# Multiclass MLPPP LCP Extensions Overview

Link Control Protocol (LCP) establishes an MLPPP link by negotiating LCP options with the MLPPP peer at the receiving end of a proposed connection. Peers negotiate multiclass MLPPP during the initial phase of the LCP option negotiation.

LCP uses the following new LCP configuration options for establishing a multiclass MLPPP link:

- Multilink header format—Multilink header format has three functions:
  - It informs the receiving peer that the multiclass MLPPP feature is supported.
  - It informs the peer of the multilink header format that will be used.
  - It informs the peer of the number of multilink classes configured.

  The router currently supports only the multilink header format option. The two number formats that are negotiated for the multilink header format option are:

  - Short sequence number
  - Long sequence number—The router currently supports only long sequence numbers
- Prefix elision—Prefix elision informs the receiving peer that only packets with a certain prefix must be accepted. This prefix is not transmitted as part of the information in the fragments of a multilink class. When the prefix is negotiated, all multilink packets must be transmitted with the negotiated prefix removed from the start of the packet. The prefix is empty for all classes, by default. The router currently does not support the prefix elision option.

#### Related Documentation

- Multiclass MLPPP Overview
- Configuring Multiclass MLPPP
- Link Control Protocol in Chapter 8, Point-to-Point Protocol