/*
* Copyright (c) 1982, 1986, 1988, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)ip_icmp.c 8.2 (Berkeley) 1/4/94
* $FreeBSD: src/sys/netinet/ip_icmp.c,v 1.101 2005/05/04 13:23:54 andre Exp $
*/
/*
* $Id$
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/socket.h>
#include <sys/sysctl.h>
#include <net/if.h>
#include <net/route.h>
#define _IP_VHL
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip_var.h>
#include <netinet/icmp_var.h>
#ifdef IPSEC
#include <netinet6/ipsec.h>
#include <netkey/key.h>
#endif
#ifdef FAST_IPSEC
#include <netipsec/ipsec.h>
#include <netipsec/key.h>
#define IPSEC
#endif
#include <machine/in_cksum.h>
/*
* ICMP routines: error generation, receive packet processing, and
* routines to turnaround packets back to the originator, and
* host table maintenance routines.
*/
struct icmpstat icmpstat;
SYSCTL_STRUCT(_net_inet_icmp, ICMPCTL_STATS, stats, CTLFLAG_RD,
&icmpstat, icmpstat, "");
static int icmpmaskrepl = 0;
SYSCTL_INT(_net_inet_icmp, ICMPCTL_MASKREPL, maskrepl, CTLFLAG_RW,
&icmpmaskrepl, 0, "");
static int icmpbmcastecho = 1;
SYSCTL_INT(_net_inet_icmp, OID_AUTO, bmcastecho, CTLFLAG_RW, &icmpbmcastecho,
0, "");
static int icmpallecho = 1;
SYSCTL_INT(_net_inet_icmp, OID_AUTO, allecho, CTLFLAG_RW, &icmpallecho,
0, "");
/* #define ICMPPRINTFS 1 */
#ifdef ICMPPRINTFS
int icmpprintfs = 0;
#endif
static void icmp_reflect(struct mbuf *);
static void icmp_send(struct mbuf *, struct mbuf *);
extern struct protosw inetsw[];
unsigned int icmplenPanicAvoided;
/*
* Generate an error packet of type error
* in response to bad packet ip.
*/
void
icmp_error(n, type, code, dest, destifp)
struct mbuf *n;
int type, code;
n_long dest;
struct ifnet *destifp;
{
register struct ip *oip = mtod(n, struct ip *), *nip;
#ifdef _IP_VHL
register unsigned oiplen = IP_VHL_HL(oip->ip_vhl) << 2;
#else
register unsigned oiplen = oip->ip_hl << 2;
#endif
register struct icmp *icp;
register struct mbuf *m;
unsigned icmplen;
#ifdef ICMPPRINTFS
if (icmpprintfs)
printf("icmp_error(%p, %x, %d)\n", oip, type, code);
#endif
if (type != ICMP_REDIRECT)
icmpstat.icps_error++;
/*
* Don't send error if not the first fragment of message.
* Don't error if the old packet protocol was ICMP
* error message, only known informational types.
*/
if (oip->ip_off &~ (IP_MF|IP_DF))
goto freeit;
if (oip->ip_p == IPPROTO_ICMP && type != ICMP_REDIRECT &&
n->m_len >= oiplen + ICMP_MINLEN &&
!ICMP_INFOTYPE(((struct icmp *)((caddr_t)oip + oiplen))->icmp_type)) {
icmpstat.icps_oldicmp++;
goto freeit;
}
/* Don't send error in response to a multicast or broadcast packet */
if (n->m_flags & (M_BCAST|M_MCAST))
goto freeit;
/* Don't send error in response to malicious packet */
icmplen = min(oiplen + 8, oip->ip_len);
if (icmplen < sizeof(struct ip)) {
icmplenPanicAvoided++;
goto freeit;
}
/*
* First, formulate icmp message
*/
m = m_gethdr(M_DONTWAIT, MT_HEADER);
if (m == NULL)
goto freeit;
#ifdef MAC
mac_create_mbuf_netlayer(n, m);
#endif
m->m_len = icmplen + ICMP_MINLEN;
MH_ALIGN(m, m->m_len);
icp = mtod(m, struct icmp *);
if ((u_int)type > ICMP_MAXTYPE)
panic("icmp_error");
icmpstat.icps_outhist[type]++;
icp->icmp_type = type;
if (type == ICMP_REDIRECT)
icp->icmp_gwaddr.s_addr = dest;
else {
icp->icmp_void = 0;
/*
* The following assignments assume an overlay with the
* zeroed icmp_void field.
*/
if (type == ICMP_PARAMPROB) {
icp->icmp_pptr = code;
code = 0;
} else if (type == ICMP_UNREACH &&
code == ICMP_UNREACH_NEEDFRAG && destifp) {
icp->icmp_nextmtu = htons(destifp->if_mtu);
}
}
icp->icmp_code = code;
bcopy((caddr_t)oip, (caddr_t)&icp->icmp_ip, icmplen);
nip = &icp->icmp_ip;
nip->ip_len = htons((u_short)(nip->ip_len + oiplen));
/*
* Now, copy old ip header (without options)
* in front of icmp message.
*/
if (m->m_data - sizeof(struct ip) < m->m_pktdat)
panic("icmp len");
m->m_data -= sizeof(struct ip);
m->m_len += sizeof(struct ip);
m->m_pkthdr.len = m->m_len;
m->m_pkthdr.rcvif = n->m_pkthdr.rcvif;
nip = mtod(m, struct ip *);
bcopy((caddr_t)oip, (caddr_t)nip, sizeof(struct ip));
nip->ip_len = m->m_len;
#ifdef _IP_VHL
nip->ip_vhl = IP_VHL_BORING;
#else
nip->ip_v = IPVERSION;
nip->ip_hl = 5;
#endif
nip->ip_p = IPPROTO_ICMP;
nip->ip_tos = 0;
icmp_reflect(m);
freeit:
m_freem(n);
}
static struct sockaddr_in icmpsrc = { sizeof (struct sockaddr_in), AF_INET };
static struct sockaddr_in icmpdst = { sizeof (struct sockaddr_in), AF_INET };
static struct sockaddr_in icmpgw = { sizeof (struct sockaddr_in), AF_INET };
/*
* Process a received ICMP message.
*/
void
icmp_input(m, off)
struct mbuf *m;
int off;
{
struct icmp *icp;
struct in_ifaddr *ia;
struct ip *ip = mtod(m, struct ip *);
int hlen = off;
int icmplen = ip->ip_len;
int i, code;
void (*ctlfunc)(int, struct sockaddr *, void *);
/*
* Locate icmp structure in mbuf, and check
* that not corrupted and of at least minimum length.
*/
#ifdef ICMPPRINTFS
if (icmpprintfs) {
char buf[4 * sizeof "123"];
strcpy(buf, inet_ntoa(ip->ip_src));
printf("icmp_input from %s to %s, len %d\n",
buf, inet_ntoa(ip->ip_dst), icmplen);
}
#endif
if (icmplen < ICMP_MINLEN) {
icmpstat.icps_tooshort++;
goto freeit;
}
i = hlen + min(icmplen, ICMP_ADVLENMIN);
if (m->m_len < i && (m = m_pullup(m, i)) == 0) {
icmpstat.icps_tooshort++;
return;
}
ip = mtod(m, struct ip *);
m->m_len -= hlen;
m->m_data += hlen;
icp = mtod(m, struct icmp *);
if (in_cksum(m, icmplen)) {
icmpstat.icps_checksum++;
goto freeit;
}
m->m_len += hlen;
m->m_data -= hlen;
#ifdef ICMPPRINTFS
if (icmpprintfs)
printf("icmp_input, type %d code %d\n", icp->icmp_type,
icp->icmp_code);
#endif
/*
* Message type specific processing.
*/
if (icp->icmp_type > ICMP_MAXTYPE)
goto raw;
icmpstat.icps_inhist[icp->icmp_type]++;
code = icp->icmp_code;
switch (icp->icmp_type) {
case ICMP_UNREACH:
switch (code) {
case ICMP_UNREACH_NET:
case ICMP_UNREACH_HOST:
case ICMP_UNREACH_PROTOCOL:
case ICMP_UNREACH_PORT:
case ICMP_UNREACH_SRCFAIL:
code = PRC_UNREACH_NET;
break;
case ICMP_UNREACH_NEEDFRAG:
code = PRC_MSGSIZE;
break;
case ICMP_UNREACH_NET_UNKNOWN:
case ICMP_UNREACH_NET_PROHIB:
case ICMP_UNREACH_TOSNET:
code = PRC_UNREACH_NET;
break;
case ICMP_UNREACH_HOST_UNKNOWN:
case ICMP_UNREACH_ISOLATED:
case ICMP_UNREACH_HOST_PROHIB:
case ICMP_UNREACH_TOSHOST:
code = PRC_UNREACH_HOST;
break;
case ICMP_UNREACH_FILTER_PROHIB:
case ICMP_UNREACH_HOST_PRECEDENCE:
case ICMP_UNREACH_PRECEDENCE_CUTOFF:
code = PRC_UNREACH_PORT;
break;
default:
goto badcode;
}
goto deliver;
case ICMP_TIMXCEED:
if (code > 1)
goto badcode;
code += PRC_TIMXCEED_INTRANS;
goto deliver;
case ICMP_PARAMPROB:
if (code > 1)
goto badcode;
code = PRC_PARAMPROB;
goto deliver;
case ICMP_SOURCEQUENCH:
if (code)
goto badcode;
code = PRC_QUENCH;
deliver:
/*
* Problem with datagram; advise higher level routines.
