Information Technology Reference
In-Depth Information
If the router and the provider do use the same traffic parameters, then there is a real problem. In other
words, either the router is not shaping well or the provider is not policing accurately. If this happens,
refer to the documentation of the ATM card for known limitations, and check for known bugs. Also keep
in mind that no two implementations of traffic shaping give exactly the same resulting traffic; small
variations can be accepted, but it should always generate only a negligible amount of traffic loss.
Some traffic analyzers on the market can check the traffic compliance according to a given set of traffic
parameters. Among them, the most classic are from GN Nettest and HP. Those devices can determine
whether the traffic from the router is shaped accurately.
If you find that a Cisco router is not shaping accurately and you cannot find any documented bug or card
limitation, it is wise to open a case with the TAC.
Troubleshooting PVC Total Connectivity Failure
The previous section focused on a partial packet loss. We will now focus on total connectivity loss (Table
22-1).
Table22-1 Total Connectivity Loss Between Two ATM-Attached Routers
Possible Problem
Solution
The PVC is
broken inside the
provider's cloud.
This is the most common problem. If the provider has a big
problem inside its ATM cloud, the signal coming from the
provider's equipment will still be good. As a result, the router's
interface will still be up/up. At the same time, any cell sent by the
router will be accepted by the provider but will never reach the
destination.
Usually, calling the provider will give a quick answer. But,
because the interface is not going down, the Layer 3 route will
not be removed by the routing table, and alternative or backup
routes cannot be used.
1
The best solution in this environment is
to enable OAM management to automate the process. Refer to
the WAN configuration guide on CCO.
You can prove that the ATM card is okay by using loopbacks.
Refer to the solution of the next problem in this table.
One of the
interfaces is
down/down.
1.
Locate one ATM interface in down/down state. Ensure that
it is not administratively down (that is, that the interface or
subinterface has not been shut down).
2.
Check that the framing and scrambling are correctly
configured.
The framing can be checked via
sh atm int atm
and must be
agreed upon with the provider. It can be configured via
atm
framing xxx
in interface configuration mode.
