NOTE
If the router receives an ARP request packet that it is unable to deliver to the nal destination because of the ARP timeout and
no ARP response is received (the Layer 3 switch knows of no route to the destination address), the router sends an ICMP Host
Unreachable message to the source.
FIGURE 4 ARP supplies the MAC address corresponding to an IP address
If Device A wants to communicate with Device B, knowing the IP address of Device B is not sucient; the MAC address is also required.
ARP supplies the MAC address.
Rate limiting ARP packets
You can limit the number of ARP packets the Brocade device accepts during each second. By default, the software does not limit the
number of ARP packets the device can receive. Since the device sends ARP packets to the CPU for processing, if a device in a busy
network receives a high number of ARP packets in a short period of time, some CPU processing might be deferred while the CPU
processes the ARP packets.
To prevent the CPU from becoming
ooded by ARP packets in a busy network, you can restrict the number of ARP packets the device
will accept each second. When you congure an ARP rate limit, the device accepts up to the maximum number of packets you specify,
but drops additional ARP packets received during the one-second interval. When a new one-second interval starts, the counter restarts at
zero, so the device again accepts up to the maximum number of ARP packets you specied, but drops additional packets received within
the interval.
To limit the number of ARP packets the device will accept each second, enter the rate-limit-arp command at the global CONFIG level of
the CLI.
device(config)# rate-limit-arp 100
This command congures the device to accept up to 100 ARP packets each second. If the device receives more than 100 ARP packets
during a one-second interval, the device drops the additional ARP packets during the remainder of that one-second interval.
Syntax:[no] rate-limit-arp num
The num variable species the number of ARP packets and can be from 0 through 100. If you specify 0, the device will not accept any
ARP packets.
Conguring IP parameters - Layer 3 switches
FastIron Ethernet Switch Layer 3 Routing
54 53-1003627-04
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