Frame Relay Tutorial
In the last part we will mainly learn about LMI, which is the signaling protocol of Frame Relay
LMI
Local Management Interface (LMI) is a signaling standard protocol used between your router (DTE) and the first Frame Relay switch. The LMI is responsible for managing the connection and maintaining the status of your PVC.
LMI includes:
+ A keepalive mechanism, which verifies that data is flowing
+ A multicast mechanism, which provides the network server (router) with its local DLCI.
+ A status mechanism, which provides PVC statuses on the DLCIs known to the switch
In our example, when HeadQuarter is configured with Frame Relay, it sends an LMI Status Inquiry message to the DCE. The response from the DCE might be a small Hello message or a full status report about the PVCs in use containing details of all the VCs configured (DLCI 23 & 51). By default, LMI messages are sent out every 10 seconds.
The four possible PVC states are as follows:
+ Active state: Indicates that the connection is active and that routers can exchange data.
+ Inactive state: Indicates that the local connection to the Frame Relay switch is working, but the remote router connection to the Frame Relay switch is not working.
+ Deleted state: Indicates that no LMI is being received from the Frame Relay switch, or that there is no service between the customer router and Frame Relay switch.
+ Static state: the Local Management Interface (LMI) mechanism on the interface is disabled (by using the “no keepalive” command). This status is rarely seen so it is ignored in some books.
We can use the “show frame-relay lmi” to display LMI statistics of Frame Relay on enabled interfaces of the router. The output shows the LMI type used by the Frame Relay interface and the counters for the LMI status exchange sequence, including errors such as LMI timeouts.
Cisco routers support the following three LMI types:
* Cisco: LMI type de?ned jointly by Cisco, StrataCom, Northern Telecom (Nortel), and Digital Equipment Corporation
* ANSI: ANSI T1.617 Annex D
* Q.933A: ITU-T Q.933 Annex A
Notice that three types of LMI are not compatible with each others so the LMI type must match between the provider Frame Relay switch and the customer DTE device.
From Cisco IOS Release 11.2, the router attempts to automatically detect the type of LMI used by the provider switch.
Note: LMI is required for Inverse ARP to function because it needs to know that the PVC is up before sending out Inverse ARP Request.
Now you learn most of Frame Relay mentioned in CCNA, some other Frame Relay’s characteristics you should know are mentioned below.
Other Frame Relay characteristics
+ Frame Relay provides no error recovery mechanism. It only provides CRC error detection.
+ Unlike with LANs, you cannot send a data link layer broadcast over Frame Relay. Therefore, Frame Relay networks are called nonbroadcast multiaccess (NBMA) networks.
+ Depending on the bandwidth needed for each virtual connection, the customer can order a circuit with a guaranteed amount of bandwidth. This amount is the Committed Information Rate (CIR). CIR defines how much bandwidth the customer is “guaranteed” during normal network operation.
+ Any data transmitted above this purchased rate (CIR) is available for discard by the network if the network doesn’t have available bandwidth.
+ If the Frame relay switch begins to experience congestion, it sends the upstream site (to the source) a Backward explicit congestion notification (BECN) and the downstream site (to the destination) a Forward explicit congestion notification (FECN).
+ There are two Frame Relay encapsulation types: the Cisco encapsulation and the IETF Frame Relay encapsulation, which is in conformance with RFC 1490 and RFC 2427. The former is often used to connect two Cisco routers while the latter is used to connect a Cisco router to a non-Cisco router.
+ Frame Relay does not define the way the data is transmitted within the service provider’s network once the traffic reaches the provider’s switch. So the providers can use Frame Relay, ATM or PPP… inside their networks.
Layer 2 Encapsulation Protocols
Besides Frame Relay there are other Layer 2 Encapsulation Protocols that you can implement instead:
High-Level Data Link Control (HDLC): The default encapsulation type for Cisco routers on point-to-point dedicated links and circuit-switched connections. HDLC is a Cisco proprietary protocol.
Point-to-Point Protocol (PPP): Provides connections between devices over several types of physical interfaces, such as asynchronous serial, High-Speed Serial Interface (HSS1), ISDN, and synchronous. PPP works with many network layer protocols, including IP and IPX. PPP can use either Password Authentication Protocol (PAP) or Challenge Handshake Authentication Protocol (CHAP) for authentication.
X.25/Link Access Procedure, Balanced (LAPB): Defines connections between DTE and DCE for remote terminal access. LAPB is a data link layer protocol specified by X.25.
Asynchronous Transfer Mode (ATM): International standard for cell relay using fixed-length (53-byte) cells for multiple service types. Fixed-length cells allow hardware processing, which greatly reduces transit delays. ATM takes advantage of high-speed transmission media such as E3, T3, and Synchronous Optical Network (SONET).
If you want to learn how to configure Frame Relay in GNS3, please read my Frame Relay Lab in GNS3 tutorial.
