arcs - etsi...a bicasted routing (ex) cursor cursor 2 packet copies are colored by the colors of the...

ARCs

ETSI, 9-11 April 2013

Pascal Thubert (Cisco Systems)

Patrice Bellagamba (Cisco Systems)

Centralized Routing Goals

� Distributed was created for high availability (DARPA)

� Centralized can optimize routing from God’s view

Traffic Engineering

Deterministic Routing

© 2013 Cisco and/or its affiliates. All rights reserved. UnclassifiedARCs 2

� Yet must provide additional reliability measures

Multipath redundancy

Duo/bicasting

� Room for both centralized and distributed

Centralized for optimization and virtualization

Distributed for autonomic and ultra available

Problem: routing availability

� Classical trees and Directed Acyclic Graph (DAG) topologies do not provide non-congruent alternate routes for all nodes

� State of the art Fast Reroute (FRR) tolerates 1 failure but may drop traffic or loop upon 2


failure but may drop traffic or loop upon 2

� Yet accidental damage to a fiber harness hits multiple links (Shared Risk Link Group)

� Same goes for interferences in wireless

Arc concept

An Arc is a 2 ended reversible path

C

Rev

Re

v

Re

v Rev

EdgeCursor


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

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 cursor

cursor

cursorcursor

cursor

Omega

Forwarding

In normal operations, traffic flows away from the cursor and cascades from ARC to ARC along shortest path

cursor

cursor cursor


cursor

cursor cursor

cursor

cursorcursor

cursor

Omega

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


A

cursor

cursor cursor

cursor

cursorcursor

Bcursor

Omega

A

Double breakage

Each ARC is its own domain of fault recovery

cursor

cursor cursor


A

cursor

cursor cursor

cursor

cursor

cursor

Bcursor

Omega

A

Bicasted routing (ex)

cursor

cursor

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 theorange and green paths are Left and Right paths (via H2 and H6)

cursor


A

cursor

cursor

cursor

cursorcursor

cursor

Bcursor

H2 H6

Omega

A

Bicasted reservation (ex)

cursor

cursor

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


A

cursor

cursor

cursor

cursorcursor

cursor

Bcursor

Omega

Load Balancing & complex destinations

The cursor may send traffic on both directionsOther ingresses send traffic away from cursor

cursor

cursor cursor


cursor

cursor cursor

cursor

cursor

cursor

Omega

cursor

50/50

Load Balancing (light congestion)

The cursor may balanceClassical control loop, no routing change, no « ARPANET » oscillation

cursor

cursor cursor Fwd plane


cursor

cursor cursor

cursor

cursor

Omega

cursor

75/25

Fwd plane Control loop

cursor

Load Balancing (hard congestion)

Congestion notification is injected in incoming ARCs

cursor

cursor cursor


cursor

cursor cursor

cursor

cursor

Omega

cursor

50/50

cursor

Load Balancing (hard congestion)

Load spreads over slightly longer paths

cursor

cursor cursor


cursor

cursor cursor

cursor

cursor

Omega

cursor

50/50

cursor

oLAF

© 2010 Cisco and/or its affiliates. All rights reserved. 15UnclassifiedBRKEWN-3012

Notations for Link types

A is SPF successor of BA B

A is non shortest path successor of

BA B


B -> A is unresolved for Safe Node SA B

A B

A B

B is standby alternate on A isolation

Non SPF Link used to join an ARC

B

Rev

?-S

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

B


F

M

N

L

A

E

G H

I

M

K

J

D

C

B

oLAF Example: Initial topology

R

A

D

B

K

C


L

K

J

EF

GH I

M

N

Running the modified Algo, Start from R:

A

D

B

K

C

Root

R(A) R(B) A and B are Heir

Since we have a

single root wecreate virtual rootsR(A) and R(B)

We note the set

?-A


L

K

J

EF

GH I

We note the set dependent on R(A)

as ?-A for

convenience

N

Picking A (closest to root), and D, and C:

R

A

D

B

K

C

Then pickPick D,

Pick C,

Each time place in the parent set

?-A ?-A

?-A


L

K

J

EF

GH I

N

Picking B:R(A)

A

D

B

K

C

Pick K, startbuilding up B’s

dependent set

?-A ?-A?-B

R(B)

?-A ?-B


L

K

J

EF

GH I

M

N

Picking M and J:

A

D

B

K

C - The dependent

sets grow.

?-A ?-A?-B

?-B

R(A) R(B)

?-A ?-B


L

K

J

EF

GH I

?-BM

?-B

N

Running the AlgoPicking L and then E:

A

D

B

K

C?-B

?-A?-A

?-A ?-A

?-B

?-A ?-BR(A) R(B)


L

K

J

EF

GH I

?-B

?-A?-AM

?-B

N

Picking G:

A

D

B

K

C?-B

?-A?-A

?-A ?-A

?-B

?-A ?-BR(A) R(B)


L

K

J

EF

GH I

?-B

?-A?-A

?-A

M

?-B

N

Picking F; F is a Safe node!

