12 - OSPF Routing - Implementing OSPF over NBMA 1

Lets go over and cover the network types:

Hub and Spoke (Star)
Most cost effective (cheapest) but major draw backs are reduancy and LATENCY is a big hit, ecspecially on VoIP and delay, sensitive traffic!

Partial MESH
Only the major Sites have meshing and less important sites do not

Full MESG
Very expensive, but with newer technologies such as MPLS or PIVPN not such a big deal,
however we are not focusing on the technology at this point :oP

SO the MODES:
Well we have already covered and implemented 2 of the 5 modes;

Additional notes:
Here it acts just like it was an ethernet segment, but over the WAN instead, we have
multicast messages, we elect a DR and BDR ... BUT we have the neighbours set statically,

Also the DR and BDR ... it has to be R4, as both R2 and R3 do not have full connectivity and because of this will form a FULL relationship with R4 (however if this was a full mesh
then it would not matter who was DR and BDR as everyone would form a FULL relationship and this would be just like a ethernet segment)

But with partial mesh or hub and spoke you need to get involved and tweak it alittle

So, R4 will exchange routes with neighbours on 224.0.0.6 and then send the msgs back out on 224.0.0.5

But this depends on your network topology! If we take the example below a single subnet does not make sense here .... so you could  ...

Here we have chosen a different mode of OSPF for the 2 companies below who have just a PVC running between them, you can mix and match the modes!

The goal is to get these guys exchanging routes and forming neighbours over our NBMA cloud, so the point-2-multipoint is just another tool to make it happen :0)

Makes connections work exactly like point to point (multicast to 224.0.0.5) ...no DR and BDR
but its over NBMA,
ONLY DRAWBACK,. you need a unique subnet per neighbour that you are using over the cloud

IMPLEMENTING BASIC OSPF






Core OSPF Configuration
Route Summarisation
DR Election
OSPF cost calculation




OBJECTIVE 1

Configure OSPF for the above network diagram. R1 will act as an ASBR by redistributing a series of static routes into the OSPF network. These routes should NOT increment their metric as they pass through the network and should have an initial OSPF cost of 200. All routers should have a router-id reflecting their hostname; you should be able to ping this router-id throughout the entire OSPF network.

Lets start off with Router1 and get OSPF up and running (I have already configured the basic networking)


R1(config)#router ospf 1
R1(config-router)#network 172.30.0.1 0.0.0.0 area 0
R1(config-router)#router-id 1.1.1.1
As mentioned before, it is worth while specifying the router-id now, rather than after the OSPF neighbourship as once it has formed you would have to clear the OSPF process or reboot the router(s) - by default it would of chosen the loopback interface as the RID

Lets setup the redistribution of the static routes into OSPF

R1(config-router)#redistribute static subnets

DONT forget the metric ...

R1(config-router)#redistribute static subnets metric ?
  <0-16777214>  OSPF default metric

We also need to specify the seed metric that these routes will start off with (looking at the objective it is 200)

and they must not increment when prograting thru the network (remember this from EIGRP/OSPF redistributition ...)

By default they are E2 routes which do not increment, E1 routes doo incriment

WHY AND WHEN TO USE WHICH METRIC-TYPE
Since our ASBR is the only exit point for these OSPF routes ... it doesnt matter which way the routers go to get to it, So their is no point the routers taking CPU cycles doing all the math, however if we had another exit point for them, then we would want the intelligence in the route decisions and we would use E1 routes



R1(config-router)#redistribute static subnets metric 200


Lets get our neighbours up and running ..

R2(config)#router ospf 1
R2(config-router)#network 172.30.0.2 0.0.0.0 area 0
R2(config-router)#network 172.30.10.2 0.0.0.0 area 10

*Mar  1 00:50:53.083: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on FastEthernet0/0 from LOADING to FULL, Loading Done


R2#show ip ospf ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           1   FULL/DR         00:00:39    172.30.0.1      FastEthernet0/0



Lets check R1;

R1#show ip ospf ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
172.30.10.2       1   FULL/BDR        00:00:33    172.30.0.2      FastEthernet0/0

Ah, yes notice the RID, lets try and change it:

R2(config)#router ospf 1
R2(config-router)#router-id 2.2.2.2
Reload or use "clear ip ospf process" command, for this to take effect

Soooo...

