69PPPoE client fundamentalsPPPoE (RFC 2516) is a commonly used application in the deployment ofDSL One of the main advantages of PPPoE is that it offers authenticationbased on Password Authentication Protocol (PAP) or Challenge HandshakeAuthentication Protocol (CHAP).With the SR4134, the PPPoE client must be deployed with a DSL modemproviding a connection to a PPPoE server for access to Internet resources.The main purpose of PPPoE is to serve as a backup and fail-over solution.When the primary connectivity goes down, traffic can switch over to abackup interface, in this case the virtual PPPoE interface. In this scenario,a PPPoE client session is established with a PPPoE server and traffic isrouted through this path until the primary connectivity is restored.The PPPoE client only transmits traffic if it is up and running and a routelookup picks a route pointing to the PPPoE interface.For PPP to run over Ethernet, it needs to learn the Ethernet address of theremote peer, and establish a session ID. In order to do this the PPPoEprotocol defines a discovery stage, followed by a session stage. In thediscovery stage the host acts as a client and the remote access concentratoracts as a server. This allows the host to learn the Ethernet address of theremote peer and to set up a session ID. After the discovery stage, thesession stage begins with the normal PPP LCP and IPCP negotiation.On the SR4134, the PPPoE client supports the following features• The client connection to the PPPoE server is established when theclient is configured.• Traffic is routed to the PPPoE based on route selection. When theoptimal route becomes inactive and a route pointing to the PPPoEinterface is active, traffic switches over to the PPPoE interface. Trafficstops using the PPPoE interface when a more optimal route becomesactive.• The PPPoE client can learn its IP address from the remote PPPoEserver.• The PPP session sends keepalives at a regular interval to detect PPPoEserver failure.Nortel Secure Router 4134Security — Configuration and ManagementNN47263-600 01.02 Standard10.0 3 August 2007Copyright © 2007, Nortel Networks.
