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ViAggre: Making Routers Last Longer!
Hitesh Ballani
Paul Francis, Tuan Cao and Jia WangCornell University and AT&T Labs – Research
HotNets 2008
Motivation: Rapid Routing Table Growth
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0806040200989694929088
Act
ive
BG
P e
ntrie
s (F
IB S
ize)
Year
282,000 prefixes (Sep’08)
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0806040200989694929088
Act
ive
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P e
ntrie
s (F
IB S
ize)
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282,000 prefixes (Sep’08)
Motivation: Rapid Routing Table Growth
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100000
200000
300000
400000
500000
140806040200989694929088
Act
ive
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P e
ntrie
s (F
IB S
ize)
Year
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200000
300000
400000
500000
140806040200989694929088
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ntrie
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ize)
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??Rapid future growth
I IPv4 exhaustionI IPv6 deployment
Typical Router Innards
Route Processor
CPU RIB
Line Card
ASIC FIB
Line Card
Line Card
Line Card
Typical Router Innards
Route Processor
CPU RIB
Line Card
ASIC FIB
Line Card
Line Card
Line Card
Routing Information Base
(DRAM $)
Typical Router Innards
Route Processor
CPU RIB
Line Card
ASIC FIB
Line Card
Line Card
Line Card
Forwarding Information Base
(SRAM $$$)
Does (FIB) Size Matter?
Technical concerns
I More Memory
I More ProcessingI Power and Heat dissipation problems
Does (FIB) Size Matter?
Technical concerns
I More Memory
I More ProcessingI Power and Heat dissipation problems
Business concerns
I Less cost-effective networksI Price per byte forwarded increases
I Router memory upgrades
Does (FIB) Size Matter?
Technical concerns
I More Memory
I More ProcessingI Power and Heat dissipation problems
Business concerns
I Less cost-effective networksI Price per byte forwarded increases
I Router memory upgrades
ISPs are willing to undergo some pain to reduce FIBsize
Routing Scalability Problem Space
[Deering, ’96]
[O’Dell, ID’97]
[Zhang et. al., ICNP’06]
[Farinacci, ID’07]
[Massey et. al., ID’07]
[Jen et. al., HotNets’08]
[Francis, CNIS’94]
[Deering et. al., ID’00]
[Hain, ID’02]
[Krioukov et. al., Arxiv’05]
FIB growthRIB growth
Routing Convergence,Update Churn, ....
Routing Scalability Problem Space
[Deering, ’96]
[O’Dell, ID’97]
[Zhang et. al., ICNP’06]
[Farinacci, ID’07]
[Massey et. al., ID’07]
[Jen et. al., HotNets’08]
[Francis, CNIS’94]
[Deering et. al., ID’00]
[Hain, ID’02]
[Krioukov et. al., Arxiv’05]
Separate edge from the core
FIB growthRIB growth
Routing Convergence,Update Churn, ....
Routing Scalability Problem Space
[Deering, ’96]
[O’Dell, ID’97]
[Zhang et. al., ICNP’06]
[Farinacci, ID’07]
[Massey et. al., ID’07]
[Jen et. al., HotNets’08]
[Francis, CNIS’94]
[Deering et. al., ID’00]
[Hain, ID’02]
[Krioukov et. al., Arxiv’05]
Geographical routing
FIB growthRIB growth
Routing Convergence,Update Churn, ....
Routing Scalability Problem Space
[Deering, ’96]
[O’Dell, ID’97]
[Zhang et. al., ICNP’06]
[Farinacci, ID’07]
[Massey et. al., ID’07]
[Jen et. al., HotNets’08]
[Francis, CNIS’94]
[Deering et. al., ID’00]
[Hain, ID’02]
[Krioukov et. al., Arxiv’05]
Compact routing
FIB growthRIB growth
Routing Convergence,Update Churn, ....
Routing Scalability Problem Space
[Deering, ’96]
[O’Dell, ID’97]
[Zhang et. al., ICNP’06]
[Farinacci, ID’07]
[Massey et. al., ID’07]
[Jen et. al., HotNets’08]
[Francis, CNIS’94]
[Deering et. al., ID’00]
[Hain, ID’02]
[Krioukov et. al., Arxiv’05]
All require architectural changeSo many ideas, so little impact!
