Cabletron Systems CSX200 User Manual

Also see for SPECTRUM: User guide User guide User guide User guide Guide

Contents

CSX WAN Configuration4-16Configuring the PPP ProtocolReception of a Magic Number field equal to the negotiated local Magic Numbershould indicate a looped-back link. Reception of a Magic Number other than thenegotiated local Magic Number, the peer’s negotiated Magic Number, or zero (ifthe peer didn’t negotiate one), indicates a link which has been (mis)configured forcommunications with a different peer.Recovery procedures from a looped-back or misconfigured PPP Link areunspecified by the PPP protocol, and may vary from implementation toimplementation. One recovery procedure is to assume a LCP Down event whichrequires a further Open event to begin re-establishing the link (an Open eventcan’t complete until the looped-back condition is terminated, and MagicNumbers are successfully negotiated). A more optimistic procedure (in the case ofa looped-back link) is to begin transmitting LCP Echo-Request packets until anappropriate Echo-Reply is received, indicating a termination of the looped- backcondition.FCS SizeThe size of the FCS, in bits, the local node will attempt to negotiate for use withthe remote node. Regardless of the value of this object, the local node will complywith any FCS size negotiations initiated by the remote node, per the PPPspecification. Changing this object will have effect when the link is next restarted.Currently only a 16 bit FCS is supported.Configuring Link Control Protocol OptionsYou can use the PPP Link Control Protocol Configuration window to set theInitial MRU and enable or disable Magic Number Negotiation for the CSX’sinterfaces on which a PPP link has been established.To establish the Initial MRU for a PPP Link:1. Use the Set Selection button to specify the scope of interfaces to whichconfiguration changes will apply:a. Choose Selected Interfaces to apply changes only to those interfaceshighlighted in the scroll list.Click mouse button 1 to highlight one or more interfaces in the LinkControl Protocol: Configuration scroll list.b. Choose All Interfaces to apply changes to all WAN interfaces on thedevice that are configured for LCP.2. Click mouse button 1 in the Initial MRU text field, type in the MRU which youwant to be negotiated for the local PPP peer(s) on the CSX, and press Enteror Return on the keyboard.3. Click mouse button 1 on to save the changes or torestore the original configuration.To determine whether the local peer of a PPP Link will use Magic NumberNegotiation to check for loop-back conditions or other Datalink Layer errors: