Configuring Transparent Bridging
Transparent and SRT Bridging Configuration Task List
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Cisco IOS Bridging and IBM Networking Configuration Guide
Configuring Transparent Bridging over SMDS
We support fast-switched transparent bridging for Switched Multimegabit Data Service (SMDS)
encapsulated serial and HSSI networks. Standard bridging commands are used to enable bridging on an
SMDS interface.
To enable transparent bridging over SMDS, use the following commands beginning in global
configuration mode:
Broadcast Address Resolution Protocol (ARP) packets are treated differently in transparent bridging
over an SMDS network than in other encapsulation methods. For SMDS, two packets are sent to the
multicast address. One is sent using a standard (SMDS) ARP encapsulation; the other is sent with the
ARP packet encapsulated in an 802.3 MAC header. The native ARP is sent as a regular ARP broadcast.
Our implementation of IEEE 802.6i transparent bridging for SMDS supports 802.3, 802.5, and FDDI
frame formats. The router can accept frames with or without frame check sequence (FCS). Fast-switched
transparent bridging is the default and is not configurable. If a packet cannot be fast switched, it is
process switched.
An example configuration is provided in the section “Fast-Switched Transparent Bridging over SMDS
Example” later in this chapter. For more information on SMDS, refer to the “Configuring SMDS”
chapter in the Cisco IOS Wide-Area Networking Configuration Guide.
Configuring Transparent Bridging over X.25
The transparent bridging software supports bridging of packets in X.25 frames. This ability is useful for
such tasks as transmitting packets from proprietary protocols across an X.25 network.
The X.25 bridging software uses the same spanning-tree algorithm as the other bridging functions, but
allows packets to be encapsulated in X.25 frames and transmitted across X.25 media. You specify the
IP-to-X.121 address mapping, and the system maintains a table of both the Ethernet and X.121
addresses. To configure X.25 transparent bridging, use the following command in interface
configuration mode:
For more information about configuring X.25, refer to the “Configuring X.25 and LAPB” chapter in the
Cisco IOS Wide-Area Networking Configuration Guide.
Command Purpose
Step1 interface serial number Specifies the serial interface.
Step2 encapsulation smds Configures SMDS encapsulation on the serial interface.
Step3 bridge-group bridge-group Associates the interface with a bridge group.
Step4 smds multicast bridge smds-address Enables transparent bridging of packets across an SMDS network.
Command Purpose
x25 map bridge x.121-address broadcast
[options-keywords]
Specifies IP-to-X.121 mapping.