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Monday, October 25, 2010

OSPF Point-to-Multipoint config

While playing a little bit with an OSPF lab i had to configure Point-to-Multipoint network type,
Using the following Scenario:
(the post is related to R2, R5 and R6 only)

R2, R5 and R6 are all connected using frame-relay, dlci 205-502 connect R2 to R5 and dlci 206-602 connect R2 to R6.

R2 config:
interface Serial0/0
ip address 10.1.56.2 255.255.255.0
encapsulation frame-relay
ip ospf network point-to-multipoint non-broadcast
clock rate 2000000
frame-relay map ip 10.1.56.5 205 broadcast
frame-relay map ip 10.1.56.6 206 broadcast
frame-relay interface-dlci 205
frame-relay interface-dlci 206
no frame-relay inverse-arp
router ospf 1
router-id 2.2.2.2
log-adjacency-changes
network 10.1.56.2 0.0.0.0 area 1
network 10.1.123.2 0.0.0.0 area 0
neighbor 10.1.56.6
neighbor 10.1.56.5

R5 config:
interface Serial0/0
ip address 10.1.56.5 255.255.255.0
encapsulation frame-relay
clock rate 2000000
frame-relay map ip 10.1.56.2 502 broadcast
frame-relay interface-dlci 502
no frame-relay inverse-arp
router ospf 1
router-id 5.5.5.5
log-adjacency-changes
network 5.5.5.5 0.0.0.0 area 1
network 10.1.56.5 0.0.0.0 area 1
neighbor 10.1.56.2

R6 config:
interface Serial0/0
ip address 10.1.56.6 255.255.255.0
encapsulation frame-relay
clock rate 2000000
frame-relay map ip 10.1.56.2 602 broadcast
frame-relay interface-dlci 602
no frame-relay inverse-arp
router ospf 1
router-id 6.6.6.6
log-adjacency-changes
network 6.6.6.6 0.0.0.0 area 1
network 10.1.56.6 0.0.0.0 area 1
network 10.6.0.0 0.0.3.255 area 1
neighbor 10.1.56.2

As you may recall OSPF network type point-to-multipoint doesn't use DR/BDR election and due to the use of the neighbor statement, hello and updates, are exchange via unicast.
But still, although i have configured ospf network type point-to-multipoint on R2 s0/0 interface something is missing and because of that i do see adjacency's but no routing exchange has occur?!

R2#sh ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
R1 1 FULL/DROTHER 00:00:39 10.1.123.1 FastEthernet0/0
R3 1 FULL/BDR 00:00:36 10.1.123.3 FastEthernet0/0
6.6.6.6 0 FULL/ - 00:01:46 10.1.56.6 Serial0/0
5.5.5.5 0 FULL/ - 00:01:33 10.1.56.5 Serial0/0

R2# 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

2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
10.0.0.0/24 is subnetted, 6 subnets
O 10.1.3.0 [110/11] via 10.1.123.1, 00:44:09, FastEthernet0/0
O 10.1.2.0 [110/11] via 10.1.123.1, 00:44:09, FastEthernet0/0
O 10.1.1.0 [110/11] via 10.1.123.1, 00:44:09, FastEthernet0/0
O 10.1.0.0 [110/11] via 10.1.123.1, 00:44:09, FastEthernet0/0
C 10.1.56.0 is directly connected, Serial0/0
C 10.1.123.0 is directly connected, FastEthernet0/0

The reason for this behavior is because i didn't configure the network type on R5 and R6.

R5# sh ip ospf interface s0/0
Serial0/0 is up, line protocol is up
Internet Address 10.1.56.5/24, Area 1
Process ID 1, Router ID 5.5.5.5, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 5.5.5.5, Interface address 10.1.56.5
Backup Designated router (ID) 2.2.2.2, Interface address 10.1.56.2
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
oob-resync timeout 120
Hello due in 00:00:16
Supports Link-local Signaling (LLS)
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 6
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Backup Designated Router)
Suppress hello for 0 neighbor(s)

R5 believe that the network is NON_BROADCAST which act differently (DR/BDR election) form PtMP network type.

Configuring the network type on interface s0/0 on R5 and R6 will fix the problem.

R2#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

2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, Loopback0
5.0.0.0/24 is subnetted, 1 subnets
O 5.5.5.0 [110/65] via 10.1.56.5, 00:00:01, Serial0/0
6.0.0.0/24 is subnetted, 1 subnets
O 6.6.6.0 [110/65] via 10.1.56.6, 00:00:01, Serial0/0
10.0.0.0/8 is variably subnetted, 12 subnets, 2 masks
O 10.1.3.0/24 [110/11] via 10.1.123.1, 00:51:08, FastEthernet0/0
O 10.1.2.0/24 [110/11] via 10.1.123.1, 00:51:08, FastEthernet0/0
O 10.1.1.0/24 [110/11] via 10.1.123.1, 00:51:08, FastEthernet0/0
O 10.1.0.0/24 [110/11] via 10.1.123.1, 00:51:08, FastEthernet0/0
O 10.6.0.0/24 [110/65] via 10.1.56.6, 00:00:01, Serial0/0
O 10.6.1.0/24 [110/65] via 10.1.56.6, 00:00:01, Serial0/0
O 10.6.2.0/24 [110/65] via 10.1.56.6, 00:00:01, Serial0/0
O 10.6.3.0/24 [110/65] via 10.1.56.6, 00:00:01, Serial0/0
C 10.1.56.0/24 is directly connected, Serial0/0
O 10.1.56.6/32 [110/64] via 10.1.56.6, 00:00:01, Serial0/0
O 10.1.56.5/32 [110/64] via 10.1.56.5, 00:00:01, Serial0/0
C 10.1.123.0/24 is directly connected, FastEthernet0/0

So do pay attention to the network type while configuring OSPF.

2 comments:

  1. Thank you and very usefull. Sorry i have a couple questions im a slow learner. So when you are configuring a point to multipoint on framerelay with OSPF, i dont understand why we are adding the broadcast keyword when we are mapping the IP's with the correlating DLCI's? Another question, so we are configuring on R2 as the hub so it can map both r5 and r6 but why isnt r2 using subinterfaces? So would this be NBMA network and why? would sending broadcasts cause routing loops and how?
    Thanks

    Amir

    ReplyDelete
  2. Hi Amir,

    Sorry for the late response....hope my answers will still be valid :)
    I added the broadcast keyword to allow OSPF to work (multicast)
    R2 is using point-to-multipoint interface, so no sub-interface is required.
    Frame-relay is NBMA network by nature
    Sending broadcast would not cause routing loops because routers doesn't forward broadcast.

    Thx,
    Tal

    ReplyDelete