Juniper JUNOSE 11.2.X BGP AND MPLS, Руководство по настройке

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MPLS Shim Interfaces for Layer 2 Services over MPLS Overview
An MPLS shim interface is stacked on a layer 2 interface to do either of the following:
• Create a layer 2 circuit by cross-connecting the layer 2 interface to an LSP corresponding
to the VC label.
•
Create a local cross-connect by cross-connecting the layer 2 interface to another layer
2 interface.
You can create or remove MPLS shim interfaces with the mpls-relay or route interface
commands. Shim interfaces are also created in or removed implicitly from a
load-balancing group by the
member interface command when you configure the group.
Each MPLS shim interface exists in a particular virtual router.
Each MPLS shim interface points to a single MPLS next hop. When layer 2 frames arrive
on the layer 2 interface below the MPLS shim interface, they are encapsulated in an MPLS
packet and forwarded to that MPLS next hop. The details of the encapsulation are
determined by the attributes of the shim interface.
The MPLS next hop to which the shim interface points is set by an MPLS signaling protocol,
which adds a special entry with implicit null in label to the interface label-space MPLS
forwarding table of the shim interface. For traffic arriving from the core, the MPLS signaling
protocol adds a normal entry with a real in label to the platform label-space MPLS
forwarding table whose next hop points to the MPLS shim interface.
You can configure the following attributes for each MPLS shim interface:
•
The administrative state, enabled or disabled, configured with the mpls-relay disable
command.
• The IP address of the remote PE router for the layer 2 circuit, configured with the
mpls-relay command. The shim interface is cross-connected to an LSP corresponding
to the VC label received from the specified remote PE router, or to another shim interface
in the local cross-connects case. For local cross-connects the IP address is local to
the PE router.
•
The name of an RSVP-TE base tunnel to be used for the layer 2 circuit, configured with
the
route interface command.
• The group ID of the shim interface, configured using the group-id option of the
mpls-relay and route interface commands. Even though you can configure the group
ID, the JunosE Software does not currently use it.
•
Whether the control word is used, configured with the control-word and
no-control-word options of the mpls-relay and route interface commands. The layer
2 interface determines the default preference if this option is not configured. Some
layer 2 interfaces require a control word; others do not support it.
•
Whether sending nonzero sequence numbers in the control word is preferred, configured
with the
sequencing and no-sequencing options of the mpls-relay and route interface
commands. The layer 2 interface determines the default preference if this option is
not configured. Even when preferred, the sequence numbers might not be sent if the
Copyright © 2010, Juniper Networks, Inc. 514
JunosE 11.2.x BGP and MPLS Configuration Guide