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ARCs
Uni.lu, December 2012
Pascal Thubert (Cisco Systems)
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 2
Agenda
ARCs Concept
oLAF algorithm
Bicasting
fArctals
© 2010 Cisco and/or its affiliates. All rights reserved. 3UnclassifiedBRKEWN-3012
Available Routing Constructs
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 4
Arc concept
An Arc is a 2 ended reversible path
Edges are directed outwards; links within are reversible
An arc is resilient to any link or Junction break by returning links
Links are oriented from cursor to edges and returned by moving the cursor.
We build Arcs between Safe Nodes
C
Re
v
Re
v
Re
v Re
v
EdgeCursor
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 5
ARC topology
ARCs form dual or multi-ended structures
• An ARC stitches 2 SPF subpaths together
• ARCs + buttressing ARCs = Comb
• One cursor per ARC / Comb as the water separation line
cursor
cursor
cursor cursor
cursor
cursorcursor
cursor
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 6
Forwarding
In normal operations, traffic flows away from the cursor and cascades
from ARC to ARC along shortest path
cursor
cursor
cursor cursor
cursor
cursorcursor
cursor
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 7
A
Forwarding errors
Are Addressed inside an ARC by returning the incoming link,
In order to exit via the other edge of this ARC
In control plane, this means that the Cursor is placed at the failure location
cursor
cursor
cursor cursor
cursor
cursorcursor
Bcursor
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 8
A
Double breakage
Each ARC is its own domain of fault recovery
cursor
cursor
cursor cursor
cursor
cursor
cursor
Bcursor
Omega
© 2010 Cisco and/or its affiliates. All rights reserved. 9UnclassifiedBRKEWN-3012
oLAF
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 10
Notations for Link types
A is SPF successor of B
B -> A is unresolved for Safe Node S
A B
A B
A B
A B
B is standby alternate on A isolation
Non SPF Link used to join an ARC
A is non shortest path successor of
B
A B
Rev
?-S
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 11
LAF (Lowest ARC First)
LAF is a SPF variation that creates ARCs by connecting SPF paths
- The ARCs include the SPF tree
- The algorithm identifies the mono-connected zones
- and provides redundancy inside such zones
R
F
M
N
L
A
E
G H
I
M
K
J
D
C
B
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 12
oLAF Example: Initial topology
R
A
D
L
B
K
J
C
EF
GH
I
M
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 13
Running the modified Algo, Start from R:
A
D
L
B
K
J
C
EF
GH
I
R
o
o
t
R(A) R(B) A and B are Heir
Since we have a
single root we
create virtual roots
R(A) and R(B)
We note the set
dependent on R(A)
as ?-A for
convenience
?-A
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 14
Picking A (closest to root), and D, and C:
R
A
D
L
B
K
J
C
EF
GH
I
Then pick
Pick D,
Pick C,
Each time place in
the parent set?-A ?-A
?-A
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 15
Picking B:R(A)
A
D
L
B
K
J
C
EF
GH
I
Pick K, start
building up B’s
dependent set
?-A ?-A?-B
M
R(B)
?-A ?-B
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 16
Picking M and J:
A
D
L
B
K
J
C
EF
GH
I
- The dependent
sets grow.
?-A ?-A?-B
?-BM
?-B
R(A) R(B)
?-A ?-B
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 17
Running the AlgoPicking L and then E:
A
D
L
B
K
J
C
EF
GH
I
?-B
?-B
?-A?-A
?-A ?-A
M
?-B
?-A ?-BR(A) R(B)
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 18
Picking G:
A
D
L
B
K
J
C
EF
GH
I
?-B
?-B
?-A?-A
?-A ?-A
?-A
M
?-B
?-A ?-BR(A) R(B)
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 19
Picking F; F is a Safe node!
A
D
L
B
K
J
C
EF
G
H I
Examining F’s
neighbors we find J
that is B-dependent
F has 2 non
congruent path to 2
Safe Nodes, though
virtual this time
since they are R(A)
and R(B)
?-B
?-B
?-A?-A
?-A
?-A
?-A
?-A
M
?-B
?-A ?-BR(A) R(B)
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 20
We can form the first infrastructure ARC!
