Wednesday, February 16, 2011

Lab 4 - OSPF in Point-to-Multipoint

Prerequisites: CCNP level skills.

Cisco IOS OSPF modes:
  1. Point-to-point (Cisco)
  2. Broadcast (Cisco)
  3. Non-broadcast (RFC 2328)
  4. Point-to-multipoint (RFC 2328)
  5. Point-to-multipoint non-broadcast (Cisco)
Topology

Pic. 1 - Topology Diagram.
Icons designed by: Andrzej Szoblik - http://www.newo.pl

Workflow
  1. Get familiar with the topology.
  2. Read the 'Task List'.
  3. Read the 'Questions' and provide the answers BEFORE configuring the routers.
  4. Configure the lab according to the 'Task List' .
  5. Compare the answers (step 3) with the lab results.
Task List
  • Configure IP addresses as per topology diagram and use encapsulation Frame-Relay on S0/0 interfaces.
  • Make sure that you use only DLCIs specified in the topology diagram (pic. 1) and routers do not learn any other DLCIs dynamically.
  • R2 should use only one layer 3 to layer 2 mapping. Also R3 should use only one layer 3 to layer 2 mapping.
  • Configure OSPF with all links in area 0. Make sure that R2 can ping R3's loopback0 and S0/0 interfaces (R2 must not have frame-relay mapping to R3).
Questions
  1. What are the differences betweent OSPF point-to-multipoint and non-broadcast on Frame-Relay links?
  2. Does point-to-multipoint mode networks use multicast or unicast to transmit OSPF packets? Why?
  3. What are the default hello/dead interval timers on point-to-multipoint links?

Lab Solution

R1 Configuration:
!
interface loopback0
 ip address 172.16.101.1 255.255.255.0
 ip ospf network point-to-point
!
interface Serial0/0
 ip address 10.1.1.1 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-multipoint
 frame-relay map ip 10.1.1.2 102 broadcast
 frame-relay map ip 10.1.1.3 103 broadcast
 no frame-relay inverse-arp
!
router ospf 1
 router-id 1.1.1.1
 log-adjacency-changes
 network 10.1.1.1 0.0.0.0 area 0
 network 172.16.101.1 0.0.0.0 area 0
!

R2 Configuration:
!
interface Loopback0
 ip address 172.16.102.2 255.255.255.0
 ip ospf network point-to-point
!
interface Serial0/0
 ip address 10.1.1.2 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-multipoint
 frame-relay map ip 10.1.1.1 201 broadcast
 no frame-relay inverse-arp
!
router ospf 1
 router-id 2.2.2.2
 log-adjacency-changes
 network 10.1.1.2 0.0.0.0 area 0
 network 172.16.102.2 0.0.0.0 area 0
!

R3 Configuration:
!
interface Loopback0
 ip address 172.16.103.3 255.255.255.0
 ip ospf network point-to-point
!
interface Serial0/0
 ip address 10.1.1.3 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-multipoint
 frame-relay map ip 10.1.1.1 301 broadcast
 no frame-relay inverse-arp
!
router ospf 1
 router-id 3.3.3.3
 log-adjacency-changes
 network 10.1.1.3 0.0.0.0 area 0
 network 172.16.103.3 0.0.0.0 area 0
!

Verification
Note!
OSPF point-to-multipoint treats the circuits as point-to-point links so no DR/BDR are elected. In addition to that, the spokes do not have to have IP-to-DLCI mapping via R1. R1 resolves the reachability between spokes by injecting itself as the next-hop. Both spokes know how to reach R1 according to IP-to-DLCI static mapping.

Pic. 2 - Only DLCIs as per Topology Diagram.

Pic. 3 - R1's Adjacencies with R2 and R3.

 Pic. 4 - R2 /32 Route Injected by R1.

Pic. 5 - Traceroute.
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