Foundry Networks Switch and Router, Руководство по установке и настройке

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Configuring Virtual LANs (VLANs)
December 2000 25 - 5
not in themselves provide routing services for these protocols. This is true even of the source and destination IP
sub-nets, IPX networks, or AppleTalk cable ranges are on the same device.
ISR eliminates the need for an external router by allowing you to route between VLANs using virtual interfaces
(VEs). A
virtual interface is a logical port on which you can configure Layer 3 routing parameters. You configure
a separate virtual interface on each VLAN that you want to be able to route from or to. For example, if you
configure two IP sub-net VLANs on a Layer 3 Switch, you can configure a virtual interface on each VLAN, then
configure IP routing parameters for the sub-nets. Thus, the Layer 3 Switch forwards IP sub-net broadcasts within
each VLAN at Layer 2 but routes Layer 3 traffic between the VLANs using the virtual interfaces.
NOTE: The Layer 3 Switch uses the lowest MAC address on the device (the MAC address of port 1 or 1/1) as
the MAC address for all ports within all virtual interfaces you configure on the device.
The routing parameters and the syntax for configuring them are the same as when you configure a physical
interface for routing. The logical interface allows the Layer 3 Switch to internally route traffic between the protocol-
based VLANs without using physical interfaces.
All the ports within a protocol-based VLAN must be in the same port-based VLAN. The protocol-based VLAN
cannot have ports in multiple port-based VLANs, unless the ports in the port-based VLAN to which you add the
protocol-based VLAN are 802.1q tagged.
You can configure multiple protocol-based VLANs within the same port-based VLAN. In addition, a port within a
port-based VLAN can belong to multiple protocol-based VLANs of the same type or different types. For example,
if you have a port-based VLAN that contains ports 1 – 10, you can configure port 5 as a member of an AppleTalk
protocol VLAN, an IP protocol VLAN, and an IPX protocol VLAN, and so on.
IP Sub-Net, IPX Network, and AppleTalk Cable VLANs
The protocol-based VLANs described in the previous section provide separate protocol broadcast domains for
specific protocols. For IP, IPX, and AppleTalk, you can provide more granular broadcast control by instead
creating the following types of VLAN:
• IP sub-net VLAN – An IP sub-net broadcast domain for a specific IP sub-net.
• IPX network VLAN – An IPX network broadcast domain for a specific IPX network.
• AppleTalk cable VLAN – An AppleTalk broadcast domain for a specific cable range.
You can configure these types of VLANs on Layer 3 Switches only. The Layer 3 Switch sends broadcasts for the
IP sub-net, IPX network, or AppleTalk cable range to all ports within the IP sub-net, IPX network, or AppleTalk
cable VLAN at Layer 2.
The Layer 3 Switch routes packets between VLANs at Layer 3. To configure an IP sub-net, IPX network, or
AppleTalk cable VLAN to route, you must add a virtual interface to the VLAN, then configure the appropriate
routing parameters on the virtual interface.
NOTE: The Layer 3 Switch routes packets between VLANs of the same protocol. The Layer 3 Switch cannot
route from one protocol to another.
NOTE: IP sub-net VLANs are not the same thing as IP protocol VLANs. An IP protocol VLAN sends all IP
broadcasts on the ports within the IP protocol VLAN. An IP sub-net VLAN sends only the IP sub-net broadcasts
for the sub-net of the VLAN. You cannot configure an IP protocol VLAN and an IP sub-net VLAN within the same
port-based VLAN.
This note also applies to IPX protocol VLANs and IPX network VLANs, and to AppleTalk protocol VLANs and
AppleTalk cable VLANs.
Default VLAN
By default, all the ports on a Foundry device are in a single port-based VLAN. This VLAN is called DEFAULT-
VLAN and is VLAN number 1. Foundry devices do not contain any protocol VLANs or IP sub-net, IPX network, or
AppleTalk cable VLANs by default.