 Adv rtr 192.168.7.1 Seq 80000002 to flood
list
Mar 17 08:17:55.587: OSPF-1 LSGEN: Build
sum 192.168.5.0, mask 255.255.255.0, type 3, age 3600, seq 0x80000002 to
area 0
Mar 17 08:17:55.587: OSPF-1 LSGEN:
MTID Metric Origin Topology Name
Mar 17 08:17:55.587: OSPF-1 LSGEN: 0 16777215 Base
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.5.0 Adv rtr 192.168.7.1 Seq 80000002 to
10.0.0.2 retransmission list
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.5.0 Adv rtr 192.168.7.1 Seq 80000002 to flood
list
Mar 17 08:17:55.587: OSPF-1 LSGEN: Build
sum 192.168.4.0, mask 255.255.255.0, type 3, age 3600, seq 0x80000002 to
area 0
Mar 17 08:17:55.587: OSPF-1 LSGEN:
MTID Metric Origin Topology Name
Mar 17 08:17:55.587: OSPF-1 LSGEN: 0 16777215 Base
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.4.0 Adv rtr 192.168.7.1 Seq 80000002 to
10.0.0.2 retransmission list
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.4.0 Adv rtr 192.168.7.1 Seq 80000002 to flood
list
Mar 17 08:17:55.587: OSPF-1 LSGEN: Build
sum 192.168.3.0, mask 255.255.255.0, type 3, age 3600, seq 0x80000002 to
area 0
Mar 17 08:17:55.587: OSPF-1 LSGEN:
MTID Metric Origin Topology Name
Mar 17 08:17:55.587: OSPF-1 LSGEN: 0 16777215 Base
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.3.0 Adv rtr 192.168.7.1 Seq 80000002 to
10.0.0.2 retransmission list
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.3.0 Adv rtr 192.168.7.1 Seq 80000002 to flood
list
Mar 17 08:17:55.587: OSPF-1 LSGEN: Build
sum 192.168.2.0, mask 255.255.255.0, type 3, age 3600, seq 0x80000002 to
area 0
Mar 17 08:17:55.587: OSPF-1 LSGEN:
MTID Metric Origin Topology Name
Mar 17 08:17:55.587: OSPF-1 LSGEN: 0 16777215 Base
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.2.0 Adv rtr 192.168.7.1 Seq 80000002 to
10.0.0.2 retransmission list
Mar 17 08:17:55.587: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.2.0 Adv rtr 192.168.7.1 Seq 80000002 to flood
list
Mar 17 08:17:55.587: OSPF-1 LSGEN: Build
sum 192.168.1.0, mask 255.255.255.0, type 3, age 3600, seq 0x80000002 to
area 0
Mar 17 08:17:55.587: OSPF-1 LSGEN:
MTID Metric Origin Topology Name
Mar 17 08:17:55.587: OSPF-1 LSGEN: 0 16777215 Base
Mar 17 08:17:55.591: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.1.0 Adv rtr 192.168.7.1 Seq 80000002 to
10.0.0.2 retransmission list
Mar 17 08:17:55.591: OSPF-1 FLOOD
Vl1000: Add Type 3 LSA ID 192.168.1.0 Adv rtr 192.168.7.1 Seq 80000002 to flood
list
Mar 17 08:17:55.591: OSPF-1 LSGEN: No
change in sum LSA 10.0.0.0, mask 255.255.255.0, type 3, age 1578, seq
0x80000023 to area 1
Mar 17 08:17:55.591: OSPF-1 LSGEN: No
change in sum LSA 192.168.1.2, mask 0.0.0.0, type 4, age 1578, seq 0x80000023
to area 0
Mar 17 08:17:55.619: OSPF-1 FLOOD
Vl1000: Flooding update to 224.0.0.5 Area 0
Mar 17 08:17:55.619: OSPF-1 FLOOD
Vl1000: Send Type 3, LSID 192.168.7.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002 (0)
Mar 17 08:17:55.619: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.7.0 Adv rtr 192.168.7.1 Seq 80000002 flood
list
Mar 17 08:17:55.619: OSPF-1 FLOOD
Vl1000: Send Type 3, LSID 192.168.6.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002 (1)
Mar 17 08:17:55.619: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.6.0 Adv rtr 192.168.7.1 Seq 80000002 flood
list
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Send Type 3, LSID 192.168.5.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002 (2)
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.5.0 Adv rtr 192.168.7.1 Seq 80000002 flood
list
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Send Type 3, LSID 192.168.4.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002 (3)
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.4.0 Adv rtr 192.168.7.1 Seq 80000002 flood
list
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Send Type 3, LSID 192.168.3.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002 (4)
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.3.0 Adv rtr 192.168.7.1 Seq 80000002 flood
list
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Send Type 3, LSID 192.168.2.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002 (5)
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.2.0 Adv rtr 192.168.7.1 Seq 80000002 flood
list
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Send Type 3, LSID 192.168.1.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002 (6)
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.1.0 Adv rtr 192.168.7.1 Seq 80000002 flood
list
Mar 17 08:17:55.622: OSPF-1 FLOOD
Vl1000: Stop flood timer
Aquí se procesa
el que será el paquete #6 en la captura de Wireshark:
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Received ACK from 10.0.0.2
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Rcv Ack Type 3, LSID 192.168.0.0, Adv rtr 192.168.7.1, age 1, seq
0x80000001
Mar 17 08:17:58.090: OSPF-1 FLOOD Vl1000:
Remove Type 3 LSA ID 192.168.0.0 Adv rtr 192.168.7.1 Seq 80000001 from 10.0.0.2
retransmission list
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Rcv Ack Type 3, LSID 192.168.7.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.7.0 Adv rtr 192.168.7.1 Seq 80000002 from
10.0.0.2 retransmission list
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Rcv Ack Type 3, LSID 192.168.6.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.6.0 Adv rtr 192.168.7.1 Seq 80000002 from
10.0.0.2 retransmission list
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Rcv Ack Type 3, LSID 192.168.5.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.5.0 Adv rtr 192.168.7.1 Seq 80000002 from
10.0.0.2 retransmission list
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Rcv Ack Type 3, LSID 192.168.4.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.4.0 Adv rtr 192.168.7.1 Seq 80000002 from
10.0.0.2 retransmission list
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Rcv Ack Type 3, LSID 192.168.3.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.3.0 Adv rtr 192.168.7.1 Seq 80000002 from
10.0.0.2 retransmission list
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Rcv Ack Type 3, LSID 192.168.2.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002
Mar 17 08:17:58.090: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.2.0 Adv rtr 192.168.7.1 Seq 80000002 from
10.0.0.2 retransmission list
Mar 17 08:17:58.093: OSPF-1 FLOOD
Vl1000: Rcv Ack Type 3, LSID 192.168.1.0, Adv rtr 192.168.7.1, age 3600, seq
0x80000002
Mar 17 08:17:58.093: OSPF-1 FLOOD
Vl1000: Remove Type 3 LSA ID 192.168.1.0 Adv rtr 192.168.7.1 Seq 80000002 from
10.0.0.2 retransmission list
RT-ABR#
2.5.- Verificamos en Wireshark:
No hace falta
ninguna conexión especial para analizar con Wireshark ya que todo el tráfico
OSPF es multicast (entiéndase broadcast) y se puede capturar
conectándonos a
un port cualquiera de la LAN 10.0.0.0/24. Detallaremos sólo los paquetes #3 y
#4 de los updates OSPF.
Frame 3: 90 bytes on wire (720 bits), 90 bytes captured (720 bits) on interface
\Device\NPF_{D518808F-A171-499C-852F-D3BCE1D0FEF2}, id 0
Ethernet II,
Src: Cisco_bf:76:c7 (70:6b:b9:bf:76:c7), Dst: IPv4mcast_05 (01:00:5e:00:00:05)
Internet
Protocol Version 4, Src: 10.0.0.1, Dst: 224.0.0.5
Open Shortest Path First
OSPF Header
LS Update Packet
Number of LSAs: 1
LSA-type 3 (Summary-LSA (IP network)),
len 28
.000 0000 0000 0001 = LS Age (seconds):
1
0... .... .... .... = Do Not Age
Flag: 0
Options: 0x22, (DC) Demand
Circuits, (E) External Routing
LS Type: Summary-LSA (IP network)
(3)
Link State ID:
192.168.0.0
Advertising Router: 192.168.7.1
Sequence Number: 0x80000001
Checksum: 0x7bec
Length: 28
Netmask: 255.255.248.0 (abarca
las redes sumarizadas, ver punto 1.2.)
