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ec(4) [bsd man page]

EC(4)							     Kernel Interfaces Manual							     EC(4)

NAME
ec - 3Com 10 Mb/s Ethernet interface SYNOPSIS
/sys/conf/SYSTEM: NEC ec_controllers # 3Com Ethernet DESCRIPTION
The ec interface provides access to a 10 Mb/s Ethernet network through a 3com controller. The hardware has 32 kilobytes of dual-ported memory on the UNIBUS. This memory is used for internal buffering by the board, and the inter- face code reads the buffer contents directly through the UNIBUS. The address of this memory is given in the flags field in the configura- tion file. The first interface normally has its memory at Unibus address 0. Each of the host's network addresses is specified at boot time with an SIOCSIFADDR ioctl. The ec interface employs the address resolution protocol described in arp(4P) to dynamically map between Internet and Ethernet addresses on the local network. The interface normally tries to use a ``trailer'' encapsulation to minimize copying data on input and output. The use of trailers is nego- tiated with ARP. This negotiation may be disabled, on a per-interface basis, by setting the IFF_NOTRAILERS flag with an SIOCSIFFLAGS ioctl. The interface software implements an exponential backoff algorithm when notified of a collision on the cable. This algorithm utilizes a 16-bit mask and the VAX-11's interval timer in calculating a series of random backoff values. The algorithm is as follows: 1. Initialize the mask to be all 1's. 2. If the mask is zero, 16 retries have been made and we give up. 3. Shift the mask left one bit and formulate a backoff by masking the interval timer with the smaller of the complement of this mask and a 5-bit mask, resulting in a pseudo-random number between 0 and 31. This produces the number of slot times to delay, where a slot is 51 microseconds. 4. Use the value calculated in step 3 to delay before retransmitting the packet. The delay is done in a software busy loop. DIAGNOSTICS
ec%d: send error. After 16 retransmissions using the exponential backoff algorithm described above, the packet was dropped. ec%d: input error (offset=%d). The hardware indicated an error in reading a packet off the cable or an illegally sized packet. The buffer offset value is printed for debugging purposes. ec%d: can't handle af%d. The interface was handed a message with addresses formatted in an unsuitable address family; the packet was dropped. SEE ALSO
intro(4N), inet(4F), arp(4P) BUGS
The hardware is not capable of talking to itself. The software implements local sending and broadcast by sending such packets to the loop interface. This is a kludge. Backoff delays are done in a software busy loop. This can degrade the system if the network experiences frequent collisions. 3rd Berkeley Distribution August 20, 1987 EC(4)

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ARP(4P) 																   ARP(4P)

NAME
arp - Address Resolution Protocol SYNOPSIS
/sys/conf/SYSTEM: NETHER 1 # ether pseudo-device DESCRIPTION
ARP is a protocol used to dynamically map between DARPA Internet and 10Mb/s Ethernet addresses. It is used by all the 10Mb/s Ethernet interface drivers. It is not specific to Internet protocols or to 10Mb/s Ethernet, but this implementation currently supports only that combination. 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 associated network requesting the address mapping. If a response is pro- vided, the new mapping is cached and any pending message is transmitted. ARP will queue at most one packet while waiting for a mapping request to be responded to; only the most recently ``transmitted'' packet is kept. To facilitate communications with systems which do not use ARP, ioctls are provided to enter and delete entries in the Internet-to-Ethernet tables. Usage: #include <sys/ioctl.h> #include <sys/socket.h> #include <net/if.h> struct arpreq arpreq; ioctl(s, SIOCSARP, (caddr_t)&arpreq); ioctl(s, SIOCGARP, (caddr_t)&arpreq); ioctl(s, SIOCDARP, (caddr_t)&arpreq); Each ioctl takes the same structure as an argument. SIOCSARP sets an ARP entry, SIOCGARP gets an ARP entry, and SIOCDARP deletes an ARP entry. These ioctls may be applied to any socket descriptor s, but only by the super-user. The arpreq structure contains: /* * ARP ioctl request */ struct arpreq { struct sockaddr arp_pa; /* protocol address */ struct sockaddr arp_ha; /* hardware address */ int arp_flags;/* flags */ }; /* arp_flags field values */ #define ATF_COM 0x02/* completed entry (arp_ha valid) */ #define ATF_PERM 0x04 /* permanent entry */ #define ATF_PUBL 0x08 /* publish (respond for other host) */ #define ATF_USETRAILERS 0x10 /* send trailer packets to host */ The address family for the arp_pa sockaddr must be AF_INET; for the arp_ha sockaddr it must be AF_UNSPEC. The only flag bits which may be written are ATF_PERM, ATF_PUBL and ATF_USETRAILERS. ATF_PERM causes the entry to be permanent if the ioctl call succeeds. The peculiar nature of the ARP tables may cause the ioctl to fail if more than 8 (permanent) Internet host addresses hash to the same slot. ATF_PUBL specifies that the ARP code should respond to ARP requests for the indicated host coming from other machines. This allows a host to act as an ``ARP server,'' which may be useful in convincing an ARP-only machine to talk to a non-ARP machine. ARP is also used to negotiate the use of trailer IP encapsulations; trailers are an alternate encapsulation used to allow efficient packet alignment for large packets despite variable-sized headers. Hosts which wish to receive trailer encapsulations so indicate by sending gra- tuitous ARP translation replies along with replies to IP requests; they are also sent in reply to IP translation replies. The negotiation is thus fully symmetrical, in that either or both hosts may request trailers. The ATF_USETRAILERS flag is used to record the receipt of such a reply, and enables the transmission of trailer packets to that host. 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
duplicate IP address!! sent from ethernet address: %x:%x:%x:%x:%x:%x. ARP has discovered another host on the local network which responds to mapping requests for its own Internet address. SEE ALSO
ec(4), de(4), il(4), inet(4F), arp(8C), ifconfig(8C) ``An Ethernet Address Resolution Protocol,'' RFC826, Dave Plummer, Network Information Center, SRI. ``Trailer Encapsulations,'' RFC893, S.J. Leffler and M.J. Karels, Network Information Center, SRI. BUGS
ARP packets on the Ethernet use only 42 bytes of data; however, the smallest legal Ethernet packet is 60 bytes (not including CRC). Some systems may not enforce the minimum packet size, others will. 3rd Berkeley Distribution August 1, 1987 ARP(4P)

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