Chapter 3 Layer 2 Ethernet Port Configuration; Introduction To Layer 2 Ethernet Ports - 3Com 3C13636 Configuration Manual

3Com Router 3000 Ethernet Family
Configuration Guide

Chapter 3 Layer 2 Ethernet Port Configuration

3.1 Introduction to Layer 2 Ethernet Ports

The legacy routers are only operating at layer 3. Now, the use of switching chips on
routers allows the AR 18-22-24 and the AR 28/46, through an 8-/16-port layer 2
switching interface module/card (8LS/16LS or FIC-8LS/FIC-16LS), to implement layer
2 switching, providing more 10/100 Base-Tx Ethernet ports. They are nice and cost
effective switching-routing integrated devices on an enterprise network for providing
connectivity between the PCs and network devices on the network.
The layer 2 Ethernet ports support:
Layer 2 forwarding
Broadcast storm suppression
MAC address aging
Port-based VLAN (802.1Q)
These layer 2 Ethernet ports however do not support:
STP/MSTP/RSTP (Loop prevention must be considered at the time of
networking.)
Link aggregation
RMON statistics
Ethernet is a medium sharing data network communications technology based on the
access method of carrier sense multiple access/collision detect (CSMA/CD). On a
small local area network (LAN), it can work well. On a large LAN, however, the
likelihood exists that the network be overwhelmed by collisions and broadcasts. The
worst case is the paralysis of the entire network. Using switches to provide LAN
interconnectivity eliminates collisions, but the problem of broadcast storms still exists.
Virtual LAN (VLAN) technology was thus developed. It divides a LAN into smaller
logical LANs called VLANs, each being a broadcast domain. The hosts on a VLAN can
communicate with each other as they would on a LAN but they cannot communicate
with the hosts on other VLANs. Thus, broadcasts are restricted to a VLAN, as shown in
the following figure:
Chapter 3 Layer 2 Ethernet Port Configuration
3Com Corporation
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