Information Technology Reference
In-Depth Information
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The authenticator checks the response against its own calculation of the expected hash
value. If the values match, the authentication is acknowledged; otherwise, the connection
should be terminated.
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At random intervals, the authenticator sends a new challenge to the peer and repeats the
previous steps.
PPP Network Control Protocol (NCP)
After LCP link establishment and authentication, NCPs determine and configure the network
layer protocols. The NCP uses the IP Control Protocol (IPCP) to negotiate and establish IP
peering over a PPP link. Described in RFC 1332, IPCP is responsible for configuring, enabling,
and disabling the IP protocol modules on both ends of the point-to-point link. IPCP uses the
same packet exchange mechanism as the LCP.
PPP Multilink Protocol (MP)
Described in RFC 1990, the MP provides a means to group or bundle multiple independent
links between two systems to aggregate the bandwidth of the individual links. The individual
links can be ISDN B channels, async lines, or other PPP links, such as synchronous links, Frame
Relay, or X.25. The bundle does not need to be composed of identical link types. Physical links
are configured to be part of the MP bundle. A virtual interface represents the bundle. The MP
bundle is either configured to be connected indefinitely, as might be the case when multiple T1
circuits make up the bundle, or to be activated as traffic load reaches a predefined threshold,
such as when dial-up links provide extra bandwidth between two routers. When the combined
load on the active physical links reaches a configured load threshold, additional links are
activated. The load threshold can be based on inbound traffic, outbound traffic, or either but
cannot be based on the combined total of inbound and outbound traffic.
MP provides packet fragmentation and reassembly, sequencing, multivendor interoperability,
and load balancing. Packets are fragmented and sent simultaneously on the individual physical
links to the remote destination, which reassembles the packet. MP enables bandwidth on
demand and reduces transmission latency across WAN links.
MP links are configured during the LCP link establishment phase. Particular elements that must
be negotiated are the Maximum Received Reconstructed Unit (MRRU) and the Endpoint
Discriminator (Endpoint Disc). These values must be the same on both ends of each connection.
After LCP and authentication is complete, a Virtual Access interface is created for the bundle
and NCP operates over the bundle.
ISDN Configuration
ISDN is configured on the router by specifying the ISDN switch type that the router is
connecting to and then configuring the interface parameters.
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