Table of Contents
Advertisement
Chapter 8: Layer 2 Services over MPLS Overview
between two ATM ports instead of between ATM VCs using a single VC over a single
pseudowire, all the necessary VCs had to be configured separately. Also, in such cases,
the corresponding pseudowires for each of the VCs had to be configured individually.
This method was not efficient because of the amount of manual configuration and MPLS
signaling protocol (LDP) state that had to be maintained.
Now, you can emulate physical connectivity between two ATM ports that are not directly
connected. This emulation is made possible by transporting ATM cells belonging to a
subset of matching ATM VCs on both the ATM ports over a single pseudowire. Multiple
VCs over a single psuedowire is useful in scenarios when ATM switches are connected
using a high-speed packet switched network, instead of expensive physical cables.
Support for configuration of multiple ATM VCs over a single pseudowire is based on RFC
4816, Pseudowire Emulation Edge-to-Edge (PWE3) Asynchronous Transfer Mode (ATM)
Transparent Cell Transport Service. Although this RFC requires all the ATM cells,
corresponding to all possible ATM virtual circuits, received on an ATM port to be
transported on the associated single pseudowire, the current implementation does not
enable all possible ATM virtual circuits on an ATM port to be transported. This condition
occurs because of hardware limitations on the ATM line modules supported on ERX14xx
models, ERX7xx models, and the ERX310 router. As a result, it is necessary to explicitly
open virtual circuits on the segmentation and reassembly (SAR) scheduler to enable
ATM cells corresponding to those virtual circuits to be received and transported over a
pseudowire. Because of the scaling limitations on the number of virtual circuits that can
be opened on the SAR scheduler, all possible ATM virtual circuits for a single ATM port
cannot be opened on the SAR device. Therefore, to enable multiple VCs over a single
pseudowire to be configured on the ERX routers, you must specify the subset of ATM
virtual circuits on a port that must be carried on the single pseudowire.
To configure the subset of ATM virtual circuits, you must configure a VPI/VCI range using
the new mpls-relay atm vpi-range vpiStart vpiEnd vci-range vciStart vciEnd command
in global configuration mode. You can configure this VPI/VCI range only for ATM ports
for which you have associated a pseudowire using the MPLS Martini circuit configuration.
Before the support for multiple ATM VCs over a single pseudowire was available, MPLS
Martini circuit configuration was allowed only on ATM subinterfaces and not on ATM
ports. To enable a subset of ATM virtual circuits to be transported over a single
pseudowire, you must add the MPLS Martini circuit configuration on an ATM port
(associating the ATM port with the single pseudowire) and then specify the subset of
ATM virtual circuits whose cells need to be transported on the single pseudowire using
the VPI/VCI range configuration.
You can specify a maximum of four non-overlapping VPI/VCI ranges for each ATM port.
The cumulative number of ATM virtual circuits in the specified VPI/VCI ranges must not
exceed the scaling limitation of the SAR scheduler. The SAR scheduler limitation is not
for each port, but for the entire line module. The VPI/VCI range configurations specified
on the ATM ports on both ends of the pseudowire must match. Even if the VPI/VCI range
configurations do not match on both ends of the pseudowire, Label Discovery Protocol
(LDP) brings up the pseudowire. However, on the remote provider edge (PE) router, ATM
cells received from the pseudowire that are not within the configured ranges are discarded.
Copyright © 2010, Juniper Networks, Inc.
525
Advertisement
Table of Contents
Troubleshooting
