D-Link DFL-260 Product Manual - Page 110

Creating ARP Objects, ARP Hash Size, Interface, IP Address

Page 110 highlights

3.4.3. Creating ARP Objects Chapter 3. Fundamentals Hash tables are used to rapidly look up entries in the ARP Cache. For maximum efficiency, a hash table should be twice as large as the entries it is indexing, so if the largest directly connected LAN contains 500 IP addresses, the size of the ARP entry hash table should be at least 1000. The administrator can modify the ARP advanced setting ARP Hash Size to reflect specific network requirements. The default value of this setting is 512. The setting ARP Hash Size VLAN setting is similar to the ARP Hash Size setting, but affects the hash size for VLAN interfaces only. The default value is 64. 3.4.3. Creating ARP Objects To change the way NetDefendOS handles ARP on an interface, the administrator can create NetDefendOS ARP objects, each of which has the following parameters: Mode The type of ARP object. This can be one of: • Static - Create a fixed mapping in the local ARP cache. • Publish - Publish an IP address on a particular MAC address (or this interface). • XPublish - Publish an IP address on a particular MAC address and "lie" about the sending MAC address of the Ethernet frame containing the ARP response. Interface The local physical interface for the ARP object. IP Address The IP address for the MAC/IP mapping. MAC Address The MAC address for the MAC/IP mapping. The three ARP modes of Static, Publish and XPublish are discussed next. Static Mode ARP Objects A Static ARP object inserts a particular MAC/IP address mapping into the NetDefendOS ARP cache. The most frequent use of static ARP objects is in situations where some external network device is not responding to ARP requests correctly and is reporting an incorrect MAC address. Some network devices, such as wireless modems, can have such problems. It may also be used to lock an IP address to a specific MAC address for increasing security or to avoid denial-of-service if there are rogue users in a network. However, such protection only applies to packets being sent to that IP address. It does not apply to packets being sent from that IP address. Example 3.15. Defining a Static ARP Entry This example will create a static mapping between IP address 192.168.10.15 and Ethernet address 4b:86:f6:c5:a2:14 on the lan interface: Command-Line Interface gw-world:/> add ARP Interface=lan IP=192.168.10.15 Mode=Static MACAddress=4b-86-f6-c5-a2-14 Web Interface 1. Go to Interfaces > ARP > Add > ARP 110

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Hash tables are used to rapidly look up entries in the ARP Cache. For maximum efficiency, a hash
table should be twice as large as the entries it is indexing, so if the largest directly connected LAN
contains 500 IP addresses, the size of the ARP entry hash table should be at least 1000. The
administrator can modify the ARP advanced setting
ARP Hash Size
to reflect specific network
requirements. The default value of this setting is
512
.
The setting
ARP Hash Size VLAN
setting is similar to the
ARP Hash Size
setting, but affects the
hash size for VLAN interfaces only. The default value is
64
.
3.4.3. Creating ARP Objects
To change the way NetDefendOS handles ARP on an interface, the administrator can create
NetDefendOS
ARP objects
, each of which has the following parameters:
Mode
The type of ARP object. This can be one of:
Static - Create a fixed mapping in the local ARP cache.
Publish - Publish an IP address on a particular MAC address (or this
interface).
XPublish - Publish an IP address on a particular MAC address and "lie" about
the sending MAC address of the Ethernet frame containing the ARP
response.
Interface
The local physical interface for the ARP object.
IP Address
The IP address for the MAC/IP mapping.
MAC Address
The MAC address for the MAC/IP mapping.
The three ARP modes of
Static
,
Publish
and
XPublish
are discussed next.
Static Mode ARP Objects
A
Static
ARP object inserts a particular MAC/IP address mapping into the NetDefendOS ARP
cache.
The most frequent use of static ARP objects is in situations where some external network device is
not responding to ARP requests correctly and is reporting an incorrect MAC address. Some network
devices, such as wireless modems, can have such problems.
It may also be used to lock an IP address to a specific MAC address for increasing security or to
avoid denial-of-service if there are rogue users in a network. However, such protection only applies
to packets being sent to that IP address. It does not apply to packets being sent from that IP address.
Example 3.15. Defining a Static ARP Entry
This
example
will
create
a
static
mapping
between
IP
address
192.168.10.15
and
Ethernet
address
4b:86:f6:c5:a2:14
on the
lan
interface:
Command-Line Interface
gw-world:/>
add ARP Interface=lan IP=192.168.10.15 Mode=Static
MACAddress=4b-86-f6-c5-a2-14
Web Interface
1.
Go to
Interfaces > ARP > Add > ARP
3.4.3. Creating ARP Objects
Chapter 3. Fundamentals
110