Local Proxy Arp; Arp Filtering - OmniSwitch os6900 Network Configuration Manual

IP Forwarding

Local Proxy ARP

The Local Proxy ARP feature is an extension of the Proxy ARP feature, but is enabled on an IP interface
and applies to the VLAN bound to that interface. When Local Proxy ARP is enabled, all ARP requests
received on VLAN member ports are answered with the MAC address of the IP interface that has Local
Proxy ARP enabled. In essence, all VLAN traffic is now routed within the VLAN instead of bridged.
This feature is intended for use with port mapping applications where VLANs are one-port associations.
This allows hosts on the port mapping device to communicate through the router. ARP packets are still
bridged across multiple ports.
Local Proxy ARP takes precedence over any switch-wide Proxy ARP or ARP function. In addition, it is
not necessary to configure Proxy ARP to use Local Proxy ARP. The two features are independent of each
other.
By default, Local Proxy ARP is disabled when an IP interface is created. To enable this feature, use the
interface command. For example:
-> ip interface Accounting local-proxy-arp
When Local Proxy ARP is enabled for any one IP router interface associated with a VLAN, the feature is
applied to the entire VLAN. It is not necessary to enable it for each interface. However, if the IP interface
that has the Local Proxy ARP feature enabled is moved to another VLAN, Local Proxy ARP is enabled for
the new VLAN and must be enabled on another interface for the old VLAN.

ARP Filtering

ARP filtering is used to determine whether the switch responds to ARP requests that contain a specific IP
address. ARP filtering is used in conjunction with the Local Proxy ARP application; however, it is
available for use on its own or with other applications.
By default, no ARP filters exist in the switch configuration. When there are no filters present, all ARP
packets are processed, unless they are blocked or redirected by some other feature.
Use the arp filter command to specify the following parameter values required to create an ARP filter:
•
An IP address (for example, 193.204.173.21) used to determine whether an ARP packet is filtered.
•
An IP mask (for example, 255.0.0.0) used to identify which part of the ARP packet IP address is
compared to the filter IP address.
•
An optional VLAN ID to specify that the filter is only applied to ARP packets from that VLAN.
•
Which ARP packet IP address to use for filtering (sender or target). If the target IP address in the ARP
packet matches a target IP specified in a filter, then the disposition for that filter applies to the ARP
packet. If the sender IP address in the ARP packet matches a sender IP specified in a filter, then the
disposition for that filter applies to the ARP packet.
•
The filter disposition (block or allow). If an ARP packet meets filter criteria, the switch is either
blocked from responding to the packet or allowed to respond to the packet depending on the filter
disposition. Packets that do not meet any filter criteria are responded to by the switch.
The following arp filter command example creates an ARP filter, which blocks the switch from
responding to ARP packets that contain a sender IP address that starts with 198:
-> arp filter 198.0.0.0 mask 255.0.0.0 sender block
page 15-14 OmniSwitch AOS Release 7 Network Configuration Guide
Configuring IP
ip
June 2013