Allied Telesis Layer 3 Switches Istruzioni di installazione e manutenzione

C613-16103-00 REV A www.alliedtelesis.com

How To |

Introduction

Allied Telesis switches include a range of sophisticated security features at layer 2 and layer 3.

This How To Note describes these features and includes brief examples of how to configure

them.

The implementations shown in this How To Note should be thought of as industry-standard

best practices.

Contents

Introduction .............................................................................................................................................. 1

Which products and software versions does this information apply to? ................................... 2

Securing the device ................................................................................................................................. 3

Protecting the network .......................................................................................................................... 3

Protecting against packet flooding ................................................................................................ 3

Protecting against rapid MAC movement ................................................................................... 6

Controlling multicast traffic ........................................................................................................... 7

Managing the device securely ................................................................................................................ 9

Using Secure Shell (SSH) ................................................................................................................ 9

Using SSL for secure web access ................................................................................................ 10

Using SNMPv3 ................................................................................................................................ 10

Whitelisting telnet hosts .............................................................................................................. 12

Identifying the user ................................................................................................................................ 14

IP spoofing and tracking ................................................................................................................ 14

Rejecting Gratuitous ARP (GARP) ............................................................................................ 15

DHCP snooping ............................................................................................................................. 15

Using 802.

x port authentication ............................................................................................... 17

Protecting the user ................................................................................................................................ 18

Using private VLANs ..................................................................................................................... 18

Using local proxy ARP and MAC-forced forwarding ............................................................. 19

Using IPsec to make VPNs ........................................................................................................... 24

Protecting against worms ............................................................................................................. 25

Create A Secure Network With Allied Telesis

Managed Layer 3 Switches

Which products and software versions does this information apply to?

Create A Secure Network With Allied Telesis Managed Layer 3 Switches 2

Appendix: Configuration scripts for MAC-forced forwarding example ................................... 27

Edge switch

1 .................................................................................................................. 27

Edge switch 2 .................................................................................................................................. 28

Edge switch 3 .................................................................................................................................. 29

Access Router ................................................................................................................................. 30

For information about the AlliedWare firewall, see the Firewall chapter of your Software

Reference, and the following How To Notes:

zHow To Configure Some Basic Firewall And VPN Scenarios

zHow To Apply Firewall Policies And Rules

How To Notes are available from www.alliedtelesis.com/resources/literature/howto.aspx.

Which products and software versions does this

information apply to?

This How To Note applies to the following Allied Telesis switch series:

zAT-8600

zAT-8700XL

zAT-8800

zRapier i

zSwitchBlade

zAT-9800

zAT-8948 and x900-48

zAT-9900

zAT-9900s and x900-24

Some features are only available on some switches and/or some software versions.

Therefore, when this How To Note describes each feature, it lists the applicable switches and

versions.

Create A Secure Network With Allied Telesis Managed Layer 3 Switches 3

Securing the device

The first step towards making a secure network is to secure

the networking equipment itself.

There are two aspects to this. Firstly, physical security is

vital—lock your networking equipment away.

Secondly, straight after powering up any new piece of

networking equipment, change the default administrator user’s password. On an Allied

Telesis managed layer 3 switch, the default user is “manager”. To change the password, use

the following command:

set user=manager password=<new-password>

The default password is well-known. If you do not change it, anyone with physical or IP access

could reconfigure the switch.

Protecting the network

This section describes layer 2 based methods for controlling the negative impact of

misconfigured devices and misuse of the network. These solutions work at the Ethernet level

of a packet and cause no degradation in the switch's throughput.

You can protect your network against the following:

ztraffic storms (“Protecting against packet flooding” on page 3)

zexcessive MAC address learning (“Protecting against rapid MAC movement” on page 6)

zunwanted multicast traffic (“Controlling multicast traffic” on page 7)

Protecting against packet flooding

Service providers are often vulnerable to traffic storms, primarily when incorrectly

configured customer equipment is directly connected to the provider. Storms overwhelm a

subnet, and all of the switches in that subnet, with traffic. Such misconfiguration can quickly

lead to widespread outages and compromise guaranteed service levels.

Storms are a reality in any network. They can occur by accident, maliciously, or when a

network device fails. They occur naturally in a network where switches are connected more

than once to the same VLAN, so administrators must employ a method to prevent these

switch loops.

Spanning Tree Protocol based solutions are the most common method of preventing loops.

However, incorrect configuration or other network issues can cause STP to fail. For example,

if a single switch in the VLAN does not have STP enabled, the STP tree will not converge

properly. Spanning tree protocols can even fail if a broadcast storm drowns out STP

messages.

Products

All switches listed on page 2

Software Versions

All

Protecting the network

Create A Secure Network With Allied Telesis Managed Layer 3 Switches 4

Service providers need to prevent storms from disrupting services to customers. AlliedWare

offers the following options for mitigating storms:

zlimiting broadcasts and multicasts on a port (“Bandwidth limiting” on page 4)

zdetecting a storm and disabling that port or VLAN (“Using QoS policy-based storm

protection” on page 5)

Bandwidth limiting

ARP packets are the most frequent trigger for broadcast

storms. One ARP packet is flooded around and around a

network, crowding out all other traffic.

You can use a simple Quality of Service (QoS) configuration

to match ARP packets and make sure that when a broadcast

storm occurs, the effect is minimised.

Configuration

To limit the bandwidth for ARPs:

1. Create a classifier to match ARP packets.

2. Create a QoS framework of policy, traffic class, and flow group. In the traffic class settings,

specify the maximum bandwidth for ARP traffic.

3. Apply the policy—and therefore the bandwidth limit—to one or more ports.

Example

The following configuration limits ARP packets to

00kbps on port 48.

create classifier=1 protocol=0806 ethformat=ethii-untagged

create qos policy=1

create qos trafficclass=1 maxbandwidth=100

create qos flowgroup=1

add qos policy=1 trafficclass=1

add qos trafficclass=1 flowgroup=1

add qos flowgroup=1 classifier=1

set qos port=48 policy=1

Products

All switches listed on page 2

Software Versions

All

port

misconfigured

customer switch

misconfigured

customer switch flood of ARPs

flood of ARPs

ISP switch

When ISP switch has

no bandwidth control:

When ISP switch has

bandwidth limiting:

secure-switch-bandwidth.eps

Create A Secure Network With Allied Telesis Managed Layer 3 Switches 5

Protecting the network

Using QoS policy-based storm protection

Policy-based storm protection lets you specify one of a

range of actions for the switch to take when it detects a

broadcast storm. It is a part of the QoS functionality.

Policy-based storm protection is more powerful than simple

bandwidth limiting. It lets you restrict storm damage to

within the storming VLAN, and it gives you the flexibility to

define what traffic rate makes a broadcast storm.

Configuration

To use storm protection:

1. Turn on the switch enhanced mode qoscounters, unless it is already enabled. After this,

you need to restart the switch.

2. Create a classifier to match the desired traffic. To match all broadcast packets specify a

destination MAC address of ff-ff-ff-ff-ff-ff.

3. Create a QoS traffic class and define the following storm protection settings in it:

zWindow (stormwindow) specifies how often the switch measures traffic to decide

whether to activate storm protection (in seconds).

zRate (stormrate) specifies the amount of traffic per second that must be exceeded

before the switch takes action.

zAction (stormaction) specifies what the switch does when it detects a storm:

Link Down (linkdown) makes the switch physically disable the port on which the

storm is occurring, so that the link goes down.

Port Disable (portdisable) makes the switch logically disable the port on which the

storm is occurring, leaving the link up.

VLAN Disable (vlandisable) makes the switch block traffic only on the VLAN on

which the storm is occurring.

zTimeout (stormtimeout) specifies the number of seconds that the port remains

disabled for.

4. Create the rest of the QoS framework: a flow group and policy. Add the classifier to the

flow group, the flow group to the traffic class, and the traffic class to the policy.

5. Apply the policy—and therefore the storm protection—to one or more ports.

The procedure above applies storm protection to classified traffic, and uses a classifier to

select all broadcast traffic. This is the most common approach. If you want to, you can instead

classify to select important non-broadcast traffic and apply storm protection to unmatched

traffic. Unimportant or unwanted unicast and multicast traffic then counts towards the storm

calculations.

To apply storm protection to unclassified traffic, configure storm protection on the default

traffic class in the QoS policy settings. Use the parameters dtcstormwindow,

dtcstormrate, dtcstormaction, and dtcstormtimeout.

Products

AT-8948

x900-48 Series

AT-9900 Series

AT-9924Ts

x900-24 Series

Software Versions

2.8.

and later

Protecting the network

Create A Secure Network With Allied Telesis Managed Layer 3 Switches 6

Example

The following example applies storm protection to classified broadcast traffic on port

. If

there is a storm, it takes the link down for 60 seconds.

set switch enhancedmode=qoscounters

Reboot after turning on enhanced mode.

create classifier=1 macdaddr=ff-ff-ff-ff-ff-ff

create qos trafficclass=1 stormstatus=enable stormwindow=100

stormrate=100 stormaction=linkdown stormtimeout=60

The rest of the QoS configuration is as normal, so:

create qos flowgroup=1

add qos flowgroup=1 classifier=1

add qos trafficclass=1 flowgroup=1

create qos policy=1

add qos policy=1 trafficclass=1

set qos port=1 policy=1

You can view matching traffic at the port level with the command:

show qos port=1 count trafficclass

Protecting against rapid MAC movement

Rapid MAC movement protection detects excessive MAC

address learning on a specific switch port. Once excessive

learning is detected, the switch stops learning MAC

addresses via the affected port.

