address-based route reflection ruichuan chen (mpi-sws) aman shaikh (at&t labs - research) jia...
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Address-based Route Reflection
Ruichuan Chen (MPI-SWS)Aman Shaikh (AT&T Labs - Research)Jia Wang (AT&T Labs - Research)Paul Francis (MPI-SWS)
CoNEXT 2011
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iBGP reality Original full-mesh iBGP
All routers in an AS peer with all others Scales poorly
Route reflection Introduces routing anomalies
AS confederations
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MED-based oscillation (MED: Multi-Exit Discriminator)
Routing anomalies in RR
C1
RR1
C3
RR2
C2
20
AS2AS1
2 1 3
1
10 30
y
IGP metric = x
MED = y
x
MEDs aren’t comparable between routes learned from different ASes!
RR1 prefers C2 > C1 > C3 > C2 > …
BGP best path decision:……Step 4: Lowest MED……Step 6: Lowest IGP metric……
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Routing anomalies in RR Topology-based oscillation
C1
RR1
5
RR2
RR3
C2 C3
55
2
22
x IGP metric = x
Each RR is closer to another RR’s client.
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Routing anomalies in RR
Forwarding loop
Path inefficiency
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Routing anomalies in RR Why?
Different routers learn different routes!
Common solution RRs always prefer the routes learned from
clients over those from non-clients. Restricts RR placement. Not sufficient!
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Design
Full-mesh’s semantics&
RR’s scalability
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Our contribution Address-Based Route Reflection (ABRR)
Is decentralized Solves all oscillations and forwarding loops Has no path inefficiency Puts no restriction on RR placement Operates with no new BGP message
formats
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Key insight BGP best-path decision for any given
prefix at a given router is highly dependent on information provided by other routers.
BGP best-path decision for any given prefix is independent of that of any other prefix.
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Comparison Topology-Based Route Reflection (TBRR) Address-Based Route Reflection (ABRR)
Topology-Based Route Reflection Address-Based Route Reflection
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ABRR - Client behaviors Each client peers with all ARRs
Advertise best route (if not iBGP-learned) to associated ARR
Advertise best route to eBGP neighbors
C1
ARR1
C3
ARR2
C2
AP: 0.0.0.0/1 AP: 128.0.0.0/1
Prefix: 1.2.0.0/16
AP: short for Address Partition
Prefix: 200.0.0.0/8
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ABRR - RR behaviors
R2
TRR1 R1
R4
R3TRR2
Full-mesh: router learns multiple routes per prefixTBRR: router learns one single route per prefix
Full-mesh vs. TBRR Full-mesh TBRR
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ABRR - RR behaviors (cont.)
Semantics equal to Full-mesh? ARR advertises multiple routes Routes flow through only one ARR
Scalability comparable to TBRR? Address partition
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ABRR - RR behaviors (cont.) Each ARR peers with all clients
Advertise all best AS-level routes to clients ARR redundancy
Multiple ARRs for each AP
C1
ARR1
C3
ARR2
C2
AP: 0.0.0.0/1 AP: 128.0.0.0/1
1. Highest Local Preference2. Shortest AS Path3. Lowest Origin Type4. Lowest MED5. eBGP-learned over iBGP-learned6. Lowest IGP Metric7. Lowest Router ID8. Lowest Peer Address
AS-level criteria
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No routing anomalies
ABRR emulates full-mesh semantics
No path inefficiency Full-mesh emulation Placement of ARRs within ISP network is
irrelevant
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No routing anomalies (cont.)
No MED-based oscillation
No topology-based oscillation
No forwarding loop
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Performance analysis
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RIB-In and RIB-Out sizes of RRs
Parameters # routers: 2000 # APs / clusters: 50 # ARRs / TRRs per AP / cluster: 2 # peer ASes: 30
# best AS-level routes per prefix
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RIB-In and RIB-Out sizes of RRs
For all parameter settings, ABRR has substantially smaller RIB size!
#APs or #Clusters #APs or #Clusters
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iBGP sessions of RRs Modern routers or general-purpose
computers can handle thousands of sessions each with the full routing table.
iBGP convergence time
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Implementation results
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Fully functional implementation based on Quagga Less than 2K lines of code
Tier-1 ISP trace over 2 weeks
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RIB-In and RIB-Out sizes
TBRR
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# updates during two weeks
TBRR
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Conclusion Address-Based Route Reflection
Solves all oscillations Finds efficient paths Places no constraints on RR placement Operates with no new BGP message
formats
Semantics equal to full-mesh Scalability comparable to TBRR