Introduction to Frame-Relay for CCNA Students

Hi Rene,

Really a gr8…explanation. Now I understand actual Frame Relay concept…Thanks once again,

I think now in Network MPLS is used instead of Frame Relay…may be I have wrong…but please explain me difference between this MPLS vs Frame Relay…?

Waiting for your reply,

Imran Ghumara

Hi Imran,

Frame-relay is pretty old and you won’t see it in networks anymore. MPLS is very popular nowadays but it’s a completely different protocol compared to frame-relay…hard to explain in a few sentences here. I’ll write some more tutorials on MPLS in the future to explain it.


Thanks but give also the configuration parameters under frame relay

You are welcome iLeana and thanks :slight_smile:

The configuration examples for point-to-point and point-to-multipoint are here:

Thank you so much rene,ur article made me to master 60% of frame relay next configuration…

I think we cannot be more clear about basics of frame relay

thanks rene.
great explantion.

I felt how many times had you concerned about easily teaching! On reading your Introduction, I understood at one time.


Thanks that answered a lot of my questions.


Can u explained the steps involved after u completed and order for a VC.
What is the service provider obligation/responsibilities to get the VC up and running for u?
What equipment will they installed on ur premise? What cables will they run to ur premise?

Hi Raymond,

To be honest, I never worked with frame-relay on a production network here :slight_smile: It’s pretty old and here in the Netherlands a lot of companies switched to DSL / fibre / cable around 2000.

The installation is similar to any other link that you would get today (Fibre perhaps). The ISP takes care of the cabling and normally supplies the customer with a router for each site. These routers are normally managed by the ISP and you are not allowed to change the configuration.

Routers nowadays have WIC modules with an integrated CSU/DSU, older WIC modules so you needed a separate modem that was connected to your router. About the cabling, frame-relay supports a lot of different cabling options…copper and fibre.



Someone can explain me what is the relationship between the DE and the CIR in Frame Relay?


Hi Dominik,

The CIR rate is the committed rate, in other words the rate that the ISP guarantees that you will get.

The DE bit indicates that the frame has a lower importance. When there is congestion, the frames with the DE-bit set can be dropped.

Normally, all frames that exceed the CIR rate will have their DE-bit set so that’s the relationship between the two.



when HQ and sites are connected through physical serial interface. what is the use of virtual circuit(logical).
is it just to provide DLCI num

Hello Dheeraj!

As you mentioned correctly, the virtual circuit is a logical connection between two DTE (Data Terminal Equipment) devices within the framework of a Frame Relay implementation.

Regardless of how many physical serial interfaces you have connected to the frame relay network, you still require a virtual circuit for each logical connection. In other words, if you only have one physical serial interface, and you only have one virtual circuit connecting to a remote device via a frame relay connection, then you still require the virtual circuit. The virtual circuit is what defines the connection (via the DLCI as you mentioned) and the physical interface just provides the “pipe” through which the DTE connects to the network.

I hope this has been helpful!


19 posts were merged into an existing topic: Introduction to Frame-Relay for CCNA Students

Is it possible to do the lab in unetlab

Can you explain the below

If you use point-to-point it will solve your split-horizon problem but you’ll need to use a different IP subnet per PVC. Point-to-multipoint means you have the split-horizon problem but you can use a single IP subnet for all PVCs.

Hello Sims.

When designing frame-relay topologies, there are a couple of options.

First you can create a point-to-multipoint topology where each router on the frame-relay network has an IP address within the same subnet. Let’s say the subnet is Take a look at the following diagram and assume that each S0/0 interface of each router has an IP address of 10.10.10.X/24:

Keep in mind that point-to-multipoint means that Spoke1 cannot communicate directly with Spoke2. All communication between them MUST go through the Hub router. The Hub is the “point” and the Spokes are the “multipoints.”

So, using a routing protocol like EIGRP or OSPF, Spoke1 sends a routing update to the Hub router. Because of the split horizon rule, Spoke 2 will NEVER receive this update.

(Split horizon rule states that no routing update will be sent out of the same interface that it was received on. This is used to prevent routing loops.)

So because the Hub router received the routing update on S0/0, it will not send it out from there.

To solve this split-horizon problem, you can create point-to-point links between the routers such that each router has a direct path to every other router using subinterfaces. Take a look at the following figure:

Here you can see that there are subinterfaces configured on each of the serial links and each subinterface connects to a single subinterface on another router. The point to multipoint links are replaced by three point to point links, each with its own subnet. So now, for example, any advertisements that are received via subinterface S0/0/1.102 on R1 can be readvertised via S0/0/1.103 on the same router without violating the split-horizon rule.

Note that even though the readvertisement is exiting the same PHYSICAL interface, it is in essence exiting a different LOGICAL (sub)interface, thus it is not violating the split-horizon rule.

I hope this has been helpful!