R2#clear ip ospf process
Reset ALL OSPF processes? [no]: y
R2#y
*Mar  1 01:01:06.835: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Interface down or detached

R1#show ip ospf ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           1   FULL/BDR        00:00:38    172.30.0.2      FastEthernet0/0

and lets check for that route from area 10;

R1#show ip route

     172.16.0.0/24 is subnetted, 4 subnets
S       172.16.0.0 is directly connected, Null0
S       172.16.1.0 is directly connected, Null0
S       172.16.2.0 is directly connected, Null0
S       172.16.3.0 is directly connected, Null0
     172.30.0.0/24 is subnetted, 2 subnets
C       172.30.0.0 is directly connected, FastEthernet0/0
O IA    172.30.10.0 [110/210] via 172.30.0.2, 00:00:30, FastEthernet0/0


Also R2 has got the static routes with their new cost of 200 (and notice the E2 flag);

R2#show ip route
     172.16.0.0/24 is subnetted, 4 subnets
O E2    172.16.0.0 [110/200] via 172.30.0.1, 00:00:09, FastEthernet0/0
O E2    172.16.1.0 [110/200] via 172.30.0.1, 00:00:09, FastEthernet0/0
O E2    172.16.2.0 [110/200] via 172.30.0.1, 00:00:09, FastEthernet0/0
O E2    172.16.3.0 [110/200] via 172.30.0.1, 00:00:09, FastEthernet0/0
     172.30.0.0/24 is subnetted, 2 subnets
C       172.30.0.0 is directly connected, FastEthernet0/0
C       172.30.10.0 is directly connected, Serial0/0

 Lets do R3;

R3(config)#router ospf 1
R3(config-router)#router-id 3.3.3.3
R3(config-router)#network 172.30.0.3 0.0.0.0 area 0
R3(config-router)#
*Mar  1 01:10:19.827: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from LOADING to FULL, Loading Done
R3(config-router)#
*Mar  1 01:10:25.883: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on FastEthernet0/0 from LOADING to FULL, Loading Done
R3(config-router)#network 172.30.20.3 0.0.0.0 area 20

Lets check his router table:


R3#show ip route

     172.16.0.0/24 is subnetted, 4 subnets
O E2    172.16.0.0 [110/200] via 172.30.0.1, 00:01:36, FastEthernet0/0
O E2    172.16.1.0 [110/200] via 172.30.0.1, 00:01:36, FastEthernet0/0
O E2    172.16.2.0 [110/200] via 172.30.0.1, 00:01:36, FastEthernet0/0
O E2    172.16.3.0 [110/200] via 172.30.0.1, 00:01:36, FastEthernet0/0
     172.30.0.0/24 is subnetted, 3 subnets
C       172.30.20.0 is directly connected, Serial0/0
C       172.30.0.0 is directly connected, FastEthernet0/0
O IA    172.30.10.0 [110/210] via 172.30.0.2, 00:01:37, FastEthernet0/0



lets do R4

R4(config)#router ospf 1
R4(config-router)#router-id 4.4.4.4
R4(config-router)#network 10.0.0.0 0.255.255.255 area 20
R4(config-router)#network 172.30.20.4 0.0.0.0 area 20
R4(config-router)#
*Mar  1 01:16:29.455: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial0/0 from LOADING to FULL, Loading Done
R4(config-router)#


R4#show ip route

     172.16.0.0/24 is subnetted, 4 subnets
O E2    172.16.0.0 [110/200] via 172.30.20.3, 00:00:40, Serial0/0
O E2    172.16.1.0 [110/200] via 172.30.20.3, 00:00:40, Serial0/0
O E2    172.16.2.0 [110/200] via 172.30.20.3, 00:00:40, Serial0/0
O E2    172.16.3.0 [110/200] via 172.30.20.3, 00:00:40, Serial0/0
     172.30.0.0/24 is subnetted, 3 subnets
C       172.30.20.0 is directly connected, Serial0/0
O IA    172.30.0.0 [110/210] via 172.30.20.3, 00:00:40, Serial0/0    (Area 0)
O IA    172.30.10.0 [110/410] via 172.30.20.3, 00:00:42, Serial0/0  (Area 10)
     10.0.0.0/24 is subnetted, 4 subnets
C       10.20.2.0 is directly connected, Loopback3
C       10.20.3.0 is directly connected, Loopback4
C       10.20.0.0 is directly connected, Loopback1
C       10.20.1.0 is directly connected, Loopback2


and R5;
R5(config)#router ospf 1
R5(config-router)#router-id 5.5.5.5
R5(config-router)#network 172.30.10.5 0.0.0.0 area 10
R5(config-router)#network 10.10.0.0 0.0.255.255 area 10


We now have our new neighbour up and running;

