1 copyright 1999, cisco systems, inc. module10.ppt10/7/1999 8:27 am bgp — border gateway protocol...
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![Page 1: 1 Copyright 1999, Cisco Systems, Inc. Module10.ppt10/7/1999 8:27 AM BGP — Border Gateway Protocol Routing Protocol used between AS’s Currently Version](https://reader036.vdocuments.net/reader036/viewer/2022062712/56649cae5503460f94971028/html5/thumbnails/1.jpg)
1Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP — Border Gateway Protocol
• Routing Protocol used between AS’s
• Currently Version 4
• Runs over TCP
• Path Vector Protocol
• Incremental Updates
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2Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
AS 100 AS 101
AS 102
AA CC
BGP speakers are called peers
BGP Peers
eBGP TCP/IP
Peer Connection
Peers in different AS’sare called External Peers
Note: eBGP Peers normally should be directly connected.
EE
BB DD220.220.8.0/24 220.220.16.0/24
220.220.32.0/24
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3Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
AS 100 AS 101
AA CC
BGP speakers are called peers
BGP Peers
iBGP TCP/IP
Peer Connection
Peers in the same ASare called Internal Peers
AS 102
EE
BB DD
Note: iBGP Peers don’t have to be directly connected.
220.220.8.0/24 220.220.16.0/24
220.220.32.0/24
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4Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
AS 100 AS 101
AA CC
BGP Peers
AS 102
DD220.220.8.0/24 220.220.16.0/24
220.220.32.0/24
EE
BB
BGP Peers exchange Update messages containing Network Layer Reachability Information (NLRI)
BGP Update
Messages
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5Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
Configuring BGP Peers
interface Serial 0ip address 222.222.10.2 255.255.255.252
router bgp 100 network 220.220.8.0 mask 255.255.255.0 neighbor 222.222.10.1 remote-as 101neighbor 222.222.10.1 remote-as 101
interface Serial 0ip address 222.222.10.1 255.255.255.252
router bgp 101 network 220.220.16.0 mask 255.255.255.0 neighbor 222.222.10.2 remote-as 100neighbor 222.222.10.2 remote-as 100
eBGP TCP Connection
• BGP Peering sessions are established using the BGP “neighbor” configuration command
222.222.10.0/30
BB CC DDAA
AS 100 AS 101
.2220.220.8.0/24 220.220.16.0/24.2 .1 .2 .1.1
– External (eBGP) is configured when AS numbers are different
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6Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
– Internal (iBGP) is configured when AS numbers are same
AS 100 AS 101
Configuring BGP Peers
222.222.10.0/30
.2
interface Serial 1ip address 220.220.16.2 255.255.255.252
router bgp 101 network 220.220.16.0 mask 255.255.255.0 neighbor 220.220.16.1 remote-as 101neighbor 220.220.16.1 remote-as 101
BB
interface Serial 1ip address 222.220.16.1 255.255.255.252
router bgp 101 network 220.220.16.0 mask 255.255.255.0 neighbor 220.220.16.2 remote-as 101neighbor 220.220.16.2 remote-as 101
CC
iBGP TCP Connection
• BGP Peering sessions are established using the BGP “neighbor” configuration command
DD220.220.8.0/24 220.220.16.0/24AA .2 .1 .2 .1.1
– External (eBGP) is configured when AS numbers are different
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7Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
Configuring BGP Peers
• Each iBGP speaker must peer with every other iBGP speaker in the AS
iBGP TCP/IP
Peer Connection
AS 100
AABB
CC
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8Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
Configuring BGP Peers
• Loopback interface are normally used aspeer connection end-points
AS 100215.10.7.1
215.10.7.2
215.10.7.3
AABB
CC
iBGP TCP/IP
Peer Connection
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9Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
iBGP TCP/IP
Peer Connection
Configuring BGP Peers
AS 100
AA
215.10.7.1215.10.7.2
215.10.7.3
CC
BB
interface loopback 0 ip address 215.10.7.1 255.255.255.255
router bgp 100 network 220.220.1.0 neighbor 215.10.7.2 remote-as 100 neighbor 215.10.7.2 update-source loopback0neighbor 215.10.7.2 update-source loopback0 neighbor 215.10.7.3 remote-as 100 neighbor 215.10.7.3 update-source loopback0neighbor 215.10.7.3 update-source loopback0
AA
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10Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
Configuring BGP Peers
AS 100
AA
215.10.7.1215.10.7.2
215.10.7.3
CC
AA
interface loopback 0 ip address 215.10.7.2 255.255.255.255
router bgp 100 network 220.220.5.0 neighbor 215.10.7.1 remote-as 100 neighbor 215.10.7.1 update-source loopback0neighbor 215.10.7.1 update-source loopback0 neighbor 215.10.7.3 remote-as 100 neighbor 215.10.7.3 update-source loopback0neighbor 215.10.7.3 update-source loopback0
BB
iBGP TCP/IP
Peer Connection
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11Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
Configuring BGP Peers
AS 100
AA
215.10.7.1215.10.7.2
215.10.7.3
AABB
interface loopback 0 ip address 215.10.7.3 255.255.255.255
router bgp 100 network 220.220.1.0 neighbor 215.10.7.1 remote-as 100 neighbor 215.10.7.1 update-source loopback0neighbor 215.10.7.1 update-source loopback0 neighbor 215.10.7.2 remote-as 100 neighbor 215.10.7.2 update-source loopback0neighbor 215.10.7.2 update-source loopback0
CC
iBGP TCP/IP
Peer Connection
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12Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
Unfeasible Routes Length (2 Octets)
Withdrawn Routes (Variable)
Total path Attribute Length (2 Octets)
Network Layer Reachability Information (Variable)
Path Attributes (Variable)
The BGP UPDATE Message Length (I Octet)
Prefix (Variable)
Attribute Type
Length (I Octet)
Prefix (Variable)
Attribute Length
Attribute Value
• A BGP update is used to advertise a single feasible route to a peer, or to withdraw multiple unfeasible routes
• Each update message contains attributes, like origin, AS-Path, Next-Hop, …….
BGP Update Messages
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13Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP Updates — NLRI
• Network Layer Reachability Information
• Used to advertise feasible routes
• Composed of:– Network Prefix
– Mask Length
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14Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP Updates — Attributes
• Used to convey information associated with NLRI– AS path
– Next hop
– Local preference
– Multi-Exit Discriminator (MED)
– Community
– Origin
– Aggregator
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15Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
• Sequence of ASes a route has traversed
• Loop detection
• Apply policy
AS 100
AS 300
AS 200
AS 500
AS 400
170.10.0.0/16 180.10.0.0/16
150.10.0.0/16
Network Path
180.10.0.0/16 300 200 100
170.10.0.0/16 300 200
150.10.0.0/16 300 400
Network Path180.10.0.0/16 300 200 100170.10.0.0/16 300 200
AS-Path Attribute
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16Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
160.10.0.0/16
150.10.0.0/16
192.10.1.0/30
.2
AS 100
AS 200
Network Next-Hop Path160.10.0.0/16 192.20.2.1 100
CC
Next Hop Attribute
.1
BGP Update
Messages
BB
AA
.1
.2
192.
20.2
.0/3
0
AS 300
EE
DD
• Next hop to reach a network
• Usually a local network is the next hop in eBGP session
140.10.0.0/16
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17Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
• Next hop to reach a network
• Usually a local network is the next hop in eBGP session
160.10.0.0/16
150.10.0.0/16
192.10.1.0/30
.2
AS 100
AS 200CC
Next Hop Attribute
.1
BB
AA
.1
.2
192.
20.2
.0/3
0
BGP Update
Messages
EE
DD
• Next Hop updated betweeneBGP Peers
AS 300140.10.0.0/16
Network Next-Hop Path150.10.0.0/16 192.10.1.1 200160.10.0.0/16 192.10.1.1192.10.1.1 200 100
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18Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
• Next hop not changedbetween iBGP peers
160.10.0.0/16
150.10.0.0/16
192.10.1.0/30
.2
AS 100
AS 200
Network Next-Hop Path150.10.0.0/16 192.10.1.1 200160.10.0.0/16 192.10.1.1192.10.1.1 200 100
CC
Next Hop Attribute
.1
BB
AA
.1
.2
192.
