Question related to Frame Relay

mohsin.khan · ‎08-28-2008

Hi guys, i have few questions related to Frame Relay that have become some puzzles for me. I would appreciate if you answer them seperately, i mean 1 by 1.

Here they go.

You might find some of them silly, but i could not resist to know the answers so my quesiton are..

1) What is the difference between both of these commands

> Frame-relay interface-dlci {dlci_num}

> Frame-relay map ip {ip_addrs} {dlci_num}

2) Scott (IPExpert) says map and interface-dlci commands should not be used in conjunction, but cisco says in FR FAQ that to have one spoke talk to other on ICMP, you must use map command even if interface-dlci is there. Who is rite, and how?

3) According to theory, every VC must have a unique DLCI, but in point-to-point we use the same DLCI on a spoke (or hub) router, why?

4) Cisco Reference sheet says that if we configure multipoint and do not use inverse arp, then we MUST use interface-dlci command, why must in multipoint?? I have seen this command even if the inverse arp is enabled, so wats the difference?

5) Can you share any link where i could find some topologies where inverse arp is disabled?

Thanks in advance.

mohsin.khan · ‎08-30-2008

Guys, some one, please help....

Edison Ortiz · ‎08-30-2008

1) What is the difference between both of these commands

> Frame-relay interface-dlci {dlci_num}

> Frame-relay map ip {ip_addrs} {dlci_num}

The first command is often used on subinterfaces to allocate a DLCI on that subinterface that was previously allocated to the main interface. Just do a quick lab and you will notice that all DLCIs are assigned to the main physical interface and as soon as you use the frame interface-dlci command, the pointer changes to the subinterface.

When this command is used in the main interface, it's often for Frame-Relay Traffic Shaping when assigning per-PVC QoS.

The second command, creates a static mapping of the IP address to a DLCI.

2) Scott (IPExpert) says map and interface-dlci commands should not be used in conjunction, but cisco says in FR FAQ that to have one spoke talk to other on ICMP, you must use map command even if interface-dlci is there. Who is rite, and how?

If you don't get a dynamic entry on the DLCI with inverse-arp, you need to use the Frame-Relay map ip command. You can check your mappings (dynamic or static) with the show frame map command.

3) According to theory, every VC must have a unique DLCI, but in point-to-point we use the same DLCI on a spoke (or hub) router, why?

The DLCI is local significant to the Frame Relay Switch. You are connected directly to a Frame-Relay switch that expect a DLCI value. The frame-relay switch switches this value to another of its interfaces that has a different set of DLCI values. Those interfaces are facing to other spokes. The DLCI values on these interfaces can be the same or different.

4) Cisco Reference sheet says that if we configure multipoint and do not use inverse arp, then we MUST use interface-dlci command, why must in multipoint?? I have seen this command even if the inverse arp is enabled, so wats the difference?

I believe you mean, 'we need to use the frame-relay map command'. In multipoint, similar to the physical interface, if inverse-arp is disabled, frame-interface-dlci does nothing.

5) Can you share any link where i could find some topologies where inverse arp is disabled?

I don't have any links at the moment. The best suggestion I can give you is, lab it up :)

HTH,

__

Edison.

Please rate helpful posts

mohsin.khan · ‎09-01-2008

Thanks for the info. I have rated your post accordingly. However, i have few pointsthat still need some argument.

- I haven't come accorss configuration of frame-relay for SVCs. Is it something that i should worry about and look for? Almost all the books explain frame-relay for PVCs and not for SVCs,so i m just curious.

- Regarding my question 4, i really meant "interface-dlci" command, as it is stated in the quick sheet that:

"If you configured a point-to-point subinterface, or if you configured multipoint and are not using IARP-you must configure the local DLCI using the following command:

Router(config-subif)# frame-relay interface-dlci dlci-number

"

My question is same as what you stated, if inverse-arp is disabled, "frame interface-dlci" does nothing, then what is the meaning of above quick ref's statement?

- my question 3 got wrong, it was like "in MULTIPOINT, we use ONE DLCI on the hub router, whereas according to theory every VC has a unique DLCI, then why ONE DLCI on the hub that is configured for MULTIPOINT?

Hope you'll get some time to answer these as well :)

Edison Ortiz · ‎09-02-2008

Hi,

Thanks for the rating and sorry for the delay.

- I haven't come accorss configuration of frame-relay for SVCs. Is it something that i should worry about and look for? Almost all the books explain frame-relay for PVCs and not for SVCs,so i m just curious.

It's not common to see SVC configurations.

I highly recommend you reading the following book:

Cisco Frame Relay Solutions Guide

by Jonathan Chin

Publisher: Cisco Press

Pub Date: March 17, 2004

Print ISBN-10: 1-58705-116-8

Print ISBN-13: 978-1-58705-116-6

I will not plagiarize the book on this post, but the book explains the SVC configuration in detail and any other question or concern you have regarding Frame-Relay. If you really want to know Frame-Relay inside/out, please read it.

HTH,

__

Edison.