OSPF example, SonicWall OS Enhanced as ASBR with multiple routers and multiple AREA configuration?

03/26/2020 37 People found this article helpful 120,620 Views

Description

Resolution

Network details>>

SonicWall X0:192.168.168.168

SonicWall X2:192.168.200.2

SonicWall, Router A and Router B are connected to a switch.

Router B interface in 192.168.168.0 subnet has an ip 192.168.168.2 and router A interface has 192.168.168.144.

Router B is an ABR connecting Area o and Area 1.

Router B interface in area 1 is configured at 10.10.10.1 and router C interface at 10.10.10.2>>

Router C is connected to a 172.16.31.0 lan cloud at another interface 172.16.31.1(area 1).

Goal: Dynamically update routes at SonicWall and routers A, B and C.

So at the end, SonicWall routing table should have route to 172.16.31.0 and 10.10.10.0.

OSPF terminologies>>

AREA:

In OSPF, a single AS can be divided into smaller groups called areas. This reduces the number of link-state advertisements and other OSPF overhead traffic sent on the network, and it reduces the size of the
topological database that each router must maintain.

An area is a set of networks and hosts within an AS that have been administratively grouped together. We recommend that you configure an area as a collection of contiguous IP subnetted networks. Routers that
are wholly within an area are called internal routers. All interfaces on internal routers are directly connected to networks within the area. The topology of an area is hidden from the rest of the AS, thus significantly reducing routing traffic in the AS. Also, routing within the area is determined only by the area's topology, providing the area with some protection from bad routing data.All routers within an area have identical topological databases.

ABR:

Area Border Routers
Routers that belong to more than one area are called area border routers. They maintain a separate topological database for each area to which they are connected.

ASBR:(autonomous system border router)

AS Boundary Routers
Routers that exchange routing information with routers in other ASs are called AS boundary routers. They advertise externally learned routes throughout the AS. Any router in the AS an internal router, an
area border router, or a backbone router can be an AS boundary router.Every router within the AS knows the path to the AS boundary routers.

Router-id:

It is the highest physical ip address configured on a router>>if loop back address is configured>>that takesprecedance>> if router id is hard coded on the device,then that over rides the other two and becomes the router id and new router id will come into picture only if ospf process or router itself is restarted>>

eg:in a Cisco router>>

#clear ip ospf process

Link state adverisements(lsa):

LSA>>link state advertisemnets>>they are ospf updates that carries information about networks>>

lsa 1>>router lsa>>carries info about networks>>

lsa 2>>network lsa>>generated by DR>>informs neighboring router about the routers and interfaces taking part in ospf in that area>>

lsa3>>summary lsa>>>routes from ABR>>routes from different areas>>

lsa 4>>ASBRlsa>>asbr informing routers in ospf that he is the asbr by publishing its own ip address>>

lsa 5>>asbr summary lsa>>external routes from other autonomous system passed on to internal routers from asbr router>>

DR and BDR:designated router and back up designated routers >>they are the only routers in an area that would broadcast updates>>internal routers listens only at 224.0.0.5 but dr and bdr listens at 224.0.0.5 and 224.0.0.6.

Step 1: Enabling ospf in SonicWall>>

To enable advance routing>>
Browse to network>> Routing>>
Routing mode>>click on the drop down>>select advanced routing>>

Configure the interface on which we need to configure ospf>>
In this scenario, configuring on X0>>

Click on configure ospf for X0>>
By default ospf would be disabled>>

Click on drop down for ospf v2>>select enabled>>

OSPF AREA (by default area is elected as 0>>
In this scenario lets go with default, if SonicWall interface(x0 in this case) belongs to area 0 or else select the apppropriate area>>

In this scenario we are going to select area 0>>

OSPFv2 area type>>
Select normal >>To enable lsa1 ,2,3,4 and lsa 5>>

Hello and dead interval are 10 seconds and 40 seconds respectively by default in broadcast and point to point links.If neighboring OSPF routers are configured with non-default values, match the same in SonicWall or else SonicWall would not become a neighbor to the existing OSPF routers.

Auto-Cost Reference BW (Mb/s):
OSPF cost = 100/bw in mbps
Auto-Cost Reference = 100

Note: Auto-Cost Reference has to be same on all ospf routers>>

Router priority>>Used for DR election>>By default all routers have Router priority set as 1>>
Greater the value,more is the chance of being a DR>>
1 DR and 1 BDR would be required in all shared segments>>

Router priority = 0, would make SonicWall to not participate in DR election>>

Note: In point to point links , no DR or BDR is required>>

In this case we will go with default,
ie Router priority = 1

OSPF router id>>

Router id is the name of a router in ospf process.In this case we will go with 1.1.1.1 as router id.

Originate default route>never>>If selected,it never advertises default internet route to peer ospf routers>>
Originate default route>>when wan is up and always (self-explanatory) are selected mostly when SonicWall acts as last resort to internet>>
Metric is that metric that should be advertised to peers about the routes being sent from SonicWall>>

ABR type >>Standard

SonicWall OSPF Configuration:

OSPF configuration in router A>>

#config t

#router ospf

#network 192.168.168.0 0.0.0.255 area 0

#router id 5.5.5.5

OSPF configuration in router B>>(ABR)

#config t

#router ospf

#network 192.168.168.0 0.0.0.255 area 0

#network 10.10.10.0 0.0.0.255 area 1

#router id 2.2.2.2

OSPF configuration in router C>

#config t

#router ospf

#network 10.10.10.0 0.0.0.255 area 1

#network 172.16.31.0 0.0.0.255 area 1

Now in routers A, B and C

#clear ip ospf 1 process //restarting ospf process. Note:this would reset and renogotiate OSPF

Output at router B

Router#sh 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

172.16.0.0/24 is subnetted, 1 subnets
O 172.16.31.0 [110/65] via 10.10.10.2, 00:03:59, Serial1/0
10.0.0.0/24 is subnetted, 1 subnets
C 10.10.10.0 is directly connected, Serial1/0
C 192.168.0.0/24 is directly connected, FastEthernet0/1
C 192.168.168.0/24 is directly connected, FastEthernet0/0

Output at router A>>

router5>en
router5#sh 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 leve
ia - IS-IS inter area, * - candidate default, U - per-user static
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 1 subnets
O IA 172.16.31.0 [110/66] via 192.168.168.2, 00:20:21, FastEthernet0/0
10.0.0.0/24 is subnetted, 1 subnets
O IA 10.10.10.0 [110/65] via 192.168.168.2, 00:20:27, FastEthernet0/0
C 192.168.168.0/24 is directly connected, FastEthernet0/0

Output at router C>>

routerC#sh 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 l
ia - IS-IS inter area, * - candidate default, U - per-user stat
o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 1 subnets
C 172.16.31.0 is directly connected, FastEthernet0/0
10.0.0.0/24 is subnetted, 1 subnets
C 10.10.10.0 is directly connected, Serial1/0
O IA 192.168.168.0/24 [110/65] via 10.10.10.1, 00:23:01, Serial1/0

Now let's check whether ospf routes are learned at SonicWall.