OSPF LAB - Stub/Totally Stub Area

We will consider the same OSPF LAB which we build and proceed after that for further route injection on each router and troubleshoot for various issue and see how it works.
For OSPF LAB building, refer OSPFLAB BUILDING

First, we will insert external route on router R7.
For external route, we can advertise default route with the help of command “default-information originate”.
OSPF won’t advertise a default route if you don’t already have it in your routing table. If you add the always keyword, it will advertise the default route even if you don’t have it in the routing table.

Let advertise default route on router R7
Note: This default route feature of OSPF is just demo , I will not configure in actual lab

configure terminal
router ospf 1
default-information originate always
exit
!
end
wr

Once you have advertised the default route, it will look like this on other routers, like on router R1:

R1#show ip ospf database | begin Type-5
                Type-5 AS External Link States
 
Link ID         ADV Router      Age         Seq#       Checksum Tag
0.0.0.0         7.7.7.7         688         0x80000001 0x00682E 1
R1#

So, Now let configure external network as EIGRP, and then we will advertise external route from EIGRP domain from Router R12.

Configuration for Router R12       
configure terminal
interface f1/0
ip address 192.168.127.0 255.255.255.254
no shut
exit
!
interface loopback0
ip address 12.12.12.12 255.255.255.255
!
interface loopback11
ip address 11.0.0.1 255.255.255.255
exit
!
interface loopback12
ip address 12.0.0.1 255.255.255.255
exit
!
interface loopback13
ip address 13.0.0.1 255.255.255.255
exit
!
interface loopback14
ip address 14.0.0.1 255.255.255.255
exit
!
interface loopback15
ip address 15.0.0.1 255.255.255.255
exit
!
interface loopback16
ip address 16.0.0.1 255.255.255.255
exit
!
interface loopback17
ip address 17.0.0.1 255.255.255.255
exit
!
interface loopback18
ip address 18.0.0.1 255.255.255.255
exit
!
interface loopback19
ip address 19.0.0.1 255.255.255.255
exit
!
interface loopback20
ip address 20.0.0.1 255.255.255.255
exit
!
router eigrp 12
no auto-summary
network 192.168.127.0 255.255.255.0
network 12.12.12.12 255.255.255.255
network 11.0.0.1 255.255.255.255
network 12.0.0.1 255.255.255.255
network 13.0.0.1 255.255.255.255
network 14.0.0.1 255.255.255.255
network 15.0.0.1 255.255.255.255
network 16.0.0.1 255.255.255.255
network 17.0.0.1 255.255.255.255
network 18.0.0.1 255.255.255.255
network 19.0.0.1 255.255.255.255
network 20.0.0.1 255.255.255.255
exit
!
end
wr

Configuration for Router R7
configure terminal
interface f1/0
ip address 192.168.127.1 255.255.255.254
no shut
exit
!
router eigrp 12
no auto-summary
network 192.168.127.0 255.255.255.0
redistribute ospf 1 metric 1 1 1 1 1
exit
!
router ospf 1
redistribute eigrp 12 subnets
!
end
wr

R7#
*Feb 26 22:32:03.955: %DUAL-5-NBRCHANGE: EIGRP-IPv4 12: Neighbor 192.168.127.0 (FastEthernet1/0) is up: new adjacency
R7#

Once you have advertised the eigrp route in ospf on router R7, it will look like this on other routers, like on router R1:

R1#show  ip ospf database | begin Type-5
                Type-5 AS External Link States
 
Link ID         ADV Router      Age         Seq#       Checksum Tag
0.0.0.0         7.7.7.7         1001        0x80000001 0x00682E 1
11.0.0.1        7.7.7.7         88          0x80000001 0x007BFC 0
12.0.0.1        7.7.7.7         88          0x80000001 0x006E09 0
12.12.12.12     7.7.7.7         250         0x80000001 0x00EA69 0
13.0.0.1        7.7.7.7         88          0x80000001 0x006115 0
14.0.0.1        7.7.7.7         87          0x80000001 0x005421 0
15.0.0.1        7.7.7.7         87          0x80000001 0x00472D 0
16.0.0.1        7.7.7.7         86          0x80000001 0x003A39 0
17.0.0.1        7.7.7.7         85          0x80000001 0x002D45 0
18.0.0.1        7.7.7.7         85          0x80000001 0x002051 0
19.0.0.1        7.7.7.7         85          0x80000001 0x00135D 0
20.0.0.1        7.7.7.7         250         0x80000001 0x000669 0
192.168.127.0   7.7.7.7         250         0x80000001 0x00E2B9 0
R1#

Ensure, Area 123 and Area 8 should not accept Type 3, 4, or 5 LSAs. Area 56 and Area 10 should not accept Type 4 or 5 LSAs. However, all areas should accept Type 7 LSA

As for Area 123 and Area 8, we don’t need Type 3, 4, and 5 LSA. For these  we know that we need to set the Area 123  and Area 8 as Totally Stub Area.

For Area 123
Router R1, R2 and R3 configuration
configure terminal
router ospf 1
area 123 stub no-summary
exit
!
end
wr 

For Area 8
Router R7 and R8 configuration
configure terminal
router ospf 1
area 8 stub no-summary
exit
!
end
wr

So, now if we look at the routing table of Area 123/Area 8, we will not see O IA and O E1/E2 route (no route for LSA Type 3, 4 and 5), instead we will see the summary default route for external and inter-area routes

R1#show ip route
Gateway of last resort is 192.168.13.1 to network 0.0.0.0
 
O*IA  0.0.0.0/0 [110/2] via 192.168.13.1, 00:12:49, GigabitEthernet0/0
      1.0.0.0/32 is subnetted, 1 subnets
C        1.1.1.1 is directly connected, Loopback0
      2.0.0.0/32 is subnetted, 1 subnets
O        2.2.2.2 [110/3] via 192.168.13.1, 00:12:44, GigabitEthernet0/0
      192.168.13.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.13.0/31 is directly connected, GigabitEthernet0/0
L        192.168.13.0/32 is directly connected, GigabitEthernet0/0
      192.168.23.0/31 is subnetted, 1 subnets
O        192.168.23.0 [110/2] via 192.168.13.1, 00:12:49, GigabitEthernet0/0
R1#
 
Also, in OSPF database, no Type 3, 4 and 5 database
R1#show ip ospf database
 
            OSPF Router with ID (1.1.1.1) (Process ID 1)
 
                Router Link States (Area 123)
 
Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         776         0x80000005 0x0064C1 2
2.2.2.2         2.2.2.2         774         0x80000004 0x000AFC 2
3.3.3.3         3.3.3.3         770         0x80000005 0x00868F 2
 
                Net Link States (Area 123)
 
Link ID         ADV Router      Age         Seq#       Checksum
192.168.13.1    3.3.3.3         775         0x80000003 0x00A601
192.168.23.1    3.3.3.3         774         0x80000003 0x006A2F
 
                Summary Net Link States (Area 123)
 
Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         3.3.3.3         780         0x80000001 0x0057DA
R1#

Also, for Area 56 and Area 10, we don’t need Type 4 and 5 LSAs. For these, we know  we need to set the Area 56 and Area 10 as Stub area.

For Area 56
Router R4, R5 and R6 configuration
configure terminal
router ospf 1
area 56 stub
exit
!
end
wr 

For Area 10
Router R9, R10 and R11 configuration
configure terminal
router ospf 1
area 10 stub
exit
!
end
wr

So, now if we look at the routing table of Area 56/Area 10, we will not see O E1/E2 route (no route for LSA Type 4 and 5), instead we will see the summary default route for external routes.

Ensure  all networks are reachable

R1#ping 12.0.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 12.0.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 68/108/140 ms
R1#
 
R10#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)
  1 192.168.109.0 36 msec 40 msec 28 msec
  2 192.168.79.0 24 msec 44 msec 44 msec
  3 192.168.127.0 72 msec 92 msec 72 msec
R10#
 
R8#ping 12.12.12.12
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 12.12.12.12, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/50/60 ms
R8#