20.2
.0/3
0
BGP Update
Messages
DD
EE
AS 300140.10.0.0/16
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19Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
Next Hop Attribute (more)
• IGP should carry route to next hops
• Recursive route look-up
• Unlinks BGP from actual physical topology
• Allows IGP to make intelligent forwarding decision
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20Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP Updates — Withdrawn Routes
• Used to “withdraw” network reachability
• Each Withdrawn Route is composed of:– Network Prefix
– Mask Length
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21Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP Updates — Withdrawn Routes
AS 321AS 123
192.168.10.0/24
192.192.25.0/24
.1 .2
x
Connectivity lost
BGP Update
Message
Withdraw Routes192.192.25.0/24Withdraw Routes192.192.25.0/24
Network Next-Hop Path150.10.0.0/16 192.168.10.2 321 200192.192.25.0/24 192.168.10.2 321
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22Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP Routing Information Base
BGP RIB
D 10.1.2.0/24D 160.10.1.0/24D 160.10.3.0/24R 153.22.0.0/16S 192.1.1.0/24
Network Next-Hop Path
router bgp 100 network 160.10.0.0 255.255.0.0 no auto-summary
Route Table
*>i160.10.1.0/24 192.20.2.2 i*>i160.10.3.0/24 192.20.2.2 i
BGP ‘network’ commands are normally used to populate the BGP RIB with routes from the Route Table
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23Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP Routing Information Base
BGP RIB
router bgp 100 network 160.10.0.0 255.255.0.0 aggregate-address 160.10.0.0 255.255.0.0 summary-only no auto-summary
Route Table
Network Next-Hop Path
D 10.1.2.0/24D 160.10.1.0/24D 160.10.3.0/24R 153.22.0.0/16S 192.1.1.0/24
*> 160.10.0.0/16 0.0.0.0 i*> 160.10.0.0/16 0.0.0.0 i* i 192.20.2.2 i* i 192.20.2.2 is> 160.10.1.0/24 192.20.2.2 is> 160.10.3.0/24 192.20.2.2 i
BGP ‘aggregate-address’ commands may be used to install summary routes in the BGP RIB
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24Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP ‘redistribute’ commands can also be used to populate the BGP RIB with routes from the Route Table
BGP Routing Information Base
BGP RIBNetwork Next-Hop Path
router bgp 100 network 160.10.0.0 255.255.0.0 redistribute static route-map foo no auto-summary
access-list 1 permit 192.1.0.0 0.0.255.255
route-map foo permit 10 match ip address 1
Route Table
D 10.1.2.0/24D 160.10.1.0/24D 160.10.3.0/24R 153.22.0.0/16S 192.1.1.0/24
*> 160.10.0.0/16 0.0.0.0 i* i 192.20.2.2 is> 160.10.1.0/24 192.20.2.2 is> 160.10.3.0/24 192.20.2.2 i*> 192.1.1.0/24 192.20.2.2 ?*> 192.1.1.0/24 192.20.2.2 ?
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25Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP Routing Information Base
BGP RIBIN Process
Update
Network Next-Hop Path173.21.0.0/16 192.20.2.1 100
* 173.21.0.0/16 192.20.2.1 100
• BGP “in” process• receives path information from peers
• results of BGP path selection placed in the BGP table
• “best path” flagged (denoted by “>”)
Update
Network Next-Hop Path*>i160.10.1.0/24 192.20.2.2 i*>i160.10.3.0/24 192.20.2.2 i
OUT Process
>
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26Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP Routing Information Base
OUT Process
Network Next-Hop Path160.10.1.0/24 192.20.2.2 200160.10.3.0/24 192.20.2.2 200173.21.0.0/16 192.20.2.2 200 100192.20.2.1 192.20.2.1
BGP RIB
> 173.21.0.0/16 192.20.2.1 100
Network Next-Hop Path*>i160.10.1.0/24 192.20.2.2 i*>i160.10.3.0/24 192.20.2.2 i*
IN Process
Update Update
• BGP “out” process• builds update using info from RIB
• may modify update based on config
• Sends update to peers
Next-Hop changed
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27Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
BGP Routing Information Base
BGP RIB
D 10.1.2.0/24D 160.10.1.0/24D 160.10.3.0/24R 153.22.0.0/16S 192.1.1.0/24
Network Next-Hop Path*>i160.10.1.0/24 192.20.2.2 i*>i160.10.3.0/24 192.20.2.2 i*> 173.21.0.0/16 192.20.2.1 100
• Best paths installed in routing table if:
B 173.21.0.0/16
Route Table
• prefix and prefix length are unique• lowest “protocol distance”
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28Copyright1999, Cisco Systems, Inc.Module10.ppt 10/7/1999 8:27 AM
The ‘Bible’ & other resources
• Route-views.oregon-ix.net
• Internet Routing Architectures– Bassam Halabi
– pg. 168 BGP Decision Process Summary