Advanced Juniper Networks Routing
Release 5.1, Revision 0
Module 8: BGP Confederations
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
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
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 ];
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
Copyright © 2001, Juniper Networks, Inc.
Confederations
Copyright © 2001, Juniper Networks, Inc.
Review Questions
 What form of BGP is run between the routers in a BGP
Confederation?
Copyright © 2001, Juniper Networks, Inc.