Cabletron Systems CSX200 User Manual

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

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Configuring the PPP Protocol4-15CSX WAN ConfigurationInitial MRUThe initial Maximum Receive Unit (MRU) that the local PPP entity will advertiseto the remote entity. If the value of this variable is 0, then the local PPP entity willnot advertise any MRU to the remote entity and the default MRU will beassumed. Changes to this object take effect when the link is next restarted.The default MRU for the CSX is 8191.Magic Num. Neg.The Magic Number Negotiation Option enables the detection of looped-backlinks and other Data Link Layer anomalies.If Magic Number Negotiation is set to True, the local node will attempt toperform Magic Number Negotiation with the remote node; if set to False, thenegotiation is not performed by the local node. In any event, the local node willcomply with any Magic Number negotiations attempted by the remote node, perthe PPP specification. By default, the Magic Number is not negotiated, and zero isinserted where a Magic Number might otherwise be used. Changes to this objecttake effect when the link is next restarted.The Magic Number is a number that should be selected randomly by the deviceimplementing PPP (e.g., based on unique seed, such as a machine serial number, anetwork hardware address, a time-of-day clock, or the precise measurement ofthe inter-arrival time of physical events such as packet reception on otherconnected networks).When a PPP peer has the Magic Number Configuration option enabled, andreceives a Configure-Request with a randomly generated Magic Number, itcompares that number with that of the last Configure-Request it received.• If the two Magic Numbers are different, then the link is not looped-back, andthe Magic Number SHOULD be acknowledged.• If the two Magic Numbers are equal, then it is possible (but not certain) thatthe link is looped-back and that the Configure-Request just received wasactually the last one issued by the receiving peer. Further checks are carriedout to determine whether a loopback condition exists.The Magic Number also may be used to detect looped-back links during normaloperation, as well as during Configuration Option negotiation. All LCP Echo-Request, Echo-Reply, and Discard-Request packets have a Magic Number field. Ifa Magic Number has been successfully negotiated, an implementation MUSTtransmit these packets with the Magic Number field set to its negotiated MagicNumber. The Magic Number field of these packets SHOULD be inspected onreception.All received Magic Number fields MUST be equal to either zero or the peer’sunique Magic Number, depending on whether or not the peer negotiated a MagicNumber.