3Com 3CRWER300-73 Router Manual PDF (Setup & Configuration Guide)

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■

MSS Clamping — You might not be able to browse some Web sites or

to send email messages that contain attachments from an Internet

Connection Sharing client computer if your outbound connection is

through a Windows XP-based Internet Connection Sharing host

computer that uses Point-to-Point Protocol over Ethernet (PPPoE).

This issue may occur if the Windows XP-based Internet Connection

Sharing host computer uses a smaller Maximum Transmission Unit

(MTU) size on the WAN interface (the PPPoE connection to the

Internet) than it uses on the private interface (the Ethernet connection

to the Internet Connection Sharing client). If a packet is larger than

the MTU size on the WAN interface, the client sends an Internet

Control Message Protocol (ICMP) error to the external server to

request that the server negotiate the TCP Maximum Segment Size

(MSS). However, this message may be blocked by some firewalls.

When this occurs, the packet is dropped. To allow the message to go

through the firewall, enable MSS Clamping. MSS clamping will make

Internet Connection Sharing set the MSS value low enough to match

the external interface.

■

Remote Administration — This feature allows you to make changes to

your Router’s settings from anywhere on the Internet. Four options are

available:

■

If you do not want to use this feature, select

Disable Remote

Administration

.

■

Select

Enable administration from a single Internet Host

, and enter

the IP address, to allow only one computer to use the remote

administration. This is more secure, as only the specified IP address

will be able to manage the Router.

■

Select

Enable administration from a whole Subnet Internet Host

,

and enter the IP address and subnet mask, to allow PCs from that

specific subnet group to use the remote administration.

■

Select

Enable administration from any Internet Host

, this allows

any computer to access the Router remotely.

Before you enable this function, ensure that you have changed the

factory default Administration Password.

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Advanced

95

VLAN

A VLAN is a flexible group of devices that can be located anywhere in a

network, but they communicate as if they are on the same physical

segment. With VLANs, you can segment your network without being

restricted by physical connections - a drawback of traditional network

design. As an example, with VLANs you can segment your network

according to:

■

Departmental groups - For example, you can have one VLAN for the

Marketing department, another for the Finance department, and

another for the Development department.

■

Hierarchical groups - For example, you can have one VLAN for

directors, another for managers, and another for general staff.

■

Usage groups - For example, you can have one VLAN for users of

e-mail, and another for users of multimedia.

The main benefit of VLANs is that they provide a network segmentation

system that is far more flexible than any traditional network. Using VLANs

also provides you with three other benefits:

■

It eases the change and movement of devices on IP networks: With

traditional IP networks, network administrators spend much of their

time dealing with moves and changes. If users move to a different IP

subnet, the IP addresses of each endstation must be updated

manually.

With a VLAN setup, if an endstation in VLAN 1 is moved to a port in

another part of the network, you only need to specify that the new

port forwards VLAN 1 traffic.

■

It provides extra security: Devices within each VLAN can only

communicate directly with devices in the same VLAN. If a device in

VLAN 1 needs to communicate with devices in VLAN 2, the traffic

needs to pass through a routing device or Layer 3 switch.

■

It helps to control broadcast traffic: With traditional networks,

congestion can be caused by broadcast traffic that is directed to all

network devices whether they require it or not. VLANs increase the

efficiency of your network because each VLAN can be set up to

contain only those devices that need to communicate with each other.

The VLAN screen allows you to setup VLAN groups. Note that Wireless

LAN is permanently assigned to Default VLAN.

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Figure 75

VLAN Screen

Click

Add VLAN

to create a new entry (see

Figure 76

).

Figure 76

VLAN Profile Screen

■

Enter a description for your VLAN in the

Description

field.

■

Enter the IP Address and subnet mask in the corresponding fields.

■

Select to set the

NAT Domain

as public or private.

■

IGMP Snooping: enabling it will turn on the feature that allows an

Ethernet switch to “listen in” on the IGMP conversation between

hosts and routers.

■

IGMP Querier: enabling this function will send out periodic IGMP

queries.

Click

Apply

.

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Advanced

97

Static Routes

You can configure static routes in this screen. You can setup a static route

that will get all traffic with destination to business network to go through

VPN tunnel and the rest outside of the VPN tunnel.

Figure 77

Static Routes Screen

To add a static route entry to the table, click

Add

(see

Figure 78

).

To change an existing entry, click

Edit

. To delete an entry, click

Delete

.

Figure 78

Add Static Route Screen

Enter the following information:

■

Network Address

— the network address of the static route.

■

Subnet Mask

— the subnet mask of the route.

A network address of 0.0.0.0 and a subnet mask of 0.0.0.0 indicates the

default route.

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■

Gateway

— the Router used to route data to the network specified by

the network address.

■

Interface — select the interface.

Note that you should only confiqure either the Gateway information or

select the Interface. After you have finished making changes to the table,

click

Apply

.

Here is an example of setting up a static route.

■

IP address of your PC: 10.1.4.52

■

Subnet mask: 255.255.252.0

■

Default Gateway: 10.1.4.254

■

Network Address: 10.1.4.0

Figure 79

Add Static Route Example Screen

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