Kanak Agarwal, Colin Dixon*, Eric Rozner, John Carter IBM Research, Austin, TX

19 Pages·2014·2.83 MB·English

Shadow MACs:
Scalable Label-switching

for Commodity Ethernet
Kanak Agarwal, Colin Dixon*, Eric Rozner, John Carter

IBM Research, Austin, TX
* now at Brocade
1
SDN: The Future!
Rose-colored glasses: 

•
Fine-grained, dynamic control of the network
Supported by:
•
Flow mod’s based on diverse set of pkt hdr fields
•
Network measurements obtained in milliseconds1
•
Flow mods installed hundreds of times a second2
•
1. Rasley, et al. Planck: Millisecond-scale Monitoring and Control for Commodity Networks. SIGCOMM’14.
2. Rostos et al. OFLOPS: An Open Framework for OpenFlow Switch Evaluation. PAM’12.
2
SDN: The Future!
Rose-colored glasses: 

•
Fine-grained, dynamic control of the network
Supported by:
•
o
d t
e
m i t
• Flow mod’s based on divemresen t ss e l ti of pkt hdr fields
o y
p l
M o s t S D N d e a l l p r o d u c t i o n
m
o r s
a y s
Network moevaesrul rements obtanint es d in milliseconds1
• m e
n
n v i r o
e
Flow mods installed hundreds of times a second2
•
1. Rasley, et al. Planck: Millisecond-scale Monitoring and Control for Commodity Networks. SIGCOMM’14.
2. Rostos et al. OFLOPS: An Open Framework for OpenFlow Switch Evaluation. PAM’12.
3
SDN: The Future?
Significant issues can arise at scale!
•
Flow mod’s based on diverse set of pkt hdr fields
•
TCAMs expensive, only few 1,000 rules supported
!
Network measurements obtained in milliseconds
•
Flow mods installed hundreds of times a second
•
Consistent network updates are hard!
4
Label Switching to the Rescue!
Label switching common forwarding mechanism
•
(Frame Relay, ATM, MPLS, …)
!
!
ingress egress
Label-switched

!
core
We’ll borrow:
•
!
Label-switched core: fixed-width, exact-match
•
lookups map easily into large forwarding tables

Opaque labels: not assoc to physical endpoint in n/w
•
5
Our solution: Shadow MACs
Opaque forwarding label: Destination MAC address
•
Fast, cheap and large fwd’ing tables already in switch!
•
OpenFlow flow mods on ingress/egress guide onto paths

•

MAC


ACTION
DST

B1 route
1. Ingress switch assigns
 B1 -> B


B1
labels to packets out: port

A 
 B2 route B2 -> B

ingress egress B2
out: port

MAC
 
 MAC
 PORT
 3. Egress switch

ACTION 2. Core fwd’s on labels
SRC DST DST
rewrites MAC B

B -> B1
 address
A B 80
out: port
B -> B2

A B *
out: port
6
Shadow MACs: Rerouting
Opaque labels: no physical host → preinstall routes
•
Ingress guiding: Changing routes now an atomic action!

•

1. Controller preinstalls four routes from A to B,
Ctlr
MAC


each with own shadow MAC address ACTION
DST
B1 -> B


B1
out: port
B2 -> B


B2
out: port
B1 B3 -> B


B3
out: port
B2
B4 -> B


B4
out: port
A
ingress egress
2. Controller also


B3
preinstalls rewrite


rules on egress
B
B4
7
Shadow MACs: Rerouting
Opaque labels: no physical host → preinstall routes
•
Ingress guiding: Changing routes now an atomic action!

•

1. Controller preinstalls four routes from A to B,
Ctlr
MAC


each with own shadow MAC address ACTION
DST
B1 -> B


B1
out: port
B2 -> B


B2
out: port
B1 B3 -> B


B3
out: port
B2
B4 -> B


B4
out: port
A
ingress egress
2. Controller also


B3
preinstalls rewrite


rules on egress
B
B4
8
Shadow MACs: Rerouting
Opaque labels: no physical host → preinstall routes
•
Ingress guiding: Changing routes now an atomic action!

•

1. Single flow mod to ingress switch
 MAC

ACTION
Ctlr
DST

 switches paths
B1 -> B

B1
out: port

MAC
 MAC

ACTION
B2 -> B

SRC DST B2
out: port

 B -> B3

A B
B3 -> B

out: green B3
out: port
B1

B4 -> B

B4
B2
out: port

A B
ingress egress

B3

2. Traffic immediately switches

to green route
B4
9
Benefits
• Controller guides pkts onto intelligently selected paths
• Load balancing, link fail-over, route via middleboxes,
differentiated services, …
• Decouples network edge from core
• Consistent n/w updates, fast rerouting, multi-pathing, …
• Maps fine-grained matching to fixed destination-based rules
• Pushes TCAM rules to FDB, limits TCAM usage in core
• Implementable today!
10