It seems easy when you’re reading it, because the examples are simple.
When you are given network diagrams, sometimes the frame relay connection is portrayed as a solid line from router to router, implying a physical connection (as in the leased line example at the top) when this is not actually the case.
The first thing to do in these cases is work out where the frame relay cloud is situated, and (from the routing perspective), focus on the endpoints of each VC.
If you are dealing with a full mesh or ‘hub and spoke’ design, you can ignore the connections within the cloud itself. This is only important for a partial mesh where more than one router is taking on a distributive role.
When you are also required to perform configuration, it may help to use your note-taking materials in the exam to construct your own diagram. This way, you can keep the question on screen with your console, while having a diagram that you can edit if required.
Great work!
Thank you so much!
said Ed Perrott, there are actually numerous patchwork purses you can pick from. were piped over a distance of 16km to a tailing dam sited in Lohan Valley about 980m below the mine.?
i want to download this in pdf document how can i download it\.
thanks a lot for the tutorial, it clarified things…
so there is a frame-relay encapsulation type “cisco” and an LMI type “cisco” as well. 2 different things but the same name..
hi there,
I have appreciate your explanation and the tutorial was simple and nice to understanding .
thanks
madja
Thank you for a well explained and presented article
very easy for study
This is very easy to understand and usefully for a newbie like me. THANK YOU!
arrr
Hi,
Very nice explanation.Really helful.
I think there is a small mistake in diagram labeling. For branch-2 DLCI 51, but in diagram it shows DLCI -49..
Nasir uddin Pavel
Linux pathshala
Hi,
Very nice explanation.Really helful.
I think there is a small mistake in diagram labeling. For branch-2 DLCI 51, but in diagram it shows DLCI -49..
Nasir uddin Pavel
Linux pathshala
@Linux Pathshala: It is not a mistake. The DLCI 49 is used on Branch 2 for traffic to the HeadQuarter.
plsssssssssssss help for dis exami need dumps oooo
what is the difference b/w RARP and InARP…?
@ Adex
if u need CCNA 200-120 dumps i will provide of other then sorry…
HI
Very nice explaniation
But I have a question
For branch-2 DLCI 51, but in diagram it shows DLCI -49..
It is not a mistake. The DLCI 49 is used on Branch 2 for traffic to the HeadQuarter.
why HQ & branch-1 DLCI is 23 both sides, and HQ DLCI 51,For branch-2 DLCI is 49.
what about it if I had more than 2 branches
are those standards
Thank you
@jefdezp: It is not a mistake. We implied DLCI is a random number used by both devices so they can be the same (DLCI 23 between HQ & Branch1) or different (DLCI 51 & 49 between HQ & Branch2). If more branches are added they just use other DLCIs, provided they are different at the local routers.
In Frame Relay InARP is the extension for ARP whereas RARP is the Reverse Address Resolution Protocol.
nice
very easy explanation.. thanks
HI
very nice tutorial
Frame-relay is not a problem to me, is easy to work with it dose not require that much typing commands. good luck guys.
Excellent tutorial
Great article. A little confusion here—why do we need DLCI when we already have PVC Number?
superb tutorial
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nice explanation
Very nice explanations with simple understanding examples ..i love it
VCE PLAYER 1.1.7 crack is needed for my exams , can any one help ?
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Did anyone do Boson simulations? I mean there are ICND1 ,ICND2 and CCNP for old syllabus. Is CCNP frame relay of Boson applicable to new CCNA(200-120) ?
Great work. thanks alot
the exam has changed. the dumps is now uselesss
what is the types that frame relay network transfer data?
Great piece of work! Full of information.
how bout CSU/DSU. how does it work?
got the frame relay concept..
This is the simplest way for explaining things in detail.
Hi, I think there is a mistake in the Quiz 11 question 43 about frame-relay mapping.
You have this situation.
R1 DLCI 100——————————————————–R2 DLCI 200
IP: 172.16.100.2/16 172.16.100.1
The configuration on R1 was : #frame-relay map ip 172.16.100.1 100 broadcast
Which in my concept is good!!
But in the quiz answers when you choose : “incorrect map statement ” then you have it right. But actually the configuration was good!!
Great tutorial!
VCE player higher version 1.1.7 or above , needed for my exam prctice. please help me >>>
my email : sarohan.sanjaya@gmail.com
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if you are only concerned with this MATERIAL because you want to pass the test…you have NO BUSINESS administering a live production site.
GET understanding first…and the exam will just be another boring example to you and you’ll be able to concentrate on TROUBLESHOOTING TECHNIQUES and how to GET to the answers effectively and quickly.
-M
wonderfull work thanks many
syed, to download to pdf, simply select entire text and right click (if you are using chrome) and choose print; one of your printers needs to be set up as a pdf output; it will save to that file then print
helpful thaxs
helpful thaxs
Simple and clear
nyce