Date: Tue, 22 Jan 2002 13:43:22 -0800 (PST) From: Kenneth Stailey <kstailey@yahoo.com> To: freebsd-net@FreeBSD.ORG Subject: Re: ARP API documentation? Message-ID: <20020122214322.95295.qmail@web10005.mail.yahoo.com> In-Reply-To: <20020122204203.11832.qmail@web10001.mail.yahoo.com>
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I'm thinking that there should be some library routines for ARP to do get, set
and delete operations as simply as they used to be.
Opinions?
The new interface is driving people to write code like this:
klh10-2.0a/src/osdnet.c
[...]
#elif CENV_SYS_XBSD
/* The new BSD systems completely did away with the ARP ioctls
and instead substituted a far more complicated PF_ROUTE socket hack.
Rather than attempt to duplicate the arp(8) utility code here,
let's try simply invoking it!
arp -S <ipaddr> <ethaddr> pub
*/
FILE *f;
int err;
char arpbuff[128];
char resbuff[200];
sprintf(arpbuff, "/usr/sbin/arp -S %s %s %s",
ip_adrsprint(ipbuf, ipa),
eth_adrsprint(eabuf, eap),
(pubf ? "pub" : ""));
if (DP_DBGFLG)
dbprintln("invoking \"%s\"", arpbuff);
if ((f = popen(arpbuff, "r")) == NULL) {
syserr(errno, "cannot popen: %s", arpbuff);
[...]
Sad, isn't it?
--- Kenneth Stailey <kstailey@yahoo.com> wrote:
>
> --- Kenneth Stailey <kstailey@yahoo.com> wrote:
> >
> > --- Ruslan Ermilov <ru@FreeBSD.ORG> wrote:
> > > On Tue, Jan 22, 2002 at 09:22:12AM -0800, Kenneth Stailey wrote:
> > > > Hi,
> > > >
> > > > I search and search but cannot find any documentation on the user-space
> > > level
> > > > API for ARP. I know of only two code examples in the tree
> > > (usr.sbin/arp/arp.c
> > > > and usr.sbin/ppp/arp.c) and I do not wish to play guessing games about
> > the
> > > > protocol.
> > > >
> > > > It's clear that you open a PF_ROUTE raw socket and write a message to
> it
> > to
> > > > manipulate the ARP tables. Is the format of the message documented
> > > anywhere?
> > > >
> > > route(4).
> >
> > How is ARP documented without using the word "ARP"?
> >
> > $ man 4 route | grep -i arp | wc -l
> > 0
> >
> > Seems the old ioctl(2) interface to ARP had better documentation than that.
>
> Where's stuff like this, only for new API?
>
> % man 4 arp
>
> ARP(4P) UNIX Programmer's Manual 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 imple-
> mentation 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 message which requires the mapping and
> broadcasts a message on the associated 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 map-
> ping 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) */
>
> Printed 1/8/98 August 1, 1987 1
>
> ARP(4P) UNIX Programmer's Manual ARP(4P)
>
> #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 (per-
> manent) 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 encapsu-
> lations; 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 gratuitous ARP trans-
> lation replies along with replies to IP requests; they are
> also sent in reply to IP translation replies. The negotia-
> tion 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; how-
> ever, the smallest legal Ethernet packet is 60 bytes (not
> including CRC). Some systems may not enforce the minimum
> packet size, others will.
>
> Printed 1/8/98 August 1, 1987 2
>
> % uname -a
> BSD pdp11.xxxx.com 2.11 2.11 BSD UNIX #11: Fri Jan 4 14:59:26 EST 2002
> kstailey@pdp11.xxxx.com:/usr/src/sys/HIPPON pdp11
>
>
> > > Cheers,
> > > --
> > > Ruslan Ermilov Oracle Developer/DBA,
> > > ru@sunbay.com Sunbay Software AG,
> > > ru@FreeBSD.org FreeBSD committer,
> > > +380.652.512.251 Simferopol, Ukraine
> > >
> > > http://www.FreeBSD.org The Power To Serve
> > > http://www.oracle.com Enabling The Information Age
> >
> >
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