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Chapter 5
Advanced Configuration
40
PPPo E ha s two d istinc t sta g e s. The re is a Disc o ve ry sta g e
a nd a PPP Se ssio n sta g e . Whe n a Ho st wishe s to initia te a
PPPo E se ssio n, it must first p e rfo rm Disc o ve ry to id e ntify the
Ethe rne t MAC a d d re ss o f the p e e r a nd e sta b lish a PPPo E
SESSION_ID. While PPP d e fine s a p e e r-to -p e e r re la tio nship ,
Disc o ve ry is inhe re ntly a c lie nt-se rve r re la tio nship . In the
Disc o ve ry p ro c e ss, a Ho st (the c lie nt) d isc o ve rs a n Ac c e ss
Co nc e ntra to r (the se rve r). Ba se d o n the ne two rk to p o lo g y,
the re ma y b e mo re tha n o ne Ac c e ss Co nc e ntra to r tha t
the Ho st c a n c o mmunic a te with. The Disc o ve ry sta g e
a llo ws the Ho st to d isc o ve r a ll Ac c e ss Co nc e ntra to rs a nd
the n se le c t o ne . Whe n Disc o ve ry c o mp le te s suc c e ssfully,
b o th the Ho st a nd the se le c te d Ac c e ss Co nc e ntra to r ha ve
the info rma tio n the y will use to b uild the ir p o int-to -p o int
c o nne c tio n o ve r Ethe rne t. The Disc o ve ry sta g e re ma ins
sta te le ss until a PPP se ssio n is e sta b lishe d . Onc e a PPP
se ssio n is e sta b lishe d , b o th the Ho st a nd the Ac c e ss
Co nc e ntra to r MUST a llo c a te the re so urc e s fo r a PPP virtua l
inte rfa c e .
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IPv4:
The Inte rne t Pro to c o l (IP) is a ne two rk-la ye r (La ye r 3)
p ro to c o l in the OSI mo d e l tha t c o nta ins a d d re ssing
info rma tio n a nd so me c o ntro l info rma tio n to e na b le
p a c ke ts b e ing ro ute d in ne two rk. IP is the p rima ry ne two rk-
la ye r p ro to c o l in the TCP/ IP p ro to c o l suite . Alo ng with the
Tra nsmissio n Co ntro l Pro to c o l (TCP), IP re p re se nts the he a rt
o f the Inte rne t p ro to c o ls. IP is e q ua lly we ll suite d fo r b o th
LAN a nd WAN c o mmunic a tio ns.
IP (Inte rne t Pro to c o l) ha s two p rima ry re sp o nsib ilitie s:
p ro vid ing c o nne c tio nle ss, b e st-e ffo rt d e live ry o f d a ta g ra ms
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