Hub and spoke and "ip ospf network" command

[zillah2004]

From Internetwork Expert Lab :

(((Hub and spoke and "ip ospf network" command

With Hub and spoke topology, If R2 is hub and R1, R3 are spokes,,,,and if the question ask :

1- Configure OSPF area 0 on the Frame Relay connection between R1, R2, and R3.

2- Do not use the "ip ospf network" interface command on R2.

The task above states that the "ip ospf network" command should not be used on R2,,,hat implies that OSPF network type that must be used on this segment is non-broadcast.))).

How does it imply ?

[mheusinger]

Hi,

configure point-to-point sub-interfaces, one for each FR PVC.

OSPF by default assumes a broadcast network (i.e. FR full mesh) when you use multipoint interfaces, which can be "repaired" with "ip ospf network".

It´s different for p2p interfaces so this works also for hub-and-spoke (i.e. NO full mesh).

Regards

Martin

[zillah2004]

((OSPF by default assumes a broadcast network (i.e. FR full mesh) when you use multipoint interfaces))

Internetwork Expert Lab states this:

"Frame Relay physical and multipoint subinterfaces default to OSPF network type non-broadcast, while Frame Relay point-to-point subinterfaces default to OSPF network type point-to-point"

I feel there is contradiction between what you said and what Internetwork Expert Lab says,,,,correct me if I am wrong ?

[Georg Pauwen]

Hello,

in addition to Martin's post, you could also leave the interfaces at their default (non-broadcast), and instead configure neighbors on the hub router. The configuration would look like this:

R1

!

interface Serial0

ip address 160.12.123.1 255.255.255.0

ip ospf priority 0

!

router ospf 1

router-id 1.1.1.1

network 160.12.123.1 0.0.0.0 area 0

R2

!

interface Serial0

ip address 160.12.123.2 255.255.255.0

!

router ospf 1

router-id 2.2.2.2

network 160.12.123.2 0.0.0.0 area 0

neighbor 160.12.123.1

neighbor 160.12.123.3

R3

!

interface Serial0

ip address 160.12.123.3 255.255.255.0

ip ospf priority 0

!

router ospf 1

router-id 3.3.3.3

network 160.12.123.3 0.0.0.0 area 0

The 'ip ospf priority 0' command on the spokes ensures that the hub router becomes the DR.

HTH,

GP

[zillah2004]

((,,,that implies that OSPF network type that must be used on this segment is non-broadcast.))).

Why,,,I want to understand the concept

[zillah2004]

((OSPF by default assumes a broadcast network (i.e. FR full mesh) when you use multipoint interfaces))

Internetwork Expert Lab states this:

"Frame Relay physical and multipoint subinterfaces default to OSPF network type non-broadcast, while Frame Relay point-to-point subinterfaces default to OSPF network type point-to-point"

I feel there is contradiction between what you said and what Internetwork Expert Lab says,,,,correct me if I am wrong ?