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ARP(8)		       DragonFly System Manager's Manual		ARP(8)

NAME

arp -- address resolution display and control

SYNOPSIS

arp [-n] [-c cpu] [-i interface] hostname arp [-n] [-c cpu] [-i interface] -a arp -d hostname [pub] arp -d [-i interface] -a arp -s hostname ether_addr [temp] [pub [only]] arp -S hostname ether_addr [temp] [pub [only]] arp -f filename

DESCRIPTION

The arp utility displays and modifies the Internet-to-Ethernet address translation tables used by the address resolution protocol (arp(4)). With no flags, the program displays the current ARP entry for hostname. The host may be specified by name or by number, using Internet dot nota- tion. Available options: -a The program displays or deletes all of the current ARP entries. -c cpu On SMP systems the route table is replicated. This option allows the route table for a specific cpu to be accessed and exists pri- marily for debugging purposes. -d A super-user may delete an entry for the host called hostname with the -d flag. If the pub keyword is specified, only the ``published'' ARP entry for this host will be deleted. Alternatively, the -d flag may be combined with the -a flag to delete all entries. -i interface Limit the operation scope to the ARP entries on interface. Applicable only to the following operations: display one, display all, delete all. -n Show network addresses as numbers (normally arp attempts to dis- play addresses symbolically). -s hostname ether_addr Create an ARP entry for the host called hostname with the Ether- net address ether_addr. The Ethernet address is given as six hex bytes separated by colons. The entry will be permanent unless the word temp is given in the command. If the word pub is given, the entry will be ``published''; i.e., this system will act as an ARP server, responding to requests for hostname even though the host address is not its own. In this case the ether_addr can be given as auto in which case the interfaces on this host will be examined, and if one of them is found to occupy the same subnet, its Ethernet address will be used. If the only keyword is also specified, this will create a ``published (proxy only)'' entry. This type of entry is created automatically if arp detects that a routing table entry for hostname already exists. -S hostname ether_addr Is just like -s except any existing ARP entry for this host will be deleted first. -f filename Cause the file filename to be read and multiple entries to be set in the ARP tables. Entries in the file should be of the form hostname ether_addr [temp] [pub] with argument meanings as given above. Leading whitespace and empty lines are ignored. A `#' character will mark the rest of the line as a comment.

SEE ALSO

inet(3), arp(4), ifconfig(8)

HISTORY

The arp utility appeared in 4.3BSD. DragonFly 5.3 October 25, 2018 DragonFly 5.3 ARP(4) DragonFly Kernel Interfaces Manual ARP(4)

NAME

arp -- Address Resolution Protocol

SYNOPSIS

device ether

DESCRIPTION

The Address Resolution Protocol (ARP) is used to dynamically map between Protocol Addresses (such as IP addresses) and Local Network Addresses (such as Ethernet addresses). This implementation maps IP addresses to Ethernet, ARCnet, or Token Ring addresses. It is used by all the Ether- net interface drivers. ARP caches Internet-Ethernet address mappings. When an interface requests a mapping for an address not in the cache, ARP queues the mes- sage which requires the mapping and broadcasts a message on the associ- ated network requesting the address mapping. If a response is provided, the new mapping is cached and any pending message is transmitted. ARP will queue at most one packet while waiting for a response to a mapping request; only the most recently ``transmitted'' packet is kept. If the target host does not respond after several requests, the host is consid- ered to be down for a short period (normally 20 seconds), allowing an error to be returned to transmission attempts during this interval. The error is EHOSTDOWN for a non-responding destination host, and EHOSTUNREACH for a non-responding router. The ARP cache is stored in the system routing table as dynamically-cre- ated host routes. The route to a directly-attached Ethernet network is installed as a ``cloning'' route (one with the RTF_CLONING flag set), causing routes to individual hosts on that network to be created on demand. These routes time out periodically (normally 20 minutes after validated; entries are not validated when not in use). An entry for a host which is not responding is a ``reject'' route (one with the RTF_REJECT flag set). ARP entries may be added, deleted or changed with the arp(8) utility. Manually-added entries may be temporary or permanent, and may be ``published'', in which case the system will respond to ARP requests for that host as if it were the target of the request. In the past, ARP was used to negotiate the use of a trailer encapsula- tion. This is no longer supported. ARP watches passively for hosts impersonating the local host (i.e. a host which responds to an ARP mapping request for the local host's address).

DIAGNOSTICS

arp: %x:%x:%x:%x:%x:%x is using my IP address %d.%d.%d.%d!: ARP has dis- covered another host on the local network which responds to mapping requests for its own Internet address with a different Ethernet address, generally indicating that two hosts are attempting to use the same Inter- net address. arp: ether address is broadcast for IP address %d.%d.%d.%d!: ARP requested information for a host, and received an answer indicating that the host's ethernet address is the ethernet broadcast address. This indicates a misconfigured or broken device. arp: %d.%d.%d.%d moved from %x:%x:%x:%x:%x:%x to %x:%x:%x:%x:%x:%x: ARP had a cached value for the ethernet address of the referenced host, but received a reply indicating that the host is at a new address. This can happen normally when host hardware addresses change, or when a mobile node arrives or leaves the local subnet. It can also indicate a problem with proxy ARP. arpresolve: can't allocate llinfo for %d.%d.%d.%d: The route for the ref- erenced host points to a device upon which ARP is required, but ARP was unable to allocate a routing table entry in which to store the host's MAC address. This usually points to a misconfigured routing table. It can also occur if the kernel cannot allocate memory.

SEE ALSO

inet(4), route(4), arp(8), ifconfig(8), route(8) Plummer, D., "RFC 826", An Ethernet Address Resolution Protocol. Leffler, S.J. and Karels, M.J., "RFC 893", Trailer Encapsulations. DragonFly 5.3 April 18, 1994 DragonFly 5.3

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