Link Quality Monitoring (Lqm); Multilink Ppp (Mlppp) - Enterasys Security Router X-PeditionTM User Manual

PPP Features
The MS-CHAP challenge, response and success packet formats are identical in format to the
standard CHAP challenge, response and success packets, respectively. MS-CHAP defines a set of
reason for failure codes returned in the Failure packet Message Field.
It also defines a new packet called Change Password Packet, which enables a client to send a
response packet based on a new password. An 8-octet challenge string is generated using a
random number generator. A change password packet is sent in response to a failure packet from
the peer that contains the failure code for change password.
Currently, MS-CHAP authenticators do not send the name value field in the challenge packet but
construct the response packet with the first MS-CHAP name/secret pair retrieved from the secret
list. When MS-CHAP secrets are not configured, a configure NAK will be sent with either CHAP
(MD5) or PAP protocol in response to a MS-CHAP Authentication protocol option in the LCP
request from the Windows system.

Link Quality Monitoring (LQM)

As referenced in RFC-1989, LQM defines a protocol for generating Link-Quality-Reports. These
Report packets provide a mechanism to determine link quality, but it is up to each
implementation to decide when the link is usable. LQM carefully defines the Link-Quality-Report
packet format and specifies reference points to measure all data transmission and reception.
LQM's functionality includes:
• Maintaining LQM statistics and sending them to the peer periodically
• Determining link quality based on statistics received from the peer
• Suspending traffic over the link, if that link quality is bad
• Monitoring suspended link quality by swapping LQM packets with peer
• Restoring the link after quality reaches a desired level (configurable)

Multilink PPP (MLPPP)

Multilink PPP (MLPPP), as defined in RFC-1990, aggregates multiple point-to-point links to form
a group with higher bandwidth. Multilink is based on an LCP option negotiation that permits the
XSR to indicate to its peer that it is capable of combining multiple physical links into a bundle.
LCP negotiation indicates the following:
• The XSR can combine multiple physical links into one logical link
• The XSR can receive upper layer protocol data units (PDU) fragmented using the multilink
header and reassemble the fragments into the original PDU for processing
• The XSR can receive PDUs of size N octets where N is specified as part of the option even if N
is larger than the maximum receive unit (MRU) for a single physical link
When a packet is transmitted over a multilink bundle it is encapsulated by a multilink header,
which includes information to allow the packets sent over the links in the bundle to be sequenced.
Functionality provided by MLPPP on the XSR includes:
• Learned number of fragments to be sent on each link and the bundle
8-4 Configuring PPP
Note: The XSR does not support Multilink PPP bundles between unchannelized T3/E3 ports.
Multilink PPP bundles are supported on T1/E1 ports of channelized T3/E3 ports, but are limited to a
single T3/E3 port; that is, a Multilink PPP bundle between T1/E1s of different channelized T3/E3
ports is not supported.