A virtual router is a function of the firewall
that participates in Layer 3 routing. The firewall uses virtual
routers to obtain 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.
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:
