Configuring BGP4
December 2005 © Foundry Networks, Inc. 21 - 33
Figure 21.2 Example route reflector configuration
Support for RFC 2796
Route reflection on Foundry devices is based on RFC 2796. This updated RFC helps eliminate routing loops that
are possible in some implementations of the older specification, RFC 1966.
NOTE: The configuration procedure for route reflection is the same regardless of whether your software release
is using RFC 1966 or RFC 2796. However, the operation of the feature is different as explained below.
RFC 2796 provides more details than RFC 1966 regarding the use of the route reflection attributes,
ORIGINATOR_ID and CLUSTER_LIST, to help prevent loops.
• ORIGINATOR_ID – Specifies the router ID of the BGP4 router that originated the route. The route reflector
inserts this attribute when reflecting a route to an IBGP neighbor. If a BGP4 router receives an advertisement
that contains its own router ID as the ORIGINATOR_ID, the router discards the advertisement and does not
forward it.
• CLUSTER_LIST – A list of the route reflection clusters through which the advertisement has passed. A
cluster contains a route reflector and its clients. When a route reflector reflects a route, the route reflector
adds its cluster ID to the front of the CLUSTER_LIST. If a route reflector receives a route that has its own
cluster ID, the router discards the advertisement and does not forward it.
The Foundry device handles the attributes as follows:
• The Layer 3 Switch adds the attributes only if it is a route reflector, and only when advertising IBGP route
information to other IBGP neighbors. The attributes are not used when communicating with EBGP neighbors.
• A Layer 3 Switch configured as a route reflector sets the ORIGINATOR_ID attribute to the router ID of the
router that originated the route. Moreover, the route reflector sets the attribute only if this is the first time the
route is being reflected (sent by a route reflector). In previous software releases, the route reflector set the
attribute to the router ID of the route reflector itself. When a Layer 3 Switch receives a route that already has
the ORIGINATOR_ID attribute set, the Layer 3 Switch does not change the value of the attribute.
• If a Layer 3 Switch receives a route whose ORIGINATOR_ID attribute has the value of the Layer 3 Switch’s
own router ID, the Layer 3 Switch discards the route and does not advertise it. By discarding the route, the
Layer 3 Switch prevents a routing loop. The Layer 3 Switch did not discard the route in previous software
releases.
• The first time a route is reflected by a Layer 3 Switch configured as a route reflector, the route reflector adds
EBGP
IBGP
IBGP
AS 2
IBGP
Cluster 1
10.0.2.010.0.1.0
AS 1
Route
Reflector 1
Route
Reflector 2
Route
Reflector
Client 1
Route
Reflector
Client 2
Router
RouterRouter
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