Cisco Frame-relay Switch Configuration

This topic is to discuss the following lesson:

What happens to a dlci when it goes through a router? is this layer 2 from ISP to your remote site?

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Hello Justin,

As I was writing you answer I found that I need some deeper understanding of this topic myself. What I can say is that Rene has an excellent analogy for this.

This lesson may help you understand the topic better. I would dive into this lesson myself but I have just finished studying and need a break. Please let me know if I can help you on these forums!

I hope this helps,
Scott

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Thanks for the link. I have read this article multiple times =)

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Hello Justin

Frame relay is a layer two technology and as a result, DLCIs do not traverse a router. In this example, the Frame Relay Switch is actually physically a router, a layer three device, but its functionality in this case is a layer two device. This can be seen clearly by the encapsulation of type “frame relay” that is specified in the config. Specifically it is switching between one DLCI to another, something that the ISP would do for the customer.

The only layer three devices here are the two customer devices. Now the DLCIs and their scope actually ends at the routers themselves, in a similar way to how MAC addresses have a scope within the specific network segment in which they reside.

So to specifically answer your question, this is a layer two connection between the customer and the ISP frame relay switch. Indeed it is a layer two connection all the way to the remote site as well. There is no layer three functionality that is intervening between R1 and R2. The switchover from DLCI 102 to 201 is an exclusively layer two operation.

I hope this has been helpful!

Laz

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Thank you! It seemed that way its just so weird to me because the distance between two company sites can be very far. Thanks again for the help!

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Can I conclude that the frame relay technology has been deprecated because of its small bandwidth and non broadcast nature?

Thanks.

Hello Rocky

The reason why Frame Relay is declining in use is primarily because of the competition it’s facing from cheaper and faster technologies such as Cable, DSL, Metro Ethernet and MPLS, all of which, with the appropriate configuration, can outperform Frame Relay in most cases. Also, these technologies are more compatible with the LAN technologies used while Frame-Relay is completely different and requires the appropriate termination equipment (CSU/DSU etc) at the customer premises.

Limited bandwidth is not so much an issue as cost per bandwidth unit is. Getting a fast Frame Relay connection that is comparable to the aforementioned technologies can become prohibitively expensive. The non-broadcast nature is an issue, but can be dealt with relatively easily.

I hope this has been helpful!

Laz

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Hello Rene,

Thanks for the great explanation.
The frame relay configuration posted in the tutorial is using local significance addressing.
Can you please provide example of frame relay configuration using global significance addressing ?

Thanks,
Sachin

Hello Sachin

The mechanisms used for either globally or locally significant addressing are the same. The only difference is that with globally significant addressing, you are limited to using a particular set of DLCIs rather than choosing your own. Globally significant addressing is limited to using only 992 unique DLCIs since DLCIs are defined by 10 bits (2^10=1024) and 32 values are reserved DLCI addresses. This limitation has made globally significant addressing in frame relay an approach that is rarely used.

Nevertheless, you can find some information about globally significant addressing and how it compares to locally significant addressing at this Cisco documentation.

I hope this has been helpful!

Laz

Nowadays, still exist any serial connection? can you give me any examples of serial connection ??

Hello Giovanni

The truth is that over the past few years, serial technologies for connecting to the WAN or to the Internet have been phased out almost completely. It is difficult to find Frame-Relay or other similar WAN technologies today, although they do exist in some places.

Serial ports today are more often used for specialty applications where there are low bandwidth requirements in remote locations. Applications such as out of band management connectivity for remote devices as well as some low bandwidth satellite connections still use serial technologies.

But for WAN and Internet connectivity, technologies such as MetroEthernet, DSL, Cable, and Microwave are most commonly used, and you will rarely find serial technologies for such applications.

I hope this has been helpful!

Laz

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hello ,
i have a question … how did we get the DLCI number ? in youre explaination it was already there ?!
will the ISP provide it to us ?

apart from theis , everything is clear … thank you !

Hello Abdullah

In this particular lesson, Rene is showing how to create a Frame-Relay switch for the purpose of creating labs in an emulator to practice Frame-Relay configurations. Rene states in the lesson that:

Normally you don’t really have to think about the frame-relay switch since this is something that the service provider will configure. If you are studying frame-relay for (Cisco) exams then you only need to understand how to configure it from the customer’s perspective.

So in this scenario, you are the ISP and you are configuring in the frame relay switch, what DLCIs will be routed where. Specifically, it is this command (and smiliar commands) that configure this:

frame-relay route 102 interface serial1/2 201

It tells the FR switch that anything that arrives with a DLCI of 102 should be sent out of S1/2 with a DLCI of 201.

Now as the ISP, you would then tell your customers to configure their Frame-Relay equipment to use the appropriate DLCIs. Specifically, based on the above command, you would tell your customer that is connected to S1/2 to use a DLCI of 201.

To see how customer equipment should be configured, take a look at the following lesson:

I hope this has been helpful!

Laz

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thank you so much … :slight_smile:

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I’m loving your materials.
I have a question related to frame relay -

  1. you mentioned frame relay is something provided by ISPs and it is used to connect multiple sites of an enterprise (probably connected at different location).
    So the frame relay cloud can’t be a single physical switch. I am assuming the frame relay switch is logical representation. Is my understanding correct?

  2. I’m assuming the frame relay cloud would be a large network in itself (since it is provided by ISPs to connect different sites at different geographical locations) consisting of multiple routers. Why can’t this be another Ethernet network? Why should we need a seperate WAN protocol?

Hello Darshan

Frame-Relay is a layer 2 technology that can be used to interconnect multiple remote sites of an enterprise. You are correct, that the Frame-Relay cloud, in reality, consists of a large infrastructure of interconnected devices. When labbing this up, the Frame-Relay cloud is represented by a single device, so your understanding is correct.

As for your second question, the choice of technology to interconnect remote sites is based on several factors including availability, performance, and cost. Frame-Relay is a technology that was very popular in the 1990s as it was a cheaper alternative to leased lines.

Over the decades, it declined in use and has been largely replaced by other WAN technologies including MetroEthernet, MPLS, DSL, Cable, VPNs, wireless bridges, and fiber optic links, or some combination of several of these technologies. Once again, the choice of the WAN technologies used depends upon availability, performance, and cost, and today, most of these mentioned technologies outperform Frame-Relay and are also cheaper, and more widely available.

So to answer your question directly, yes, we could use Ethernet as a WAN technology, and in many cases, it is a good choice. However, there are quite a few other choices as well that may be more beneficial for your particular arrangement.

Why are we still talking about frame relay even though it is almost completely phased out today? Take a look at this post for the answer…

I hope this has been helpful!

Laz

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Thanks @lagapidis for clarifying my doubt.

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