Saturday, 10 November 2018

OSPF STUB, Totally stubby, NSSA, Totally NSSA and (configuration)




OSPF STUBS

OSPF stubs allow the OSPF routers in an area to use default routes for forwarding packets to Area Border Routers (ABRs), rather than more specific routes. OSPF stubs reduce memory consumption and CPU processing time on the routers inside the area because the routers in that area can have fewer LSAs in their LSDBs.

If you configure a stub area in will block all type 5 external LSAs (E1 and E2 routes).  All the prefixes you redistributed into OSPF from another routing protocol are not welcome in the stub area. Default routes are advertised into stub area by the ABR. All OSPF routers in stub area must be configured as stub.

In short: OSPF stub allow the routers in an area to use default route for forwarding packets to ABR rather than more specific routes.

OSPF has special area types called stub areas:

  • Stub
  • Totally Stubby
  • Not-So-Stubby Area (NSSA)
  • Totally Not So Stubby Area (Totally NSSA)


Stub Area Rules:
  1. In the OSPF Stub area there should not be an ASBR.
  2. The OSPF Stub area should not be Area 0.
  3. No virtual link must be passing through that area.
  4. All routers in that area must be configure as stub routers.

Stub area is isolated area that does not receive External LSA. Routers in Stub areas do not receive type 4 and type 5 LSAs it is replaced by a default route to external autonomous system advertised by the area border router (ABR) Stub area can have type 1, 2, and 3 OSPF LSAs.
  
 Totally stubby area External LSAs are stopped (E1 and E2) and summary LSAs are stopped (OIA routes). Replaced by a default routes to other areas advertised by the ABR. Totally stubs is reduces the routing table to a minimum. This is a Cisco proprietary feature.


NSSA breaks stub area rules. NSSA area creates a special type of link-state advertisement (LSA) known as type 7, type 7 LSAs is only exist in NSSA area. An NSSA autonomous system boundary router (ASBR) generates this LSA and an NSSA area border router (ABR) translates it into a type 5 LSA, ABR send default routes into NSSA instead of external routes from other ASBR.

Totally NSSAs are similar to totally stubby areas, with the exception that the routers that are internal to the totally NSSAs need to have no knowledge of subnets outside of the area (with the exception of the routes injected by the NSSA ASBR)
Stub configuration:


Topology:


GOAL:
  • configure the topology and advertise the interfaces as per diagram.
  • configure ospf as per the diagram and redistribute RIP routes in to OSPF on R4.
  • configure area 10 to stop LSA 5 and LSA 4.
  • make sure that the area 10 routers still able to reach the external routes.


R1#show ip interface brief

Interface              IP-Address      OK? Method Status              Protocol
FastEthernet0/0      10.1.1.1        YES manual up                     up
Serial3/0                   1.1.1.1         YES manual up                    up
Loopback0              11.0.0.1        YES manual up                    up
Loopback1              11.0.1.1        YES manual up                    up
Loopback2              11.0.2.1        YES manual up                    up
Loopback3              11.0.3.1        YES manual up                    up




R2#show ip interface brief

Interface              IP-Address      OK? Method Status                Protocol
FastEthernet0/0     20.1.1.1        YES manual up                    up
Serial3/0                  1.1.1.2         YES manual up                    up
Serial3/1                  2.1.1.1         YES manual up                    up
Loopback0             12.0.0.1        YES manual up                    up
Loopback1             12.0.1.1        YES manual up                    up
Loopback2             12.0.2.1        YES manual up                    up
Loopback3             12.0.3.1        YES manual up                    up




R3#show ip interface brief

Interface              IP-Address      OK? Method Status                Protocol
FastEthernet0/0       30.1.1.1        YES manual up                    up
Serial3/1                   2.1.1.2         YES manual up                    up
Serial3/2                   3.1.1.1         YES manual up                    up
Loopback0              13.0.0.1        YES manual up                    up
Loopback1              13.0.1.1        YES manual up                    up
Loopback2              13.0.2.1        YES manual up                    up
Loopback3              13.0.3.1        YES manual up                    up