R5#show ip route

     172.16.0.0/24 is subnetted, 4 subnets
O E2    172.16.0.0 [110/200] via 172.30.10.2, 00:07:25, Serial0/0
O E2    172.16.1.0 [110/200] via 172.30.10.2, 00:07:25, Serial0/0
O E2    172.16.2.0 [110/200] via 172.30.10.2, 00:07:25, Serial0/0
O E2    172.16.3.0 [110/200] via 172.30.10.2, 00:07:25, Serial0/0
     172.30.0.0/24 is subnetted, 3 subnets
O IA    172.30.20.0 [110/410] via 172.30.10.2, 00:07:25, Serial0/0
O IA    172.30.0.0 [110/210] via 172.30.10.2, 00:07:25, Serial0/0
C       172.30.10.0 is directly connected, Serial0/0
     10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
C       10.10.0.0/24 is directly connected, Loopback1
C       10.10.1.0/24 is directly connected, Loopback2
C       10.10.2.0/24 is directly connected, Loopback3
C       10.10.3.0/24 is directly connected, Loopback4
O IA    10.20.3.1/32 [110/411] via 172.30.10.2, 00:07:28, Serial0/0
O IA    10.20.2.1/32 [110/411] via 172.30.10.2, 00:07:28, Serial0/0
O IA    10.20.1.1/32 [110/411] via 172.30.10.2, 00:07:28, Serial0/0
O IA    10.20.0.1/32 [110/411] via 172.30.10.2, 00:07:28, Serial0/0



Although, in the normal working world having them loopbacks advertised as /32 is normal (even though i have configured them as a /24, OSPF is clever enough to not get fooled and shows it as the 1 address, but since we are in a lab enviroment we can tweak it, as i have shown you before to look like a /24 network)

R5(config)#int loo 1
R5(config-if)#ip ospf network point-to-point
R5(config)#inte loo 2
R5(config-if)#ip ospf network point-to-point
R5(config-if)#inte loo 3
R5(config-if)#ip ospf network point-to-point
R5(config-if)#inte loo 4
R5(config-if)#ip ospf network point-to-point


R4(config)#int loo 1
R4(config-if)#ip ospf network point-to-point
R4(config-if)#int loo 2
R4(config-if)#ip ospf network point-to-point
R4(config-if)#int loo 3
R4(config-if)#ip ospf network point-to-point
R4(config-if)#int loo 4
R4(config-if)#ip ospf network point-to-point



R1#show ip route


     172.16.0.0/24 is subnetted, 4 subnets
S       172.16.0.0 is directly connected, Null0
S       172.16.1.0 is directly connected, Null0
S       172.16.2.0 is directly connected, Null0
S       172.16.3.0 is directly connected, Null0
     172.30.0.0/24 is subnetted, 3 subnets
O IA    172.30.20.0 [110/210] via 172.30.0.3, 00:23:05, FastEthernet0/0
C       172.30.0.0 is directly connected, FastEthernet0/0
O IA    172.30.10.0 [110/210] via 172.30.0.2, 00:23:05, FastEthernet0/0
     10.0.0.0/24 is subnetted, 8 subnets
O IA    10.10.0.0 [110/211] via 172.30.0.2, 00:07:09, FastEthernet0/0
O IA    10.10.1.0 [110/211] via 172.30.0.2, 00:04:38, FastEthernet0/0
O IA    10.10.2.0 [110/211] via 172.30.0.2, 00:04:28, FastEthernet0/0
O IA    10.10.3.0 [110/211] via 172.30.0.2, 00:04:29, FastEthernet0/0
O IA    10.20.2.0 [110/211] via 172.30.0.3, 00:02:06, FastEthernet0/0
O IA    10.20.3.0 [110/211] via 172.30.0.3, 00:02:06, FastEthernet0/0
O IA    10.20.0.0 [110/211] via 172.30.0.3, 00:02:16, FastEthernet0/0
O IA    10.20.1.0 [110/211] via 172.30.0.3, 00:02:16, FastEthernet0/0


THATS BETTER :0) ... okay thats STEP 1 COMPLETE




OBJECTIVE 2.

After completing the initial step of the lab, one of the routers in Area 0 will become the DR and one will become the BDR for the Ethernet segment. Which router will become the DR and BDR? Write DR and BDR next to the respective router below.
o R1
o R2
o R3

Well, lets just reset the process as currently the order i booted these bad bois will affect the results, so..


R1#clear ip ospf process
Reset ALL OSPF processes? [no]: y
R1#
*Mar  1 00:35:35.159: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Interface down or detached
*Mar  1 00:35:35.163: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Interface down or detached
*Mar  1 00:35:35.347: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from LOADING to FULL, Loading Done
*Mar  1 00:35:35.351: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on FastEthernet0/0 from LOADING to FULL, Loading Done
Lets have a look and see what we have:

R1#show ip ospf interface
FastEthernet0/0 is up, line protocol is up
  Internet Address 172.30.0.1/24, Area 0
  Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
  Transmit Delay is 1 sec, State DROTHER, Priority 1
  Designated Router (ID) 3.3.3.3, Interface address 172.30.0.3
  Backup Designated router (ID) 2.2.2.2, Interface address 172.30.0.2
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:02
  Supports Link-local Signaling (LLS)
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 2, maximum is 4
  Last flood scan time is 0 msec, maximum is 4 msec
  Neighbor Count is 2, Adjacent neighbor count is 2
    Adjacent with neighbor 2.2.2.2  (Backup Designated Router)
    Adjacent with neighbor 3.3.3.3  (Designated Router)
  Suppress hello for 0 neighbor(s)


If we look on R2 we can see that he sees R1 as a DROTHER


R2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           1   FULL/DROTHER    00:00:32    172.30.0.1      FastEthernet0/0
3.3.3.3           1   FULL/DR         00:00:33    172.30.0.3      FastEthernet0/0
5.5.5.5           0   FULL/  -        00:00:38    172.30.10.5     Serial0/0
R2#


So in answer to the question;
o R1
o R2 BDR
o R3 DR

So,  WHY and how do we have the results we do, WELL .....

