© 2008 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialBSCI 1 BGP Overview BGP Overview © 2008 Cisco Systems, Inc. All rights reserved.BSCI 2 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Objectives Upon completion of this lesson, you will be able to perform the following tasks: – Explain the need for BGP and typical BGP usage scenarios – Describe basic BGP technical characteristics – Describe BGP path attributes – Describe BGP session establishment and routing information exchange – Configure basic BGP on Cisco router – Monitor and troubleshoot basic BGP setup © 2008 Cisco Systems, Inc. All rights reserved.BSCI 3 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Introduction to BGP www.bkacad.com © 2008 Cisco Systems, Inc. All rights reserved.BSCI 4 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Objectives Upon completion of this section, you will be able to perform the following tasks: – Explain the need for interdomain routing – Describe the need for external routing protocol – List the basic BGP technical characteristics – Identify typical BGP usage scenarios – Explain BGP limitations © 2008 Cisco Systems, Inc. All rights reserved.BSCI 5 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Interdomain Routing Goals Scalability –Internet has over 300,000 routes and is still growing Secure routing information exchange –Routers from another autonomous system cannot be trusted –Tight filters are required, authentication is desirable Routing policies support –Routing between autonomous systems might not always follow the optimum path © 2008 Cisco Systems, Inc. All rights reserved.BSCI 6 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Interdomain Routing AS65001AS65000 • An autonomous system (AS) is a collection of networks under a single technical administration • Interior routing protocol (IGP) is run inside an autonomous system resulting in optimum intra-AS routing OSPF EIGRP • Exterior routing protocol (EGP) is run between autonomous systems to enable routing policies and improve security BGP © 2008 Cisco Systems, Inc. All rights reserved.BSCI 7 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Routing Policies - Case Study Q: Assuming standard IGP route selection rules, how will the traffic between AS1 and AS20 flow? Q: Will AS 2 allow this traffic? Q: How would you solve this problem with OSPF or EIGRP? Company B (AS 2)Company A (AS 1) Service Provider (AS 10) Company X (AS 20) 2 Mbps © 2008 Cisco Systems, Inc. All rights reserved.BSCI 8 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com BGP Characteristics Distance-vector protocol with enhancements: –Reliable updates –Triggered updates only –Rich metrics (called path attributes) Designed to scale to huge internetworks © 2008 Cisco Systems, Inc. All rights reserved.BSCI 9 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Reliable Updates Uses TCP as transport protocol No periodic updates Periodic keepalives to verify TCP connectivity Triggered updates are batched and rate-limited (every 5 seconds for internal peer, every 30 seconds for external peer) © 2008 Cisco Systems, Inc. All rights reserved.BSCI 10 CCNP – BSCI Bachkhoa Networking Academy Học viện mạng Bách Khoa - www.bkacad.com Common BGP Usages Customer connected to one Internet Service Provider (ISP) Customer connected to several Service Providers Service Provider networks (transit autonomous systems) Service providers exchanging traffic at an exchange point (CIX, GIX, NAP …) Network cores of large enterprise customers [...]