Frame Relay Question

that's not as simple a question as one might think it is, however, I will try my best! One of the differences are how each type (P2P and P2MP) handles inverse arp and what type of network they represent.

point to point (one to one) links are treated like point to point links (only 2 devices on that link);basically, there is no need to map or inverse arp. Due to the nature of a point to point link, the protocol just assumes that whatever IP you're trying to reach is on the other end of that link, so the IP packet is encapsulated in a HDLC packet and sent out on the link.

Point-to-multipoint links are considered as a multi-access medium. (one to many [Hub to Spokes])

If all your remote edge devices need to be on the same logical subnet, you use multipoint, if all your remote edge devices can be addressed with individual subnets, you use point to point.

Hope this helps a bit

Billy

@ngmarowa I think that you have a simple way to explain, i asked you about the use of physical interfaces instead of virtual ones just to have a general idea and study the frame relay in every side that's it, of course i would use logical interfaces, but when you said the Multi point interface reduce the number of cables required and explain with the exemple i have understand that multipoint plays like if i have many physical lines in the same Serial cable. You still didn't give me an  idea about the point-to-point subinterfaces' use.
Can you tell me when can I use Multipoint interfaces and point-to-point and why?

@rfc1180: you said : there is no need to map or inverse arp to use point-to-point and so the IP packet is encapsulated in a HDLC packet and sent out on the link... This looks to me like if i'm configuring a simple Serial cable between 2 routers without puting Frame Relay at all !!! What about Frame Relay encapsulation?
And what you mean with  :Point-to-multipoint, can you detail this?
You also mentionned that in individual subnets i can use point-to-point, so how about a routing protocol like RIP or OSPF to be configured in other routers ?

Thank you

Multipoint interfaces are used when you want to connect 2 or more sites using one physical interface. Have used it for a Head Ofiice - Branch Offices configuration. Its like a hub and spoke setup. The branch offices will see it as a point to point. Only the Head office will have a multipoint interface. A more complicated approach would be a mesh topology where the branch offices also have multipoint interface to 2 or more point.

The bottom line is what you want to achieve and what resources are available. An example you want to link 3 sites, A, B and C. There are 2 possibilities:

1 A has a link to B and B has a link to C but  A and C do not have a direct link
2. All 3 sites have direct and independent links to each other

For scenario 1 you can have A link to C through B but the link will seem like a direct link until either the link between A and B or B and C is down. A and B will be linked with a point to point link. The same link is used for B to C. So B can use a multipoint interface.

Scenario 2 is open to a number of options. The bottom line is Technology, resources and infrastructure determines when you can use multipoint or point to point. Also point to point is used to connect 2 sites/points. When you have more than 2 then multipoint or multiple point to point links maybe required.

>there is no need to map or inverse arp to use point-to-point and so the IP packet is encapsulated in a HDLC packet and sent out on the link

"Sorry meant to say frame-relay packet not hdlc packet";it is not required to enable or disable Inverse ARP, because there is only a single remote destination on a point-to-point PVC and discovery is not necessary.

>You also mentionned that in individual subnets i can use point-to-point, so how about a routing protocol like RIP or OSPF to be configured in other routers ?

Routing protocols: this is a totally different topic. OSPF has 5 different types for FR-NBMA and how they react with point to point and point to multipoin. Some of the topics related aret:

    * OSPF treats Point-to-Multipoint networks as a series of point-to-point links, mirroring the layer 2 topology.
    * Point-to-Multipoint networks don’t have DR/BDR relationships.
    * Point-to-Multipoint networks advertise /32 routes for all the frame-realy endpoints.
    * Point-to-Multipoint networks have Hello and Dead intervals of 30 seconds and 120 seconds respectively.
    * Point-to-Multipoint non-broadcast networks are very similar to point-to-multipoint networks except that they work over layer 2 topologies that have no broadcast capability
    * Point-to-Multipoint non-broadcast networks allow you to define cost on a per neighbor basis.

There is no real simple answer to your question; it really depends on your network topology, routing infrastructure, etc. There are many designs that you can choose from based on how you want to deploy the network.

>please no web site ressources or pdf books, i need a simple explanation from your own experience

yet we have given you a simple explanation, but you still have questions; the only way you are going to understand it is from many resources on the web and possibly tech books on the subject. You are asking a question that can lead to a full chapter and more of explanations and no simple answer can honestly be given.

Billy



Billy

rfc1180: Thank you for your effort, I know this is not simple and of course this can lead to read books i just wanted something easier to explain it, web sites and tutorials seems to be complicated and they don't explain anything from the scratch.

Anyway, I've seen a scenario recently about configuring Frame relay here is the Scenario of a Hub & Spokes:

                                                                      Router1
                                                                        ||
                                                                        ||/||
                                                                          ||
                                                                    ========
                                                =======     ||   Frame   ||   =======
                  Router3      =====  \\                ||   Relay    ||               //=====  Router 2            
                                                                   =========

Router 1 is the Hub
Router 2 & 3 are the Spokes

I've seen some videos where R1 is configured as Point-to-point frame relay dlci with R2 & R3

Router2 need to go through R1 to have a communication with Router3,

Can you explain me why should we configure point-to-point and multipoint, is it about choice ? or about designing solutions? I think this is not something we guess and then say :" well i think i will configure point to point because i love it !!!" right?

If we have to configure point-to-point, what will happened if we configure multi point in this case?

Thank you again