R4#show ip interface brief

Interface              IP-Address      OK? Method Status                Protocol
FastEthernet0/0        40.1.1.1        YES manual up                    up
Serial3/2                    3.1.1.2         YES manual up                    up
Loopback0              14.0.0.1        YES manual up                    up
Loopback1              14.0.1.1        YES manual up                    up
Loopback2              14.0.2.1        YES manual up                    up
Loopback3              14.0.3.1        YES manual up                    up


R1(config)#router ospf 1
R1(config-router)# network 11.0.0.0 0.255.255.255 area 10
R1(config-router)#network 1.0.0.0 0.255.255.255 area 10
R1(config-router)#network 10.0.0.0 0.255.255.255 area 10


R2(config)#router ospf 1
R2(config-router)#network 1.0.0.0 0.255.255.255 area 10
R2(config-router)#network 2.0.0.0 0.255.255.255 area 0
R2(config-router)#network 20.0.0.0 0.255.255.255 area 0
R2(config-router)#network 12.0.0.0 0.255.255.255 area 0
R2(config-router)#end


R3(config)#router ospf 1
R3(config-router)#network 30.0.0.0 0.255.255.255 area 0
R3(config-router)#network 13.0.0.0 0.255.255.255 area 0
R3(config-router)#network 2.0.0.0 0.255.255.255 area 0
R3(config-router)#network 3.0.0.0 0.255.255.255 area 20

R4(config)#router rip
R4(config-router)#version 2
R4(config-router)#network 14.0.0.0
R4(config-router)#no auto-summary
R4(config-router)#end

R4(config)#router ospf 1
R4(config-router)#network 3.0.0.0 0.255.255.255 area 20
R4(config-router)#network 40.0.0.0 0.255.255.255 area 20
R4(config-router)#redistribute rip subnets
R4(config-router)#end

R1#show ip route ospf
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 not set

O IA  2.0.0.0/8 [110/128] via 1.1.1.2, 00:06:24, Serial3/0
O IA  3.0.0.0/8 [110/192] via 1.1.1.2, 00:06:24, Serial3/0
      12.0.0.0/32 is subnetted, 4 subnets
O IA     12.0.0.1 [110/65] via 1.1.1.2, 00:02:08, Serial3/0
O IA     12.0.1.1 [110/65] via 1.1.1.2, 00:02:08, Serial3/0
O IA     12.0.2.1 [110/65] via 1.1.1.2, 00:02:08, Serial3/0
O IA     12.0.3.1 [110/65] via 1.1.1.2, 00:02:08, Serial3/0
      13.0.0.0/32 is subnetted, 4 subnets
O IA     13.0.0.1 [110/129] via 1.1.1.2, 00:00:28, Serial3/0
O IA     13.0.1.1 [110/129] via 1.1.1.2, 00:00:28, Serial3/0
O IA     13.0.2.1 [110/129] via 1.1.1.2, 00:00:28, Serial3/0
O IA     13.0.3.1 [110/129] via 1.1.1.2, 00:00:28, Serial3/0
      14.0.0.0/24 is subnetted, 4 subnets
O E2     14.0.0.0 [110/20] via 1.1.1.2, 00:04:59, Serial3/0
O E2     14.0.1.0 [110/20] via 1.1.1.2, 00:04:59, Serial3/0
O E2     14.0.2.0 [110/20] via 1.1.1.2, 00:04:59, Serial3/0
O E2     14.0.3.0 [110/20] via 1.1.1.2, 00:04:59, Serial3/0
O IA  20.0.0.0/8 [110/65] via 1.1.1.2, 00:06:24, Serial3/0
O IA  30.0.0.0/8 [110/129] via 1.1.1.2, 00:06:24, Serial3/0

R2#show ip route ospf
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 not set

O IA  3.0.0.0/8 [110/128] via 2.1.1.2, 00:07:04, Serial3/1
O     10.0.0.0/8 [110/65] via 1.1.1.1, 00:06:54, Serial3/0
      11.0.0.0/32 is subnetted, 4 subnets
O        11.0.0.1 [110/65] via 1.1.1.1, 00:03:54, Serial3/0
O        11.0.1.1 [110/65] via 1.1.1.1, 00:03:54, Serial3/0
O        11.0.2.1 [110/65] via 1.1.1.1, 00:03:54, Serial3/0
O        11.0.3.1 [110/65] via 1.1.1.1, 00:03:54, Serial3/0
      13.0.0.0/32 is subnetted, 4 subnets
O        13.0.0.1 [110/65] via 2.1.1.2, 00:01:04, Serial3/1
O        13.0.1.1 [110/65] via 2.1.1.2, 00:01:04, Serial3/1
O        13.0.2.1 [110/65] via 2.1.1.2, 00:01:04, Serial3/1
O        13.0.3.1 [110/65] via 2.1.1.2, 00:01:04, Serial3/1
      14.0.0.0/24 is subnetted, 4 subnets
O E2     14.0.0.0 [110/20] via 2.1.1.2, 00:05:34, Serial3/1
O E2     14.0.1.0 [110/20] via 2.1.1.2, 00:05:34, Serial3/1
O E2     14.0.2.0 [110/20] via 2.1.1.2, 00:05:34, Serial3/1
O E2     14.0.3.0 [110/20] via 2.1.1.2, 00:05:34, Serial3/1
O     30.0.0.0/8 [110/65] via 2.1.1.2, 00:07:04, Serial3/1

R2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
13.0.3.1          0   FULL/  -        00:00:39    2.1.1.2         Serial3/1
11.0.3.1          0   FULL/  -        00:00:37    1.1.1.1         Serial3/0

R1#traceroute 14.0.0.1
Type escape sequence to abort.
Tracing the route to 14.0.0.1
VRF info: (vrf in name/id, vrf out name/id)
  1 1.1.1.2 36 msec 36 msec 32 msec
  2 2.1.1.2 124 msec 128 msec 144 msec
  3 3.1.1.2 132 msec 92 msec 108 msec

we configure area 10 as stub, ensure that no external routes enter in to area 10.


R1(config)#router ospf 1

R1(config-router)#area 10 stub


R2(config)#router ospf 1

R2(config-router)#area 10 stub

R2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
13.0.3.1          0   FULL/  -        00:00:31    2.1.1.2         Serial3/1
11.0.3.1          0   FULL/  -        00:00:34    1.1.1.1         Serial3/0

R1#show ip route ospf
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 1.1.1.2 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/65] via 1.1.1.2, 00:02:22, Serial3/0
O IA  2.0.0.0/8 [110/128] via 1.1.1.2, 00:02:22, Serial3/0
O IA  3.0.0.0/8 [110/192] via 1.1.1.2, 00:02:22, Serial3/0
      12.0.0.0/32 is subnetted, 4 subnets
O IA     12.0.0.1 [110/65] via 1.1.1.2, 00:02:22, Serial3/0
O IA     12.0.1.1 [110/65] via 1.1.1.2, 00:02:22, Serial3/0
O IA     12.0.2.1 [110/65] via 1.1.1.2, 00:02:22, Serial3/0
O IA     12.0.3.1 [110/65] via 1.1.1.2, 00:02:22, Serial3/0
      13.0.0.0/32 is subnetted, 4 subnets
O IA     13.0.0.1 [110/129] via 1.1.1.2, 00:02:22, Serial3/0
O IA     13.0.1.1 [110/129] via 1.1.1.2, 00:02:22, Serial3/0
O IA     13.0.2.1 [110/129] via 1.1.1.2, 00:02:22, Serial3/0
O IA     13.0.3.1 [110/129] via 1.1.1.2, 00:02:22, Serial3/0
O IA  20.0.0.0/8 [110/65] via 1.1.1.2, 00:02:22, Serial3/0
O IA  30.0.0.0/8 [110/129] via 1.1.1.2, 00:02:22, Serial3/0

R1#ping 14.0.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 14.0.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 80/90/100 ms


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