... Bachkhoa Networking Academy RFCs Covering Additions to BGP4 1965 Autonomous System Confederations for BGP 1997 BGP Communities Attribute 1998 An Application of the BGP Community Attribute in Multi-home Routing 2385 Protection of BGP sessions via the TCP MD5 Signature Option 2439 BGP Route Flap Damping 2796 BGP Route Reflection An alternative to full mesh IBGP BSCI © 2008 Cisco Systems, Inc All rights reserved... BSCI Bachkhoa Networking Academy RFCs Covering Baseline BGP4 1930 1774 BGP- 4 Protocol Analysis 1773 Experience with the BGP- 4 protocol 1772 Application of the BGP in the Internet 1771 A Border Gateway Protocol 4 (BGP- 4) 1745 BGP4 /IDRP for IP -OSPF interaction 1675 BSCI Guidelines for creation, selection, and registration of an Autonomous System BGP MIB © 2008 Cisco Systems, Inc All rights reserved Học... the concept of BGP path attribute – Explain the difference between well-known and optional BGP attributes – List common mandatory and optional BGP attributes – Describe the functionality of AS-Path, Origin and Next-Hop attributes BSCI © 2008 Cisco Systems, Inc All rights reserved Học viện mạng Bách Khoa - www.bkacad.com 19 CCNP – BSCI Bachkhoa Networking Academy BGP Path Attributes BGP metrics are... protocol – List the basic BGP technical characteristics – Identify typical BGP usage scenarios – Explain BGP limitations BSCI © 2008 Cisco Systems, Inc All rights reserved Học viện mạng Bách Khoa - www.bkacad.com 16 CCNP – BSCI Bachkhoa Networking Academy Review Questions –What is an autonomous system? –What are the design goals of an interdomain routing protocol? –When should you use BGP between a customer... Cisco Systems, Inc All rights reserved Học viện mạng Bách Khoa - www.bkacad.com 14 CCNP – BSCI Bachkhoa Networking Academy RFCs Covering BGP Extensions 2842 Capabilities Advertisement with BGP- 4 2858 Multiprotocol extensions for BGP- 4 2918 Route Refresh Capability for BGP- 4 BSCI © 2008 Cisco Systems, Inc All rights reserved Học viện mạng Bách Khoa - www.bkacad.com 15 CCNP – BSCI Bachkhoa Networking Academy... difference between well-known and optional BGP attributes – List common mandatory and optional BGP attributes – Describe the functionality of AS-Path, Origin and Next-Hop attributes BSCI © 2008 Cisco Systems, Inc All rights reserved Học viện mạng Bách Khoa - www.bkacad.com 33 CCNP – BSCI Bachkhoa Networking Academy Review Questions –What is a BGP Path Attribute? –Which BGP Path Attributes must be carried... Systems, Inc All rights reserved Học viện mạng Bách Khoa - www.bkacad.com 11 CCNP – BSCI Bachkhoa Networking Academy BGP Limitations BGP and associated tools cannot express all routing policies – You cannot influence the routing policies of downstream autonomous systems RFC 1771: BGP enabled routers make forwarding decisions based on the destination IP address only; the source IP address does not... –How are the optional transitive attributes propagated between BGP neighbors? –How do the BGP routers detect routing loops? –When is the next-hop attribute different from the IP address of the sending router? BSCI © 2008 Cisco Systems, Inc All rights reserved Học viện mạng Bách Khoa - www.bkacad.com 34 CCNP – BSCI Bachkhoa Networking Academy BGP Neighbor Configuration and Session Establishment BSCI ©... attributes are propagated to other neighbors BSCI © 2008 Cisco Systems, Inc All rights reserved Học viện mạng Bách Khoa - www.bkacad.com 21 CCNP – BSCI Bachkhoa Networking Academy Optional BGP Attributes Optional BGP attributes are transitive or nontransitive Optional transitive attributes –Propagated to other neighbors if not recognized, Partial bit set to indicate that the attribute was not recognized... viện mạng Bách Khoa - www.bkacad.com 22 CCNP – BSCI Bachkhoa Networking Academy Well-known Mandatory Attributes Origin – Specifies the origin of a BGP route IGP Route originated in an IGP EGP Route originated in EGP Unknown Route was redistributed into BGP AS_Path – Sequence of AS numbers through which the network is accessible Next_Hop – IP address of the next-hop router BSCI © 2008 Cisco Systems, . following tasks: – Explain the need for BGP and typical BGP usage scenarios – Describe basic BGP technical characteristics – Describe BGP path attributes – Describe BGP session establishment and routing. Additions to BGP4 1965 Autonomous System Confederations for BGP 1997 BGP Communities Attribute 1998 An Application of the BGP Community Attribute in Multi-home Routing 2385 Protection of BGP sessions. Baseline BGP4 1930 Guidelines for creation, selection, and registration of an Autonomous System 1774 BGP- 4 Protocol Analysis 1773 Experience with the BGP- 4 protocol 1772 Application of the BGP in