A

D

B

K

C

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

?-B

?-A?-A

?-A ?-A

?-B

?-A ?-BR(A) R(B)


L

K

J

EF

G

H I

virtual this time since they are R(A)

and R(B)?-B

?-A?-A?-A

?-A

M

?-B

N

We can form the first infrastructure ARC!

R

A

D

B

K

C

We can use F-J to

tie F’s shortest path

to R(A) with J’s shortest path to

R(B)?-B

?-A?-A

?-A ?-A

?-B

?-A ?-B


L

K

J

EF

GH I

?-B

?-A?-A?-A

?-A

M

?-B

All nodes along the ARC are Safe

R

A

D

B

K

CRev

RevNodes along the

ARC are placed alone in there own

dependent set(not represented)


L

K

J

EF

GH I

Rev

Rev

Rev

N

M

(not represented)

All other nodes are

returned to the

original set

Next is D

R

A

D

B

K

CRev

Rev- D depends on A

- D can reach C which is in

another set

?-A


L

K

J

EF

GH I

Rev

Rev

Rev

N

M

D is a collapsed ARC

R

A B

K

CRev

RevD’s parent A and

D’s preferredneighbor C are both

Safe NodesD


L

K

J

EF

GH I

Rev

Rev

Rev

N

M

Next is M

R

A B

K

CRev

Rev- Same goes for M

?-K

D


L

K

J

EF

GH I

Rev

Rev

Rev

N

M?-K

M is a collapsed ARC

R

A B

K

CRev

Rev

D


L

K

J

EF

GH I

Rev

Rev

Rev

N

M

Picking L

R

A B

K

CRev

Rev

D

?-D

All depend on D at

this point


L

K

J

EF

GH I

Rev

Rev

Rev

N

M?-D

Picking E

R

A B

K

CRev

Rev

D

?-D?-D

All depend on D at

this point


L

K

J

EF

GH I

Rev

Rev

Rev

N

M?-D?-D

E has links to C and F

R

A B

K

CRev

Rev

D

?-D?-D

E has links that end

deeper than D’s collapsed ARC


L

K

J

EF

GH I

Rev

Rev

Rev

N

M?-D?-D

E adds a buttressing ARC

R

A B

K

CRev

RevWe can form a

buttressing ARC keeping E’s links

that end deeperthan D’s collapsed

D

Rev


L

K

J

F

GH I

Rev

Rev

Rev

N

M

than D’s collapsed

ARC

E->D becomes this

reversible

L returns to the set

D being the Cursor

of the origin ARC iscursor for the Comb

E

Rev

Picking L

R

A B

K

CRev

RevL forms its own

collapsed ARC

D

Rev?-D


L

K

J

F

GH I

Rev

Rev

Rev

N

M

E

Rev?-D

Picking N

R

A B

K

CRev

Rev

D

Rev


K

J

F

GH I

Rev

Rev

Rev

N

M

EL

?-A

Rev

Picking G

R

A B

K

CRev

Rev

D

Rev


K

J

F

GH I

Rev

Rev

Rev

N

M

E

Rev

?-E

L

?-A

Picking H

R

A B

K

CRev

Rev

D

Rev


K

J

F

GH I

Rev

Rev

Rev

N

M

E

Rev

?-E

L

?-A ?-E

H adds a buttressing ARC

R

A B

K

CRev

Rev

D

Rev


K

J

F

G

I

Rev

Rev

Rev

N

M

E

Rev

L

Rev

H

Picking N and G again

R

A B

K

CRev

Rev

D

Rev


K

J

F

G

I

Rev

Rev

Rev

N

M

E

Rev

L

Rev

H

?-E?-A

Picking N again

R

A B

K

CRev

Rev

D

Rev


K

J

F

I

Rev

Rev

Rev

N

M

E

Rev

L

Rev

HG

?-A

Picking N again and then I

R

A B

K

CRev

Rev

D

Rev

We’re done with the set

N is still dependent


K

J

F

I

Rev

Rev

Rev

N

M

E

Rev

L

Rev

H

N’s subgraph ismonoconnected

If N has a dependent set we

run the algorithm in

that set using N as

root.G

?-A

Original Graph and Classical rev-SPF

R

A B

K

CD

R

A

D

B

K

C


K

J

F

N

M

EL

HG

I

L

K

J

EF

GH I

M

N

Original Graph and SPF-based DAG

R

A B

K

CD

R

A

D

B

K

C


K

J

F

N

M

EL

HG

I

L

K

J

EF

GH I

M

N

Only 3 nodes are Safe but in all cases packet end in Single point of failurewaterbasins

Original Graph and resulting construct

R

A B

K

CDRev

Rev

Rev

R

A

D

B

K

C


K

J

F

N

M

EL

HG

I

Rev

Rev

Rev

Rev

Rev

L

K

J

EF

GH I

M

N

Constructed ARCs

R

A

K

D

C

B


F

M

N

LE

G HI

M

K

J

Conclusion

ARCs Concept

Unicast, bicast, multicast

Fast reroute

Load Balancing


oLAF algorithm

Simple, can be optimized

Destination Oriented

)

Questions?


arcs - etsi...a bicasted routing (ex) cursor cursor 2 packet copies are colored by the colors of the...

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