LAB IX – RIPv2 -> OSPF Case Study

Building a use case from the CCDP FLG:

Topology:

Each site has two links to their HQ (top) via WAN (Prio) and Internet ( backup ).
Internet and WAN connectivity goes over multipoint GRE tunnels to the sites with static NHRP mappings.
Cost of Internet links are increased so they’re used as backup links.
Backbone area configured over WAN and Internet

Building the LAB:

OSPF Design

Building the Backbone:

Adding the tunnel interface and NHRP mappings on the WAN Hub Router (R1):

And we have some routing on the Hubs:

LAB I ( OSPF over GRE with and without IPsec )

Setup:

R1 functions as the internet.
R2 is the first location with Public IP 1.1.1.2/30
R3 is the second location with Public IP 1.1.2.2/30

There must be a GRE tunnel configured between R2 and R3 so that OSPF can be used between them. In the example we will use a tunnel with and without IPsec.

Configuration without IPsec:

ROUTER 2:

R2:

# WAN ADDRESS
interface FastEthernet0/0
 ip address 1.1.1.2 255.255.255.0
 duplex auto
 speed auto
!

# TUNNEL ADDRESS
interface Tunnel0
 ip address 10.10.10.1 255.255.255.252
 tunnel source 1.1.1.2
 tunnel destination 1.1.2.2
!

# LAN ADDRESS
interface Loopback0
 ip address 192.168.10.1 255.255.255.0
!

# OSPF CONFIG
router ospf 1
 log-adjacency-changes
 network 10.10.10.0 0.0.0.3 area 0
 network 192.168.10.0 0.0.0.255 area 0
!

# DEFAULT ROUTE (TRAFFIC TOWARDS R3)
ip route 0.0.0.0 0.0.0.0 1.1.1.1

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OSPF Stub Areas

There are four types of stub areas

stub
totally-stubby
not-so-stubby areas (NSSA)
totally not-so-stubby areas
All stub areas do not allow Type 5 (external) LSAs (ABR always filters them)
For the totally stub areas the ABR filters the Type 3 LSAs.

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OSPF Default Routing

Create a default route into a specific area
Create a default route into the entire OSPF domain
Default-information originate
- Creates a default route into OSPF, external Type 2 route, using a Type 5 LSA with metric 20
- default-information originate (always) metric 30 metric-type 1 route-map NAME
  - Default metric 20
  - Default metric-type 2
    - metric-type 1 cost can be changed
    - metric-type 2 cost can’t be changed
- The metric-type defines LSA is Type 1 External or Type 2 External (default)
- Route-map is used for tracking networks. If Route-map condition is met, default route is advertized.

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OSPF Route Filtering and Summarization

OSPF Route filtering between areas

Filtering prevents the creation of LSAs.
LSDB’s have to be the same for all routers ifnot SPF logic will fail
OSPF can filter the originiation of LSA between areas
Type 3 LSAs are filtered prior to origination ABR
- - With multiple ABRs filtering should be done on both.
  - ospf# area number prefix-list prefix name in|out
    - In: IOS filters routes comming in to that area
    - out: IOS filters routes comming out of that area
```
ip prefix-list NAME seq 5 deny 10.10.10.0/24 le 32
ip prefix-list NAME seq 10 permit 0.0.0.0/0 le 32

R1#(config-router)#area 1 filter-list prefix NAME in
R1#show ip ospf database summary self-originate
```
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OSPF Metric Calculations & Tuning

- Analyse the LSDB to find all possible routes to reach the subnet.
- Per route, add the interface cost for all outgoing interfaces in that route.
- Pick the route with the lowest cost.
  - Cost is derived from the egress interface bandwith.