Configuring Transparent Bridging
Transparent and SRT Bridging Configuration Task List
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Cisco IOS Bridging and IBM Networking Configuration Guide
forwarding decision and only switch the traffic to local interfaces configured as belonging to the same
VLAN broadcast domain. Router A provides an inter-VLAN mechanism that lets Router A function as
a gateway for stations on a given LAN segment by transmitting VLAN encapsulated traffic to and from
other switched VLAN domains or simply transmitting traffic in native (non-VLAN) format.
Figure 10 Inter-VLAN Connectivity between Multiple Switching Platforms
Figure 10 illustrates the following scenarios:
•Clients on VLAN 300 want to establish sessions with a server attached to a port in a different VLAN
(600). In this scenario, packets originating on LAN interface 3 of the Catalyst 1200B switch are
tagged with an 802.10 header with a security association identifier of 300 as they are forwarded onto
the FDDI ring. Router A can accept these packets because it is configured to route VLAN 300,
classify and make a layer 3 forwarding decision based on the destination network address and the
route out (in this case Fast Ethernet 3/1), and adding the ISL VLAN header (color200) appropriate
to the destination subnet as the traffic is switched.
•There is a network requirement to bridge two VLANs together through the system rather than
selectively route certain protocols. In this scenario the two VLAN IDs are placed in the same bridge
group. Note that they form a single broadcast domain and spanning tree, effectively forming a single
VLAN.
See the “Routing between VLANs Configuration Example” section on page 70 for an example
configuration of the topology shown in Figure 10.
To configure bridging between VLANs, enter the following commands, beginning in interface
configuration mode:
Wide area link
100BT ISL
100BT ISL
VLAN400 VLAN500 VLAN400 VLAN500
VLAN400 VLAN600
1/1
2/1
Router A
3/1
Catalyst 1200A Catalyst 1200B
802.10 FDDI VLAN
Backbone
1
2
3
1
2
3
ProStack
Mainframe
VLAN100
VLAN200
VLAN300
VLAN100
VLAN200
VLAN300
S3902
Command Purpose
Step1 interface type
slot/port.subinterface-number
Specifies a subinterface.
Step2 encapsulation {sde | isl} domain Specifies the encapsulation type (either ISL or SDE) and associates the
subinterface with the VLAN.
Step3 bridge-group bridge-group Enables bridged traffic between the subinterface and other interfaces in
the same bridge group.