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Inter-domain Routing: Today and Tomorrow
Dr. Jia [email protected]
AT&T Labs ResearchFlorham Park, NJ 07932, USA
http://www.research.att.com/~jiawang/
Prof. Zhuoqing Morley [email protected]
Department of EECSUniversity of Michigan
Ann Arbor, MI 48109, USAhttp://www.eecs.umich.edu/~zmao/
IEEE INFOCOM 2004 TutorialMarch 8, 2004
March 8, 2004 2
Outline
1. Overview of Inter-domain routing2. Routing policies3. Measuring inter-domain paths4. Routing instability5. BGP Beacon - measurement
infrastructure6. Implication on network engineering7. Security issuesOur opinions should not be taken to represent AT&T policies
Part I: Overview of Inter-domain Routing
March 8, 2004 4
Internet
Loose cooperative effort of Internet Service Providers (ISPs) E.g., AT&T, Sprint, UUNet, AOL
Best effort service Connectedness
Anyone connected to the Internet can exchange traffic with anyone else connected to the Internet
March 8, 2004 5
Internet routing
: Routing session
routes
Internet
IP traffic
Data plane:forward traffic
Control plane:exchange routes
rusty.cs.berkeley.eduIP=169.229.62.116
Prefix=169.229.0.0/16
www.cnn.comIP=64.236.16.52
Prefix=64.236.16.0/20
March 8, 2004 6
Internet routing dictates application performance
www.cnn.comIP=64.236.16.52
Prefix=64.236.16.0/20
: Routing session
routes
Internet
IP traffic
Data plane:forward traffic
Control plane:exchange routes
Fail over to alternate routerusty.cs.berkeley.edu
IP=169.229.62.116Prefix=169.229.0.0/16
March 8, 2004 7
Internet routing domain
Network devices under same technical and administrative control
Common routing policy E.g., ISPs, enterprise networks
March 8, 2004 8
Autonomous System (AS)
Autonomous routing domain with an AS number (ASN)
AS numbers 16 bits integer Public AS number: 1 – 64511 Private AS number: 64512 – 65535 Examples
AT&T: 7018, 6431, … Sprint: 1239, 1240, … MIT: 3
March 8, 2004 9
More than 14,000 ASes today
Qwest Sprint UUnet
University company
AT&T
business
ISP ISP ISP
ISP ISP ISP ISP
ISP
Qwest Sprint UUnet
University company
AT&T
business
ISP ISP ISP
ISP ISP ISP ISP
ISP
Berkeley
Internet
CNN
Calren
Level3
GNN
IP traffic
AutonomousSystem
Berkeley
Calren
Level3
Berkeley
Calren
Level3 Qwest Sprint UUnet
University Company
AT&T
Business
ISP ISP ISP
ISP ISP ISP ISP
ISP
March 8, 2004 10
Internet Initiative Japan (IIJ)
March 8, 2004 11
IIJ, Tokyo
March 8, 2004 12
Telstra international
March 8, 2004 13
WorldCom (UUNet)
March 8, 2004 14
UUNet, Europe
March 8, 2004 15
Sprint, USA
March 8, 2004 16
Charlotte
Portland
Providence
Newark
Cedar Knolls
Syracuse
Buffalo
White Plains
Rochester
Columbia
New Orleans
Nashville
AustinHouston
TulsaOklaho
maCity
Albuquerque
Phoenix
AnaheimAnaheim
Las Vegas
Salt LakeCity
ColoradoSprings
Milwaukee
Detroit
Columbus
Cincinnati
SeattleSpokane
Portland
Louisville
Little Rock
Jacksonville
Ft. Lauderdale
Miami
RaleighRichmond
DenverIndianapolis
Pittsburgh
Baltimore
Plymouth
Atlanta
Minneapolis
Gardena
Tampa
SanBernardino
Arlington
Ft. Worth
Rochelle Pk
Honolulu
Orlando
Sherman Oaks
Ojus
Hamilton SquareSilver
Springs
Wayne
Chicago
RollingMeadows
Omaha
St Louis
San Diego
Anchorage, AK
N X OC48
Backbone Node
Gateway Node
N X DS3N X OC3
Remote Access Router
R Remote GSR Access Router
N X OC12
NX OC192
CambridgeFramingham
Stamford Bridgeport
Grand Rapids Providence
Glenview
Albany
Sacramento
Oakland
Redwood City
San Jose
San Francisco
ChicagoSan
Francisco
Florissant
Davenport
Worcester
Madison
Camden, NJ
Norcross
New Brunswick
Birmingham
San Antonio
Oak Brook
South Bend
Dayton Bohemia
Hartford
San Juan PR
W. Palm Beach
Harrisburg
Des Moines
Memphis
Greensboro
Norfolk
R
KansasCity
AkronRR
RLos Angeles
Dallas
Wash.DC
St. Paul
Freehold
R
Manchester
R
RR
Ft. Lauderdale
Dunwoody
Note: Connectivity and nodes shown are targeted for deployment; actual deployment
may vary. Maps should not be used to predict service availability.
