Configuring Default route in OSPF:
·
Let
me take a small topology to configure default route in OSPF
R1------S1/0-------------s1/0----R2----s1/1--------------s1/1------R3
10.1.12.1--------------10.1.12.2-----10.1.13.2--------------10.1.13.3
·
Configured
OSPF between R1-R2
·
Trying
to configure in R2, so that it will generate default route towards R1
R1(config-router)#do show run | sec router
router
ospf 1
log-adjacency-changes
network 10.1.12.1 0.0.0.0 area 0
R1(config-router)#
R1(config-router)#do show 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 not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.12.0 is directly connected,
Serial1/0
R1(config-router)#
R2(config-router)#do show run | sec router
router
ospf 1
log-adjacency-changes
network 10.1.12.2 0.0.0.0 area 0
R2(config-router)#
R2(config-router)#do
show 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 not set
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 2 subnets
C 10.1.13.0 is directly connected,
Serial1/1
C 10.1.12.0 is directly connected, Serial1/0
R2(config-router)#
·
Let
me configure a default route in R2, towards R1:
R2(config-router)#default-information originate
R1(config-router)#do show 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 not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.12.0 is directly connected,
Serial1/0
R1(config-router)#
Observation:
·
R1
don’t see default route in its routing table
·
This
is because R2 doesn’t have any default route in its routing table.
·
If
we want R2 to generate a default route irrespective of default route in its
routing table, then we need to use always keyword
R2(config-router)#default-information originate always
R1(config-router)#do show 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 10.1.12.2 to
network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.12.0 is directly connected,
Serial1/0
O*E2 0.0.0.0/0 [110/1] via 10.1.12.2,
00:00:03, Serial1/0
R1(config-router)#
Observation:
·
Now,
R1 has default route in its routing table
·
If
we want R2 to generate default route only if its Serial 1/1 link is up, then we
need to use a route-map keyword along with default-information originate.
R2(config-router)#default-information originate always route-map
CONN
R2(config-router)#do
show run | begin CONN
default-information originate always route-map
CONN
!
ip
forward-protocol nd
!
!
ip
http server
no
ip http secure-server
!
access-list
1 permit 10.1.13.0 0.0.0.255 log
!
route-map
CONN permit 10
match ip address 1
!
·
Now,
if I shut the ser1/1 interface in R2, then default-route in R1 should
disappear:
R2(config)#int
ser1/1
R2(config-if)#shut
R2(config-if)#
*Mar 1 00:42:36.563: %LINK-5-CHANGED: Interface
Serial1/1, changed state to administratively down
*Mar 1 00:42:37.563: %LINEPROTO-5-UPDOWN: Line
protocol on Interface Serial1/1, changed state to down
R2(config-if)#
R1(config-router)#do show 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 not set
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.12.0 is directly connected,
Serial1/0
R1(config-router)#
·
Yes,
default route in R1 has disappeared now
R2(config-if)#no shut
R2(config-if)#
*Mar 1 00:43:03.447: %LINK-3-UPDOWN: Interface
Serial1/1, changed state to up
R2(config-if)#
*Mar 1 00:43:04.451: %LINEPROTO-5-UPDOWN: Line
protocol on Interface Serial1/1, changed state to up
R2(config-if)#
R1(config-router)#do show 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 10.1.12.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.12.0 is directly connected,
Serial1/0
O*E2 0.0.0.0/0 [110/1] via 10.1.12.2,
00:00:13, Serial1/0
R1(config-router)#
Observation:
·
Default
route in R1 is back!
