Alcatel Omni Switch/Router User Manual Download

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Application Example 2

Page 24-6

In this example one Group was created – Group 3 – that includes all ports to which

IPX

serv-

ers and clients are connected. Within this Group five

VLAN

s were created, one for each server:

When the Omni Switch/Router receives frames from the five servers, each server is assigned
to the appropriate

VLAN

and no conflict occurs.

IPX

routing is enabled for each

VLAN

– with

appropriate framing specified – so that traffic can route between the

VLAN

When a client workstation boots up and queries for a server, the Omni Switch/Router assigns
the client to the appropriate

VLAN

(s) based on encapsulation type. If the client uses 802.2

encapsulation,

SNAP

encapsulation, or

IPX

802.3 encapsulation,

VLAN

assignment is simple:

the client is assigned to

VLAN

D (802.2 encapsulation),

VLAN

E (

SNAP

encapsulation), or

VLAN

F (

IPX

802.3 encapsulation), respectively.

However, when a client workstation using Ethernet-

encapsulation boots up and queries for

a server, the Omni Switch/Router initially assigns the client to both

VLAN

B and

VLAN

C, since

both of these

VLAN

s specify Ethernet-

encapsulation. However, the Omni Switch/Router

recognizes that the client’s frame is a “Get_Nearest_Server” query and remembers that the
client is in search of its network number. While the client remains in this transitional state, it
remains assigned to all

VLAN

s that specify Ethernet-

encapsulation. Once the client has

received response from a server or servers or from an intervening router, the client selects its
network number and begins transmitting frames with the network number embedded. The
Omni Switch/Router detects these frames, removes the client from all previously-assigned

IPX

network address

VLAN

s (but not from

VLAN

s of other policy types) and assigns it to the

proper

IPX

network address

VLAN

according to network number.

Please Take Note

IPX

clients often are not particular about the server to which they

attach. However, clients can select a preferred server if the

(preferred server name) option is included in their start-up script.

Why is this Solution Recommended?

As as been explained, isolating each

IPX

server in its own

IPX

network address

VLAN

is the

recommended way to avoid conflicts. No problems occur if a client receives broadcast and
multicast traffic from multiple servers, especially for the brief period that the client remains in
a transitional state in search of a server.

Problems do occur if two servers with different network numbers and the same encapsula-
tion type are members of the same

VLAN

, because each server will detect the other’s frames,

notice conflicting network numbers for the same

VLAN

, and respond with a router configura-

tion error. For this reason it is not advisable to create four

VLAN

s based on

IPX

network

address policies within the same Group, each configured for one of the four encapsulation
types. It is important to isolate the servers, but it is not important to isolate the clients – at
least immediately.

While it is not important to isolate

IPX

clients immediately at bootup, it is desirable to isolate

them as soon as possible. Isolating clients – rather than letting them remain in multiple

VLAN

that specify the same encapsulation type – increases efficiency and reduces broadcast and
multicast traffic in the network. If a client remains in multiple

VLAN

s that specify the same

encapsulation type, the client receives all broadcast and multicast traffic from each server
using that encapsulation type, even though the client only communicates with the server that
shares its network number. In addition, when a

VLAN

is extended across a

WAN

backbone, it

is wasteful and inefficient to transmit unnecessary frames across the

WAN

. For these reasons,

as soon as a client learns its network number and begins transmitting frames with that
number, the Omni Switch/Router removes the client from all previously-assigned

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