draft-ietf-pim-sm-v2-new-03.ps

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F0(Although ha)72 225.8 Q(ving the RP join back to)-.22 E -.11(wa)-.275
G(rds the source remo).11 E -.165(ve)-.165 G 2.75(st).165 G
(he encapsulation o)-2.75 E -.165(ve)-.165 G(rhead, it does).165 E
(not completely optimize the forw)72 238.8 Q(arding paths.)-.11 E -.165
(Fo)5.5 G 2.75(rm).165 G(an)-2.75 E 2.75(yr)-.165 G(ecei)-2.75 E -.165
(ve)-.275 G(rs the route via the RP may).165 E(in)72 251.8 Q -.22(vo)
-.44 G(lv).22 E 2.75(eas)-.165 G(igni\214cant detour when compared with\
 the shortest path from the source to the recei)-2.75 E -.165(ve)-.275 G
-.605(r.).165 G 1.76 -.88(To o)72 268.4 T(btain lo).88 E
(wer latencies, a router on the sender')-.275 E 2.75(sL)-.605 G
(AN, typically the DR, may optionally initiate)-2.75 E 2.75(at)72 281.4
S(ransfer from the shared tree to a source-speci\214c shortest-path tre\
e \(SPT\).)-2.75 E 1.76 -.88(To d)5.5 H 2.75(ot).88 G(his, it issues)
-2.75 E(an \(S,G\) Join to)72 294.4 Q -.11(wa)-.275 G(rds S.).11 E
(This instantiates state in the routers along the path to S.)5.5 E(Ev)
5.5 E(entually this)-.165 E(join either reaches S')72 307.4 Q 2.75(ss)
-.605 G(ubnet, or reaches a router that already has \(S,G\) state.)-2.75
E(When this happens,)5.5 E(data pack)72 320.4 Q
(ets from S start to \215o)-.11 E 2.75(wf)-.275 G(ollo)-2.75 E
(wing the \(S,G\) state until the)-.275 E 2.75(yr)-.165 G
(each the recei)-2.75 E -.165(ve)-.275 G -.605(r.).165 G
(At this point the recei)72 337 Q -.165(ve)-.275 G 2.75(r\().165 G
(or a router upstream of the recei)-2.75 E -.165(ve)-.275 G
(r\) will be recei).165 E(ving tw)-.275 E 2.75(oc)-.11 G(opies of the)
-2.75 E(data - one from the SPT and one from the RPT)72 350 Q 5.5(.W)
-.814 G(hen the \214rst traf)-5.5 E(\214c starts to arri)-.275 E .33
-.165(ve f)-.275 H(rom the).165 E(SPT)72 363 Q 2.75(,t)-.814 G
(he DR or upstream router starts to drop the pack)-2.75 E
(ets for G from S that arri)-.11 E .33 -.165(ve v)-.275 H
(ia the RP tree.).165 E
(In addition, it sends an \(S,G\) prune message to)72 376 Q -.11(wa)
-.275 G(rds the RP).11 E 5.5(.T)-1.221 G(his is kno)-5.5 E
(wn as an \(S,G,rpt\) Prune.)-.275 E(The prune message tra)72 389 Q
-.165(ve)-.22 G(ls hop-by-hop, instantiating state along the path to)
.165 E -.11(wa)-.275 G(rds the RP).11 E(indicating that traf)72 402 Q
(\214c from S for G should NO)-.275 E 2.75(Tb)-.44 G 2.75(ef)-2.75 G
(orw)-2.75 E(arded in this direction.)-.11 E(The prune is)5.5 E(propag)
72 415 Q
(ated until it reaches the RP or a router that still needs the traf)
-.055 E(\214c from S for other recei)-.275 E -.165(ve)-.275 G(rs.).165 E
(By no)72 431.6 Q 1.43 -.715(w, t)-.275 H(he recei).715 E -.165(ve)-.275
G 2.75(rw).165 G(ill be recei)-2.75 E(ving traf)-.275 E