TOS: 0
Metric: 1 (la
setea con el costo OSPF de la interface)
Frame 4: 258 bytes on wire (2064 bits), 258 bytes captured (2064 bits) on
interface \Device\NPF_{D518808F-A171-499C-852F-D3BCE1D0FEF2}, id 0
Ethernet II,
Src: Cisco_bf:76:c7 (70:6b:b9:bf:76:c7), Dst: IPv4mcast_05 (01:00:5e:00:00:05)
Internet
Protocol Version 4, Src: 10.0.0.1, Dst: 224.0.0.5
Open Shortest Path First
OSPF Header
LS
Update Packet
Number of LSAs: 7
LSA-type 3 (Summary-LSA (IP network)),
len 28
.000 1110 0001 0000 = LS Age
(seconds): 3600
0... .... .... .... = Do Not Age
Flag: 0
Options: 0x22, (DC) Demand
Circuits, (E) External Routing
LS Type: Summary-LSA (IP network)
(3)
Link State ID: 192.168.7.0
Advertising Router: 192.168.7.1
Sequence Number: 0x80000002
Checksum: 0x4515
Length: 28
Netmask: 255.255.255.0
TOS: 0
Metric: 16777215 (la
setea con métrica
infinita)
LSA-type 3 (Summary-LSA (IP network)), len 28
.000 1110 0001 0000 = LS Age
(seconds): 3600
0... .... .... .... = Do Not Age
Flag: 0
Options: 0x22, (DC) Demand
Circuits, (E) External Routing
LS Type: Summary-LSA (IP network)
(3)
Link State ID: 192.168.6.0
Advertising Router: 192.168.7.1
Sequence Number: 0x80000002
Checksum: 0x500b
Length: 28
Netmask: 255.255.255.0
TOS: 0
Metric: 16777215 (la setea con métrica
infinita)
LSA-type 3 (Summary-LSA (IP network)), len 28
.000 1110 0001 0000 = LS Age
(seconds): 3600
0... .... .... .... = Do Not Age Flag:
0
Options: 0x22, (DC) Demand
Circuits, (E) External Routing
LS Type: Summary-LSA (IP network)
(3)
Link State ID: 192.168.5.0
Advertising Router: 192.168.7.1
Sequence Number: 0x80000002
Checksum: 0x5b01
Length: 28
Netmask: 255.255.255.0
TOS: 0
Metric: 16777215
LSA-type 3 (Summary-LSA (IP network)),
len 28
.000 1110 0001 0000 = LS Age
(seconds): 3600
0... .... .... .... = Do Not Age
Flag: 0
Options: 0x22, (DC) Demand
Circuits, (E) External Routing
LS Type: Summary-LSA (IP network)
(3)
Link State ID: 192.168.4.0
Advertising Router: 192.168.7.1
Sequence Number: 0x80000002
Checksum: 0x66f6
Length: 28
Netmask: 255.255.255.0
TOS: 0
Metric: 16777215 (la setea con métrica
infinita)
LSA-type 3 (Summary-LSA (IP network)), len 28
.000 1110 0001 0000 = LS Age
(seconds): 3600
0... .... .... .... = Do Not Age
Flag: 0
Options: 0x22, (DC) Demand Circuits,
(E) External Routing
LS Type: Summary-LSA (IP network)
(3)
Link State ID: 192.168.3.0
Advertising Router: 192.168.7.1
Sequence Number: 0x80000002
Checksum: 0x71ec
Length: 28
Netmask: 255.255.255.0
TOS: 0
Metric: 16777215 (la setea con métrica
infinita)
LSA-type 3 (Summary-LSA (IP network)), len 28
.000 1110 0001 0000 = LS Age
(seconds): 3600
0... .... .... .... = Do Not Age
Flag: 0
Options: 0x22, (DC) Demand
Circuits, (E) External Routing
LS Type: Summary-LSA (IP network)
(3)
Link State ID: 192.168.2.0
Advertising Router: 192.168.7.1
Sequence Number: 0x80000002
Checksum: 0x7ce2
Length: 28
Netmask: 255.255.255.0
TOS: 0
Metric: 16777215 (la setea con métrica
infinita)
LSA-type 3 (Summary-LSA (IP network)), len 28
.000 1110 0001 0000 = LS Age
(seconds): 3600
0... .... .... .... = Do Not Age
Flag: 0
Options: 0x22, (DC) Demand
Circuits, (E) External Routing
LS Type: Summary-LSA (IP network)
(3)
Link State ID:
192.168.1.0
Advertising Router: 192.168.7.1
Sequence Number: 0x80000002
Checksum: 0x87d8
Length: 28
Netmask: 255.255.255.0
TOS: 0
Metric: 16777215 (la setea con métrica
infinita)
Detalle: podemos ver que la
red 192.168.0.0/24 no se incluye en este update porque no existe como tal en la
topología.
2.6.- Verificamos en
tabla de enrutamiento:
RT-Backbone#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
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, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is 10.0.0.1
to network 0.0.0.0
O*E2
0.0.0.0/0 [110/1] via 10.0.0.1, 00:02:40, Vlan1000
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.0.0.0/24 is directly connected,
Vlan1000
L 10.0.0.2/32 is directly connected,
Vlan1000
O IA 192.168.0.0/21 [110/2] via 10.0.0.1, 00:00:11, Vlan1000
RT-Backbone#
2.7.- Prueba de
agregado de una red que fuera de la sumarización:
RT-ABR#conf t
Enter configuration commands, one per
line. End with CNTL/Z.
