Impb Entry Settings - D-Link xStack Reference Manual

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xStack DGS-3200 Series Layer 2 Managed Gigabit Ethernet Switch Web UI Reference Guide
Parameter
From Port/To Port
IPv4 State / IPv6 State
Zero IP
DHCP Packet
Mode
Stop Learning
Threshold
Click Apply to implement the changes made.

IMPB Entry Settings

This window is used to create static IP-MAC-binding port entries and view all IMPB entries on the Switch.
Description
Select a range of ports to set for IP-MAC-port binding.
Use the drop-down menu to enable or disable these ports for IP-MAC Binding.
Enabled (Strict) – This state provides a stricter method of control. If the user selects this
mode, all packets are blocked by the Switch by default. The Switch will compare all
incoming ARP and IP Packets and attempt to match them against the IMPB white list. If the
IP-MAC pair matches the white list entry, the packets from that MAC address are
unblocked. If not, the MAC address will stay blocked. While the Strict state uses more CPU
resources from checking every incoming ARP and IP packet, it enforces better security and
is thus the recommended setting.
Enabled (Loose) – This mode provides a looser way of control. If the user selects loose
mode, the Switch will forward all packets by default. However, it will still inspect incoming
ARP packets and compare them with the Switch's IMPB white list entries. If the IP-MAC
pair of a packet is not found in the white list, the Switch will block the MAC address. A major
benefit of Loose state is that it uses less CPU resources because the Switch only checks
incoming ARP packets. However, it also means that Loose state cannot block users who
send only unicast IP packets. An example of this is that a malicious user can perform DoS
attacks by statically configuring the ARP table on their PC. In this case, the Switch cannot
block such attacks because the PC will not send out ARP packets.
Use the drop-down menu to enable or disable this feature. Once Enabled, the Switch will
allow ARP packets with a Source IP of 0.0.0.0 to pass through.
This is useful in some scenarios when a client (for example, a wireless Access Point,)
sends out an ARP request packet before accepting the IP address from a DHCP server. In
this case, the ARP request packet sent out from the client will contain a Source IP of
0.0.0.0. The Switch will need to allow such packets to pass, or else the client cannot know if
there is another duplicate IP address in the network.
By default, the Switch will forward all DHCP packets. However, if the port state is set to
Strict, all DHCP packets will be dropped. In that case, select Enabled so that the port will
forward DHCP packets even under Strict state. Enabling this feature also ensures that
DHCP snooping works properly.
Use the drop-down menu to select ARP or ACL mode.
ARP – When selecting this mode, the Switch will perform ARP Packet Inspection only and
no ACL rules will be used.
ACL – When selecting this mode, the Switch will perform IP Packet Inspection in addition to
ARP Packet Inspection. ACL rules will be used under this mode.
Whenever a MAC address is blocked by the Switch, it will be recorded in the Switch's L2
Forwarding Database (FDB) and each entry associated with a particular port. To prevent
the Switch FDB from overloading in case of an ARP DoS attack, the administrator can
configure the threshold when a port should stop learning illegal MAC addresses.
Enter a stop learning threshold between 0 and 500. Entering 500 means the port will enter
the Stop Learning state after 500 illegal MAC entries and will not allow additional MAC
entries, neither legal nor illegal, to be learned on this port. In the Stop Learning state, the
port will also automatically purge all blocked MAC entries on this port. Traffic from legal
MAC entries is still forwarded.
Entering 0 means no limit has been set and the port will keep learning illegal MAC
addresses.
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