(\214c from S along the shortest-path tree between the)-.275 E(recei)72
444.6 Q -.165(ve)-.275 G 2.75(ra).165 G(nd S.)-2.75 E
(In addition, the RP is recei)5.5 E(ving the traf)-.275 E
(\214c from S, b)-.275 E(ut this traf)-.22 E(\214c is no longer)-.275 E
(reaching the recei)72 457.6 Q -.165(ve)-.275 G 2.75(ra).165 G
(long the RP tree.)-2.75 E(As f)5.5 E(ar as the recei)-.11 E -.165(ve)
-.275 G 2.75(ri).165 G 2.75(sc)-2.75 G(oncerned, this is the \214nal)
-2.75 E(distrib)72 470.6 Q(ution tree.)-.22 E F1(Sour)72 509.6 Q
(ce-speci\214c J)-.198 E(oins)-.165 E F0(IGMPv3 permits a recei)72 526.2
Q -.165(ve)-.275 G 2.75(rt).165 G 2.75(oj)-2.75 G
(oin a group and specify that it only w)-2.75 E(ants to recei)-.11 E .33
-.165(ve t)-.275 H(raf).165 E(\214c for a)-.275 E(group if that traf)72
539.2 Q(\214c comes from a particular source.)-.275 E(If a recei)5.5 E
-.165(ve)-.275 G 2.75(rd).165 G(oes this, and no other recei)-2.75 E
-.165(ve)-.275 G(r).165 E(on the LAN requires all the traf)72 552.2 Q
(\214c for the group, then the DR may omit performing a \(*,G\) join to)
-.275 E(set up the shared tree, and instead issue a source-speci\214c \
\(S,G\) join only)72 565.2 Q(.)-.715 E(The range of multicast addresses\
 from 232.0.0.0 to 232.255.255.255 is currently set aside for)72 581.8 Q
(source-speci\214c multicast in IPv4.)72 594.8 Q -.165(Fo)5.5 G 2.75(rg)
.165 G(roups in this range, recei)-2.75 E -.165(ve)-.275 G
(rs should only issue source-).165 E(speci\214c IGMPv3 joins.)72 607.8 Q
(If a PIM router recei)5.5 E -.165(ve)-.275 G 2.75(san).165 G
(on-source-speci\214c join for a group in this)-2.75 E
(range, it should ignore it, as described in Section 4.8.)72 620.8 Q F1
(Sour)72 646.8 Q(ce-speci\214c Prunes)-.198 E F0
(IGMPv3 also permits a recei)72 663.4 Q -.165(ve)-.275 G 2.75(rt).165 G
2.75(oj)-2.75 G(oin a group and specify that it only w)-2.75 E
(ants to recei)-.11 E .33 -.165(ve t)-.275 H(raf).165 E(\214c for)-.275
E 2.75(ag)72 676.4 S(roup if that traf)-2.75 E<8c63>-.275 E/F2 11
/Times-Italic@0 SF(does not)2.75 E F0
(come from a speci\214c source or sources.)2.75 E
(In this case, the DR will)5.5 E(perform a \(*,G\) join as normal, b)72
689.4 Q(ut may combine this with an \(S,G,rpt\) prune for each of the)
-.22 E(sources the recei)72 702.4 Q -.165(ve)-.275 G 2.75(rd).165 G
(oes not wish to recei)-2.75 E -.165(ve)-.275 G(.).165 E(Fenner/Handle)
72 769 Q(y/Holbrook/K)-.165 E(ouv)-.385 E 182.971(elas Section)-.165 F
2.75(3. [P)2.75 F(age 7])-.165 E EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 71.587(-DRAFT Expires:)-1.012 F
(January 2002)2.75 E(July 2001)123.726 E/F1 11/Times-Bold@0 SF
(Multi-access T)72 85 Q(ransit LANs)-.814 E F0(The o)72 101.6 Q -.165
(ve)-.165 G(rvie).165 E 2.75(ws)-.275 G 2.75(of)-2.75 G
(ar has concerned itself with point-to-point links.)-2.86 E(Ho)5.5 E(we)