*/
if (icmplen < ICMP_ADVLENMIN || icmplen < ICMP_ADVLEN(icp) ||
#ifdef _IP_VHL
IP_VHL_HL(icp->icmp_ip.ip_vhl) < (sizeof(struct ip) >> 2)) {
#else
icp->icmp_ip.ip_hl < (sizeof(struct ip) >> 2)) {
#endif
icmpstat.icps_badlen++;
goto freeit;
}
NTOHS(icp->icmp_ip.ip_len);
/* Discard ICMP's in response to multicast packets */
if (IN_MULTICAST(ntohl(icp->icmp_ip.ip_dst.s_addr)))
goto badcode;
#ifdef ICMPPRINTFS
if (icmpprintfs)
printf("deliver to protocol %d\n", icp->icmp_ip.ip_p);
#endif
icmpsrc.sin_addr = icp->icmp_ip.ip_dst;
#if 1
/*
* MTU discovery:
* If we got a needfrag and there is a host route to the
* original destination, and the MTU is not locked, then
* set the MTU in the route to the suggested new value
* (if given) and then notify as usual. The ULPs will
* notice that the MTU has changed and adapt accordingly.
* If no new MTU was suggested, then we guess a new one
* less than the current value. If the new MTU is
* unreasonably small (arbitrarily set at 296), then
* we reset the MTU to the interface value and enable the
* lock bit, indicating that we are no longer doing MTU
* discovery.
*/
if (code == PRC_MSGSIZE) {
struct rtentry *rt;
int mtu;
rt = rtalloc1((struct sockaddr *)&icmpsrc, 0,
RTF_CLONING | RTF_PRCLONING);
if (rt && (rt->rt_flags & RTF_HOST)
&& !(rt->rt_rmx.rmx_locks & RTV_MTU)) {
mtu = ntohs(icp->icmp_nextmtu);
if (!mtu)
mtu = ip_next_mtu(rt->rt_rmx.rmx_mtu,
1);
#ifdef DEBUG_MTUDISC
printf("MTU for %s reduced to %d\n",
inet_ntoa(icmpsrc.sin_addr), mtu);
#endif
if (mtu < 296) {
/* rt->rt_rmx.rmx_mtu =
rt->rt_ifp->if_mtu; */
rt->rt_rmx.rmx_locks |= RTV_MTU;
} else if (rt->rt_rmx.rmx_mtu > mtu) {
rt->rt_rmx.rmx_mtu = mtu;
}
}
if (rt)
RTFREE(rt);
}
#endif
ctlfunc = inetsw[ip_protox[icp->icmp_ip.ip_p]].pr_ctlinput;
if (ctlfunc)
(*ctlfunc)(code, (struct sockaddr *)&icmpsrc,
(void *)&icp->icmp_ip);
break;
badcode:
icmpstat.icps_badcode++;
break;
case ICMP_ECHO:
if (!icmpallecho) {
icmpstat.icps_allecho++;
break;
}
if (!icmpbmcastecho
&& (m->m_flags & (M_MCAST | M_BCAST)) != 0
&& IN_MULTICAST(ntohl(ip->ip_dst.s_addr))) {
icmpstat.icps_bmcastecho++;
break;
}
icp->icmp_type = ICMP_ECHOREPLY;
goto reflect;
case ICMP_TSTAMP:
if (!icmpbmcastecho
&& (m->m_flags & (M_MCAST | M_BCAST)) != 0
&& IN_MULTICAST(ntohl(ip->ip_dst.s_addr))) {
icmpstat.icps_bmcasttstamp++;
break;
}
if (icmplen < ICMP_TSLEN) {
icmpstat.icps_badlen++;
break;
}
icp->icmp_type = ICMP_TSTAMPREPLY;
icp->icmp_rtime = iptime();
icp->icmp_ttime = icp->icmp_rtime; /* bogus, do later! */
goto reflect;
case ICMP_MASKREQ:
#define satosin(sa) ((struct sockaddr_in *)(sa))
if (icmpmaskrepl == 0)
break;
/*
* We are not able to respond with all ones broadcast
* unless we receive it over a point-to-point interface.
