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Mixed Mode Support for MLPPP and PPP Subscribers Overview

Existing customer edge subscriber services separate MLPPP and PPP support for subscribers. However, if a subscriber interface is configured for MLPPP and the customer premises equipment (CPE) does not support MLPPP, then the subscriber login fails.

In an environment where MLPPP and PPP subscribers are mixed and you cannot easily manage the subscriber types by classifying them into separate groups using dynamic profiles, the MX Series needs the capability to renegotiate Link Control Protocol (LCP) in PPP if the CPE rejects LCP negotiation in MLPPP. This capability is known as mixed mode support.

Mixed mode uses common configuration and flexibility to support PPP and MLPPP. If you configure a subscriber interface using the family mlppp and family inet/inet6 statements for PPP-only CPE, mixed mode support enables additional LCP negotiation exchanges to successfully negotiate LCP in PPP. Mixed mode supports static and dynamic PPPoE (terminated and tunneled) and LNS (L2TP network server) subscribers.

This section contains the following topics:

PPPoE Terminated and Tunneled Subscribers

If you do not configure the family mlppp statement for a subscriber interface, the MX Series negotiates LCP in PPP as it currently does, and any LCP request that contains MLPPP options is rejected.

However for PPPoE subscribers, if you configure the family mlppp statement for a subscriber interface, the MX Series negotiates LCP in MLPPP with the CPE. If the CPE rejects MLPPP, then the MX Series renegotiates LCP in PPP with the CPE.

Mixed mode operation for a LAC (tunneled PPPoE) subscriber is the same as for a terminated PPPoE subscriber. The authentication phase has no effect on LAC mixed mode operation because LCP negotiation must be completed prior to authentication.

LNS Subscribers

For LNS subscribers, the MX Series negotiates LCP as follows:

  • If proxy data from the LAC indicates that MLPPP was negotiated, and the proxy data is acceptable, and the lcp-renegotiation statement is not configured, then the proxy is accepted and the subscriber is MLPPP.

  • If proxy data from the LAC indicates that PPP was negotiated, or if there was no proxy data from LAC, or if the lcp-renegotiation statement is configured for the LAC, then the MX Series starts LCP negotiation in MLPPP with the CPE.

    If the CPE rejects MLPPP, then the MX Series renegotiates LCP in PPP with the CPE.

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