Virtual Router Overview
A virtual router on the firewall participates in Layer
3 routing.
The firewall uses virtual routers to
obtain Layer 3 routes to other subnets by you manually defining
static routes or through participation in one or more Layer 3 routing
protocols (dynamic routes). The routes that the firewall obtains
through these methods populate the IP routing information base (RIB)
on the firewall. When a packet is destined for a different subnet
than the one it arrived on, the virtual router obtains the best
route from the RIB, places it in the forwarding information base
(FIB), and forwards the packet to the next hop router defined in
the FIB. The firewall uses Ethernet switching to reach other devices
on the same IP subnet. (An exception to one best route going in
the FIB occurs if you are using
ECMP, in which
case all equal-cost routes go in the FIB.)
The Ethernet, VLAN, and tunnel interfaces defined on the firewall
receive and forward Layer 3 packets. The destination zone
is derived from the outgoing interface based on the forwarding criteria,
and the firewall consults policy rules to identify the security
policies that it applies to each packet. In addition to routing
to other network devices, virtual routers can route to other virtual
routers within the same firewall if a next hop is specified to point
to another virtual router.
You can
configure Layer 3
interfaces on a virtual router to participate with dynamic
routing protocols (BGP, OSPF, OSPFv3, or RIP) as well as add static
routes. You can also create multiple virtual routers, each maintaining
a separate set of routes that aren’t shared between virtual routers,
enabling you to configure different routing behaviors for different
interfaces.
You can configure dynamic routing from one virtual router to another by configuring a loopback
interface in each virtual router, creating a static route between the two loopback
interfaces, and then configuring a dynamic routing protocol to peer between these two
interfaces. The firewall supports only one hop between virtual routers. For example,
with virtual routers A, B, and C, a route cannot go from A to B to C; it would have to
go from A to C.
Each Layer 3 Ethernet, loopback, VLAN, and tunnel interface defined
on the firewall must be associated with a virtual router. While each
interface can belong to only one virtual router, you can configure
multiple routing protocols and static routes for a virtual router. Regardless
of the static routes and dynamic routing protocols you configure
for a virtual router, one general configuration is required.