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ARP.C
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1994-04-17
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/* Address Resolution Protocol (ARP) functions. Sits between IP and
* Copyright 1991 Phil Karn, KA9Q
* Level 2, mapping IP to Level 2 addresses for all outgoing datagrams.
*
* Mods by G1EMM
*
* Mods by SM6RPZ
* 1992-05-28 - Added interface to arp_lookup() and arp_add().
* 1992-07-07 - Added arp_timeout(). This function now works according to the
* last page in RFC826. When an ARP entry times out we will first
* try an ARP reply before deleting the entry.
* 1992-07-08 - We will update the ARP table and create new entries each time
* we hear an ARP request message on the channel. By doing so we
* will gain knowledge of other stations hardware addresses
* whithout sending a lot of ARP requests. If we are running RSPF,
* it will be informed about these "findings".
* 1992-07-11 - Datagrams to be sent while awaiting an resolution will be put
* on a queue. The length of this queue in datagrams is defined
* in arp.h (ARP_QUEUE).
*
* 1992-10-27 The above 3 behaviours are now configurable via additional
* arp subcommands - WG7J
*
*/
#include "global.h"
#include "mbuf.h"
#include "timer.h"
#include "iface.h"
#include "enet.h"
#include "ax25.h"
#include "icmp.h"
#include "ip.h"
#include "arp.h"
#include "icmp.h"
#include "rspf.h"
extern int Maxarpq;
static void arp_output __ARGS((struct iface *iface,int16 hardware,int32 target,char *hw_addr));
static void arp_timeout __ARGS((void *p)); /* sm6rpz */
/* Hash table headers */
struct arp_tab *Arp_tab[HASHMOD];
struct arp_stat Arp_stat;
/* Resolve an IP address to a hardware address; if not found,
* initiate query and return NULLCHAR. If an address is returned, the
* interface driver may send the packet; if NULLCHAR is returned,
* res_arp() will have saved the packet on its pending queue,
* so no further action (like freeing the packet) is necessary.
*/
char *
res_arp(iface,hardware,target,bp)
struct iface *iface; /* Pointer to interface block */
int16 hardware; /* Hardware type */
int32 target; /* Target IP address */
struct mbuf *bp; /* IP datagram to be queued if unresolved */
{
register struct arp_tab *arp;
struct ip ip;
if((arp = arp_lookup(hardware,target,iface)) != NULLARP && arp->state == ARP_VALID)
return arp->hw_addr;
if(arp != NULLARP){
if(len_q(arp->pending) > Maxarpq) {
/* Earlier packets are already pending, kick
* this one back as a source quench
*/
ntohip(&ip,&bp);
icmp_output(&ip,bp,ICMP_QUENCH,0,NULL);
free_p(bp);
} else
enqueue(&arp->pending,bp);
} else {
/* Create an entry and put the datagram on the
* queue pending an answer
*/
arp = arp_add(target,hardware,NULLCHAR,0,iface);
enqueue(&arp->pending,bp);
arp_output(iface,hardware,target,NULLCHAR);
}
return NULLCHAR;
}
/* Handle incoming ARP packets. This is almost a direct implementation of
* the algorithm on page 5 of RFC 826, except for:
* 1. Outgoing datagrams to unresolved addresses are kept on a queue
* pending a reply to our ARP request.
* 2. The names of the fields in the ARP packet were made more mnemonic.
* 3. Requests for IP addresses listed in our table as "published" are
* responded to, even if the address is not our own.
*/
void
arp_input(iface,bp)
struct iface *iface;
struct mbuf *bp;
{
struct arp arp;
struct arp_tab *ap;
struct arp_type *at;
int i;
int32 wanted;
Arp_stat.recv++;
if(ntoharp(&arp,&bp) == -1) /* Convert into host format */
return;
if(arp.hardware >= NHWTYPES){
/* Unknown hardware type, ignore */
Arp_stat.badtype++;
return;
}
at = &Arp_type[arp.hardware];
if(arp.protocol != at->iptype){
/* Unsupported protocol type, ignore */
Arp_stat.badtype++;
return;
}
if((int16)uchar(arp.hwalen) > MAXHWALEN || uchar(arp.pralen) != sizeof(int32)){
/* Incorrect protocol addr length (different hw addr lengths
* are OK since AX.25 addresses can be of variable length)
*/
Arp_stat.badlen++;
return;
}
if(arp.sprotaddr == 0L || arp.tprotaddr == 0L){
/* We are going to dead-end references for [0.0.0.0], since
* experience shows that these cause total lock up -- N1BEE
*/
Arp_stat.badaddr++;
return;
}
if(memcmp(arp.shwaddr,at->bdcst,at->hwalen) == 0){
/* This guy is trying to say he's got the broadcast address! */
Arp_stat.badaddr++;
return;
}
/* Try to refine ARP according to section 5.7 in Douglas E.
