Understanding IP OSPF Network Types.

jskfan
jskfan used Ask the Experts™
on
Understanding IP OSPF Network Types.

On the screenshot below, it shows a table of IP OSPF Network Types.
Regardless of how neighbors are discovered, if DR/BDR are elected,etc...
I would like to know in which scenario should I use one type and not the other.

Thank you

ospf
Comment
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
I'm not sure what you're asking, the network type is the key point

http://packetlife.net/blog/2008/jun/19/ospf-network-types/

Author

Commented:
For instance:

Non-Broadcast :  if OSPF is used  in Frame -Relay  
Broadcast :  if all OSPF routers are in a shared Segment
Point to Point : if 2 OSPF Routers are directly connected to each other

Etc...

Wanted just to know in which case each type is used
kevinhsiehNetwork Engineer

Commented:
Which type depends on the L2 network type. Generally you are using Ethernet, so that is broadcast.
Ensure you’re charging the right price for your IT

Do you wonder if your IT business is truly profitable or if you should raise your prices? Learn how to calculate your overhead burden using our free interactive tool and use it to determine the right price for your IT services. Start calculating Now!

Distinguished Expert 2018
Commented:
Not necessary. Most of time you can manually configure network type to override default type.
For example, you can configure on broadcast network point-to-multipoint non-broadcast and will have to configure neighbors statically.

I am saying this because I had request once that OSPF advertisements should not be received on any device in network segment that are not participating in OSPF routing. My solution was to configure point-to-multipoint non-broadcast network type on interfaces and static neighbor configuration which forced unicast packet exchange instead of multicast.

Some general rules can be found in tables below (did not check if all details are correct - someone else created those):

OSPF network types
More

Author

Commented:
to my unerstanding either you have for instance:

---R1 connected to R2 : this is point to point
-- R1,R2,R3 all connected to Ethernet Switch : This is Broadcast

--R1,R2,R3 connected to Frame Relay Switch , if R1 is the Hub , you can configure its sub-interfaces as point to point or point to multipoint , this is independent from OSPF Network Type. I am not sure if OSPF Network Type configured on Frame Relay should match the existing Frame relay interfaces type.



Outside from Frame Relay, I am not sure why would you configure Non-Broadcast or point to Multipoint.
Distinguished Expert 2018

Commented:
If you are searching for some significant meaning, there is no one.
Standards are created to "cover all possible use cases". Even if there is just one case where some specific technology is planned to be used, part of being architect/designer/engineer is to know corner cases.

Frame-relay, ATM, SMDS, & X.25 are non broadcast network types, so it is not just frame relay. So, on any of those network types we can't use (at least not natively), other network types.

Point to point accepts only two neighbors (and by this wasting 2 or 4 IP addresses), while configuring point-to-multipoint on non broadcast network can preserve IP address space.

I know it is boring for many engineers, but RFCs can point you in the right direction, but I guess book from the person who invented OSPF would be more useful than RFC itself.
John T Moy - OSPF: Anatomy of an Internet Routing Protocol

Author

Commented:
JustInCase

I mentioned Frame Relay because it is one of the odd ones...ATM,X.25 , etc... can also be taken as example.

Let's forgot about OSPF for a moment and talk about Frame-Relay

when configuring Frame-relay , you configure the physical Interface with Encapsulation, then you create  sub-interfaces as Point to Point or one Sub-interface as Point to MultiPoint.  Reading online, it says that in Frame relay you configure a sub-interface as  Multipoint if you have your Frame Relay Branches (Spokes) in the same subnet as the Hub.. If your Branches (Spokes) are in different subnets than the hub, then you create sub-interfaces as Point-to-Point
Now, let's bring OSPF into the game... If I configure OSPF  with the Frame Relay already in Place, then which OSPF Network Type should I use when Frame-Relay is using Multipoint sub-interface and  which OSPF Network Type should I use when Frame-Relay is using point to point sub-interfaces ?

Thank you

Author

Commented:
Thank you Guys

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial