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Management Guide
Port Overlapping
Ports can be assigned to multiple tagged VLANs. However, ports can only be
assigned to a single untagged VLAN. This is the only way that traffic coming from
a VLAN-unaware device can be assigned to specific VLAN group (i.e., the port's
default VID). Port overlapping can be used to allow access to commonly shared
network resources, such as file servers or printers. Note that VLANs that do not
overlap can be joined using the Layer-3 routing provided by this switch. (See the
following section.)
Connecting VLAN Groups
The switch supports intra-VLAN communication using hardware-assisted store-
and-forward switching. However, if you have devices in separate VLANs that must
communicate, and it is not practical to include these devices in a common VLAN,
then the VLANs can be connected via the Layer-3 routing provided by this switch.
Traditional routers use only physical port numbers in their routing tables, which
provided no support for VLANs. By contrast, this device supports Layer-3 routing
by using both logical port numbers and physical port numbers to support VLANs
and Layer-3 switching simultaneously.
By using the abstraction of a logical port number to represent a collection of
physical switch ports in the same VLAN, Layer-3 switching can occur from one
VLAN to another transparently without changing the routing protocol and IP routing
software, while Layer-2 switching is used for intra-VLAN traffic.
Class-of-Service (CoS) Support
The ES3616 provides four transmit queues on each port, with a weighted round-
robin scheme. These functions can be used to provide independent priorities for
various types of data including real-time video, real-time voice, and best-effort
data.
Priority assignment to a packet in the ES3616 is accomplished through explicit
assignment by end stations which have applications that require a higher priority
than best-effort data. The switch utilizes the IEEE 802.1p and 802.1Q tag structure
to decide priority assignments for the received packets.
BOOTP/DHCP Relay
Dynamic Host Configuration Protocol (DHCP), described in RFC 1541, is an
extension of the Bootstrap Protocol (BOOTP). DHCP allows hosts on a TCP/IP
network to dynamically obtain basic configuration information. When a DHCP
client starts, it broadcasts a DHCP Request packet, looking for DHCP servers.
DHCP servers respond to this packet with a DHCP Response packet. The client
then chooses a server to obtain TCP/IP configuration information, such as its own
IP address.
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