* Comers book "Internetworking With TCP/IP", 2nd ed. page 77.
* I.e we will use all ARP-packets we can see thereby lessen
* the ARP traffic a little. -- sm6rpz
*/
if(((ap = arp_lookup(arp.hardware,arp.sprotaddr,iface)) != NULLARP
&& dur_timer(&ap->timer) != 0)
|| ( (iface->flags & ARP_EAVESDROP) &&
ap == NULLARP && arp.opcode != REVARP_REQUEST)
) {
ap = arp_add(arp.sprotaddr,arp.hardware,arp.shwaddr,0,iface);
}
/* See if we're the address they're looking for */
if(ismyaddr(arp.tprotaddr) != NULLIF){
if(ap == NULLARP) /* Only if not already in the table */
arp_add(arp.sprotaddr,arp.hardware,arp.shwaddr,0,iface);
if(arp.opcode == ARP_REQUEST){
/* Swap sender's and target's (us) hardware and protocol
* fields, and send the packet back as a reply
*/
memcpy(arp.thwaddr,arp.shwaddr,(int16)uchar(arp.hwalen));
/* Mark the end of the sender's AX.25 address
* in case he didn't
*/
if(arp.hardware == ARP_AX25)
arp.thwaddr[uchar(arp.hwalen)-1] |= E;
memcpy(arp.shwaddr,iface->hwaddr,at->hwalen);
wanted = arp.tprotaddr;
arp.tprotaddr = arp.sprotaddr;
/* arp.sprotaddr = iface->addr;*/
/* reply with what was asked for ! From Mike Galagher */
arp.sprotaddr = wanted;
arp.opcode = ARP_REPLY;
if((bp = htonarp(&arp)) == NULLBUF)
return;
if(iface->forw != NULLIF)
(*iface->forw->output)(iface->forw,
arp.thwaddr,iface->forw->hwaddr,at->arptype,bp);
else
(*iface->output)(iface,arp.thwaddr,
iface->hwaddr,at->arptype,bp);
Arp_stat.inreq++;
#ifdef RSPF
/* Do an RSPF upcall */
rspfarpupcall(arp.tprotaddr,arp.hardware,NULLIF);
#endif /* RSPF*/
} else {
Arp_stat.replies++;
#ifdef RSPF
/* Do an RSPF upcall */
rspfarpupcall(arp.sprotaddr,arp.hardware,iface);
#endif /* RSPF*/
}
} else if(arp.opcode == ARP_REQUEST
&& (ap = arp_lookup(arp.hardware,arp.tprotaddr,iface)) != NULLARP
&& ap->pub){
/* Otherwise, respond if the guy he's looking for is
* published in our table.
*/
memcpy(arp.thwaddr,arp.shwaddr,(int16)uchar(arp.hwalen));
memcpy(arp.shwaddr,ap->hw_addr,at->hwalen);
arp.tprotaddr = arp.sprotaddr;
arp.sprotaddr = ap->ip_addr;
arp.opcode = ARP_REPLY;
if((bp = htonarp(&arp)) == NULLBUF)
return;
if(iface->forw != NULLIF)
(*iface->forw->output)(iface->forw,
arp.thwaddr,iface->forw->hwaddr,at->arptype,bp);
else
(*iface->output)(iface,arp.thwaddr,
iface->hwaddr,at->arptype,bp);
Arp_stat.inreq++;
} else if(arp.opcode == REVARP_REQUEST){
for(i=0;i<HASHMOD;i++)
for(ap = Arp_tab[i];ap != NULLARP;ap = ap->next)
if(memcmp(ap->hw_addr,arp.thwaddr,at->hwalen) == 0)
goto found;
found: if(ap != NULLARP && ap->pub){
memcpy(arp.shwaddr,iface->hwaddr,at->hwalen);
arp.tprotaddr = ap->ip_addr;
arp.sprotaddr = iface->addr;
arp.opcode = REVARP_REPLY;
if((bp = htonarp(&arp)) == NULLBUF)
return;
if(iface->forw != NULLIF)
(*iface->forw->output)(iface->forw,
arp.thwaddr,iface->forw->hwaddr,REVARP_TYPE,bp);
else
(*iface->output)(iface,arp.thwaddr,
iface->hwaddr,REVARP_TYPE,bp);
Arp_stat.inreq++;
}
}
}
/* Add an IP-addr / hardware-addr pair to the ARP table */
struct arp_tab *
arp_add(ipaddr,hardware,hw_addr,pub,iface)
int32 ipaddr; /* IP address, host order */
int16 hardware; /* Hardware type */
char *hw_addr; /* Hardware address, if known; NULLCHAR otherwise */
int pub; /* Publish this entry? */
struct iface *iface;
{
struct mbuf *bp;
register struct arp_tab *ap;
struct arp_type *at;
unsigned hashval;
if(hardware >=NHWTYPES)
return NULLARP; /* Invalid hardware type */
at = &Arp_type[hardware];