OSPF can use the interface OSPF priority to influence the selection, but by default everything has a priority of 1;

R1#show ip ospf interface
FastEthernet0/0 is up, line protocol is up
  Internet Address 172.30.0.1/24, Area 0
  Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 10
  Transmit Delay is 1 sec, State DROTHER, Priority 1

The next thing to break the tie is the highest loopback interface, which in our case was router 3, however if R3 were to be unavailable (turned off) then R2 would of been the DR and so on ...

OBJECTIVE 3.

Ensure R1 becomes the DR on the Ethernet segment in Area 0. R2 and R3 should not become a DR or BDR for the Ethernet segment in Area 0. After this change is made, what type of neighbor relationship should exist between R1 and R2? What about R2 and R3?

So looking at the output below, FA0/1 is attached the ethernet segment 172.30.0.1/24..

R1#show ip ospf interface
FastEthernet0/0 is up, line protocol is up
  Internet Address 172.30.0.1/24, Area 0

lets configure the OSPF priority, anything higher than the default of 1, will ensure this will be DR on the segment;

R1(config)#inter fa0/1
R1(config-if)#ip ospf priority ?
  <0-255>  Priority

R1(config-if)#ip ospf priority 200

BUT now we need to ensure R2 & R3 shoulfd not become a DR/BDR ... so lets change there priority to a 0

R2#show ip ospf interface
FastEthernet0/0 is up, line protocol is up
  Internet Address 172.30.0.2/24, Area 0
R2(config)#inter FastEthernet0/0
R2(config-if)#ip ospf priority 0


R3(config)#inter fa0/0
R3(config-if)#ip ospf priority 0



Lets check out the results, we should see both R2 and R3 set as DROTHER

R1#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           0   FULL/DROTHER    00:00:36    172.30.0.2      FastEthernet0/0
3.3.3.3           0   FULL/DROTHER    00:00:30    172.30.0.3      FastEthernet0/0
and R1 is now our hard coded DR, lets check what R2 see's:

R2#show ip ospf ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1         200   FULL/DR         00:00:34    172.30.0.1      FastEthernet0/0
3.3.3.3           0   2WAY/DROTHER    00:00:36    172.30.0.3      FastEthernet0/0
5.5.5.5           0   FULL/  -        00:00:31    172.30.10.5     Serial0/0

Notice the priority of 200 for R1, now R2 & R3 will stay at the 2WAY state, for each other


R3#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1         200   FULL/DR         00:00:31    172.30.0.1      FastEthernet0/0
2.2.2.2           0   2WAY/DROTHER    00:00:38    172.30.0.2      FastEthernet0/0
4.4.4.4           0   FULL/  -        00:00:33    172.30.20.4     Serial0/0

Notice the FULL relationships above for the other areas, these have no DR or BDR as they are a POINT-TO-POINT relationship


OBJECTIVE 4.
Implement summarization at the ABRs in the network to make the routing tables throughout the network as efficient as possible.

Remember with OSPF we can only summarise  at the ASBR and ABR, lets start with R2:


R2#show ip route | i 172.30.10.5
O       10.10.0.0 [110/201] via 172.30.10.5, 00:21:35, Serial0/0
O       10.10.1.0 [110/201] via 172.30.10.5, 00:21:35, Serial0/0
O       10.10.2.0 [110/201] via 172.30.10.5, 00:21:35, Serial0/0
O       10.10.3.0 [110/201] via 172.30.10.5, 00:21:35, Serial0/0

Lets summarise the routes we are learning from R5 (area 10) to area 0

So thinking in increments, (128,64,32,16,8,4,2,1) 4 would catch the above routes;
10.10.0.0
10.10.4.0
subnet mask /20


R2(config)#router ospf 1
R2(config-router)#area 10 range ?
  A.B.C.D  IP address to match

R2(config-router)#area 10 range 10.10.0.0 255.255.252.0





Lets check it out on R1;

R1#show ip route | i 172.30.0.2
O IA    172.30.10.0 [110/210] via 172.30.0.2, 00:30:08, FastEthernet0/0
O IA    10.10.0.0/22 [110/211] via 172.30.0.2, 00:01:53, FastEthernet0/0


SWEET!

Lets do the same for R3;


R3(config)#router ospf 1
R3(config-router)#area 20 range 10.20.0.0 255.255.252.0






Lets check it out .....

