Avaya Troubleshooting Routers Instrukcja Naprawy Pobierz pdf (Strona 94)

Troubleshooting Routers

5-16

PVC Transmitting, but Not Receiving

If the log reveals that the PVC (permanent virtual circuit) is active, and the

statistics reveal it is transmitting, but not receiving, do the following:

• Make sure that the Frame Relay switch at the remote side of the link supports

the A-bit.

The switch sends the A-bit to the router to indicate it is up and active. If the

switch does not support the A-bit, the router has no way of determining

whether the remote side of the link is down, and thereby fails to disable the

associated PVC.

• Determine whether the switch can loop back any data.

Frame Relay Conﬁgured with LMI Invokes an Xoff State

If a Frame Relay switch exceeds buffer thresholds and sends an R-bit, the router

invokes an Xoff state. Xoff is equivalent to a disabled VC. The router brings down

the DLCI/VC that received the R-bit, and the DLCI/VC goes away.

If the DLCI that received the R-bit is a Direct Mode DLCI, the router also disables

all the upper-layer protocols associated with the DLCI.

If the DLCI is in Group Mode, the upper-layer protocols do not stop. In this case,

the protocols may reroute.

You cannot conﬁgure the router to ignore an Xoff state. The software supports

FECNs and BECNS in place of Xoff.

If IP is available, use the Ping trace option to determine which Frame Relay node

is down.

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Avaya Troubleshooting Routers Instrukcja Naprawy Strona 94