R
A
D
L
B
K
J
C
EF
GH
I
We can use F-J to
tie F’s shortest path
to R(A) with J’s
shortest path to
R(B)?-B
?-B
?-A?-A
?-A
?-A
?-A
?-A
M
?-B
?-A ?-B
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 21
All nodes along the ARC are Safe
R
A
D
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
N
M
Nodes along the
ARC are placed
alone in there own
dependent set
(not represented)
All other nodes are
returned to the
original set
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 22
Next is D
R
A
D
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
N
M
- D depends on A
- D can reach C
which is in
another set
?-A
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 23
D is a collapsed ARC
R
A
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
N
M
D’s parent A and
D’s preferred
neighbor C are both
Safe NodesD
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 24
Next is M
R
A
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
N
M
- Same goes for M
?-K
D
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 25
M is a collapsed ARC
R
A
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
N
D
M
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 26
Picking L
R
A
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
N
D
M
?-D
All depend on D at
this point
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 27
Picking E
R
A
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
N
D
M
?-D?-D
All depend on D at
this point
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 28
E has links to C and F
R
A
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
N
D
M
?-D?-D
E has links that end
deeper than D’s
collapsed ARC
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 29
E adds a buttressing ARC
R
A
L
B
K
J
C
F
GH
I
Rev
Rev
Rev
Rev
Rev
N
M
We can form a
buttressing ARC
keeping E’s links
that end deeper
than D’s collapsed
ARC
E->D becomes this
reversible
L returns to the set
D being the Cursor
of the origin ARC is
cursor for the Comb
E
D
Rev
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 30
Picking L
R
A
L
B
K
J
C
F
GH
I
Rev
Rev
Rev
Rev
Rev
N
M
L forms its own
collapsed ARC
E
D
Rev?-D
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 31
Picking N
R
A B
K
J
C
F
GH
I
Rev
Rev
Rev
Rev
Rev
N
M
E
D
L
?-A
Rev
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 32
Picking G
R
A B
K
J
C
F
GH
I
Rev
Rev
Rev
Rev
Rev
N
M
E
D
Rev
?-E
L
?-A
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 33
Picking H
R
A B
K
J
C
F
GH
I
Rev
Rev
Rev
Rev
Rev
N
M
E
D
Rev
?-E
L
?-A ?-E
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 34
H adds a buttressing ARC
R
A B
K
J
C
F
G
I
Rev
Rev
Rev
Rev
Rev
N
M
E
D
Rev
L
Rev
H
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 35
Picking N and G again
R
A B
K
J
C
F
G
I
Rev
Rev
Rev
Rev
Rev
N
M
E
D
Rev
L
Rev
H
?-E?-A
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 36
Picking N again
R
A B
K
J
C
F
I
Rev
Rev
Rev
Rev
Rev
N
M
E
D
Rev
L
Rev
HG
?-A
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 37
Picking N again and then I
R
A B
K
J
C
F
I
Rev
Rev
Rev
Rev
Rev
N
M
E
D
Rev
L
Rev
H
We’re done with the
set
N is still dependent
N’s subgraph is
monoconnected
If N has a
dependent set we
run the algorithm in
that set using N as
root.G
?-A
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 38
Original Graph and Classical rev-SPF
R
A B
K
J
C
F
N
M
E
D
L
HG
I
R
A
D
L
B
K
J
C
EF
GH
I
M
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 39
Original Graph and SPF-based DAG
R
A B
K
J
C
F
N
M
E
D
L
HG
I
R
A
D
L
B
K
J
C
EF
GH
I
M
N
Only 3 nodes are Safe but in all cases packet end in Single point of failure
waterbasins
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 40
Original Graph and resulting construct
R
A B
K
J
C
F
N
M
E
D
L
HG
I
Rev
Rev
Rev
Rev
Rev
Rev
Rev
R
A
D
L
B
K
J
C
EF
GH
I
M
N
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 41
Constructed ARCs
R
F
M
N
L
A
E
G HI
M
K
J
D
C
B
© 2010 Cisco and/or its affiliates. All rights reserved. 42UnclassifiedBRKEWN-3012
Bicasting
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 43
Adding Bicasting to ARCs
A concept of Left and Right is introduced.
C
Re
v
Re
v
Re
v Re
v
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 44
Omega
Building L/R indicators
When an ARC is formed, each end is associated to a side.
At least one Right (green) and one Left (orange) per ARC
cursor
cursor
cursor cursor
cursor
cursorcursor
cursor
H1 H2 H3 H4 H5 H6
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 45
Building L/R indicators (cont’d)
Nodes between cursor and edge are associated to the edge side
For an edge ending at Omega, the association is free form
cursor
cursor
cursor cursor
cursor
cursorcursor
cursor
H1 H2 H3 H4 H5 H6
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 46
Building L/R indicators (cont’d)
For and ARC ending in another ARC, the end is associated to
the same heir as the node the ARC exits into. This keeps ARC
bicasting routes close to shortest path.
cursor
cursor
cursor cursor
cursor
cursorcursor
cursor
H1 H2 H3 H4 H5 H6
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 47
Building L/R indicators (cont’d)
In case of collision (both ends of an ARC select the same heir)
• One end picks that heir (shortest path)
• The other picks the heir of the other end of the ARC it falls into
cursor
cursor
cursor cursor
cursor
cursorcursor
cursor
H1 H2 H3 H4 H5 H6
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 48
A
Bicasted routing (ex)
cursor
cursor
cursor
cursor
cursorcursor
2 packet copies are colored by the colors of the ARC through which
the original packet is injected
Packet copies exit ARCs by the the edge corresponding to their color.