R
R
R
Phil
NYC
Cleveland
R
RNYC-Bdwy
Birmingham
LA-Airport
Blvd
Year end 2001
Rev. 6-4-01
AT&T IP Backbone, USA
March 8, 2004 17
GARR-B
March 8, 2004 18
Gigabit research network
March 8, 2004 19
(Summer '03)
UW-Superior
UW-StoutUW-River Falls
Fox Valley TC
UW-Oshkosh
UW-Milwaukee
UW-ParksideUW-Whitewater
UW-Madison
UW-Platteville
UW-La Crosse
UW-Eau Claire
UW-Stevens Point
UW-Green Bay
Marshfield
Rhinelander
Rice Lake
Clintonville
StilesJct.
Portage
Dodgeville
La Crosse
Genuity
OC-3 (155Mbps)
DS-3 (45Mbps)
T1 (1.5Mbps)
OC-12 (622Mbps)
Qwestand OtherProvider(s)
Internet 2& Qwest
Peering - Public and Private Commodity Internet Transit Internet2 Merit and Other State Networks National Education Network Regional Research Peers
Wausau
Gigabit Ethernet
Chicago - 1
Chicago - 2(Winter '02)
Chicago
wiscnet.net
GO BUCKY!
March 8, 2004 20
MIT.edu
http://bgp.lcs.mit.edu/
March 8, 2004 21
Internet routing architecture
IP traffic
Berkeley CNN
Level3
Internet
Calren GNN
Inter-domain routing
Intra-domain routing
March 8, 2004 22
Intra-domain routing
Run within a certain network infrastructure Optimize routes taken between points
within a network Internal Gateway Protocols (IGPs)
Metrics based OSPF (Open Shortest Path First) RIP (Routing Information Protocol) IS-IS (Intermediate System to Intermediate
System)
March 8, 2004 23
Inter-domain routing
Run between networks Provide full connectivity of entire
Internet External Gateway Protocol (EBGP)
Policy based BGP (Border Gateway Protocol)
March 8, 2004 24
Inter-domain routing and BGP
Static routing Mainly for stub networks
Default routing Small stub networks
Dynamic routing Via BGP
No need to run BGP in static routing and default routing.
March 8, 2004 25
Link state
Examples: OSPF, IS-IS Based on Dijkstra’s shortest path
computation Each router periodically floods immediate
reachability information to other routers Fast convergence High communication and computation
overhead Not scalable for large networks
Requires periodic refreshes
March 8, 2004 26
Vectoring
Distance vs. Path Vector Distance: hop count (RIP) Path: entire path (BGP)
Helps identify loops Supports policy-based routing based on path
Minimal communication overhead Takes longer to converge, i.e., in
proportion to the maximum path length
March 8, 2004 27
Link state vs. vectoring
OSPFIS-IS
RIP
BGP
IGP
EGP
Link state Vectoring
BGP is a path vector protocol
March 8, 2004 28
Classful addressing
IPv4: 32 bits Five classes of networks
Class
Address
Mask # of networks
# of hosts
A 0* 255.0.0.0 128 ~1.6M
B 10* 255.255.0.0 16384 65535
C 110* 255.255.255.0
~2.1M 255
D Used for multicast
E Reserved and currently unusedImprove scaling factor of routing in the Internet => classless
March 8, 2004 29
RFC1519: Classless Inter-domain Routing (CIDR)
No implicit mask based on the class of the network
Explicit masks passed in the routing protocol
Allow aggregation and hierarchical routing
March 8, 2004 30
CIDR addressing
00001100 00100110 00000000 00000000
11111111 11111111 11000000 00000000
IP address: 12.70.0.0 Mask: 255.255.252.0
CIDR representation: 12.70.0.0/22
Address
Mask
Network prefix Host identifier
00001100 00100110 00000000 00000000
11111111 11111111 11000000 00000000
March 8, 2004 31
Address aggregation
Internet
12.70.1.0/24
12.70.2.0/24
12.70.3.0/2412.70.0.0/24
ISP AISP B
12.70.0.0/2212.71.0.0/16
12.71.0.0/16
March 8, 2004 32
Routing and forwarding
Routing The decision process of choosing
optimal path that is consistent with the administrative or technical policy
