BGP as a Service in Contrail Release 3.1

The BGP as a Service (BGPaaS) feature allows a guest virtual machine (VM) to place routes in its own virtual routing and forwarding (VRF) instance using BGP. For more information on BGP as a Service, see BGP as a Service .

The initial implementation of BGPaaS Version 1, supported in Contrail Release 3.0, allowed a tenant VM to establish BGP sessions to the default gateway and DNS server in the VM’s subnet. A limitation of this implementation was that the tenant VM could advertise routes into the virtual network to which the VM belonged, however, the VM could not receive any routes. The tenant VM was required to use a static default route, with the subnet's default gateway as the next hop.

Contrail Release 3.1 eliminates the previous limitation and provides route export functionality for BGPaaS sessions. The next hop for all routes advertised to the tenant VM is set to the default gateway address of the subnet of the tenant VM. This allows the tenant BGP implementation to be relatively simple, by not requiring support for recursive resolution of BGP next hops.

The BGPaaS object is associated with a virtual machine interface (VMI), not just a virtual machine (VM), which enables a tenant VM to have BGP sessions in multiple virtual networks, if required.

Starting with Contrail Release 3.1, the following features and properties have been added to BGPaaS:

• By default, all BGPaaS sessions are configured to have bidirectional exchange of routes. The Boolean property bgpaas-suppress-route-advertisement ensures no advertisement of routes to the tenant VM.

• If inet6 routes are being advertised to the tenant VM, they are advertised with the IPv6 subnet's default gateway address as the BGP next hop. A Boolean property, bgpaas-ipv4-mapped-ipv6-nexthop, causes the IPv4 subnet's default gateway, in IPv4-mapped IPv6 format, to be used instead as the next hop.

• If multiple tenant VMs in the same virtual network have BGPaaS sessions and they use eBGP, the standard BGP AS path loop prevention rules prevent routes advertised by one tenant VM from being advertised to the other tenant VMs. The as-override field, added to the existing BgpSessionAttributes in the BGPaaS object, causes the control node to replace the AS number of the tenant VM with it's own AS number, when advertising routes learned from a tenant VM to another tenant VM in the same virtual network. The tenant VM does not need to implement any new functionality.