Figure 4: Label Mapping Example - Juniper EX9200 Features Manual

VPLS NLRI for Site ID 18
Length
RD
VE ID - 18
VE Block Offset - 17
VE Block Size - 8
Label Base - 262145
Related
Documentation
Copyright © 2016, Juniper Networks, Inc.
To further illustrate the one-to-one mapping of labels to sites, assume a label block with
site offset of 1 and a label base of 10. The combination of label base and block offset
contained in the VPLS NLRI provides the mapping of labels to site IDs. The block offset
is the starting site ID that can use the label block as advertised in the VPLS NLRI.
To advertise the default VPLS NLRI, a PE router picks a starting block offset that fits its
own site ID and is such that the end block offset is a multiple of a single label block. In
Junos OS a single label block is eight labels by default.
The end block offset is the last site ID that maps to the last label in the label block. The
end offset for the first block is 8 which maps to label 17 and the second block is 16. For
example, a site with ID 3 picks a block offset of 1 and advertises a label block of size 8 to
cover sites with IDs 1 to 8. A site with ID 10 picks a block offset of 9 to cover sites with IDs
9 to 16.
The VPLS NLRI shown in Figure 4 on page 43
value 262145. The block offset contains value 17. The illustration shows which site IDs
correspond to which labels.

Figure 4: Label Mapping Example

Label Base = 262145
Label 262145 262146 262147 262148 262149 262150 262151 262152
Site ID 17
Site Offset = 17
If a PE router configured with site ID 17 is in the same VPLS domain as a PE router
configured with site ID 18, it receives the VPLS NLRI as shown in Figure 2. So it uses label
262145 to send traffic to site 18. Similarly, a PE router configured with site ID 19 uses label
262147 to send traffic to a PE router configured with site ID 18. However, only PE routers
configured with site IDs 17 to 24 can use the label block shown to set up pseudowires.
Example: Building a VPLS From Router 1 to Router 3 to Validate Label Blocks
Chapter 4: Assigning Routing Instances to VPLS
is for site ID 18. The label base contains
Label Mapping for Site ID 18
Label Block
18 19 20 21
Site IDs
22 23 24
43