Below, the black path is shortest whereas the
orange and green paths are Left and Right paths (via H2 and H6)
cursor
Bcursor
H2 H6
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 49
A
Bicasted routing (2nd ex)
L/R Packets are routed away along there E/W tag,
=> independent of the cursor.
L/R tagging is used to prevent re-U-turning in a same ARC.
cursor
cursor
cursor
cursorcursor
cursor
Bcursor
cursor
H2 H5
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 50
A
Bicasted routing (2nd, with breakage)
E/W Packets are routed away along there E/W tag,
=> independent of the cursor.
E/W tagging is used to prevent re-U-turning in a same ARC.
cursor
cursor
cursor
cursorcursor
cursor
Bcursor
cursor
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 51
A
Bicasted reservation (ex)
cursor
cursor
cursor
cursor
cursorcursor
Reservation Packets are routed away along there E/W tag,
For traffic coming back from root (bi-casted, in red)
Collisions are identified and resolved (next slides)
cursor
Bcursor
Omega
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 52
Collision type 1
Reservation Packets cross in a same arc from different entry points
Resolution is to prune cross-forwarding along the ARC
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 53
Collision type 2
Reservation Packets enter a same arc at a same entry point
This means an incoming ARC faced a coloring collision (orange
below)
Resolution is to return the second reservation packet along its ARC
And prune the u-turn path. Say orange arrived first; green is sent
back.
cursor
Coloring collision: ends in
orange but cannot be
orange
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 54
Collision type 2 (cont’d)
The returned reservation packet arrives on the other end with the
wrong color for that end, which is also the color of the other end.
If the packet cannot be forwarded with its original color it is recolored
to any color but that of its copy. Returning the packet for a collision is
equivalent to a breakage or a missing link if the graph is not
biconnected.
cursor
cursorcursor
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 55
Collision type 2 (alt)
Resolution is still to return the second reservation along its ARC
And prune the u-turn path. Say orange arrived last and is sent back.
In this example the orange packet does not need to be recolored at
the other end since that terminates in an ARC that has an orange
end.
cursor
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 56
Collision type 2 (alt cont’d)
Now we are back to a collision of type 1 which is resolved by pruning
opposite paths along the ARC
© 2010 Cisco and/or its affiliates. All rights reserved. 57UnclassifiedBRKEWN-3012
fArctals
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 58
Laying labels.
Destination
We lay omega ( labels for a destination at the level of the DODAG of
ARCs
Within an ARC, the omega label is encapsulated in a lambda ( label
path that describes the ARC and is independant of the destination. The
lambda label is semected and pushed at the ARC ingress and popped
at the ARC egressLambda
labels
switched
path along
an ARC in
both dir.
Inner omega
label pops for
DODAG level
switching
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 59
Main labels along an ARC
We build to Label switch paths along an arc
Left to Right (dark blue) and Right to Left (dark red)
labels are classical MPLS labels
Note the A edge node is selecting one of its exit to build a LSP, this selection
could be balanced upon Omega labels
CB
A
C
D
Re
v
Re
v
Re
v Re
v
Intermediate Junction
edge Junction Exit node
Cursor Junction
1
2 3
4
1
23
4
21
12
13
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 60
Backup labels along an ARC
We build to backup Label switch paths along an arc
Left to Right (light red, backup of red) and Right to Left (light blue)
labels are classical MPLS labels
The light label paths are fast reroute backup for the dark labels
The light labels do not have back ups
CB
A
C
D
Re
v
Re
v
Re
v Re
v
Intermediate Junction
edge Junction Exit node
Cursor Junction
21
12
13 1bis
2bis 3bis
4bis
1bis
2bis3bis
4bis
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 61
Hierachical Drawing of ARCs in a Ring topology
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 62
Drawing ARCs between rings
We start with a ring topology where rings are interconnected at intersections
points (themselves maybe quite complex inside for redundancy)
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 63
Hierarchical ARC computation in rings (cont’d)
The Interconnection type (simple, double or more intersections) does not
matter at this level of the hierarchy. All that counts is whether rings connect
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 64
Hierarchical ARC computation in rings (cont’d)
Each ring is abstracted as a virtual supernode and a ring connection is
abstracted as a link in the super topology.
