
Configuring Bridging Services
5-4 114060 Rev. A
Defining a Closed User Group That Permits Overlapping Network
Traffic
In an NML environment, overlapping traffic occurs when members of one closed
group are allowed to exchange information with users on some, but not all, LANs
of another closed group.
To permit overlapping traffic on a LAN that is part of a closed user group, you
assign an access list to the LAN’s NML port that contains the CUGID for all
groups that are allowed access to the LAN. This requires the use of unique
CUGIDs for each involved port.
For example, members of the Star group need to exchange information with Moon
group members on LAN E (refer to Figure
5-1). To define LAN E as a LAN that
permits overlapping traffic, you assign NML Port 7 an access list that includes
both Moon CUGIDs and Star CUGIDs.
Controlling NML Traffic on a Network Trunk
Network trunks carry the frames of all closed user groups. In Figure 5-1, for
example, the FDDI link between Bridge 1 and Bridge 2 is a network trunk. The
NML service allows you to control traffic on a trunk by blocking access to the
trunk by frames that originate from LANs that you specify. If you determine, for
example, that frames originating from a LAN that is part of a given closed user
group can never reach their destination via the trunk, you can block the frames
from traveling on the trunk. This feature helps reduce network traffic on the trunk
by eliminating useless frames.
For example, the Moon closed user group in Figure
5-1 closes its office on the
West Side, dismantling LAN B and NML Port 3. To ensure that no frames
destined for Port 3 get onto the FDDI trunk (needlessly increasing the traffic
load), you create an NML trunk port, Port 4, and provide it with an access list that
contains the CUGIDs of the remaining Moon ports. The NML port checks the
CUGID of all frames that attempt to exit from the bridge onto the trunk and drops
all frames containing a Moon CUGID.
Caution: We strongly recommend that you avoid using this feature in
conjunction with the spanning tree algorithm.
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