Routing
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Tip
You can show the route(s) that apply for a specific destination IP address or address range using the
CLI command
show route
. You can also see a list of all routes in a routing table using the CLI
command
show routes
. There is also a routing display on the Diagnostics control web pages.
8.2. Routing targets
A route can specify various targets for the packet :-
Table 8.1. Example route targets
Target
Notes
an Ethernet interface (locally-atached subnet)
requires ARP or ND to find the device on the LAN to
which the traffic is to be sent.
a specific IP address (a "gateway")
the packet is forwarded to another router (gateway) ;
routing is then determined based on the gateway's IP
address instead
tunnel interface such as L2TP, PPPoE or FB105
tunnels.
such routes are created as part of the config for the
interface and relate to the specific tunnel.
special targets
e.g. the FB6000 itself, or to a black hole (causes all
traffic to be dropped)
These are covered in more detail in the following sections.
8.2.1. Subnet routes
Whenever you define a subnet or one is created dynamically (e.g. by DHCP), an associated route is
automatically created for the associated prefix. Packets being routed to a subnet are sent to the Ethernet
interface
that the subnet is associated with. Traffic routed to the subnet will use ARP or ND to find the
final MAC address to send the packet to.
In addition, a subnet definition creates a very specific single IP (a "/32" for IPv4, or a "/128" for IPv6) route
for the IP address of the FB6000 itself on that subnet. This is a separate loop-back route which effectively
internally routes traffic back into the FB6000 itself - i.e. it never appears externally.
A subnet can also have a gateway specified, either in the config or by DHCP or RA. This gateway is just like
creating a route to 0.0.0.0/0 or ::/0 as a specific route configuration. It is mainly associated with the subnet for
convenience. If defined by DHCP or RA then, like the rest of the routes created by DHCP or RA, it is removed
when the DHCP or RA times out.
Example:
<subnet ip="192.168.0.1/24"/>
creates a route for destination
192.168.0.0/24
to
the
interface
associated with that subnet. A loop-back route to
192.168.0.1
(the FB6000's own IP
address on that subnet) is also created.
8.2.2. Routing to an IP address (gateway route)
Routes can be defined to forward traffic to another IP address, which will typically be another router (often
also called a gateway) For such a routing target, the gateway's IP address is then used to determine how to
route the traffic, and another routing decision is made. This subsequent routing decision usually identifies an
interface
or other data link to send the packet via - in more unusual cases, the subsequent routing decision
identifies another gateway, so it is possible for the process to be 'recursive' until a 'real' destination is found.
Example:
<route ip="0.0.0.0/0" gateway="192.168.0.100"/>
creates a default IPv4 route
that forwards traffic to
192.168.0.100
. The routing for
192.168.0.100
then has to be looked up to find
