1. Release 5.1, Revision 0 Copyright © 2001, Juniper Networks, Inc. Advanced Juniper Networks Routing Module 8: BGP Confederations

2. Copyright © 2001, Juniper Networks, Inc. Objectives Describe the configuration options for BGP peers Explain the default “movement” of BGP routes through a router Describe the role of BGP attributes in the process of choosing routes to use and advertise Describe how BGP next hop reachability is achieved Explain options for handling IBGP scalability issues

3. Copyright © 2001, Juniper Networks, Inc. Scaling BGP IBGP full-mesh peer requirement has an N-squared problem – Addition of a new router requires new peering with all current IBGP speakers – Current IBGP speakers must update configurations Confederations (RFC 3065) is one method for scaling IBGP connectivity

4. Copyright © 2001, Juniper Networks, Inc. Scaling BGP - Confederations Breaks a global AS into multiple pieces (Sub-AS) Within each sub-AS: – Use private AS numbers – An IBGP full-mesh is still required Between each sub-AS: – EBGP-type configurations (CBGP) are required (multihop, etc.) – Most IBGP attributes are not changed – AS_Path is modified to prevent loops (but sub-AS is NOT a hop) Global AS is still viewed externally as a single AS [edit routing-options] autonomous-system 65000; confederation 2 members [ 65000 65001 65002 ];

5. Copyright © 2001, Juniper Networks, Inc. Confederation Attributes Confederation sequence – Each sub-AS is added to the AS_Path – (65000 65001 65002) 100 200 I shows a sequence – Used for loop prevention only – Sequence values are not counted as AS hops Confederation set is used when an aggregated route might lose the granularity of the sequence  192.168.24/24 (65000 65001) 100 I  192.168.100/24 (65000 65002) 100 I  192.168/16 [65000 65001 65002] 100 I Both are removed at the edge of the global AS – Other AS peers do not see the details of the confederation

6. Copyright © 2001, Juniper Networks, Inc. Confederations

7. Copyright © 2001, Juniper Networks, Inc. Review Questions What form of BGP is run between the routers in a BGP Confederation?