Requirements For Nlri Elements; How Labels Are Used In Label Blocks; Label Block Composition - Juniper EX9200 Features Manual

Table 3: NLRI Elements (continued)
Element
VE Block Size
Label Base

Requirements for NLRI Elements

How Labels are Used in Label Blocks

Label Block Composition

Copyright © 2016, Juniper Networks, Inc.
Acronym Description
VBS Indicates the number of pseudowires that
peers can have in a single block.
LB Starting value of the label in the advertised
label block.
Junos OS requires a unique route distinguisher (RD) for each routing instance configured
on a PE router. A PE router might use the same RD across a VPLS (or VPN) domain or it
might use different RDs. Using different RDs helps identify the originator of the VPLS
NLRI.
The VPLS edge (VE) ID can be a unique VE ID, site ID, or customer edge (CE) ID. The VE
ID is used by a VPLS PE router to index into label blocks used to derive the transmit and
receive VPN labels needed for transport of VPLS traffic. The VE ID identifies a particular
site, so it needs to be unique within the VPLS domain, except for some scenarios such
as multihoming.
All PE routers have full mesh connectivity with each other to exchange labels and set up
pseudowires. The VE block size (VBS) is a configurable value that represents the number
of label blocks required to cover all the pseudowires for the remote peer.
A single label block contains 8 labels (1 octet) by default. The default VBS in Junos OS
is 2 blocks (2 octets) for a total of 16 labels.
Each PE router creates a mapping of the labels in the label block to the sites in a VPLS
domain. A PE router advertising a label block with a block offset indicates which sites
can use the labels to reach it. When a PE router is ready to advertise its membership to
a VPLS domain, it allocates a label block and advertises the VPLS NLRI. In this way, other
PE routers in the same VPLS domain can learn of the existence of the VPLS and set up
pseudowires to it if needed. The VPLS NLRI advertised for this purpose is referred to as
the default VPLS NLRI. The label block in the default VPLS NLRI is referred to as the
default label block.
A label block (set of labels) is used to reach a given site ID. A single label block contains
8 labels (1 octet) by default. The VBS is 2 octets by default in Junos OS.
The label block advertised is defined as a label base (LB) and a VE block size (VBS). It
is a contiguous set of labels (LB, LB+1,...LB+VBS-1). For example, when Router PE-A
sends a VPLS update, it sends the same label block information to all other PE routers.
Each PE router that receives the LB advertisement infers the label intended for Router
PE-A by adding its own site ID to the label base.
Chapter 4: Assigning Routing Instances to VPLS
Default Size (Octets)
2
3
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