Rapid MAC movement mostly occurs because of a

broadcast storm, when one packet is storming around a

layer 2 network. Rapid MAC movement protection is

simpler to configure than QoS policy-based storm

protection but is not guaranteed to stop all the varieties of

broadcast storm.

Rapid MAC movement protection is on by default. The default action is to disable learning for

second. This gives the CPU of the switch some idle time, which may let a fast STP-type

protocol converge. You can change the amount of idle time to suit your network, or select a

different action.

Configuration

on one or

more ports

To customise the protection:

1. Set the parameters in the following command:

set switch port=<ports> thrashaction={learndisable|linkdown|none|

portdisable|vlandisable} thrashtimeout={none|1..86400}

vlanstatustrap={on|off}

The parameter thrashaction specifies the switch’s response to rapid MAC movement:

zlearndisable makes the switch temporarily disable learning on the port.

zlinkdown makes the switch physically disable the port, so that the link goes down.

zportdisable makes the switch logically disable the port, leaving the link up.

zvlandisable makes the switch block traffic on only the VLAN on which the rapid

learning occurred.

Products

AT-8948

x900-48 Series

AT-9900 Series

AT-9924Ts

x900-24 Series

Software Versions

2.8.

and later

Create A Secure Network With Allied Telesis Managed Layer 3 Switches 7

Protecting the network

2. Set the sensitivity in detecting rapid MAC movement, by using the following command to

tell the switch how many times a MAC address can move ports in one second:

set switch thrashlimit=5..255

Configuration

on trunk

groups

Rapid MAC movement protection also works with trunk groups. If one switch in a trunk fails,

the switches probably cannot negotiate STP or any other trunks that they belong to. This

immediately causes a broadcast storm. Rapid MAC movement protection on the other

switch in the trunk group detects such a storm because flooding of the same packet occurs

on all trunk ports connected to the failed switch.

For a static trunk, to make use of rapid MAC movement protection, create the trunk and

specify the optional thrashaction and thrashtimeout parameters:

create switch trunk=<name> port=<ports>

thrashaction={learndisable|linkdown|none|portdisable|

vlandisable} thrashtimeout={none|1..86400}

For a dynamic trunk using LACP, enable LACP, add ports, and set the optional thrashaction

and thrashtimeout parameters:

enable lacp

add lacp port=<ports>

set lacp thrashaction={learndisable|linkdown|none|portdisable|

vlandisable} thrashtimeout={none|1..86400}

Controlling multicast traffic

In a busy network, or one that has subscription-only access to multicast services, tight

per-port control of multicast traffic is required. IGMP makes multicasting fairly efficient, but

the extra control offered by AlliedWare helps increase efficiency.

When multicasting, it is essential to avoid filling the network with unnecessary multicast data

and to make sure that the clients who join a group are entitled to receive it. It is also

important to minimise delays in joining a group and to efficiently handle those who leave a

group.

The following sections outline some of the IGMP controls that are particularly relevant for

security. For detailed information on how to control IGMP in the network, see How To

Configure IGMP for Multicasting on Routers and Managed Layer 3 Switches. This How To Note is

available from www.alliedtelesis.com/resources/literature/howto.aspx.

IGMP snooping

IGMP snooping is enabled by default on Allied Telesis

managed layer 3 switches. IGMP snooping monitors the

streams and clients involved in each multicast group,

independent from IP itself. A snooping switch ensures that

only ports that are interested in a group are sent it. This

basic level of management works in tandem with the

subnetwork's IGMP querier and makes sure that the querier

gets notified of any client who wants to join the group.

Products

All switches listed on page 2

Software Versions

All

Protecting the network

Create A Secure Network With Allied Telesis Managed Layer 3 Switches 8

IGMP filtering

IGMP filtering lets you dictate exactly which multicast

groups a specific port can receive, by creating a filter list and

applying it to the port. Different ports may have different

filter lists applied to them.

If desired, you can select the type of message to filter. By

default, filters apply to IGMP reports. You can create extra

entries to also filter queries (type=query) and leave

messages (type=leave).

Configuration

For each port:

1. Work out which groups you want users on the port to be able to join.

2. Create an IGMP filter.

3. Create entries to allow the appropriate groups (action=include).

Note: The order of entries in a filter is important. When IGMP tries to match a message

to a filter, it performs a linear search of the filter to find a matching entry. It tries

each entry in turn, and stops processing the filter after the first match it finds.

4. Create an entry to block all groups (action=exclude). Give this entry a higher entry

number than entries for the included groups.