RT-ABR(config)#vlan 8
RT-ABR(config-vlan)#exit
RT-ABR(config)#int vlan 8
RT-ABR(config-if)#ip add
192.168.8.1 255.255.255.0
RT-ABR(config-if)#exit
RT-ABR(config)#router ospf 1
RT-ABR(config-router)#network
192.168.8.0 0.0.0.255 area 1
RT-ABR(config-router)#end
RT-ABR#
2.8.- Verificamos:
RT-Backbone#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
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, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is 10.0.0.1 to
network 0.0.0.0
O*E2
0.0.0.0/0 [110/1] via 10.0.0.1, 19:36:10, Vlan1000
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.0.0.0/24 is directly connected,
Vlan1000
L 10.0.0.2/32 is directly connected,
Vlan1000
O IA 192.168.0.0/21 [110/2] via 10.0.0.1, 00:05:42, Vlan1000
O IA 192.168.8.0/24 [110/2] via 10.0.0.1, 00:00:07, Vlan1000
RT-Backbone#
3.- Volvamos a Packet Tracer
(y
solucionémoslo):
Agregamos el comando que sabemos que redistribuye
la ruta por defecto…
Lamentablemente Packet Tracer tiene un debug de
OSPF algo limitado y no podemos graficar el por qué de estos comportamientos.
3.1.- Generamos la
sumarización:
RT-ABR#conf t
Enter configuration
commands, one per line. End with CNTL/Z.
RT-ABR(config)#router ospf 1
RT-ABR(config-router)#default-information
originate (redistribuye la ruta por defecto)
RT-ABR(config-router)#end
RT-ABR#
3.2.- Verificamos con
debug en el router RT-Backbone:
RT-Backbone#debug ip routing
IP routing
debugging is on
RT-Backbone#
RT: SET_LAST_RDB
for 0.0.0.0/0
NEW rdb: via 10.0.0.1
RT: add 0.0.0.0/0 via 10.0.0.1, ospf metric
[110/1] (agrega la ruta por defecto)
RT: NET-RED 0.0.0.0/0
3.2.- Verificamos en la
tabla de enrutamiento en el router RT-Backbone:
RT-Backbone#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 (tenemos ruta por defecto !)
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected,
FastEthernet0/0
O IA 192.168.0.0/21 [110/2] via
10.0.0.1, 00:03:17, FastEthernet0/0
O*E2 0.0.0.0/0 [110/1] via
10.0.0.1, 00:00:10, FastEthernet0/0
RT-Backbone#
3.3.- Otro detalle y que no habíamos
mencionado, es que el router ASBR al estar dentro del área 1 no recibe la orden
de sumarizar y ve
las rutas tal cual se
publican en su vecino de zona 1 RT-ABR:
RT-ASBR#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 190.0.0.2 to network 0.0.0.0
10.0.0.0/24 is subnetted, 1 subnets
O IA 10.0.0.0 [110/2] via 192.168.1.1, 00:30:21,
FastEthernet0/0
190.0.0.0/24 is subnetted, 1 subnets
C 190.0.0.0 is directly connected,
FastEthernet0/1
C 192.168.1.0/24 is directly connected,
FastEthernet0/0
O 192.168.2.0/24 [110/2] via 192.168.1.1,
00:30:21, FastEthernet0/0
O 192.168.3.0/24 [110/2] via 192.168.1.1,
00:30:21, FastEthernet0/0
O 192.168.4.0/24 [110/2] via 192.168.1.1,
00:30:21, FastEthernet0/0
O 192.168.5.0/24 [110/2] via 192.168.1.1,
00:30:21, FastEthernet0/0
O 192.168.6.0/24 [110/2] via 192.168.1.1,
00:30:21, FastEthernet0/0
O 192.168.7.0/24 [110/2] via 192.168.1.1,
00:30:21, FastEthernet0/0
S* 0.0.0.0/0 [1/0] via 190.0.0.2
RT-ASBR#
4.- Resumen:
Cuando realizamos el laboratorio en el 2014 nos concentramos en el efecto de la
sumarización y no involucramos ninguna ruta por defecto,
tal como se explica en ese lab, se realizó con
equipos reales ya que en aquel entonces PT no soportaba esta función.
Aquí probamos con la versión 8.2.0.0162 y si bien
soporta sumarización OSPF, el comportamiento no es el esperado, aunque de
alguna manera
se puede “emparchar” y solucionar de manera
elegante y sin rutas estáticas.
Queda en claro que definitivamente la palabra
final la tienen los equipos, y ante más dudas, recurriremos a la versión óptima
para realizarlo.
(2023) Your
route is my route
Rosario,
Argentina