*/
if (icmplen < ICMP_MASKLEN)
break;
switch (ip->ip_dst.s_addr) {
case INADDR_BROADCAST:
case INADDR_ANY:
icmpdst.sin_addr = ip->ip_src;
break;
default:
icmpdst.sin_addr = ip->ip_dst;
}
ia = (struct in_ifaddr *)ifaof_ifpforaddr(
(struct sockaddr *)&icmpdst, m->m_pkthdr.rcvif);
if (ia == 0)
break;
if (ia->ia_ifp == 0)
break;
icp->icmp_type = ICMP_MASKREPLY;
icp->icmp_mask = ia->ia_sockmask.sin_addr.s_addr;
if (ip->ip_src.s_addr == 0) {
if (ia->ia_ifp->if_flags & IFF_BROADCAST)
ip->ip_src = satosin(&ia->ia_broadaddr)->sin_addr;
else if (ia->ia_ifp->if_flags & IFF_POINTOPOINT)
ip->ip_src = satosin(&ia->ia_dstaddr)->sin_addr;
}
reflect:
ip->ip_len += hlen; /* since ip_input deducts this */
icmpstat.icps_reflect++;
icmpstat.icps_outhist[icp->icmp_type]++;
icmp_reflect(m);
return;
case ICMP_REDIRECT:
if (code > 3)
goto badcode;
if (icmplen < ICMP_ADVLENMIN || icmplen < ICMP_ADVLEN(icp) ||
#ifdef _IP_VHL
IP_VHL_HL(icp->icmp_ip.ip_vhl) < (sizeof(struct ip) >> 2)) {
#else
icp->icmp_ip.ip_hl < (sizeof(struct ip) >> 2)) {
#endif
icmpstat.icps_badlen++;
break;
}
/*
* Short circuit routing redirects to force
* immediate change in the kernel's routing
* tables. The message is also handed to anyone
* listening on a raw socket (e.g. the routing
* daemon for use in updating its tables).
*/
icmpgw.sin_addr = ip->ip_src;
icmpdst.sin_addr = icp->icmp_gwaddr;
#ifdef ICMPPRINTFS
if (icmpprintfs) {
char buf[4 * sizeof "123"];
strcpy(buf, inet_ntoa(icp->icmp_ip.ip_dst));
printf("redirect dst %s to %s\n",
buf, inet_ntoa(icp->icmp_gwaddr));
}
#endif
icmpsrc.sin_addr = icp->icmp_ip.ip_dst;
rtredirect((struct sockaddr *)&icmpsrc,
(struct sockaddr *)&icmpdst,
(struct sockaddr *)0, RTF_GATEWAY | RTF_HOST,
(struct sockaddr *)&icmpgw, (struct rtentry **)0);
pfctlinput(PRC_REDIRECT_HOST, (struct sockaddr *)&icmpsrc);
break;
/*
* No kernel processing for the following;
* just fall through to send to raw listener.
*/
case ICMP_ECHOREPLY:
case ICMP_ROUTERADVERT:
case ICMP_ROUTERSOLICIT:
case ICMP_TSTAMPREPLY:
case ICMP_IREQREPLY:
case ICMP_MASKREPLY:
default:
break;
}
raw:
rip_input(m, hlen);
return;
freeit:
m_freem(m);
}
/*
* Reflect the ip packet back to the source
*/
static void
icmp_reflect(m)
struct mbuf *m;
{
struct ip *ip = mtod(m, struct ip *);
struct in_ifaddr *ia;
struct in_addr t;
struct mbuf *opts = 0;
#ifdef _IP_VHL
int optlen = (IP_VHL_HL(ip->ip_vhl) << 2) - sizeof(struct ip);
#else
int optlen = (ip->ip_hl << 2) - sizeof(struct ip);
#endif
if (!in_canforward(ip->ip_src) &&
((ntohl(ip->ip_src.s_addr) & IN_CLASSA_NET) !=
(IN_LOOPBACKNET << IN_CLASSA_NSHIFT))) {
m_freem(m); /* Bad return address */
goto done; /* Ip_output() will check for broadcast */
}
t = ip->ip_dst;
ip->ip_dst = ip->ip_src;
/*
* If the incoming packet was addressed directly to us,
* use dst as the src for the reply. Otherwise (broadcast
* or anonymous), use the address which corresponds
* to the incoming interface.
