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FUJITSU PSWITCH
User’s Guide
122
December/2018
first creates an INCOMPLETE entry, changes to REACHABLE if the retry is
successful, and FAILED if the retry fails.
3.1.9.7.
ARP (Address Resolution Protocol)
This product uses ARP (RFC 826) to associate an IPv4 address with an Ethernet MAC
address. The IP stack implements ARP on the out-of-band management interface,
network port and service port. The application code of this product implements ARP
on the routing interface. In this product, the following global settings of ARP on
routing interfaces can be changed.
Maximum age at which the ARP entry is updated or deleted from the ARP cache.
Time to wait for a response to an ARP request.
Maximum number of ARP requests sent when IP address resolution.
Whether to send the ARP request unconditionally for updating an entry when it
reaches the maximum age.
Static ARP entries.
When an interface becomes up, this switch software sends Gratuitous ARP (GARP)
to each IP address on the routing interface. GARP is an ARP for an IP address that is
set for itself, and it is responsible for checking whether not the IP address is
duplicated and for adding its own IP address and MAC address to the ARP table of
its connected devices.
The ARP cache has five kinds of entries: local, static, dynamic, gateway, negative.
Static entries are manually configured entries and are not subject to aging.
Dynamic entries associate the neighboring device's IP address with the MAC
address. A gateway entry is a dynamic entry whose IP address is the next hop
address of one or more routes on the routing table. Since the absence of a gateway
entry may affect IP packet forwarding to many destinations, this switch software
attempts to keep the gateway entry. Negative entries specify only IP addresses
without specifying MAC addresses and address resolution proceeds for IP addresses.
Negative entries are installed on the hardware as well as other ARP cache entries.
Hardware discards packets that match the negative entry to avoid flooding the CPU
with data packets whose next hop address cannot be resolved.
When a router forwards a data packet, if the IP address of the next hop of that
packet has not yet been address resolved with the MAC address, the hardware
traps this data packet to the CPU. This packet invokes the ARP resolution (the
router sends an ARP request to the next hop IP address of the packet). ARP stores
up to three address resolved data packets per IP address and that packet is
forwarded when the next hop address is address resolved. If the next hop address
is not address resolved, the packet is discarded.