5. Apply the filter to the port.

Example

To stop the user attached to port

from joining any group except 224.

create igmp filter=1

add igmp filter=1 entry=1 group=224.12.13.14 action=include

add igmp filter=1 entry=2 group=224.0.0.0-239.255.255.255

action=exclude

set switch port=1 igmpfilter=1

IGMP throttling

Throttling limits the number of multicast groups that an

individual port can join.

To limit port 2 to a total of 6 groups:

set switch port=2 igmpmaxgroup=6

igmpaction=replace

Products

All switches listed on page 2

that support 2.7.5 or later

Software Versions

2.7.5 or later

Products

All switches listed on page 2

that support 2.7.5 or later

Software Versions

2.7.5 or later

Example

Create A Secure Network With Allied Telesis Managed Layer 3 Switches 9

Managing the device securely

In Ethernet and broadcast networks the privacy of traffic is not guaranteed. Hubs and

networks outside the administrator's control may leak sensitive data to unwanted recipients.

A hacker may even be able to force a switch to flood unicast traffic.

Because you cannot guarantee traffic privacy, you cannot be certain that management

sessions are private. Therefore, you should always use encrypted sessions when remotely

administering network equipment, even in networks that you know well. The simplest way to

achieve this is with Secure Shell (SSH).

This section describes secure management:

z“Using Secure Shell (SSH)” on page 9

z“Using SSL for secure web access” on page 10

z“Using SNMPv3” on page 10

Then the section ends by describing how to limit telnet access if you need to use telnet

instead of one of the recommended secure options (“Whitelisting telnet hosts” on page 12).

When you are using a secure management scheme, we recommend that you block all telnet

access to the switch, by disabling the telnet server:

disable telnet server

Using Secure Shell (SSH)

The Secure Shell (SSH) protocol is most simply described as

an encrypted form of Telnet.

1. Add a security officer to your switch’s list of users.

2. Create encryption keys for SSH to use.

3. Enable the SSH server.

4. Add the security officer to the list of SSH users and specify a password for it. Only users

in this list can use SSH to access the switch.

5. Enable system security.

Enabling system security makes telnet unavailable as an administrative interface—once you

have configured SSH, you have to use it.

Example

To configure SSH access for the security officer called “secoff”:

add user=secoff password=securepass privilege=security telnet=yes

create enco key=0 type=rsa length=1024 description="Host Key"

form=ssh

create enco key=1 type=rsa length=768 description="Server Key"

form=ssh

enable ssh server serverkey=1 hostkey=0 expirytime=1

logintimeout=60

add ssh user=secoff password=sameordifferentpassword

enable system security

Products

All switches listed on page 2

Software Versions

All

Configuration

Managing the device securely

Create A Secure Network With Allied Telesis Managed Layer 3 Switches 10

Using SSL for secure web access

If you prefer to configure the switch using the convenient

web-based GUI, then this is unencrypted by default. SSL lets

you use the GUI securely, by using HTTPS instead of HTTP.

1. Add a security officer to your switch’s list of users.

2. Create an encryption key for SSL to use.

3. Create a self-signed PKI certificate, or load a certificate

generated by a Certificate Authority (CA) if you have

one.

4. Add the certificate to the certificate database.

5. Turn security on for the HTTP server.

6. Enable system security.

Once you have configured SSL, HTTPS connections to the device are available only on

port 443.

Example

To allow the security officer called “secoff” to browse securely to the GUI, using a self-signed

certificate:

add user=secoff password=secoff privilege=securityofficer

create enco key=0 type=rsa length=1024

set system distinguishedname="cn=switch1,o=my_company,c=us"

create pki certificate=cer_name keypair=0 serialnumber=12345

subject="cn=172.30.1.105,o=my_company,c=us"

add pki certificate=cer_name location=cer_name.cer trust=yes

set http server security=on sslkey=0 port=443

enable system security

Using SNMPv3

Traditionally, SNMP has been a popular but insecure way to

monitor networks.

Allied Telesis devices are SNMPv3 compliant. By using

SNMPv3, you can authenticate SNMP users and restrict

their network access to parts of the network. SNMPv3 is

very flexible, as the examples in this section show.

Configuration

1. Enable SNMP.

2. Set up one or more SNMP views. Views list the objects in the MIB that users can see.

3. Set up one or more groups and add the groups to the views. Each group is a collection of

users who have the same access rights.

4. Set up one or more users and add them to the groups. Authentication parameters are set

here.

5. Set up a traphost profile, for trap messages to be remotely sent to. This is not compulsory

but we recommend it.

Products

All switches listed on page 2,

except AT-8948 and x900-48

Series which have no

graphical user interface

Software Versions

All

Configuration

Products

All switches listed on page 2

Software Versions

2.6.4 and later

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