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TCP—Source/Destination Addresses
1.1.1.1
R1
2.2.2.2 10.1.1.1 10.1.1.2
Fra Baidu bibliotek
• R2 to R1 connection
neighbor 1.1.1.1 remote-as 100 neighbor 1.1.1.1 update-source loopback 0
• Routers agree on source/destination address
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互联神州思科专业技术培训
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What Can You Expect?
• BGP peering in excruciating detail ☺
TCP details BGP TCP interaction
一品阳光
TCP—Source/Destination Addresses
1.1.1.1
R1
2.2.2.2 10.1.1.1 10.1.1.2
R2
• R1 to R2 connection
neighbor 2.2.2.2 remote-as 100 neighbor 2.2.2.2 update-source loopback 0
BGP: 2.2.2.2 passive open to 10.1.1.1 BGP: 2.2.2.2 passive open failed - 10.1.1.1 is not update-source Loopback0's address (1.1.1.1)
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技术论坛：www.ciscohuawei.com
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The Basics
• BGP uses TCP port 179 • Relies on TCP to successfully deliver all BGP messages • Peers exchange OPEN messages which contain basic info such as:
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• TCP port numbers
Destination will be port 179 Source port is random for added security
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Session Number Presentation_ID © 2005 Cisco Systems, Inc. All rights reserved.
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TCP—Source/Destination Addresses
neighbor x.x.x.x transport connection-mode [active|passive] 成都互联神州思科专业技术培训学校培训网站： www.ciscohuawei.net QQ:505836736
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TCP—Source/Destination Parameters
• IP Addresses
Destination IP is specified via “neighbor x.x.x.x” Source IP is outbound interface by default Source IP may be specified via “neighbor x.x.x.x updatesource interface”
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What Do I Expect from You?
• BGP operational experience
Basic configuration Show commands
• Understand the attributes
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• R2 to R1 connection
neighbor 10.1.1.1 remote-as 100 neighbor 10.1.1.1 update-source loopback 0
• R1 and R2 do not agree on what addresses to use
BGP will tear down the TCP session due to the conflict Points out configuration problemswww.ciscohuawei.net security and adds some 成都互联神州思科专业技术培训学校培训网站： QQ:505836736
• R2 attempts to open a session to R1
BGP: 10.1.1.1 open active, local address 2.2.2.2
• R1 denies the session because of the address mismatch • “debug ip bgp” on R1 shows
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TCP—Active vs. Passive Session
R1 Opens TCP Session to R2
R1
R2
• Active Session—If the TCP session initiated by R1 is the one used between R1 and R2 then R1 “actively” established the session • Passive Session—For the same scenario R2 “passively” established the session • R1 Actively opened the session • R2 Passively accepted the session • Can be configured
Session Number Presentation_ID © 2005 Cisco Systems, Inc. All rights reserved.
BGP will accept this TCP session
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互联神州思科专业技术培训
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边界网关协议 (BGP) 的故障分析
SESSION RST-3254
成都互联神州思科专业技术培训学校培训网站：
Session Number Presentation_ID © 2005 Cisco Systems, Inc. All rights reserved.
成都互联神州思科专业技术培训学校培训网站：
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Router ID AS # Capabilities
• FSM (Finite State Machine) is used to negotiate Established state • Keepalive/holdtime mechanism ensures peering validity • BGP attempts to open a TCP session to every peer
成都互联神州思科专业技术培训学校培训网站：
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技术论坛：www.ciscohuawei.com
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BGP/TCP Agenda
• EBGP Multihop Peering • Peering State Machine • Common Mistakes • Troubleshooting commands • Faster Peer Establishment • Flapping Peers • Keepalives and Holdtimers
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Fast Keepalives and Holdtimers
• BGP memory analysis
Why does BGP consume so much memory?
• BGP processes
Explanation of what each process does
• BGP table version
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BGP/TCP Agenda
• The Basics • Source/Destination Addresses and Ports • Active vs. Passive Sessions • TCP Connection Collisions • TTL—Time To Live • MSS—Max Segment Size • Security
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R2
• Both sides must agree on source/destination addresses • R1 to R2 connection
neighbor 2.2.2.2 remote-as 100 neighbor 2.2.2.2 update-source loopback 0