Arp Caching; Static And Dynamic Entries In The Arp Cache - 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
Each switch compares the IP address to its own. Only the switch with the matching IP address replies to
the switch that sends the data with a packet that contains the MAC address for the switch. The source
switch adds the destination switch MAC address to its ARP table for future reference, creates a data-link
header and trailer that encapsulates the packet, and proceeds to transfer the data.
ARP broadcast and response process.
Figure 2-1
When the destination switch lies on a remote network which is beyond another switch, the process is the
same except that the switch that sends the data sends an ARP request for the MAC address of the default
gateway. After the address is resolved and the default gateway receives the packet, the default gateway
broadcasts the destination IP address over the networks connected to it. The switch on the destination
switch network uses ARP to obtain the MAC address of the destination switch and delivers the packet.
ARP is enabled by default.
The default system-defined CoPP policy rate-limits ARP broadcast packets. The default system-defined
CoPP policy prevents an ARP broadcast storm from affecting the control plane traffic but does not affect
bridged packets.

ARP Caching

ARP caching minimizes broadcasts and limits wasteful use of network resources. The mapping of IP
addresses to MAC addresses occurs at each hop (switch) on the network for every packet sent over an
internetwork, which may affect network performance.
ARP caching stores network addresses and the associated data-link addresses in memory for a period of
time, which minimizes the use of valuable network resources to broadcast for the same address each time
a packet is sent. You must maintain the cache entries since the cache entries are set to expire periodically
because the information might become outdated. Every switch on a network updates its tables as
addresses are broadcast.

Static and Dynamic Entries in the ARP Cache

You must manually configure the IP addresses, subnet masks, gateways, and corresponding MAC
addresses for each interface of each switch when using static routes. Static routing enables more control
but requires more work to maintain the route table. You must update the table each time you add or
change routes.
Dynamic routing uses protocols that enable the switches in a network to exchange routing table
information with each other. Dynamic routing is more efficient than static routing because the route table
is automatically updated unless you add a time limit to the cache. The default time limit is 25 minutes
but you can modify the time limit if the network has many routes that are added and deleted from the
cache.
ARP Process
Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, NX-OS Release 5.0(3)U1(1)
Information About IPv4
Figure 2-1 shows the
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