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Tue Feb 21 23:32:47 2012 UTC (12 years, 4 months ago) by misho
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1: <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> 2: <HTML> 3: <HEAD> 4: <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> 5: <TITLE>Mpd Layers</TITLE> 6: </HEAD> 7: <BODY text="#000000" bgcolor="#ffffff"> 8: 9: <A HREF="mpd.html">Mpd 5.6 User Manual</A> 10: : <A HREF="mpd17.html">Configuring Mpd</A> 11: : Mpd Layers  12: Previous: <A HREF="mpd18.html">General mpd commands</A>  13: Next: <A HREF="mpd20.html">Link layer</A> 14: 15: 16: <HR NOSHADE> 17: <H2><A NAME="19"></A>4.2. Mpd Layers<A NAME="layers"></A></H2> 18: Mpd consists of several layers, corresponding 19: to the layered nature of the PPP protocol. There are two 20: types of layers hierarchy connected with two different 21: operation modes as "ppp terminator" and "ppp repeater". 22: Operation mode is getting chosen dynamically depending on link 23: configuration and user auth name (see 'set link action ...' command). 24: In "ppp terminator" mode such hierarchy used: 25:  26: <A HREF="mpd28.html#interface">interface</A> -> 27:  28: <A HREF="mpd26.html#ipcp">ipcp</A> -> 29:  30: <A HREF="mpd24.html#compression">compression</A> -> 31:  32: <A HREF="mpd23.html#encryption">encryption</A> -> 33:  34: <A HREF="mpd22.html#bundle">bundle</A> -> 35:  36: <A HREF="mpd20.html#links">links</A> 37: In "ppp repeater" mode different hierarchy used: 38:  39: <A HREF="mpd20.html#links">links</A> -> 40: Repeater -> 41:  42: <A HREF="mpd20.html#links">links</A> 43: A  44: <A HREF="mpd20.html#links">links</A> is a single point-to-point 45: connection between the local machine and a remote peer machine, 46: implemented by some kind of physical device, 47: such as a serial modem connection or a virtual PPTP connection. 48: Link parameters include whether authentication is enabled in 49: either direction, the authentication type (PAP or CHAP) 50: used, keep-alive packets, multilink negotiation options 51: and various other link specific parameters. 52: Lower half of the link layer is the physical devices layer. 53: Configuration of device type specific parameters happens at this layer. 54: Each device has a specific type 55: corresponding to one of the supported device types in mpd. 56: The type dictates how the device dependent part 57: is configured and what it's capabilities are. 58: A  59: <A HREF="mpd22.html#bundle">bundle</A> is a collection 60: of one or more links, all connecting 61: to the same remote peer, that together form a single 62: multi-link PPP connection whose effective bandwidth is 63: the sum of the bandwidths of the individual links. 64: The bundle layer in effect lies just above the link layer. 65: The bundle layer handles the task of making multiple 66: physical links appear as a single virtual link. 67: At the bundle layer you configure multi-link 68: PPP settings and the link management policy. The link management 69: policy determines whether mpd tries to keep all the links 70: connected all the time, or whether it adds and subtracts 71: links depending on demand, and if so, according to what parameters. 72: With each bundle is a corresponding 73:  74: <A HREF="mpd28.html#interface">interface</A> layer, 75: which corresponds directly to a system network interface 76: accessible via <code>ifconfig(8)</code>, such as <code>ng0</code>. 77: The interface layer handles configuring the interface, 78: bringing it up or down as appropriate, assigning 79: IP addresses, setting up static routes and configuring proxy-ARP. 80: The interface layer is also responsible for implementing 81: Dial-on-Demand and idle timeout functionality. 82: Each bundle has several corresponding NCP layers as 83:  84: <A HREF="mpd26.html#ipcp">ipcp</A> and 85:  86: <A HREF="mpd27.html#ipv6cp">ipv6cp</A>, 87: which manages the protocol specific configuration of the interface. 88: This layers handle the negotiation of local and remote addresses 89: and TCP header compression, as well as other optional 90: IP related information such as DNS servers and NBNS servers. 91: Each bundle also has corresponding 92:  93: <A HREF="mpd24.html#compression">compression</A> and 94:  95: <A HREF="mpd23.html#encryption">encryption</A> layers, which 96: allow you to enable and configure compression and encryption 97: for data sent and received over the bundle. 98: A repeater is a collection of two physical devices 99: (links). It is getting created when there is need to forward 100: connection coming from one physical device to another without 101: modification. This technology is also known as LAC 102: (L2TP Access Concentrator) and PAC (PPTP Access Concentrator). 103: While the combination of all the various layers presents 104: a large number of configuration options, mpd tries to 105: have reasonable defaults for everything. 106: 107: 108: 109: <HR NOSHADE> 110: <A HREF="mpd.html">Mpd 5.6 User Manual</A> 111: : <A HREF="mpd17.html">Configuring Mpd</A> 112: : Mpd Layers  113: Previous: <A HREF="mpd18.html">General mpd commands</A>  114: Next: <A HREF="mpd20.html">Link layer</A> 115: 116: 117: 118: </BODY> 119: </HTML>