OSPF redistribution: We can redistribute networks into OSPF from static, connected, or from other protocols such as EIGRP.
Authenticate: We can configure md5 authentication on OSPF to provide security.
ASBR: Autonomous System Boundary Router -- basically a router which connects to networks using a routing protocol other than OSPF and inject routes into OSPF from those routing protocols.
Overview: We have Area 1 connected to Area 0 and EIGRP AS 10 connected to Area 0 through R2. We will take routes learned through EIGRP and inject them into OSPF and we will also take routes learned from Area 1 and inject them into Area 0 and vice-versa.
Relevant configurations are posted below.
R2 is now configured with EIGRP 10 and note redistribute and default-metric. Redistribute OSPF 1 gets the OSPF routes into EIGRP but if you do not set the seed metric using default-metric then none of the OSPF routes will not end up in the EIGRP domain.
R2#sh run | sec eigrp
router eigrp 10
redistribute connected
redistribute ospf 1 ** This is so we can get OSPF into EIGRP **
network 10.2.2.0 0.0.0.255
default-metric 100000 1 255 1 1500 **Seed metric or else routes will not get injected **
auto-summary
R2#sh run | sec ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
redistribute eigrp 10 subnets ** This is so we can get EIGRP into OSPF **
network 10.0.0.0 0.0.0.255 area 0
R6#sh run | sec eigrp
router eigrp 10
network 10.2.2.0 0.0.0.255
network 172.16.6.0 0.0.0.255
no auto-summary ** If we do not do no auto-summary OSPF will end up with a route for 172.16.0.0/16 via 10.0.0.2 **
Notice below that on R4 has a route to loopback 172.16.6.0/24 on R6 (which is not in the OSPF domain). Thanks to our ASBR we now have route injection between EIGRP and OSPF.
R4#sh ip route
O E2 172.16.6.0 [110/20] via 10.0.0.2, 00:05:22, FastEthernet1/0
R4#ping 172.16.6.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.6.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 36/56/88 ms
Now let's look at how R2 acts as an ABR (Area border router) and interacts with Area 1.
R4#sh run int fast1/1
interface FastEthernet1/1
ip address 10.1.1.4 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 ithitman
duplex auto
speed auto
end
R5#sh run int fast1/0
interface FastEthernet1/0
ip address 10.1.1.5 255.255.255.0
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 ithitman
duplex auto
speed auto
end
** If you would like to enable authentication on an entire area use area # authentication <message-digest> under router ospf process-id and this will force every router in a certain area to use authentication.**
R4#sh run | sec ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
network 10.0.0.0 0.0.0.255 area 0
network 10.1.1.0 0.0.0.255 area 1
R5#sh run | sec ospf
router ospf 1
log-adjacency-changes
network 10.1.1.0 0.0.0.255 area 1
network 172.16.5.0 0.0.0.255 area 1
Notice R2 has a route for 172.16.5.0/24 and it is listed as IA (Inter-Area meaning it is coming from another Area which in this case Area 1)
R2#sh ip route
172.16.0.0/16 is variably subnetted, 6 subnets, 2 masks
O IA 172.16.5.1/32 [110/3] via 10.0.0.4, 00:14:05, FastEthernet1/0
O E2 172.16.4.0/24 [110/20] via 10.0.0.4, 01:48:13, FastEthernet1/0
D 172.16.6.0/24 [90/156160] via 10.2.2.6, 00:03:37, FastEthernet1/1
O E2 172.16.1.0/24 [110/20] via 10.0.0.1, 01:46:38, FastEthernet1/0
C 172.16.2.0/24 is directly connected, Loopback0
O E2 172.16.3.0/24 [110/20] via 10.0.0.3, 01:47:07, FastEthernet1/0
10.0.0.0/24 is subnetted, 3 subnets
C 10.2.2.0 is directly connected, FastEthernet1/1
O IA 10.1.1.0 [110/2] via 10.0.0.4, 00:29:29, FastEthernet1/0
C 10.0.0.0 is directly connected, FastEthernet1/0
R5#sh ip route
172.16.0.0/24 is subnetted, 6 subnets
O E2 172.16.4.0 [110/20] via 10.1.1.4, 00:39:19, FastEthernet1/0
C 172.16.5.0 is directly connected, Loopback0
O E2 172.16.6.0 [110/20] via 10.1.1.4, 00:13:33, FastEthernet1/0 ** These are E2 because they are coming from redistribute connected subnets **
O E2 172.16.1.0 [110/20] via 10.1.1.4, 00:39:19, FastEthernet1/0
O E2 172.16.2.0 [110/20] via 10.1.1.4, 00:39:19, FastEthernet1/0
O E2 172.16.3.0 [110/20] via 10.1.1.4, 00:39:19, FastEthernet1/0
10.0.0.0/24 is subnetted, 3 subnets
O E2 10.2.2.0 [110/20] via 10.1.1.4, 00:39:19, FastEthernet1/0
C 10.1.1.0 is directly connected, FastEthernet1/0
O IA 10.0.0.0 [110/2] via 10.1.1.4, 00:39:19, FastEthernet1/0 ** Notice IA. This is because it is coming from Area 0**
As you can see we have routes from Area 1 injected into Area 0 and vice-versa. We also have EIGRP routes injected into OSPF domain and vice-versa. We also have authentication between R5 and R4.
Now what if R1 has a 100mb fiber feed to the internet and you would like all routers to use R1 has its default gateway? Well we can use default-information originate to take care of that.
R1#sh run | sec ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
network 10.0.0.0 0.0.0.255 area 0
default-information originate always ** Since I do not have a static default gateway or BGP learned default in the routing table default-information originate wont work unless I add the "always" option which will inject a default route in the OSPF no matter what **
R2#sh ip route
What is next? Maybe configuring virtual-links or connecting areas using GRE tunnels and whatever else I can think of :)
Now what if R1 has a 100mb fiber feed to the internet and you would like all routers to use R1 has its default gateway? Well we can use default-information originate to take care of that.
R1#sh run | sec ospf
router ospf 1
log-adjacency-changes
redistribute connected subnets
network 10.0.0.0 0.0.0.255 area 0
default-information originate always ** Since I do not have a static default gateway or BGP learned default in the routing table default-information originate wont work unless I add the "always" option which will inject a default route in the OSPF no matter what **
R2#sh ip route
<-- output shortened -->
O*E2 0.0.0.0/0 [110/1] via 10.0.0.1, 00:00:03, FastEthernet1/0
What is next? Maybe configuring virtual-links or connecting areas using GRE tunnels and whatever else I can think of :)
More articles to come so stay tuned!!
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