-.275 E -.165(ve)-.275 G .88 -.44(r, u).165 H(sing multi-access).44 E
(LANs such as Ethernet for transit is not uncommon.)72 114.6 Q
(This can cause complications for three)5.5 E(reasons:)72 127.6 Q 7.15
<8354>72 144.2 S .22 -.11(wo o)-8.03 H 2.75(rm).11 G
(ore routers on the LAN may issue \(*,G\) Joins to dif)-2.75 E
(ferent upstream routers on the)-.275 E(LAN because the)83 157.2 Q 2.75
(yh)-.165 G -2.475 -.22(av e)-2.75 H(inconsistent MRIB entries re)2.97 E
-.055(ga)-.165 G(rding ho).055 E 2.75(wt)-.275 G 2.75(or)-2.75 G
(each the RP)-2.75 E 5.5(.B)-1.221 G(oth paths)-5.5 E
(on the RP tree will be set up, causing tw)83 170.2 Q 2.75(oc)-.11 G
(opies of all the shared tree traf)-2.75 E(\214c to appear on the)-.275
E(LAN.)83 183.2 Q 7.15<8354>72 199.8 S .22 -.11(wo o)-8.03 H 2.75(rm).11
G(ore routers on the LAN may issue \(S,G\) Joins to dif)-2.75 E
(ferent upstream routers on the)-.275 E(LAN because the)83 212.8 Q 2.75
(yh)-.165 G -2.475 -.22(av e)-2.75 H(inconsistent MRIB entries re)2.97 E
-.055(ga)-.165 G(rding ho).055 E 2.75(wt)-.275 G 2.75(or)-2.75 G
(each source S.)-2.75 E(Both)5.5 E
(paths on the source-speci\214c tree will be set up, causing tw)83 225.8
Q 2.75(oc)-.11 G(opies of all the traf)-2.75 E(\214c from S to)-.275 E
(appear on the LAN.)83 238.8 Q 7.15<8341>72 255.4 S(router on the LAN m\
ay issue a \(*,G\) Join to one upstream router on the LAN, and another)
-4.4 E(router on the LAN may issue an \(S,G\) Join to a dif)83 268.4 Q
(ferent upstream router on the same LAN.)-.275 E -.385(Tr)83 281.4 S(af)
.385 E(\214c from S may reach the LAN o)-.275 E -.165(ve)-.165 G 2.75
(rb).165 G(oth the RPT and the SPT)-2.75 E 5.5(.I)-.814 G 2.75(ft)-5.5 G
(he recei)-2.75 E -.165(ve)-.275 G 2.75(rb).165 G(ehind the)-2.75 E(do)
83 294.4 Q(wnstream \(*,G\) router doesn')-.275 E 2.75(ti)-.198 G
(ssue an \(S,G,rpt\) prune, then this condition w)-2.75 E(ould persist.)
-.11 E(All of these problems are caused by there being more than one up\
stream router with join state for)72 311 Q
(the group or source-group pair)72 324 Q 5.5(.P)-.605 G(IM does not pre)
-5.5 E -.165(ve)-.275 G(nt such duplicate joins from occurring -).165 E
(instead when duplicate data pack)72 337 Q
(ets appear on the LAN from dif)-.11 E(ferent routers, these routers)
-.275 E(notice this, and then elect a single forw)72 350 Q(arder)-.11 E
5.5(.T)-.605 G(his election is performed using PIM Assert)-5.5 E
(messages, which resolv)72 363 Q 2.75(et)-.165 G(he problem in f)-2.75 E
-.22(avo)-.11 G 2.75(ro).22 G 2.75(ft)-2.75 G
(he upstream router which has \(S,G\) state, or if)-2.75 E
(neither or both router has \(S,G\) state, then in f)72 376 Q -.22(avo)
-.11 G 2.75(ro).22 G 2.75(ft)-2.75 G
(he router with the best metric to the RP for)-2.75 E
(RP trees, or the best metric to the source to source-speci\214c trees.)