R1#show ip route | i 172.30.0.3
O IA    172.30.20.0 [110/210] via 172.30.0.3, 00:33:17, FastEthernet0/0
O IA    10.20.0.0 [110/211] via 172.30.0.3, 00:01:26, FastEthernet0/0

Koool!


OBJECTIVE 5.
Implement summarization at the ASBR. The summary route should have the same attributes as the original, individual routes redistributed into the network.

With an ASBR we dont have the area, as we could be redistributing routes from another protocol, so no area exists ....

R1(config)#router ospf 1
R1(config-router)#summary-address ?
  A.B.C.D  IP summary address

R1(config-router)#summary-address 172.16.0.0 255.255.252.0 ?
  not-advertise  Do not advertise when translating OSPF type-7 LSA
  tag            Set tag
  <cr>

R1(config-router)#summary-address 172.16.0.0 255.255.252.0

Lets check R1 and see the summary ...

R2#show ip route

     172.16.0.0/22 is subnetted, 1 subnets
O E2    172.16.0.0 [110/200] via 172.30.0.1, 00:02:00, FastEthernet0/0


It will inherit the other attributes like cost etc by default from the original route :0)


OBJECTIVE 6.
The organization plans to upgrade to Gigabit Ethernet in the coming months. OSPF should accurately calculate its metric assuming Gigabit Ethernet will be the fastest link in the network.

R1(config-router)#auto-cost reference-bandwidth 1000
% OSPF: Reference bandwidth is changed.
        Please ensure reference bandwidth is consistent across all routers.

This command needs to be done accross all the OSPF routes (be careful not to go tooo high on this one otherwise it will render small links like 64kbps as unreachable as the metric will be too high ( it will be mistaken for infinite ....)





I have now gone and done the rest of the routers, soooo lets look at our new metrics

BEFORE
     172.16.0.0/24 is subnetted, 4 subnets
O E2    172.16.0.0 [110/200] via 172.30.10.2, 00:07:46, Serial0/0
O E2    172.16.1.0 [110/200] via 172.30.10.2, 00:07:46, Serial0/0
O E2    172.16.2.0 [110/200] via 172.30.10.2, 00:07:46, Serial0/0
O E2    172.16.3.0 [110/200] via 172.30.10.2, 00:07:46, Serial0/0
     172.30.0.0/24 is subnetted, 3 subnets
O IA    172.30.20.0 [110/410] via 172.30.10.2, 00:10:14, Serial0/0
O IA    172.30.0.0 [110/210] via 172.30.10.2, 00:10:14, Serial0/0
C       172.30.10.0 is directly connected, Serial0/0
     10.0.0.0/24 is subnetted, 8 subnets
C       10.10.0.0 is directly connected, Loopback1
C       10.10.1.0 is directly connected, Loopback2
C       10.10.2.0 is directly connected, Loopback3
C       10.10.3.0 is directly connected, Loopback4
O IA    10.20.2.0 [110/411] via 172.30.10.2, 00:08:00, Serial0/0
O IA    10.20.3.0 [110/411] via 172.30.10.2, 00:08:00, Serial0/0
O IA    10.20.0.0 [110/411] via 172.30.10.2, 00:08:10, Serial0/0
O IA    10.20.1.0 [110/411] via 172.30.10.2, 00:08:10, Serial0/0

AFTER


R5#show ip route

     172.16.0.0/22 is subnetted, 1 subnets
O E2    172.16.0.0 [110/200] via 172.30.10.2, 00:01:07, Serial0/0
     172.30.0.0/24 is subnetted, 3 subnets
O IA    172.30.20.0 [110/4100] via 172.30.10.2, 00:01:07, Serial0/0
O IA    172.30.0.0 [110/2100] via 172.30.10.2, 00:01:07, Serial0/0
C       172.30.10.0 is directly connected, Serial0/0
     10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks
C       10.10.0.0/24 is directly connected, Loopback1
C       10.10.1.0/24 is directly connected, Loopback2
C       10.10.2.0/24 is directly connected, Loopback3
C       10.10.3.0/24 is directly connected, Loopback4
O IA    10.20.0.0/22 [110/4101] via 172.30.10.2, 00:01:09, Serial0/0
NOTICE, the E2 route stays the same ... which is what we wanted :0)

OSPF Routing - Foundation Concepts 2

OSPF's cost
Understanding the DR and BDR
The flurry of OSPF packet types


OSPF's cost

This is the view that the topology table (the informarion that thye know) gives of an area to a router in that area :0)


NOW, the main difference over the topology table between EIGRP and OSPF, is OSPF throws away as it were the routes that are not the best routes that dont make it into the routing table (well it does keep them, they stay in the topology table but if the best route (i.e the route in the routing table) goes down, then OSPF process has to be ran again ...