FIB growthRIB growth
Routing Convergence,Update Churn, ....
Routing Scalability Problem Space
[Deering, ’96]
[O’Dell, ID’97]
[Zhang et. al., ICNP’06]
[Farinacci, ID’07]
[Massey et. al., ID’07]
[Jen et. al., HotNets’08]
[Francis, CNIS’94]
[Deering et. al., ID’00]
[Hain, ID’02]
[Krioukov et. al., Arxiv’05]
Tackle routing scalability through a series ofincremental, individually cost-effective upgrades
FIB growthRIB growth
Routing Convergence,Update Churn, ....
Routing Scalability Problem Space
[Deering, ’96]
[O’Dell, ID’97]
[Zhang et. al., ICNP’06]
[Farinacci, ID’07]
[Massey et. al., ID’07]
[Jen et. al., HotNets’08]
[Francis, CNIS’94]
[Deering et. al., ID’00]
[Hain, ID’02]
[Krioukov et. al., Arxiv’05]
This Paper: Focuses on reducing FIB size
FIB growthRIB growth
Routing Convergence,Update Churn, ....
Virtual Aggregation, aka ViAggre
A “configuration-only” approach to shrinking routerFIBs
I Applies to legacy routersI Can be adopted independently by any ISP
Key Insight: Divide the routing burden
A router only needs to keep routes for a fraction ofthe address space
Talk Outline
I Introduction[]y
I ViAggre: Basic Idea[]y
I ViAggre Design[]y
I Evaluation[]y
I Deployment[]y
I Conclusions
ViAggre: Basic Idea
PoP A PoP C
PoP B
ISP
IPv4AddressSpace
0.0.0.0
255.255.255.255
External Router External Router
Today: All routers have routes to all destinations
ViAggre: Basic Idea
PoP A PoP C
PoP B
ISP
0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2
VirtualPrefixes
Divide address space into Virtual Prefixes (VPs)
ViAggre: Basic Idea0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2
VirtualPrefixes
Aggregation Pointsfor Green VP
Assign Virtual Prefixes to the routersRouters only have routes to a fraction of the address
space
ViAggre: Basic Idea0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2
VirtualPrefixes
Aggregation Pointsfor Green VP
How to achieve such division of the routing table?Without changes to routers and routing protocols
Without cooperation from external networks
Talk Outline
I Introduction[]y
I ViAggre: Basic Idea[]y
I ViAggre Design[]y
I Evaluation[]y
I Deployment[]y
I Conclusions
ViAggre Control-Plane0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 Full Routing Table
eBGP Peers may advertise full routing table
ViAggre Control-Plane0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 Full Routing Table
Load full routing table into RIB
Supress all but blue routes from FIB
FIB SuppressionBlue routers only load blue routes into their FIB
Data-Plane paths0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 Virtual Prefix
Packets destined to a prefix in Red
Consider packets destined to a prefix in the red VP
Data-Plane paths0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2
12
ViAggre pathIngress (I) → Aggregation Pt (A) → Egress (E)
Ingress → Aggregation Point0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2
1
Router I doesn’t have a route for destination prefix
Ingress → Aggregation Point0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2
1
Advertise Red VP
Aggregation Points advertise corresponding VirtualPrefixes
Ingress → Aggregation Point0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2
1
Advertise Red VP
Prefix Next-HopP1P2
........
0/2 A128/2192/2 ....
....
Blue router has a route for the red Virtual Prefix
Aggregation Point → Egress0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2 2
Prefix Next-HopP3P4
X....
64/2 ....
128/2 192/2 ....
....
Aggregation Pt. A tunnels packet to external router
Aggregation Point → Egress0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2
1
Strip tunnel headerfrom outgoing pkts
Egress Router strips the tunnel header off outgoingpackets
Failure of Aggregation Point0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2
1
What if Aggregation Pt. A fails?
Failure of Aggregation Point0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2
Prefix Next-HopP1P2
........
0/2 A2128/2192/2 ....
....
Router I installs the route advertised by A2
Failure of Aggregation Point0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2
Prefix Next-HopP1P2
........
0/2 A2128/2192/2 ....
....