72 389 Q(These Assert messages are also recei)72 405.6 Q -.165(ve)-.275
G 2.75(db).165 G 2.75(yt)-2.75 G(he do)-2.75 E
(wnstream routers on the LAN, and these cause)-.275 E
(subsequent join messages to be sent to the upstream router that w)72
418.6 Q(on the Assert.)-.11 E F1(RP Disco)72 444.6 Q -.11(ve)-.11 G(ry)
.11 E F0(PIM-SM routers need to kno)72 461.2 Q 2.75(wt)-.275 G
(he address of the RP for each group for which the)-2.75 E 2.75(yh)-.165
G -2.475 -.22(av e)-2.75 H(\(*,G\))2.97 E 2.75(state. This)72 474.2 R(a\
ddress is obtained either through a bootstrap mechanism or through stat\
ic)2.75 E/F2 10/Symbol SF<ef>555 486.2 Q<ef>-4.94 -10 M<ef>-4.94 -10 M
F0(con\214guration.)72 487.2 Q(One dynamic w)72 503.8 Q(ay to do this i\
s to use the Bootstrap Router \(BSR\) mechanism [4]. One router in)-.11
E(each PIM domain is elected the Bootstrap Router through a simple elec\
tion process.)72 516.8 Q(All the)5.5 E(routers in the domain that are c\
on\214gured to be candidates to be RPs periodically unicast their)72
529.8 Q(candidac)72 542.8 Q 2.75(yt)-.165 G 2.75(ot)-2.75 G(he BSR.)
-2.75 E(From the candidates, the BSR picks an RP-set, and periodically)
5.5 E(announces this set in a bootstrap message.)72 555.8 Q
(Bootstrap messages are \215ooded hop-by-hop)5.5 E F2<ef>555 567.8 Q<ef>
-4.94 -10 M<ef>-4.94 -10 M<ef>-4.94 -10 M<ef>-4.94 -10 M<ef>-4.94 -10 M
<ef>-4.94 -10 M F0
(throughout the domain until all routers in the domain kno)72 568.8 Q
2.75(wt)-.275 G(he RP-Set.)-2.75 E 1.76 -.88(To m)72 585.4 T
(ap a group to an RP).88 E 2.75(,ar)-1.221 G
(outer hashes the group address into the RP-set using an order)-2.75 E
(-)-.22 E(preserving hash function \(one that minimizes changes if the \
RP set changes\).)72 598.4 Q(The resulting RP is)5.5 E
(the one that it uses as the RP for that group.)72 611.4 Q F1(4.)72
650.4 Q/F3 14/Times-Bold@0 SF(Pr)5.5 E(otocol Speci\214cation)-.252 E F0
(The speci\214cation of PIM-SM is brok)72 667 Q(en into se)-.11 E -.165
(ve)-.275 G(ral parts:).165 E 7.15<8353>72 683.6 S
(ection 4.1 details the protocol state stored.)-7.15 E 7.15<8353>72
700.2 S(ection 4.2 speci\214es the data pack)-7.15 E(et forw)-.11 E
(arding rules.)-.11 E(Fenner/Handle)72 769 Q(y/Holbrook/K)-.165 E(ouv)
-.385 E 182.971(elas Section)-.165 F 2.75(4. [P)2.75 F(age 8])-.165 E EP
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/F0 11/Times-Roman@0 SF(INTERNET)72 49 Q 71.587(-DRAFT Expires:)-1.012 F
(January 2002)2.75 E(July 2001)123.726 E 7.15<8353>72 85 S
(ection 4.3 speci\214es the PIM Re)-7.15 E
(gister generation and processing rules.)-.165 E 7.15<8353>72 101.6 S(e\
ction 4.4 speci\214es the PIM Join/Prune generation and processing rule\
s.)-7.15 E 7.15<8353>72 118.2 S
(ection 4.5 speci\214es the PIM Assert generation and processing rules.)
