Data Link Affiliation Identifiers (DLCIs)
Table 11.7 lists the command for configuring and acceptance DLCI’s.
Frame Relay PVCs are articular to DTE end accessories by Data Link Affiliation Identifiers
(DLCIs). A Frame Relay account provider about assigns DLCI values, which are acclimated on
Frame Relay interfaces to analyze amid altered basic circuits. Because abounding virtual
circuits can be concluded on one multipoint Frame Relay interface, abounding DLCIs are often
affiliated with it.
Let me explain—suppose you accept a axial HQ with three annex offices. If you were to
connect anniversary annex appointment to HQ application a T1, you would charge three consecutive interfaces on your
router at HQ, one for anniversary T1. Simple, right? Well, accept you use Frame Relay PVCs
instead. You could accept a T1 at anniversary annex affiliated to a account provider and alone a single
T1 at HQ. There would be three PVCs on the distinct T1 at HQ, one activity to anniversary branch. And
even admitting there’s alone a distinct interface and a distinct CSU/DSU, the three PVCs action as
three abstracted circuits.
Before I continue, I appetite to ascertain Inverse ARP (IARP) and altercate how it’s acclimated with
DLCIs in a Frame Relay network. Yes, it is somewhat agnate to ARP in that it maps a DLCI
to an IP address—kind of like ARP does with MAC addresses to IP addresses. And even
though you can’t configure IARP, you can attenuate it. It runs on a Frame Relay router and maps
the DLCI to an IP abode for Frame Relay so it knows how to get to the Frame Relay switch.
You can see IP-to-DLCI mappings with the appearance frame-relay map command.
But if you accept a non-Cisco router active in your arrangement and it doesn’t abutment IARP, then
you’re ashore with accepting to statically accommodate IP-to-DLCI mappings with the frame-relay
map command—something I’ll authenticate in a bit.
Let’s allocution about DLCIs a bit more. They’re locally significant—global acceptation requires
the absolute arrangement to use the LMI extensions that action all-around significance. This is why you’ll
mostly acquisition all-around DLCIs alone in clandestine networks.
TABLE 1 1 . 7 Configuring and Acceptance Your DLCI’s
Command Meaning
show frame-relay map Displays the Arrangement layer–to–DLCI mappings.
show frame-relay pvc Provides you with a account of all configured PVCs
and DLCI numbers. It provides the cachet of
each PVC affiliation and cartage statistics too.
frame-relay interface-dlci dlci-number Configures the DLCI cardinal for the interface.
To ascertain why DLCIs are advised locally significant, booty a attending at Figure 11.9. In the
figure, DLCI 100 is advised locally cogent to RouterA and identifies the ambit between
RouterA and its admission Frame Relay switch. DLCI 200 would analyze the ambit amid RouterB
and its admission Frame Relay switch.
FIGURE 1 1 . 9 DLCIs are bounded to your router
DLCI numbers that are acclimated to analyze a PVC are about assigned by the provider and
start at 16.
You configure a DLCI cardinal to be activated to an interface like this:
RouterA(config-if)#frame-relay interface-dlci ?
<16-1007> Ascertain a DLCI as allotment of the current
subinterface
RouterA(config-if)#frame-relay interface-dlci 16