OSPF's METRIC is COST

COST is 100 divided by bandwidth

56kbps is .056 mps = 1785 in cost


Cost at 100Gbps:          1
Cost at 40Gbps:           1    
Cost at 10Gbps:           1   
Cost at 1Gps:             1    
Cost at 100Mbps:          1    
Cost at 10Mbps:          10                      
Cost at 6.176Mbps:       16                     
Cost at 4.632Mbps:       21                      
Cost at 3.088Mbps:       32                     
Cost at 1.544Mps:        64               
Cost at 768kbps:        133                      
Cost at 384kbps:        266                   
Cost at 128kbps:        800      

NOTICE anything over FASTETHERNET has a cost of 1, so this is something we have to tweak in the config



               
Understanding the DR and BDR

 The DR and BDR are in charge of sending out router updates for when a network or the shared segment goes down, to stop this .... (each router every over router on the segment of the failure)

DR AND BDR is not per Area  or AS, its per shared segment! so looking at the below image you can see its possible just to have a DR and thats it! 

Notice with OSPF it uses x2 multicast addresses, 224.0.0.5 is used for OSPF hellos, whilst 224.0.0.6 is used just to send updates to the DR and BDR

Now with a Point-to-Point link, there is no DR and BDR, there is no need, so they communicate just on  224.0.0.5

Does it matter which router is DR and BDR ... on a shared segment, no .... not really, leaving it to chance is just fine as their is no requirment to dictate which one gets it (but setting the priority higher than the default 1 will win the election, 2nd to that if they are tied is the RID)

Where it does matter, is in say a FRAME-RELAY enviroment (becuase the DR will need full connectivity to all peers)

 
In these shared segment, only the DR and BDR are going to have the FULL state, all other neighbours will stay at the 2-WAY state.




The flurry of OSPF packet types

HelloForms neighbour relationships
 
DBD       We can have routers exchange routing tables without the whole database being exchanged (like they are submitted the index of a book)

LSRMaster sends dbd first, once other router (slave) recieves dbd, it will respond with lsr's about networks it does not know about

LSUIs the response back from the master to the lsr, which would update the other router with the information about that route

LSAAre contained within the lsu (think of lsa inside the lsu envelope) its being more efficient rather than reply back to each network, it can reply back once (same with the LSR coming over in the first place, it will go inside the lsu)

LSACKIs the reliablitiy mechanism for OSPF, OSPF is its own transport layer protocol (like tcp/udp etc, but it is its own) .... making OSPF a realiable protocol

OSPF Routing - Foundation Concepts 1


Link State Routing Protocols

Two Types:
IS-IS
OSPF

All other routing protocols are distance vector (yup even big bad Mr. Internet BGP)

Maintains 3 Tables (just like EIGRP, but with a difference)

NEIGHBOUR TABLE
tracks neighbours all neighbour it has relationships with and exchange routes with and directly connected to (ONLY FORMS NEIGHBOURS WITH ROUTERS IN SAME AREA ONLY)

TOPOLOGY TABLE
every link state protocol maintains this table, but this is a ROAD MAP for that AREA, so they see the whole layout (all links), all the routers in that router

EIGRP, does have this too, - but its not a roadmap of everything in the area, it is just a list of what the neighbour has past on ....."routing by rumour"

ROUTING TABLE
Best path


Uses Dijkstra's shortest path first (SPF) algorithm

Advantage
Each router knows everypath and knows the best path with that area (network added or removed, they all know about it)

Disadvantage
Can be an intense process (CPU) (so make sure the areas dont get too BIG) as each router has to make decisions on whole area


Sends triggered updates to announce network changes (unlike RIP sending whole routing table)


Sends periodic updates (LS refresh) on long intervals, this is the whole routing table to its neighbour if after 30 minutes there has been no activity (so pokes neighbour and says, just in case you missed it, this is what i see road map as)




OSPF AREA DESIGN AND TERMS

All areas must connect to area 0 (1 interface)

All routers in an area have the same topology table (convergence/load gets more the bigger the area)

Goal: localise updates within an area (Area 2 does not have to both the backbone etc or cross a slow WAN link)

Requires a hierarchical design (i.e Area 2 10.1.0.0, 10.2.0.0., area 3 has 172.16.0.0, 172.17.0.0. ....) as this is the whole pupose of an area (contiguous network/discontiguous network), keep updates local and this is achived by summarisation


All Areas are considered to be in the OSPF AS (divided by the ABR's,) whereas the ASBR is the AS Boundary Router ...Now these two types of routers are the only place you can do summarisation ...(unlike good ole EIGRP, where you can summarise on any interface on any router)


 
UNDERSTANDING OSPF NEIGHBOUR RELATIONSHIPS

RID
Only changes when you restart the OSPF process or reboot the router

dead timers are x4 the hello (if you take the hello message interval over NBMA network, the dead time is 2 minutes! ... these can be tweaked and should be tweaked, 2 minutes is WAY TO LONG!)