-7.15 E 7.15<8344>72 134.8 S
(esignated Router \(DR\) election is speci\214ed in Section 4.6.)-7.15 E
/F1 10/Symbol SF<ef>555 150.4 Q F0 7.15<8353>72 151.4 S
(ection 4.7 speci\214es the RP disco)-7.15 E -.165(ve)-.165 G
(ry mechanisms.).165 E 7.15<8354>72 168 S(he subset of PIM required to \
support Source-Speci\214c Multicast, PIM-SSM, is described in)-7.15 E
(Section 4.8.)83 181 Q 7.15<8350>72 197.6 S(IM pack)-7.15 E
(et formats are speci\214ed in Section 4.9.)-.11 E 7.15<8341>72 214.2 S
(summary of PIM-SM timers and their def)-4.4 E(ault v)-.11 E
(alues is gi)-.275 E -.165(ve)-.275 G 2.75(ni).165 G 2.75(nS)-2.75 G
(ection 4.10.)-2.75 E/F2 11/Times-Bold@0 SF(4.1.)72 240.2 Q/F3 13
/Times-Bold@0 SF(PIM Pr)5.5 E(otocol State)-.234 E F0(This section spec\
i\214es all the protocol state that a PIM implementation should maintai\
n in order to)72 256.8 Q(function correctly)72 269.8 Q 5.5(.W)-.715 G
2.75(et)-6.38 G(erm this state the)-2.75 E/F4 11/Times-Italic@0 SF
-1.947 -.605(Tr e)2.75 H 2.75(eI).605 G(nformation Base)-2.75 E F0
(or TIB, as it holds the state of all)2.75 E(the multicast distrib)72
282.8 Q(ution trees at this router)-.22 E 5.5(.I)-.605 G 2.75(nt)-5.5 G
(his speci\214cation we de\214ne PIM mechanisms in)-2.75 E
(terms of the TIB.)72 295.8 Q(Ho)5.5 E(we)-.275 E -.165(ve)-.275 G .88
-.44(r, o).165 H(nly a v).44 E(ery simple implementation w)-.165 E
(ould actually implement pack)-.11 E(et)-.11 E(forw)72 308.8 Q
(arding operations in terms of this state.)-.11 E
(Most implementations will use this state to b)5.5 E(uild a)-.22 E
(multicast forw)72 321.8 Q(arding table, which w)-.11 E
(ould then be updated when the rele)-.11 E -.275(va)-.275 G
(nt state in the TIB).275 E(changes.)72 334.8 Q
(Although we specify precisely the state to be k)72 351.4 Q
(ept, this does not mean that an implementation of)-.11 E
(PIM-SM needs to hold the state in this form.)72 364.4 Q
(This is actually an abstract state de\214nition, which is)5.5 E
(needed in order to specify the router')72 377.4 Q 2.75(sb)-.605 G(eha)
-2.75 E(vior)-.22 E 5.5(.A)-.605 G
(PIM-SM implementation is free to hold)-2.75 E(whate)72 390.4 Q -.165
(ve)-.275 G 2.75(ri).165 G(nternal state it requires, and will still be\
 conformant with this speci\214cation so long as it)-2.75 E
(results in the same e)72 403.4 Q(xternally visible protocol beha)-.165
E(vior as an abstract router that holds the)-.22 E(follo)72 416.4 Q
(wing state.)-.275 E 1.76 -.88(We d)72 433 T -.275(iv).88 G
(ide TIB state into four sections:).275 E(\(*,*,RP\) state)72 449.6 Q
(State that maintains per)97 462.6 Q(-RP trees, for all groups serv)-.22
E(ed by a gi)-.165 E -.165(ve)-.275 G 2.75(nR).165 G -1.221(P.)-2.75 G
(\(*,G\) state)72 479.2 Q(State that maintains the RP tree for G.)97
492.2 Q(\(S,G\) state)72 508.8 Q(State that maintains a source-speci\
\214c tree for source S and group G.)97 521.8 Q(\(S,G,rpt\) state)72
538.4 Q(State that maintains source-speci\214c information about source\
 S on the RP tree for G.)97 551.4 Q -.165(Fo)5.5 G(r).165 E -.165(ex)97
564.4 S(ample, if a source is being recei).165 E -.165(ve)-.275 G 2.75
(do).165 G 2.75(nt)-2.75 G
(he source-speci\214c tree, it will normally ha)-2.75 E .33 -.165(ve b)
-.22 H(een).165 E(pruned of)97 577.4 Q 2.75(ft)-.275 G(he RP tree.)-2.75
E(This prune state is \(S,G,rpt\) state.)5.5 E
(The state that should be k)72 594 Q(ept is described belo)-.11 E 4.18
-.715(w. O)-.275 H 2.75(fc).715 G
(ourse, implementations will only maintain)-2.75 E
(state when it is rele)72 607 Q -.275(va)-.275 G(nt to forw).275 E
(arding operations - for e)-.11 E(xample, the "NoInfo" state might be)