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OSPF NBMA Topology

 
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sadiqsaad



Joined: 13 Jul 2007
Posts: 58

PostPosted: Mon Oct 15, 2007 3:08 pm    Post subject: OSPF NBMA Topology Reply with quote

Hello,

I am trying to make an OSPF NBMA network. What I'd like to ask is is it really necessary to make subinterfaces in frame relay like

S0/0.1
S0/0.2
S0/0.3

or I can do like this

S0/1
S0/2
S0/3

Help me out in this matter please.
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conspathas



Joined: 28 Mar 2007
Posts: 1217
Location: CCIE

PostPosted: Mon Oct 15, 2007 4:47 pm    Post subject: Reply with quote

Depending on your topology requirements - you can use either physical interface or subinterfaces.

This decision will also impact how certain things like routing protocols, multicast etc will behave as well.

Do you have a specific topology requirement or just asking in general?
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sadiqsaad



Joined: 13 Jul 2007
Posts: 58

PostPosted: Mon Oct 15, 2007 5:29 pm    Post subject: Reply with quote

Hi Conspathas

Thank you for your reply.


This image is from CBT Nuggets. I am trying to make this topology. Anyhow its not possible to make subinterfaces in the .net file, so shall I do this with physical interfaces?

Note: The cloud is a router.

Thanks
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conspathas



Joined: 28 Mar 2007
Posts: 1217
Location: CCIE

PostPosted: Mon Oct 15, 2007 7:35 pm    Post subject: Reply with quote

Yeh you can use any combination of physical, point-to-point or multipoint subinterfaces.

For example - using physical interfaces:

R4:
Code:
interface serial1/0
 encap frame
 no frame inverse
 ip address 10.1.1.4 255.255.255.0
 frame map ip 10.1.1.2 402 broadcast
 frame map ip 10.1.1.3 403 broadcast
 no shut


R2:
Code:
interface serial1/0
 encap frame
 no frame inverse
 ip address 10.1.1.2 255.255.255.0
 frame map ip 10.1.1.3 204
 frame map ip 10.1.1.4 204 broadcast
 no shut


R3:
Code:
interface s1/0
 encap frame
 no frame inverse
 ip address 10.1.1.3 255.255.255.0
 frame map ip 10.1.1.2 304
 frame map ip 10.1.1.4 304 broadcast
 no shut


In this scenario the default interface type for OSPF will be NON_BROADCAST on all the interfaces. You will need to ensure the HUB is the DR and that the SPOKES never become a DR or BDR by manipulating the OSPF priority on the interface.

Or if you wanted a ptp subif's on the spokes then:

R4:
Code:
interface serial1/0
 encap frame
 no frame inverse
 ip address 10.1.1.4 255.255.255.0
 frame map ip 10.1.1.2 402 broadcast
 frame map ip 10.1.1.3 403 broadcast
 no shut


R2:
Code:
interface serial1/0
 encap frame
 no shut
int s1/0.204 point
 ip address 10.1.1.2 255.255.255.0
 frame interface-dlci 204


R3:
Code:
interface s1/0
 encap frame
 no shut
interface s1/0.304 point
 ip address 10.1.1.3 255.255.255.0
 frame interface-dlci 304


This scenario creates a mismatch of the OSPF interfaces types - the hub is NON_BROADCAST whereas the spokes are POINT-TO-POINT. Therefore you will need to manipulate the OSPF network type under the interface to make things compatible.

And the list goes on...

The .net file would look something like this if you were using the built in Dynamips frame-relay switch:

Code:
[[Router R2]]
  s1/0 = FRSW1 2

[[Router R3]]
 s1/0 = FRSW1 3

[[Router R4]]
 s1/0 = FRSW1 4

[[FRSW FRSW1]]
 2:203 = 3:302
 2:204 = 4:402
 3:304 = 4:403


Whilst you could get away with not having the 2:203 = 3:302 PVC configured for this topology - at least the underlying layer 2 is fully meshed and then depending on your config on the routers - whether you use it or not - just bear in mind LMI will report the UNUSED pvc.
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sadiqsaad



Joined: 13 Jul 2007
Posts: 58

PostPosted: Mon Oct 15, 2007 8:36 pm    Post subject: Reply with quote

Thank you very much for your great help.

May God Bless You.
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