How to configure LXD as a BGP server

Note

The BGP server feature is available for the Bridge network and the Physical network. These network types are often used as the uplink network for an OVN network, and you must configure the BGP peers on the uplink network. See Configure BGP peers for OVN networks for instructions.

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BGP is a protocol that allows exchanging routing information between autonomous systems.

If you want to directly route external addresses to specific LXD servers or instances, you can configure LXD as a BGP server. LXD will then act as a BGP peer and advertise relevant routes and next hops to external routers, for example, your network router. It automatically establishes sessions with upstream BGP routers and announces the addresses and subnets that it’s using.

The BGP server feature can be used to allow a LXD server or cluster to directly use internal/external address space by getting the specific subnets or addresses routed to the correct host. This way, traffic can be forwarded to the target instance.

For bridge networks, the following addresses and networks are being advertised:

  • Network ipv4.address or ipv6.address subnets (if the matching nat property isn’t set to true)

  • Network ipv4.nat.address or ipv6.nat.address subnets (if the matching nat property is set to true)

  • Network forward addresses

  • Addresses or subnets specified in ipv4.routes.external or ipv6.routes.external on an instance NIC that is connected to the bridge network

Make sure to add your subnets to the respective configuration options. Otherwise, they won’t be advertised.

For physical networks, no addresses are advertised directly at the level of the physical network. Instead, the networks, forwards and routes of all downstream networks (the networks that specify the physical network as their uplink network through the network option) are advertised in the same way as for bridge networks.

Note

At this time, it is not possible to announce only some specific routes/addresses to particular peers. If you need this, filter prefixes on the upstream routers.

Configure the BGP server

To configure LXD as a BGP server, set the following server configuration options on all cluster members:

For example, set the following values:

lxc config set core.bgp_address=192.0.2.50:179
lxc config set core.bgp_asn=65536
lxc config set core.bgp_routerid=192.0.2.50

Once these configuration options are set, LXD starts listening for BGP sessions.

Configure next-hop (bridge only)

For bridge networks, you can override the next-hop configuration. By default, the next-hop is set to the address used for the BGP session.

To configure a different address, set bgp.ipv4.nexthop or bgp.ipv6.nexthop.

Configure BGP peers for OVN networks

If you run an OVN network with an uplink network (physical or bridge), the uplink network is the one that holds the list of allowed subnets and the BGP configuration. Therefore, you must configure BGP peers on the uplink network that contain the information that is required to connect to the BGP server.

Set the following configuration options on the uplink network:

  • bgp.peers.<name>.address - the peer address to be used by the downstream networks

  • bgp.peers.<name>.asn - the ASN for the local server

  • bgp.peers.<name>.password - an optional password for the peer session

  • bgp.peers.<name>.holdtime - an optional hold time for the peer session (in seconds)

Once the uplink network is configured, downstream OVN networks will get their external subnets and addresses announced over BGP. The next-hop is set to the address of the OVN router on the uplink network.