Complex connection points can be itemized at that level as well
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 65
Computing the Omega label Path
R
A
D
L
B
K
J
C
EF
GH
I
M
M
To reach a destination R we compute an ARC set over the super topology.
ring
connection
between
rings
destination
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 66
Result of the OLAF algorithm:
DAG visualization
R
A
D
L
B
K
J
C
EF
GH
I
== ARC visualization
R
A
D
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
RevMM
NN Rev
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 67
(Alt) Result of the COMB algorithm:
Buttressing ARC links
R
A
D
L
B
K
J
C
EF
GH
I
Rev
Rev
Rev
Rev
Rev
M
NRev
RevRev
E
R
A
D
L
B
K
J
C
F
G I
M
NH
Comb vizualization
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 68
Computing Omega Labels
Now we have computed an omega
ARC set to destination R. In a Ring,
this determines the egresses and the
cursor location
Again we can lay 4 Omega Labels
per Omega ARC. Omega labels are
per destination but not processed
within the rings
Note that for Combs, the labels follow
the labyrinth logic (Combs and comb
path are discussed in another paper)
Omega Labels are switched at the
connection points. They are invisible
within the Rings (they are
encapsulated in lambda labels).
E
R
A
D
L
B
K
J
C
F
G I
M
NH
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 69
Omega level ARC (in ARC set of rings)
Dbis
CbisBbis
Abis
B
C D
E
a f
b c
a
b
c
f
Ebis
DbisCbis
Bbis
A
B C
D
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 70
Drawing ARCs within a ring (simple connection)
When a Ring has a simple connection to another we draw a single ARC that
goes around this ring to reach the other on both side of the connection
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 71
Olympic style rings
Olympic style rings have a two intersection to one another so we draw a pair of
ARCs that interconnect the connection points that lead to the next ring
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 72
Multiple interconnections
We draw ARCs between contiguous intersection with another ring.
Each ARC is a redundant path to that next ring
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 73
Label encapsulation
When a packet to is injected in a ring ARC,
A MPLS label is added to allow forwarding along the ARC
In ARC, is the destination node in which FEC are defined
ARC label
( )packet
Incoming label
Preferred switched
label
L
Backup switched label Rbis
A table indicates the preferred and the backup labels along the ARC
The preferred is the one that goes away from the cursor
FEC label
( )
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 74
In infrastructure Junction e.g. B
Incoming label B Bbis Bbis B
Preferred switch label A Abis Cbis B
Encapsulating ARC
Alternate label Bbis N/A N/A Bbis
A
B
Cbis
Bbis
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 75
Operation in infra junction ring
Incoming label B Bbis Bbis B
Preferred switch label A Abis Cbis B
Encapsulating ARC
Alternate label Bbis N/A N/A Bbis
• Packet incoming Ring with label B.
• Table indicates to encaps in ARC towards A’s intersections
• A Label is added to forward the packet away from cursor
• Say the ARC is broken in that direction
• is switch to bis to follow the backup label path towards the other edge
• Say the ARC is broken there too. bis has no backup so it is popped
• Thus forwarding over to A is broken. A is switched to alternate Bbis
• Packet now follows ARC towards ring C over the backup LSP
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 76
In edge Junction e.g. A
Incoming label A abis bbis cbis
Preferred switch label a b c Abis
Encapsulating ARC
Alternate label abis bbis cbis Bbis
a
b
c
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 77
Operation in edge Junction
Incoming label A abis bbis cbis
Preferred switch label a b c Abis
Encapsulating ARC
Alternate label abis bbis cbis Bbis
• Packet incoming Ring with label A.
• Table indicates to encaps in ARC towards a’s intersections
• A Label is added to forward the packet away from cursor
• Say the ARC is broken in that direction
• is switch to bis to follow the backup label path towards the other edge
• Say the ARC is broken there too. bis has no backup so it is popped
• Thus forwarding over to a is broken. a is switched to alternate abis
• Packet now follows ARC towards ring b over
• All possible exits a, b, c are tried and if all fail packet goes back to B
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 78
Parallel rings
B
C D
E F
A
G
IH
B
C
D
E
F
A
G
I
H
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 79
Parallel rings (cont’d)
E
A
H
B
C D
E F
A
G
IH
B
C D
E F
A
G
IH
B
C D
E F
A
G
IH
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 80
Label encapsulation
When a packet to is injected in a ring ARC,
A MPLS label is added to allow forwarding along the ARC
In ARC, is the destination node in which FEC are defined
ring label
( )packet
ARC to reach the next hop in a Ring
ARC to reach the next ring
ARC to reach the destination
interring label
( )
intra label
( )
© 2012 Cisco and/or its affiliates. All rights reserved. UnclassifiedUni.lu 81
Questions?
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