3. This Hello msg .... is considered the "DOWN STATE"

4. Upon recieving the HELLO; we enter the  "INIT STATE" - the routers haven't formed neighbourship as of yet, but it is checking..

5. Is the "2-WAY STATE"

6. We enter the "EXSTART STATE"- Exchange Start state, this means the HELLO packets agree, lets being exchanging our link state databases

7.  Is the "LOADING STATE" state

Which leads on to CONCEPTS PART II

Just recapping over all the concepts and fundamnetals i have covered so far .... there is alot to take in and its no race .... wanna get this stuff down kold

Okay, i thought i would now revert the changes back, so that R2 favours going via R1 for the network 10.1.0.0/24 .... but then thought, lets make it interesting, lets get the preferred route back to go via R2 via some policy routing! yeah boi!

So currently, we are still going via R3 to get to 10.1.0.0/24 - due to lower AD change :0)


R2#  show ip route | i 10.1.0.0
D EX    10.1.0.0 [101/6917120] via 10.1.23.3, 00:26:49, Serial0/0
Lets create an ACL that will match any traffic talking to the network 10.1.0.0/24

R2#show run | s NEXT-HOP
ip access-list extended NEXT-HOP
 permit ip any 10.1.0.0 0.0.0.255

then lets have a new route map, match any traffic in that ACL and set the next-hop to R1 :0)

R2#show run | s route-map HOP
route-map HOP permit 10
 match ip address NEXT-HOP
 set ip next-hop 10.1.12.1

Lets apply the new route-map under the serial interface of R2


R2(config)interface Serial0/2
 ip policy route-map HOP


Lets restest:
 
 R4#traceroute 10.1.0.1

Type escape sequence to abort.
Tracing the route to 10.1.0.1

  1 10.1.24.2 44 msec 8 msec 0 msec
  2 10.1.12.1 28 msec *  12 msec  <---- Our Friend R1

R4#show ip route | i 10.1.0.0
D EX    10.1.0.0 [170/7429120] via 10.1.24.2, 00:35:45, Serial0/0

Lets check the route-map;
R2#show route-map HOP
route-map HOP, permit, sequence 10
  Match clauses:
    ip address (access-lists): NEXT-HOP
  Set clauses:
    ip next-hop 10.1.12.1
  Policy routing matches: 11 packets, 712 bytes

SWEEEEEET

IPv4 Redistribution - Implementing Advanced Redistribution.......Cont

Okay, so what we need to ensure here, is routes in EIGRP land aren't being redistributed into OSPF (R4/R2 to R1) then redistributed again from OSPF from R3 back into EIGRP, and round and round we gooo ...

What we can do is modify one the route-maps we created earlier, as we are tagging OSPF routes that are being redistributed into EIGRP with tag 40, so we could setup a filter than blocks them coming back into R2 from EIGRP


Likewise we have EIGRP routes that are being redistibuted into OSPF with tags 10, 20 and 30, so again we can put a filter on R3 stopping them from coming back into EIGRP

It really helps drawing this stuff out first .... otherwise as Jeremy says "you can blow your own mind" lol!

So lets modify the route-map on R2, and deny the redistributed OSPF routes in EIGRP with tag 40 from leaving R2. (so deny anything trying to get into OSPF domain with tag 40)

R2(config)#route-map EIGRP-TO-OSPF deny 5
R2(config-route-map)#match tag 40
 
So iv sneaked in this sequence, so it is processed first and it will match EVERYTHING as we have not specified anything, and its matching tag 40; 

R2#show run | s route-map EIGRP-TO-OSPF

route-map EIGRP-TO-OSPF deny 5
 match tag 40
route-map EIGRP-TO-OSPF permit 10
 match ip address METRIC100
 set metric 100
 set tag 10
route-map EIGRP-TO-OSPF permit 20
 match ip address METRIC200
 set metric 200
 set tag 20
route-map EIGRP-TO-OSPF deny 25
 match ip address DENY-10.4.4.0
route-map EIGRP-TO-OSPF permit 30
 set metric 300
 set tag 30
 
Now lets fix the otherway lol, these will be the redistributed  OSPF routes in EIGRP
 
R2(config)#route-map OSPF-TO-EIGRP deny 5
R2(config-route-map)#match tag 10 20 30*

*(when aligned this acts as OR, when on new line, its AND)

So just to clarify;

route-map OSPF-TO-EIGRP, deny, sequence 5
  Match clauses:
    tag 10 20 30
  Set clauses:
  Policy routing matches: 0 packets, 0 bytes
route-map OSPF-TO-EIGRP, permit, sequence 10
  Match clauses:
  Set clauses:
    metric 400 20 255 1 1500
    tag 40

Excellent, lets copy these new sequence numbers onto R3 and we are good to go

Lets check which route R4 currently favours for the 10.1.0.0/24;


