Advanced Juniper Networks Routing
Release 5.1, Revision 0
Module 7: BGP Route Reflection
Copyright © 2001, Juniper Networks, Inc.
Objectives
 Describe the operation of BGP route reflection
 Configure a route reflector
 Explain the flow of routing information in a route
reflection network
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
 Route Reflection (RFC 2796) is one method for scaling
IBGP connectivity
Copyright © 2001, Juniper Networks, Inc.
Route Reflection Concepts
 Allows an IBGP speaker to re-advertise an IBGP
learned route to another IBGP speaker
 Route Reflector (RR) only re-advertises the best route
to “clients”
 IBGP attributes are not changed by reflection
 Routing Loops are prevented by new BGP attributes of
Cluster-id, Cluster-list, and Originator-id
Copyright © 2001, Juniper Networks, Inc.
Route Reflection Attributes
 Cluster-id represents each RR cluster in the network
– RR will drop routes that have already transited the cluster
– Added to the cluster-list when the RR advertises outside of
the cluster
 Cluster-list operates like an AS_Path
– RR use it for loop prevention
– Routers can use it in the route selection algorithm
 Originator-id denotes the first router to inject a route in
a RR network
Copyright © 2001, Juniper Networks, Inc.
Route Reflection Configuration
 Route reflector clients are configured in a separate
peer group
 Each peer group uses the cluster keyword
– Unique 32-bit number if used as the cluster-id
– Often the router-id of the RR is used
[edit protocols bgp]
group int-peers {
type internal;
local-address 172.16.1.1;
cluster 172.16.1.1;
neighbor 172.16.2.2;
neighbor 172.16.3.3;
neighbor 172.16.4.4;
}
 Clients only peer to their route reflectors
[edit protocols bgp]
group int-peers {
type internal;
local-address 172.16.2.2;
neighbor 172.16.1.1;
}
Copyright © 2001, Juniper Networks, Inc.
RR Client Full Mesh
 Clients may also peer with each other member of the
RR cluster
 To stop unnecessary advertisements, configure the RR
with the no-client-reflect command
[edit protocols bgp]
user@rr-client-1# show
group int-peers {
type internal;
local-address 172.16.2.2;
neighbor 172.16.1.1;
neighbor 172.16.3.3;
}
[edit protocols bgp]
user@rr-client-2# show
group int-peers {
type internal;
local-address 172.16.3.3;
neighbor 172.16.1.1;
neighbor 172.16.2.2;
}
[edit protocols bgp]
user@route-reflector# show
group int-peers {
type internal;
local-address 172.16.1.1;
cluster 172.16.1.1;
no-client-reflect;
neighbor 172.16.2.2;
neighbor 172.16.3.3;
}
Copyright © 2001, Juniper Networks, Inc.
“Basic” Route Reflection
Client –> RR –> clients & non-clients
Non-client –> RR –> clients only
Copyright © 2001, Juniper Networks, Inc.
Hierarchical Route Reflection
Client –> RR –> clients & non-clients
Non-client –> RR –> clients only
Copyright © 2001, Juniper Networks, Inc.
Route Propagation (1 of 3)
Routes are sent from a client to all peers (route reflector)
10.10.10.0/24
Copyright © 2001, Juniper Networks, Inc.
Route Propagation (2 of 3)
Route reflector sends routes to all clients in the cluster
and all peers
10.10.10.0/24
10.10.10.0/24
10.10.10.0/24
Copyright © 2001, Juniper Networks, Inc.
Route Propagation (3 of 3)
Route reflector sends routes from peers to all clients in
the cluster
10.10.10.0/24
10.10.10.0/24
Copyright © 2001, Juniper Networks, Inc.
Review Questions
 What does a BGP route reflector do with BGP routes
received from a configured RR client router?
 What three BGP attributes are introduced when BGP
route reflection is used and what is their role?
Copyright © 2001, Juniper Networks, Inc.