CCIE Written: Frame Relay

Frame Relay Overview

* NBMA (Non Broadcast Multi Access)

                - Address resolution issues implied

                - It has problem on L3 to L2 address resolution

* Data Link Connection Identifier (DLCI)

                - Layer 2 addressing

                - DLCI number only locally significant

* Local Management Interface (LMI)

                - DTE/DCE (router/switch) communications

                - Reports virtual circuit (VC) status

Frame Relay LMI

* encapsulation frame-relay

* LMI types

                - Automatically detected

                - frame-relay lmi-type [cisco | ansi | q933a]

                - show frame-relay lmi

* LMI advertises VC Status

* Status can be

                - Active: working on both end

                - Inactive: one site is not configured

                - Deleted: DLCI doesn’t match with the frame-relay switch

                - Static: Have a manual back to back configuration

Full Mesh Network

* Topology where all devices have a direct layer 2 circuit to each other

* More closely emulates a LAN

* More expensive to provision than partial mesh network

Partial Mesh Network

* Topology where not all devices have a direct layer 2 circuit to each other

                - i.e. not fully meshed circuits

                - i.e. Hub-and-Spoke is a type of partial mesh

* Design problems occur when layer 3 network does not map exactly to layer 2 network

                - Devices without direct layer 2 circuits cannot resolve each other via Inverse-ARP

                - Some higher layer protocols (OSPF, PIM, etc) do not understand this disconnect

* Ideally layer 3 is point to point with layer 2 network

                - Separate IPv4/IPv6 subnet and point-to-point sub-interface for each DLCI