Different Frame-Relay Commands

[daudparvez]

I am trying to figure out the real difference between the following two commands:

frame-relay map ip "IP Address" "DLCI"

and

frame-relay interface-dlci "DLCI"

command, but get confused in their purpose.

As far as I know is that the first command is used on physical interfaces to get control over the routing updates, i.e, to have a control over to which neighbor to send updates by using the "broadcast" keyword. This control is not available in case of dynamic mappings using inverse-arp in which case updates are sent to all the neighbors known to a router via inverse-arp.

An for the second command, i just know that it is used on sub-interfaces but it's purpose is really not clear to me.

Can someone please explain their true difference and where to use them?

Best Regards,

[viswamin]

Both these command have a totally different functionality.

The first command "frame-relay map ip DLCI" is used to create a static mapping between the Near Side DLCI to the far side IP address.

The second command is used to associate the interface with the DLCI.. it has nothing to do with mapping. the Mapping in this case is performed by the INARP feature.

HTH

-Vijay

[JohnTylerPearce · Accepted solution]

You configure 'frame-relay interface-dlci "DLCI" on a point-to-point connection generally.

This command basically says send everything out via this interface. So everything on that specific interface is

sent out on that particular DLCI only.

You can setup the 'frame-relay map ip (ip_address) DLCI' command when you want to setup a static routing.

You can configure this on NBMA, point-to-multipoint, and even on point-to-point networks. You can configure

multiple frame-relay map statements on a interface.

You don't need the broadcast keyword on the frame-relay interface-dlci command because it's only going to have one

destination.

the broadcast keyword on the frame-relay map ip command will take a broadcast and turn it into a unicast to the specified recipients.

[daudparvez]

Thanks all for your replies.

Dear John, you say that the frame-relay map command is used to setup static routing. But with the frame-relay map command we can only specify a single IP Address and not a route. Then how can we setup static routing and will it be scalabe?

Best Regards,

[cadet alain]

Hi,

as already stated by Vijay these are 2 different things.

By default all dlcis are linked to the physical interface so if you want to link some dlci to a multipoint or point-to-point subinterface you have to use the frame-relay interface-dlci command.

If you do this on a multipoint subinterface the L2-L3 mapping will still use InARP unless you configure a static map with the frame-relay map command.

On point-to-point you can only use frame-relay interface-dlci command and InARP is disabled but you can't use and don't need a static mapping as all destinations are reachable via this interface as it is point-to-point.

So it has got nothing to do with routing but with L2-L3 mapping.

Regards.

Alain

[JohnTylerPearce]

Sorry, I ment static mapping and not static routing, that was a typo

[daudparvez]

Dear All,

Thanks for your kind guidance.

Can someone please share a link explaining the basic functionality of Inverse ARP?

I just want to correlate it with that of ARP on Ethernet Media.

In case of ARP a node knows the remote IP Address and it generates an ARP broadcast to find the corresponding MAC Address. In response of which the node having that IP Address replies with ARP Reply mentioning it's MAC Address.

However, in case of Inverse ARP, both the DLCI/IP Address are provided by the Inverse ARP which needs some further clarification.

Will be grateful if some one can explain Inverse ARP functionality and share a link regarding that.

Best Regards

[Thotsaphon Lueangwattanaphong]

Hello,

    It's some kinda address-to-DLCI mapping. You are already provided DLCI by ISP.  Router sends Inverse ARP requests  on PVC(already provided by ISP on FR Switches) to discover IP of the remote device. 

HTH,

Toshi

[cadet alain]

Hi,

http://astorinonetworks.com/2011/06/15/understanding-frame-relay-inverse-arp/

Regards.

Alain