Forwarding The act of receiving a packet, doing a
lookup, and copying a packet to the next hop
March 8, 2004 33
Classless forwarding
Internet
135.120.0.1
12.70.0.20
IP traffic
Prefix Next hop12.70.0.0/24 10.20.0.112.70.0.0/16 10.20.1.112.0.0.0/8 10.20.128.10.0.0.0 10.20.128.10
10.20.0.1
10.20.1.1
10.20.128.1
10.20.128.10
March 8, 2004 34
Inter-domain routing with CIDR support
BGP-4 [RFC1771] De facto EGP Path vector protocol Run on top of TCP for reliability Carry routing information between
ASes Policy based routing
March 8, 2004 35
BGP basic operations
Set up BGP session Exchange all candidate routes Send incremental updates
March 8, 2004 36
Establish BGP session
12.10.0.1 12.10.0.2
Establish neighboring session between 12.10.0.1 and 12.10.0.2
Prefix Next hop12.70.0.0/24 10.20.0.112.9.0.0/16 10.20.1.1
Prefix Next hop135.120.0.0/24 10.128.0.168.35.0.0/16 10.192.1.1
TCP 179
March 8, 2004 37
Exchange all candidate routes
12.10.0.1 12.10.0.2
Prefix Next hop12.70.0.0/24 10.20.0.112.9.0.0/16 10.20.1.1135.120.0.0/24 10.128.0.168.35.0.0/16 10.192.1.1
Prefix Next hop135.120.0.0/24 10.128.0.168.35.0.0/16 10.192.1.112.70.0.0/24 10.20.0.112.9.0.0/16 10.20.1.1
12.70.0.0/24 10.20.0.112.9.0.0/16 10.20.1.1
135.120.0.0/24 10.128.0.168.35.0.0/16 10.192.1.1
March 8, 2004 38
Send incremental updates
12.10.0.1 12.10.0.2
Prefix Next hop12.70.0.0/24 10.20.0.112.9.0.0/16 10.20.1.1135.120.0.0/24 10.128.0.168.35.0.0/16 10.192.1.1
Prefix Next hop135.120.0.0/24 10.128.0.168.35.0.0/16 10.192.1.112.70.0.0/24 10.20.0.112.9.0.0/16 10.20.1.1
Withdraw 12.9.0.0/16
March 8, 2004 39
BGP messages
OPEN: set up a peering session UPDATE: announce new routes or
withdraw previously announced routes
NOTIFICATION: shut down a peering session
KEEPALIVE: confirm active connection at regular interval
March 8, 2004 40
Internal vs. external BGP
Internet I-BGP
E-BGP
AS A
AS B
AS C
March 8, 2004 41
I-BGP mesh
I-BGP update
E-BGP update I-B
GP update
I-BGP update
March 8, 2004 42
Make I-BGP scale for large AS
Route reflectors Confederations
March 8, 2004 43
Route reflector
E-BGP update
RR RR
Only best paths being sent by RR
March 8, 2004 44
Confederation
AS 1000
EBGP
EBGP
EBGPIBGP IBGP
AS 65010 AS 65020
March 8, 2004 45
BGP updates
Three blocks Prefix Path attributes Unreachable routes
March 8, 2004 46
BGP attributes
Value Code Reference1 ORIGIN [RFC1771] 2 AS_PATH [RFC1771] 3 NEXT_HOP [RFC1771] 4 MULTI_EXIT_DISC [RFC1771] 5 LOCAL_PREF [RFC1771] 6 ATOMIC_AGGREGATE
[RFC1771] 7 AGGREGATOR [RFC1771] 8 COMMUNITY [RFC1997] 9 ORIGINATOR_ID [RFC1998] 10 CLUSTER_LIST [RFC1998]
11 DPA [Chen] 12 ADVERTISER [RFC1863] 13 RCID_PATH / CLUSTER_ID
[RFC1863] 14 MP_REACH_NLRI [RFC2283] 15 MP_UNREACH_NLRI
[RFC2283] 16 EXTENDED COMMUNITIES
[Rosen] 17 NEW_AS_PATH [E.Chen] 18 NEW_AGGREGATOR [E.Chen] 19 SAFI Specific Attribute
(SSA) [Nalawade] 20-254 Unassigned 255 reserved for development
http://www.iana.org/assignments/bgp-parameters
March 8, 2004 47
Establish connectivity
135.120.0.0/16
12.10.0.1
12.10.0.2
Prefix Next hop AS path135.120.0.0/16 12.10.0.1 1
EBGP
IBGPIBGP
IBGPEBGP
12.10.0.5
12.10.0.6
AS 1 AS 2
AS 3Prefix Next hop AS path135.120.0.0/16 12.10.0.5 2 1
Prefix Next hop AS path135.120.0.0/16 12.10.0.1 1
March 8, 2004 48
IGP and BGP working together
135.120.0.0/1612.10.0.1
12.10.0.2
Prefix Next hop AS path135.120.0.0/16 12.10.0.1 1
EBGP
IBGPIBGP
IBGPEBGP
12.10.0.5
12.10.0.6
AS 1 AS 2
AS 3Prefix Next hop AS path135.120.0.0/16 12.10.0.1 1
10.10.0.1
Prefix Next hop12.10.0.0/30 10.10.0.1135.120.0.0/16 10.10.0.1
12.10.0.0/30