Vpls Label Blocks Operation; Elements Of Network Layer Reachability Information; Table 3: Nlri Elements - Juniper EX9200 Features Manual

VPLS Feature Guide for EX9200 Switches

VPLS Label Blocks Operation

Elements of Network Layer Reachability Information

Table 3: NLRI Elements

Element
Length
Route Distinguisher
VPLS Edge ID
VE Block Offset
40
A virtual private LAN service (VPLS) is a Layer 2 (L2) service that emulates a local area
network (LAN) across a wide area network (WAN). VPLS labels are defined and
exchanged in the Border Gateway Protocol (BGP) control plane. In the Junos OS
implementation, label blocks are allocated and used in the VPLS control plane for two
primary functions: autodiscovery and signaling.
Autodiscovery—A method for automatically recognizing each provider edge (PE) router
in a particular VPLS domain, using BGP update messages.
Signaling—Each pair of PE routers in a VPLS domain sends and withdraws VPN labels
to each other. The labels are used to establish and dismantle pseudowires between
the routers. Signaling is also used to transmit certain characteristics of a pseudowire.
NOTE: In the VPLS documentation, the word router in terms such as PE router
is used to refer to any device that provides routing functions.
The PE router uses BGP extended communities to identify the members of its VPLS.
Once the PE router discovers its members, it is able to establish and tear down
pseudowires between members by exchanging and withdrawing labels and transmitting
certain characteristics of the pseudowires.
The PE router sends common update messages to all remote PE routers, using a distinct
BGP update message, thereby reducing the control plane load. This is achieved by using
VPLS label blocks.
VPLS BGP network layer reachability information (NLRI) is used to exchange VPLS
membership and parameters. The elements of a VPLS BGP NLRI are defined in
Table 3 on page 40.
Acronym Description
Total length of the NLRI size represented in
bytes.
RD Unique identifier for each routing instance
configured on a PE.
VE ID Unique number to identify the edge site.
VBO Value used to identify a label block from
which a label value is selected to set up
pseudowires for a remote site.
Default Size (Octets)
2
8
2
2
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