Routing and WAN connections
384
11.6
Advanced Routing and Forwarding
BAT54-Rail/F..
Release
7.54
06/08
D For devices supporting VLAN, multiple VLANs can be defined for each
logical interface simply by using VLAN-IDs. Although the data traffic
for the various VLANs flows via a common logical interface, the VLAN-
ID ensures that the different VLANs remain strictly separated. From
the perspective of the BAT Router the VLANs are completely separate
interfaces, meaning that a single logical interface becomes multiple
logical interfaces for the BAT Router, and each of these interfaces can
be addressed individually.
D For devices with WLAN modules, the individual logical interfaces can
be grouped together. This is handled by the LAN bridge which regu-
lates data transfer between the LAN and WLAN interfaces. The forma-
tion of bridge groups (BRG) allows multiple logical interfaces to be
addresses at once and they appear as a single interface to the BAT
Router—in effect achieving the opposite of the VLAN method.
D In the final stage, the ARF forms a connection between the logical inter-
faces with VLAN tags and the bridge groups on the one side, and the IP
networks on the other. For this reason, an IP network is configured with a
reference to a logical network (with VLAN-ID, if applicable) or to a bridge
group. Furthermore, for each IP network an interface tag can be set, with
which the IP network can be separated from other networks without hav-
ing to use firewall rules.
The definition of routing tags for IP networks as described above is one of the
main advantages of Advanced Routing and Forwarding. This option allows
"virtual routers" to be realized. By using the interface tag, a virtual router uses
only a part of the routing table for an IP network, and in this way controls the
routing specifically for that one IP network. This method allows, for example,
several default routes to be defined in the routing table, each of which is giv-
en a routing tag. Virtual routers in the IP networks use the tags to select the
default route which applies to the IP network with the appropriate interface
tag. The separation of IP networks via virtual routers even permits multiple IP
networks with one and the same address range to be operated in parallel in
just one BAT Router without problem.
For example: Within an office building, a number of companies have to be
connected to the Internet via a central BAT Router, even though each of
these companies has its own Internet provider. All of the companies want to
use the popular IP network '10.0.0.0' with the netmask '255.255.255.0'. To
implement these requirements, each company is given an IP network
'10.0.0.0/255.255.255.0' with a unique name and a unique interface tag. In
the routing table, a default route with the corresponding routing tag is created
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