R4#traceroute 10.1.0.1

Type escape sequence to abort.
Tracing the route to 10.1.0.1

  1 10.1.24.2 4 msec 4 msec 4 msec
  2 10.1.12.1 8 msec 4 msec *

As expected we go to R2, then R1

R4 knows about the route via EIGRP from R2:

R4#show ip route 10.1.0.1
Routing entry for 10.1.0.0/24
  Known via "eigrp 100", distance 170, metric 6917120
  Tag 40, type external
  Redistributing via eigrp 100
  Last update from 10.1.24.2 on Serial0/0, 00:19:38 ago
  Routing Descriptor Blocks:
  * 10.1.24.2, from 10.1.24.2, 00:19:38 ago, via Serial0/0
      Route metric is 6917120, traffic share count is 1
      Total delay is 20200 microseconds, minimum bandwidth is 400 Kbit
      Reliability 255/255, minimum MTU 150 bytes
      Loading 1/255, Hops 1
      Route tag 40
 
RIGHT, so we have to make the route from R3 look "better" than the route that R2 is getting from R1 (over OSPF)

Looking at the routing tables, R3 has the route 10.1.0.0/24 with an AD of 170
R2 has the route with an AD of 110 (from R1);

R2#  show ip route 10.1.0.1
Routing entry for 10.1.0.0/24
  Known via "ospf 1", distance 110, metric 65, type intra area

 ... so even if we were to play with metrics, it still would NOT matter, it could have a metric of 1! would not matter as the AD for the route being learnt is still 170!

We could use policy routing to correct this or another approach is we could lower the Admin Distance of External routes of EIGRP to say 105 (anything below the AD of OSPF which is 110)
Because if you look at the network map, R3 is advertising the route / redistributing that network 10.1.0.0/24 into EIGRP, but its not in the routing table as OSPF has a lower admin distance!

 Remember R4's routing table above (scroll up)

R4#show ip route 10.1.0.1
Routing entry for 10.1.0.0/24
  Known via "eigrp 100", distance 170, metric 6917120

R4#show ip route | i 10.1.0.0
D EX    10.1.0.0 [170/6917120] via 10.1.24.2, 00:45:36, Serial0/0
 
He knows about it, becuase of the redistribution and look at the AD! so if we make the AD lower than OSPFs default AD of 110, R2 will go to R3 to reach the 10.1.0.0/24 network


R2(config)#router eigrp 100
R2(config-router)#distance eigrp ?
  <1-255>  Distance for internal routes

R2(config-router)#distance eigrp 90 ?
  <1-255>  Distance for external routes

R2(config-router)#distance eigrp 90 101

*Mar  1 01:31:55.087: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.24.4 (Serial0/2) is down: route configuration changed
*Mar  1 01:31:55.119: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.23.3 (Serial0/0) is down: route configuration changed
R2(config-router)#
*Mar  1 01:31:56.243: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.23.3 (Serial0/0) is up: new adjacency
*Mar  1 01:31:57.231: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.24.4 (Serial0/2) is up: new adjacency

So.... whadda think...

R2#  show ip route | i 10.1.0.0
D EX    10.1.0.0 [101/6917120] via 10.1.23.3, 00:01:20, Serial0/0

R2#  show ip route 10.1.0.1
Routing entry for 10.1.0.0/24
  Known via "eigrp 100", distance 101, metric 6917120
  Tag 40, type external
  Redistributing via eigrp 100, ospf 1
  Last update from 10.1.23.3 on Serial0/0, 00:00:50 ago
  Routing Descriptor Blocks:
  * 10.1.23.3, from 10.1.23.3, 00:00:50 ago, via Serial0/0
      Route metric is 6917120, traffic share count is 1
      Total delay is 20200 microseconds, minimum bandwidth is 400 Kbit
      Reliability 255/255, minimum MTU 150 bytes
      Loading 1/255, Hops 1
      Route tag 40




YEAH BOI!!! check that out! R2 is now favouring the route via R3 with the new Admin Distance of 101, which beats the OSPF AD!

lets check the route on R4 again:

R4#traceroute 10.1.0.1

Type escape sequence to abort.
Tracing the route to 10.1.0.1

  1 10.1.24.2 48 msec 4 msec 0 msec
  2 10.1.23.3 40 msec 12 msec 4 msec <---- THERE's our bud, R3!!!
  3 10.1.13.1 12 msec *  36 msec

SWEEEEEEEET!


NOW! that is kool, very kool, BUT we do have to be careful with and where we make these changes, becuase if say we also go and make this change on R3, we would create ourself an infinite loop! as R3 would prefer R2 over R1 to get to 10.1.0.0/24, the packet would go back over to R2, same thing, it is going to prefer R3 ... and round and round we go! ... although split horizon would prolly kick in, but the point is still valid!