Additional Features
Media Access Control (MAC) Security
076R200-000
SpectraComm IP T1 Router Card
5-9
Issue 13
Installation and Operation Manual
MAC Filtering for Improved Performance
SCIP has a three-port integral etherswitch. Port1 and port2 are accessed at the front panel; port3 is
an internal port which is permanently connected to the SCIP interface,
e0
. (For clarity, the
etherswitch ports are not shown in the figure below.) The etherswitch automatically filters out
unicast packets that are not needed between local and remote hosts. However, broadcast packets
from all local hosts still traverse s0.
For users that want maximum performance across
s0
, a MACL can be added to SCIP-A
e0
to
filter out all unnecessary broadcasts. Here, MACL learning cannot be used. Only the MACs for
routers, servers and admin workstations on the local site necessary to talk with the remote hosts are
used to create the MACL. Any local hosts that do not need to talk with remote hosts are omitted
from the MACL on
e0
and will be filtered.
For typical networks, a ten to thirty per cent increase in performance can be achieved across the
WAN by eliminating unnecessary broadcasts.
Figure 5-5
MAC Security for Improved Performance
MAC Filtering and Spanning Tree
It is strongly recommended to enable Spanning Tree to prevent loops in LAN-X applications. When
MAC filtering is also enabled, some interesting conditions come to light. When redundant SCIPs
are used with Spanning Tree, one SCIP will be in blocking mode to prevent a loop. Typically, one
of the remote SCIPs will have its
e0
blocked, as shown below. In this example, SCIP-D
e0
will
see MAC addresses from both the local site and remote site. The local site MAC addresses (all
broadcasts and some unicast) will travel from SCIP-A to SCIP-B to SCIP-D
e0
. Typically, the
MACLs on remote site SCIPs will not include MACs from the local site. Therefore, the local MACs
will appear as a MACL violation on SCIP-D
e0
.
T1 (LAN-X)
LOCAL SITE
REMOTE SITE
ILLEGAL
FRAMES
DISCARDED
MACL
FILTER
SCIP
"B"
e0
LOCAL
HOST
LOCAL
HOST
LOCAL
HOST
LOCAL
HOST
LOCAL
HOST
LOCAL
HOST
s0
SCIP
"A"
e0
s0
Summary of Contents for SpectraComm IP T1
Page 119: ......
