Proxy Arp; Local Proxy Arp; Gratuitous Arp; Icmp - Cisco Nexus 3000 Series Configuration Manual

Chapter 2 Configuring IPv4
S e n d d o c u m e n t c o m m e n t s t o n e x u s 3 k - d o c f e e d b a c k @ c i s c o . c o m

Proxy ARP

Proxy ARP enables a switch that is physically located on one network appear to be logically part of a
different physical network connected to the same switch or firewall. Proxy ARP allows you to hide a
switch with a public IP address on a private network behind a router and still have the switch appear to
be on the public network in front of the router. By hiding its identity, the router accepts responsibility
for routing packets to the real destination. Proxy ARP can help switches on a subnet reach remote
subnets without configuring routing or a default gateway.
When switches are not in the same data link layer network but in the same IP network, they try to
transmit data to each other as if they are on the local network. However, the router that separates the
switches does not send a broadcast message because routers do not pass hardware-layer broadcasts and
the addresses cannot be resolved.
When you enable Proxy ARP on the switch and it receives an ARP request, it identifies the request as a
request for a system that is not on the local LAN. The switch responds as if it is the remote destination
for which the broadcast is addressed, with an ARP response that associates the MAC address of the
switch with the IP address of the remote destination. The local switch believes that it is directly
connected to the destination, while in reality its packets are being forwarded from the local subnetwork
toward the destination subnetwork by their local switch. By default, Proxy ARP is disabled.

Local Proxy ARP

You can use local Proxy ARP to enable a switch to respond to ARP requests for IP addresses within a
subnet where normally no routing is required. When you enable local Proxy ARP, ARP responds to all
ARP requests for IP addresses within the subnet and forwards all traffic between hosts in the subnet. Use
this feature only on subnets where hosts are intentionally prevented from communicating directly by the
configuration on the switch to which they are connected.

Gratuitous ARP

Gratuitous ARP sends a request with identical source IP address and destination IP address to detect
duplicate IP addresses. Cisco NX-OS Release 5.0(3) support enabling or disabling gratuitous ARP
requests or ARP cache updates.

ICMP

You can use ICMP to provide message packets that report errors and other information that is relevant
to IP processing. ICMP generates error messages, such as ICMP destination unreachable messages,
ICMP Echo Requests (which send a packet on a round trip between two hosts) and Echo Reply messages.
ICMP also provides many diagnostic functions and can send and redirect error packets to the host. By
default, ICMP is enabled.
Some of the ICMP message types are as follows:
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Network error messages
Network congestion messages
Troubleshooting information
Timeout announcements
Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, NX-OS Release 5.0(3)U1(1)
Information About IPv4
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