Label Blocks In Junos Os; Vpls Label Block Structure; Figure 3: Vpls Label Block Structure - Juniper EX9200 Features Manual

VPLS Feature Guide for EX9200 Switches

Label Blocks in Junos OS

VPLS Label Block Structure

64 65
1 2
42
In this manner, each receiving PE gets a unique label for PE-A for that VPLS. This simple
method is enhanced by using a VE block offset (VBO).
A label block is defined as: <Label Base (LB), VE block offset (VBO), VE block size (VBS)>
is the set {LB+VBO, LB+VBO+1,...,LB+VBO+VBS-1}.
Instead of a single large label block to cover all VE IDs in a VPLS, the Junos OS
implementation contains several label blocks, each with a different label base. This
makes label block management easier, and also allows Router PE-A to seemlessly
integrate a PE router joining a VPLS with a site ID not covered by the set of label blocks
that Router PE-A has already advertised.
This section illustrates how a label block is uniquely identified.
A VPLS BGP NLRI with site ID V, VE block offset VBO, VE block size VBS, and label base
LB communicates the following to its peers:
Label block for V: Labels from LB to (LB + VBS -1).
Remote VE set for V: from VBO to (VBO + VBS -1).
The label block advertised is a set of labels used to reach a given site ID. If there are
several label blocks, the remote VE set helps to identify which label block to use. The
example in Figure 3 on page 42
block has eight labels. In this example, the label values are 64 to 71 and 80 to 87.

Figure 3: VPLS Label Block Structure

VE Block Size = 8
66 67 68 69 70 71
Label base
3 4 5 6 7 8
VE Block Offset (1, 9)
For site range 9 through 16
To create a one-to-one mapping of these 16 labels to 16 sites, assume the site IDs are
the numbers 1 to 16, as shown in the illustration. The site block indicates which site ID
can use which label in the label block. So, in the first block, site ID 1 uses 64, site ID 2 uses
65, and so forth. Finally, site ID 8 uses 71. The 9th site ID will use the second block instead
of the first block.
The labels are calculated by comparing the values of VBO <= Local site ID < (VBO +VBS).
Consequently, site ID 9 uses 80, site ID 10 uses 81, and so on.
illustrates label blocks. There are two blocks and each
VE Block Size = 8
80 81 82 83 84
Labels
Site IDs
9 10 11 12 13
85 86 87
14 15 16
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