Packets are re-routed appropriately
ViAggre’s impact on ISP’s traffic0.0.0.0
255.255.255.255
External Router External Router
0/2
64/2
128/2
192/2 I
A
E X
A2
1
ViAggre paths can be longer than native pathsTraffic stretch, increased router and link load, etc.
Popular Prefixes
Traffic volume follows power-law distribution
I 95% of the traffic goes to 5% of prefixesI Has held up for years
Install “Popular Prefixes” in routers
I Stable over weeksI Mitigates ViAggre’s impact on the ISP’s traffic
Talk Outline
I Introduction[]y
I ViAggre: Basic Idea[]y
I ViAggre Design[]y
I Evaluation[]y
I Deployment[]y
I Conclusions
Stretch Vs FIB Size
Assigning more routers to aggregate a virtual prefix
I Reduces Stretch imposed on TrafficI Increases FIB size
Aggregation Point Assignment Problem
I Minimize Worst FIB size, subject to constrainton Worst stretch
I NP-complete problemI Implemented a greedy approximation
Performance Study
Data from tier-1 ISP
I Topology, Routing tables, Traffic matrix
Used out algorithm with varying stretch constraints
Constraining Worst Stretch
0
5
10
15
20
25
30
0 2 4 6 8 10 0
1
2
3
4
5
6
7F
IB S
ize
(%
of D
FZ
rou
ting
tabl
e)
Str
etch
(m
sec)
Worst-case Stretch Constraint (msec)
Worst-case FIB Size
0
5
10
15
20
25
30
0 2 4 6 8 10 0
1
2
3
4
5
6
7F
IB S
ize
(%
of D
FZ
rou
ting
tabl
e)
Str
etch
(m
sec)
Worst-case Stretch Constraint (msec)
Worst-case FIB Size
FIB Size reduces as Stretch constraint is relaxedWorst-case Stretch ≤ 4ms ⇒ Worst FIB = 10,226 prefixes
(4% of global routing table)
Constraining Worst Stretch
0
5
10
15
20
25
30
0 2 4 6 8 10 0
1
2
3
4
5
6
7F
IB S
ize
(%
of D
FZ
rou
ting
tabl
e)
Str
etch
(m
sec)
Worst-case Stretch Constraint (msec)
Worst-case FIB SizeWorst Stretch
Average Stretch
0
5
10
15
20
25
30
0 2 4 6 8 10 0
1
2
3
4
5
6
7F
IB S
ize
(%
of D
FZ
rou
ting
tabl
e)
Str
etch
(m
sec)
Worst-case Stretch Constraint (msec)
Worst-case FIB SizeWorst Stretch
Average Stretch
Average Stretch is negligibleWorst-case Stretch ≤ 4ms ⇒ Average Stretch = 0.2msec
Router Load
Deployment with Worst-case Stretch ≤ 4msec
I Shrinks FIB by more than 20xI Median router load increases by 31.3%
Using popular prefixes
I 5% popular prefixes carry 96.7% of trafficI Median and Worst-case router load increase ≈
1%
Talk Outline
I Introduction[]y
I ViAggre: Basic Idea[]y
I ViAggre Design[]y
I Evaluation[]y
I Deployment[]y
I Conclusions[]y
ViAggre Pros
I Shrinks router FIB substantially
I Can be incrementally deployed
I Can be deployed on a limited-scale
I Incentive for deploymentI No change to ISP’s routing setup
I Does not affect convergence timesI Does not affect routes advertised to
neighborsI Does not restrict routing policiesI
. . .
Can it be deployed?
Configuration overhead of a configuration-onlysolution
I Configuring FIB suppression on routersI Configuring LSP advertisements on edge routers
Planning Overhead
I Choosing virtual prefixes
I Assigning aggregation points
I Assuring network robustnessI
. . .
ViAggre management overhead
Deployed ViAggre on WAIL
I Cisco 7300 routersI Developed Configuration Tool
I ∼330 line python scriptI Extracts information from existing configuration filesI Generates ViAggre configuration files
I Planning tool in the works
Working with a router vendor (Huawei)
I Implement ViAggre nativelyI IETF Draft
Conclusion
ViAggre shrinks the FIB on routers
I Can extend the lifetime of installed routers
Is this a “complete” solution? No
I A simple and effective first stepI Next Step: Inter-domain ViAggre
Thank You!
IntroductionDesignEvaluationDeployment