Static routing

General concept

Routing is (normally, exclusively in the context of Binero clouds implementation) done based on destination.

The two key parameters when talking about routing is:

  • The destination IP

  • The gateway IP used as the next hop

When routing packets, a router will consult a routing table that will have various network ranges available, each matched to a next hop (or gateway) which is the next device the packet should be sent to in order to reach its destination.

When routing, an IP packets destination IP will be identified as belonging to a network in the routing table and the router will forward the packet to the next-hop (or gateway) of that network.

Should the router be directly connected to the network in question (local to the network), it will instead use Address Resolution Protocol (ARP) to map the destination IP to a hardware (MAC) address and forward the packet to its final destination.

Static routing is the process of manually defining what subnets (network ranges) there are and behind what routers they are connected so that the routers are able to forward the packets.

It is only needed if there is more then a single router in the network (as a single router would be expected to be connected to all networks directly and then would manage all the routing based on that).

If a routing entry is missing and the routers are not able to match a destination IP to a network in their tables, one of two things will happen:

  • The routers will use their default route (if present). This would normally point upstream to the internet so effectively the packet would get lost in an upstream router that does not route private networks and would drop the packet.

  • If there is no default route, the packet would get dropped.

Note

The next-hop of a routing entry will need to be reachable and on a common network (that is a network to which both the sending and receiving router are connected).

Routing cannot rely on routing to reach a gateway, all gateways need to be directly accessible. A link-network is commonly use for this (but any subnet will suffice when the routers are both connected to it), see our Routing between networks for more information.

Working with static routes

Below is shown how to add static routes to a router using the various tools.

Since you route based on destination (but also need to account for return traffic, that is the traffic that a requests reply would generate), you would want to add the routes to both (or several) sides with the distinction that the networks defined on each router are the ones not local to that router.

The routing entries are therefore not the same on any two (ore more) routers.

Important

If you (mistakenly) add a route to a router that is already local to it (that is connected to it by an interface), the affected subnet would stop working. Only add routing entries to remote networks. Local networks are already routed by being directly connected.

Static routing is currently only supported using OpenStack Horizon or the OpenStack terminal client.

OpenStack Horizon

  • Under Project, click Network and then Routers in the sidebar menu.

  • Press the name of the router you want to connect the subnet to.

  • Press the Static Routes tab on the top.

  • Press Add static route

  • In the Destination CIDR field, type the destination IP range (that is, the network behind the neighbour router that you want to reach) in CIDR format.

  • In the Next Hop field, type the gateway address, that is the address that the neighbour router has on the network which it shares with the router you are adding the static route to - and to where you want to forward traffic.

  • Press Submit.

OpenStack terminal client

  • Run: openstack router list to get the list of your available routers. Save the name of the router you want to connect the subnet to.

  • Run: openstack router add route --route destination=[DESTINATION_RANGE],gateway=[GATEWAY IP] [ROUTER NAME], replacing the items in brackets to destination IP range (the network behind the neighbour router that you want to reach) in CIDR format, the gateway address (the address that the neighbour router has on the network which it shares with the router you are adding the static route to - and to where you want to forward traffic) and the router name (from previous step).

See also