ZyXEL Communications MSC1000G User Manual page 264

Chapter 9 Subscriber Port Setup Screens
Figure 168 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.
264
Traditional
Forward by
destination MAC
IP Aware
Forward by
destination IP
Management Switch Card User's Guide