4 Replies Latest reply: Jul 13, 2019 11:49 AM by Martin RSS

    Few questions about ancient technology FR


      hi guys!


      I'm preparing for ROUTE exam and don't understand few moment about FR


      early i don't deal with FR, and have couple questions:

      1)what do we use for FR mapping?

      2) when i must configure frame relay mapping and why i need do it?

      3) when i should disable inverse arp and why?

        • 1. Re: Few questions about ancient technology FR



          I recommend you read the documents by Navneet about FR

          Introduction to Frame Relay Concepts - Documents



          • 2. Re: Few questions about ancient technology FR

            one of my friends (network ingineer) sayd that frame relay its a past technology and not uses now

            • 3. Re: Few questions about ancient technology FR

              i find interesting explanation, what for we should use dynamic or static map


              Dynammic Mapping

              Dynamic address mapping relies on Inverse ARP to resolve a next hop network protocol address to a local DLCI value. The Frame Relay router sends out Inverse ARP requests on its PVC to discover the protocol address of the remote device connected to the Frame Relay network. The router uses the responses to populate an address-to-DLCI mapping table on the Frame Relay router or access server. The router builds and maintains this mapping table, which contains all resolved Inverse ARP requests, including both dynamic and static mapping entries.


              Dynamic Inverse ARP relies on the presence of a direct point-to-point connection between two ends.


              If the router needs to map the VCs to Network layer addresses, it sends an Inverse ARP message on each VC. The Inverse ARP message includes the Network layer address of the router, so the remote DTE, or router, can also perform the mapping. The Inverse ARP reply allows the router to make the necessary mapping entries in its address-to-DLCI map table. If several Network layer protocols are supported on the link, Inverse ARP messages are sent for each one.



              Static Mapping

              The user can choose to override dynamic Inverse ARP mapping by supplying a manual static mapping for the next hop protocol address to a local DLCI. A static map works similarly to dynamic Inverse ARP by associating a speciļ¬ed next hop protocol address to a local Frame Relay DLCI.


              In other situations, a static mapping is the only option. For example, on a hub-and-spoke Frame Relay network, where there are several layer 3 networks (it is a layer-3 star topology), we can use static address mapping on the spoke routers to provide spoke-to-spoke (tips of the star) reachability. Because the spoke routers do not have direct connectivity with each other, dynamic Inverse ARP would not work between them.2 In this case, dynamic Inverse ARP only works between hub and spoke, and the spokes require static mapping to provide reachability to each other.

              • 4. Re: Few questions about ancient technology FR

                when FR was popular and on CCIE RS lab exam,  I noticed several suggestions were made to disable Inverse ARP due to fact of Inverse ARP being not stable or reliable method for mapping.  in other words, do not count on Inverse ARP