ZyXEL MES3500-24F User Guide - Page 217

ARP Inspection and MAC Address Filters, 1.2.2, Trusted vs. Untrusted Ports, 1.2.3, Syslog, 1.

Page 217 highlights

Chapter 26 IP Source Guard • It pretends to be computer A and responds to computer B. • It pretends to be computer B and sends a message to computer A. As a result, all the communication between computer A and computer B passes through computer X. Computer X can read and alter the information passed between them. 26.1.2.1 ARP Inspection and MAC Address Filters When the Switch identifies an unauthorized ARP packet, it automatically creates a MAC address filter to block traffic from the source MAC address and source VLAN ID of the unauthorized ARP packet. You can configure how long the MAC address filter remains in the Switch. These MAC address filters are different than regular MAC address filters (Chapter 12 on page 120). • They are stored only in volatile memory. • They do not use the same space in memory that regular MAC address filters use. • They appear only in the ARP Inspection screens and commands, not in the MAC Address Filter screens and commands. 26.1.2.2 Trusted vs. Untrusted Ports Every port is either a trusted port or an untrusted port for ARP inspection. This setting is independent of the trusted/untrusted setting for DHCP snooping. You can also specify the maximum rate at which the Switch receives ARP packets on untrusted ports. The Switch does not discard ARP packets on trusted ports for any reason. The Switch discards ARP packets on untrusted ports in the following situations: • The sender's information in the ARP packet does not match any of the current bindings. • The rate at which ARP packets arrive is too high. 26.1.2.3 Syslog The Switch can send syslog messages to the specified syslog server (Chapter 40 on page 313) when it forwards or discards ARP packets. The Switch can consolidate log messages and send log messages in batches to make this mechanism more efficient. 26.1.2.4 Configuring ARP Inspection Follow these steps to configure ARP inspection on the Switch. 1 Configure DHCP snooping. See Section 26.1.1.4 on page 216. Note: It is recommended you enable DHCP snooping at least one day before you enable ARP inspection so that the Switch has enough time to build the binding table. 2 Enable ARP inspection on each VLAN. 3 Configure trusted and untrusted ports, and specify the maximum number of ARP packets that each port can receive per second. MES3500-24/24F User's Guide 217

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Chapter 26 IP Source Guard
MES3500-24/24F User’s Guide
217
It pretends to be computer
A
and responds to computer
B
.
It pretends to be computer
B
and sends a message to computer
A
.
As a result, all the communication between computer
A
and computer
B
passes through computer
X
. Computer
X
can read and alter the information passed between them.
26.1.2.1
ARP Inspection and MAC Address Filters
When the Switch identifies an unauthorized ARP packet, it automatically creates a MAC address
filter to block traffic from the source MAC address and source VLAN ID of the unauthorized ARP
packet. You can configure how long the MAC address filter remains in the Switch.
These MAC address filters are different than regular MAC address filters (
Chapter 12 on page 120
).
They are stored only in volatile memory.
They do not use the same space in memory that regular MAC address filters use.
They appear only in the
ARP Inspection
screens and commands, not in the
MAC Address
Filter
screens and commands.
26.1.2.2
Trusted vs. Untrusted Ports
Every port is either a trusted port or an untrusted port for ARP inspection. This setting is
independent of the trusted/untrusted setting for DHCP snooping. You can also specify the maximum
rate at which the Switch receives ARP packets on untrusted ports.
The Switch does not discard ARP packets on trusted ports for any reason.
The Switch discards ARP packets on untrusted ports in the following situations:
The sender’s information in the ARP packet does not match any of the current bindings.
The rate at which ARP packets arrive is too high.
26.1.2.3
Syslog
The Switch can send syslog messages to the specified syslog server (
Chapter 40 on page 313
)
when it forwards or discards ARP packets. The Switch can consolidate log messages and send log
messages in batches to make this mechanism more efficient.
26.1.2.4
Configuring ARP Inspection
Follow these steps to configure ARP inspection on the Switch.
1
Configure DHCP snooping. See
Section 26.1.1.4 on page 216
.
Note: It is recommended you enable DHCP snooping at least one day before you enable
ARP inspection so that the Switch has enough time to build the binding table.
2
Enable ARP inspection on each VLAN.
3
Configure trusted and untrusted ports, and specify the maximum number of ARP packets that each
port can receive per second.