29.4.4 Negotiation of support functions

Capability negotiation is a means of negotiating which capabilities are supported by the peers. This is done by adding capability information to the OPEN message at the establishment of a BGP4+ negotiation session. Functionality that is matched (supported) by the respective peers' advertised capability information can be used by those peers.

In the Switch, the following capability information is always added to the OPEN message: IPv6 unicast routing, route refresh capability (Capability Code: 2), route refresh capability (Capability Code: 128), and the graceful restart functionality (Capability Code: 64). When an OPEN message without any capability information is received from a peer, only IPv6 unicast route advertisements will be sent over the established BGP4+ connection.

The following table describes the capabilities that can be negotiated.

Table 29-7: Features that can be negotiated

Capability	Capability information in OPEN message	Description
IPv6 routing	Capability Code: 1 AFI of Capability Value: 2 SAFI field of the Capability Value: 1	IPv6 unicast routes can be sent and received between the peers.
Route refresh capability	Capability Code : 2 AFI of Capability Value: 2#	Route refresh is supported on IPv6 routes.
	Capability Code : 128 AFI of Capability Value: 2#
Graceful restart	Capability Code : 64 AFI field of the Capability Value: 1 SAFI of Capability Value: 2	Use graceful restart.

The following figure illustrates how negotiation operates.

Figure 29-14: Concept of negotiation behavior