if((ap = arp_lookup(hardware,ipaddr,iface)) == NULLARP){
/* New entry */
ap = (struct arp_tab *)callocw(1,sizeof(struct arp_tab));
ap->hw_addr = mallocw(at->hwalen);
ap->timer.func = arp_timeout;
ap->timer.arg = ap;
ap->hardware = hardware;
ap->ip_addr = ipaddr;
ap->iface = iface;
/* Put on head of hash chain */
hashval = hash_ip(ipaddr);
ap->prev = NULLARP;
ap->next = Arp_tab[hashval];
Arp_tab[hashval] = ap;
if(ap->next != NULLARP){
ap->next->prev = ap;
}
}
if(hw_addr == NULLCHAR){
/* Await response */
ap->state = ARP_PENDING;
set_timer(&ap->timer,Arp_type[hardware].pendtime * 1000L);
} else {
/* Response has come in, update entry and run through queue */
ap->state = ARP_VALID;
set_timer(&ap->timer,ARPLIFE*1000L);
memcpy(ap->hw_addr,hw_addr,at->hwalen);
ap->pub = pub;
while((bp = dequeue(&ap->pending)) != NULLBUF)
ip_route(NULLIF,bp,0);
}
start_timer(&ap->timer);
return ap;
}
/* Remove an entry from the ARP table */
void
arp_drop(p)
void *p;
{
register struct arp_tab *ap;
ap = (struct arp_tab *)p;
if(ap == NULLARP)
return;
stop_timer(&ap->timer); /* Shouldn't be necessary */
if(ap->next != NULLARP)
ap->next->prev = ap->prev;
if(ap->prev != NULLARP)
ap->prev->next = ap->next;
else
Arp_tab[hash_ip(ap->ip_addr)] = ap->next;
free_q(&ap->pending);
free(ap->hw_addr);
free((char *)ap);
}
/* Look up the given IP address in the ARP table */
struct arp_tab *
arp_lookup(hardware,ipaddr,iface)
int16 hardware;
int32 ipaddr;
struct iface *iface;
{
register struct arp_tab *ap;
for(ap = Arp_tab[hash_ip(ipaddr)]; ap != NULLARP; ap = ap->next){
if(ap->ip_addr == ipaddr && ap->hardware == hardware \
&& ap->iface == iface)
break;
}
return ap;
}
/* Send an ARP request to resolve IP address target_ip */
static void
arp_output(iface,hardware,target,hw_addr)
struct iface *iface;
int16 hardware;
int32 target;
char *hw_addr;
{
struct arp arp;
struct mbuf *bp;
struct arp_type *at;
at = &Arp_type[hardware];
if(iface->output == NULLFP)
return;
arp.hardware = hardware;
arp.protocol = at->iptype;
arp.hwalen = at->hwalen;
arp.pralen = sizeof(int32);
arp.opcode = ARP_REQUEST;
memcpy(arp.shwaddr,iface->hwaddr,at->hwalen);
arp.sprotaddr = iface->addr;
memset(arp.thwaddr,0,at->hwalen);
arp.tprotaddr = target;
if((bp = htonarp(&arp)) == NULLBUF)
return;
if(hw_addr == NULLCHAR)
(*iface->output)(iface,at->bdcst,iface->hwaddr,at->arptype,bp);
else
(*iface->output)(iface,hw_addr,iface->hwaddr,at->arptype,bp);
Arp_stat.outreq++;
}
/* Called when an ARP entry times out. If an entry has been a valid
* one we will send out an ARP reply. If this one does not succed,
* the ARP entry will be dropped. -- sm6rpz
*
* Made configurable by WG7J.
*/
static void
arp_timeout(p)
void *p;
{
struct arp_type *at;
char *hwaddr;
struct arp_tab *ap = (struct arp_tab *)p;
if(ap == NULLARP)
return;
stop_timer(&ap->timer);
/* Check to see if the timer is set to ARPLIFE or pendtime. Set_timer()
* adds at least one tick so we must do a little more flexible check.
*/
if( (ap->iface->flags & ARP_KEEPALIVE) &&
(dur_timer(&ap->timer) >= ARPLIFE * 1000L)) {
at = &Arp_type[ap->hardware];
set_timer(&ap->timer,at->pendtime * 1000L);
/* timer functions should NEVER call blocked allocs ! - WG7J */
if((hwaddr = (char *)mallocw((unsigned)at->hwalen))!=NULLCHAR) {
memcpy(hwaddr,ap->hw_addr,at->hwalen);
arp_output(ap->iface,ap->hardware,ap->ip_addr,hwaddr);
free(hwaddr); /* clean up */
}
start_timer(&ap->timer);
} else
arp_drop(ap);
}