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Resilient MPLS Rings

draft-kompella-mpls-rmr

Kireeti KompellaIETF 91

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Using MPLS in RingTopologies

A ring is te most e!"ient topolog# tato$ers resilien"e % % &'t MPLS resilien"e in rings is far from e!"ient

Rings are often 'sed in a""ess andaggregation (ere &and(idt is pre"io's % % &'t pre-assigning &and(idt ma# &e (astef'l

Rings are a simple topolog#) and tere are

lots of tem % % so "on*g'ring tem so'ld &e as simple as

possi&le

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MPLS for Ring Transport

Te goal ere is to identif# and addressiss'es in r'nning MPLS as a transportproto"ol in a""ess rings

+asi"all#) to do (at MPLS-TP set o't to do) torepla"e T,M (it pa"ket) &'t in an e!"ient (a#

To a"iee tis) (e 'se I.P for ringdis"oer# and RS/P-TE or L,P for signaling

0 &'t in a ne( (a# Some of te di$eren"es from traditional2

signaling (ill &e e3plained

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4e( Paradigm5 Resilient MPLS Rings

,on6t "on*g're LSPs % "on*g're MPLSrings

,on6t "on*g're and signal n7n-18 LSPs %

LSPs "ome 'p on teir o(n no need for ER:s

,on6t "on*g're &and(idts % &and(idts are ded'"ed from tra!" or

seri"es

,on6t "on*g're prote"tion pats) passLSPs or deto'rs % prote"tion appens nat'rall#

,on6t "on*g're ierar"i"al LSPs %

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Ring A'to-dis"oer#

Re;'irements5 ring nodes are assigned to aring ID

Ring links are dis"oered and a'to-

&'ndled2 4on-ring links are identi*ed as s'"

All nodes agree on clockwise andcounterclockwise

Ea" node kno(s its

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Ring LSPs5 +asi"s

A ring LSP startsand endsat the samenode a pair of counter-rotating LSPs.

One direction is called clockwise(CW)

and the other counterclockwise(CCW).

!ing LSP !L"starts and ends on !"andis a multipoint LSP #ith egress !"

$ach node can send traffic to !"either

CW (e.g. !%) or CCW (e.g. !&).

Similarl' each node ! ! !* + and !,

has a ring LSP.

A ring of nodes has ring LSPs not (-")/

CW

CCW

17

R0

17

R1

17

R2

17

R5

17

R9

17

R3

17

R4

17

R6

17

R7

17

R8

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Ring LSPs5 Signaling

4ode > sends 1? Resmessages

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Ring LSPs5 Prote"tion

Since ring LSP !L" is 1idirectionalthere is a path from node 2 to node " in

1oth directions CCW (3ia node ,) and

CW (3ia node 4). 5his is used to protect

ring LSP " sa' from node % to node ".

6f the lin7 1et#een node 2 and node ,fails traffic to node " is immediatel' put

on the re3erse LSP to node ".

When the notification of the failure

propagates to node 4 the traffic on !L"

is di3erted at node 4 to the upstreamdirection.

When node % learns it sends the traffic

CCW to node ". $ffecti3el' the traffic

has s#itched to the other direction.

CW

CCW

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R0

17

R1

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R2

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R5

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R9

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R3

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R4

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R6

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R7

17

R8

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Ring LSPs5 4ode Fail're

ode (sa' !") failure is similar to lin7

failure stuff 8ust #or7s. Of course !L"

clearl' cannot reco3er its egress has

failed.

9o#e3er there is the danger of a loop:

". !protects 1' sending traffic CCW;

. !protects 1' sending traffic CW/

5his can 1e dealt #ith 1' 55L +

+ or 1' adding a ne# $SPL to indicatefailure reco3er'

CW

CCW

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R0

17

R1

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R2

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R5

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R9

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R3

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R4

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R6

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R7

17

R8

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Ring LSPs5 +and(idtManagement

!ing LSP !L"starts #ith 1and#idth. As

ser3ices are pro3isioned o3er !L" their

1and#idths are added to the LSP from #here

the' enter the ring to the egress node.

Sa' a "< PW is pro3isioned from node % to

node ". 5he LSP attempts to increase the

1and#idth from node % to node ". 6f

successful the ser3ice is accepted. Similarl'

for a < PW from node = to node ".

5he resulting signaled 1and#idth in the CW

direction for ring LSP " is from node " to

node =; node = signals a 1and#idth of "

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