Configuring the Label Block Size for VPLS
VPLS MPLS packets have a two-label stack. The outer label is used for normal MPLS forwarding in the service provider’s network. If BGP is used to establish VPLS, the inner label is allocated by a PE router as part of a label block. One inner label is needed for each remote VPLS site. Four sizes are supported. We recommend using the default size of 8, unless the network design requires a different size for optimal label usage, to allow the router to support a larger number of VPLS instances.
In the VPLS documentation, the word router in terms such as PE router is used to refer to any device that provides routing functions.
If you allocate a large number of small label blocks to increase efficiency, you also increase the number of routes in the VPLS domain. This has an impact on the control plane overhead.
Changing the configured label block size causes all existing pseudowires to be deleted. For example, if you configure the label block size to be 4 and then change the size to 8, all existing label blocks of size 4 are deleted, which means that all existing pseudowires are deleted. The new label block of size 8 is created, and new pseudowires are established.
Four label block sizes are supported: 2, 4, 8, and 16. Consider the following scenarios:
2—Allocate the label blocks in increments of 2. For a VPLS domain that has only two sites with no future expansion plans.
4—Allocate the label blocks in increments of 4.
8 (default)—Allocate the label blocks in increments of 8.
16—Allocate the label blocks in increments of 16. A label block size of 16 enables you to minimize the number of routes in the VPLS domain. Use this setting only if the number of routes is the most important concern.
Configure the label block size:
[edit routing-instances instance-name protocols vpls] user@router# set label-block-size 2