Configuring Transparent Bridging
Transparent and SRT Bridging Configuration Task List
BC-51
Cisco IOS Bridging and IBM Networking Configuration Guide
The bridging software allows you to filter LAT frames. LAT bridge filtering allows the selective
inclusion or exclusion of LAT multicast service announcements on a per-interface basis.
Note The LAT filtering commands are not implemented for Token Ring interfaces.
In the LAT protocol, a group code is defined as a decimal number in the range 0 to 255. Some of the LAT
configuration commands take a list of group codes; this is referred to as a group code list. The rules for
entering numbers in a group code list follow:
•Entries can be individual group code numbers separated with a space. (The Digital LAT
implementation specifies that a list of numbers be separated by commas; however, our
implementation expects the numbers to be separated by spaces.)
•Entries can also specify a range of numbers. This is done by separating an ascending order range of
group numbers with hyphens.
•Any number of group codes or group code ranges can be listed in one command; just separate each
with a space.
In LAT, each node transmits a periodic service advertisement message that announces its existence and
availability for connections. Within the message is a group code list; this is a mask of up to 256bits.
Each bit represents a group number. In the traditional use of LAT group codes, a terminal server only
will connect to a host system when there is an overlap between the group code list of the user on the
terminal server and the group code list in the service advertisement message. In an environment with
many bridges and many LAT hosts, the number of multicast messages that each system has to deal with
becomes unreasonable. The 256 group codes might not be enough to allocate local assignment policies,
such as giving each DECserver 200 device its own group code in large bridged networks. LAT group
code filtering allows you to have very fine control over which multicast messages actually get bridged.
Through a combination of input and output permit and deny lists, you can implement many different LAT
control policies.
You can filter LAT service advertisements by performing any of the tasks in the following sections:
•Enabling LAT Group Code Service Filtering
•Specifying Deny or Permit Conditions for LAT Group Codes on Input
•Specifying Deny or Permit Conditions for LAT Group Codes on Output
Enabling LAT Group Code Service Filtering
You can specify LAT group-code filtering to inform the system that LAT service advertisements require
special processing. To enable LAT group-code filtering, use the following command in global
configuration mode:
Specifying Deny or Permit Conditions for LAT Group Codes on Input
You can specify the group codes by which to deny or permit access upon input. Specifying deny
conditions causes the system to not bridge any LAT service advertisement that contain any of the
specified groups. Specifying permit conditions causes the system to bridge only those service
advertisements that match at least one group in the specified group list.
Command Purpose
bridge bridge-group lat-service-filtering Enables LAT service filtering.