ZyXEL Communications MSC1024G Series User Manual page 260

Chapter 11 Subscriber Port Setup Screens
Figure 160 IP Bridge: Traditional vs. IP-aware DSLAM
The IP-aware MSC does not modify the IP packet header, but it uses the destination IP address
to modify the layer-2 header, in particular the source MAC address, destination MAC address,
and VLAN tag. As a result, the MSC prevents the MAC addresses and VLAN ID downstream
of the MSC (in other words, the subscribers' MAC addresses and VLAN ID) from propagating
into the network upstream of the MSC, and vice versa.
In the end, the IP-aware MSC makes the network more secure and more scalable, as explained
below.
• User-to-user security. The MSC does not forward subscribers' MAC addresses upstream
of the MSC, so there is no way for subscribers to know each other's MAC addresses. This
prevents the spoofing of MAC addresses and IP addresses upstream of the MSC.
• Scalability. The scale of access networks is typically limited by the number of MAC
addresses in the network. Since the MSC does not forward subscribers' MAC addresses or
VLAN ID upstream, the upstream network is more scalable, and it is simpler to use the
same VLAN ID upstream of several MSC. In addition, the MSC drastically reduces the
scale of ARP traffic storms.
The MSC itself is transparent in the network.
260
Traditional
Forward by
destination MAC
IP Aware
Forward by
destination IP
MSC1000G/1024G/1224G Series User's Guide