*/
for (ia = in_ifaddr; ia; ia = ia->ia_next) {
if (t.s_addr == IA_SIN(ia)->sin_addr.s_addr)
break;
if (ia->ia_ifp && (ia->ia_ifp->if_flags & IFF_BROADCAST) &&
t.s_addr == satosin(&ia->ia_broadaddr)->sin_addr.s_addr)
break;
}
icmpdst.sin_addr = t;
if ((ia == (struct in_ifaddr *)0) && m->m_pkthdr.rcvif)
ia = (struct in_ifaddr *)ifaof_ifpforaddr(
(struct sockaddr *)&icmpdst, m->m_pkthdr.rcvif);
/*
* The following happens if the packet was not addressed to us,
* and was received on an interface with no IP address.
*/
if (ia == (struct in_ifaddr *)0)
ia = in_ifaddr;
t = IA_SIN(ia)->sin_addr;
ip->ip_src = t;
ip->ip_ttl = MAXTTL;
if (optlen > 0) {
register u_char *cp;
int opt, cnt;
u_int len;
/*
* Retrieve any source routing from the incoming packet;
* add on any record-route or timestamp options.
*/
cp = (u_char *) (ip + 1);
if ((opts = ip_srcroute()) == 0 &&
(opts = m_gethdr(M_DONTWAIT, MT_HEADER))) {
opts->m_len = sizeof(struct in_addr);
mtod(opts, struct in_addr *)->s_addr = 0;
}
if (opts) {
#ifdef ICMPPRINTFS
if (icmpprintfs)
printf("icmp_reflect optlen %d rt %d => ",
optlen, opts->m_len);
#endif
for (cnt = optlen; cnt > 0; cnt -= len, cp += len) {
opt = cp[IPOPT_OPTVAL];
if (opt == IPOPT_EOL)
break;
if (opt == IPOPT_NOP)
len = 1;
else {
if (cnt < IPOPT_OLEN + sizeof(*cp))
break;
len = cp[IPOPT_OLEN];
if (len < IPOPT_OLEN + sizeof(*cp) ||
len > cnt)
break;
}
/*
* Should check for overflow, but it "can't happen"
*/
if (opt == IPOPT_RR || opt == IPOPT_TS ||
opt == IPOPT_SECURITY) {
bcopy((caddr_t)cp,
mtod(opts, caddr_t) + opts->m_len, len);
opts->m_len += len;
}
}
/* Terminate & pad, if necessary */
cnt = opts->m_len % 4;
if (cnt) {
for (; cnt < 4; cnt++) {
*(mtod(opts, caddr_t) + opts->m_len) =
IPOPT_EOL;
opts->m_len++;
}
}
#ifdef ICMPPRINTFS
if (icmpprintfs)
printf("%d\n", opts->m_len);
#endif
}
/*
* Now strip out original options by copying rest of first
* mbuf's data back, and adjust the IP length.
*/
ip->ip_len -= optlen;
#ifdef _IP_VHL
ip->ip_vhl = IP_VHL_BORING;
#else
ip->ip_v = IPVERSION;
ip->ip_hl = 5;
#endif
m->m_len -= optlen;
if (m->m_flags & M_PKTHDR)
m->m_pkthdr.len -= optlen;
optlen += sizeof(struct ip);
bcopy((caddr_t)ip + optlen, (caddr_t)(ip + 1),
(unsigned)(m->m_len - sizeof(struct ip)));
}
m->m_flags &= ~(M_BCAST|M_MCAST);
icmp_send(m, opts);
done:
if (opts)
(void)m_free(opts);
}
/*
* Send an icmp packet back to the ip level,
* after supplying a checksum.
*/
static void
icmp_send(m, opts)
register struct mbuf *m;
struct mbuf *opts;
{
register struct ip *ip = mtod(m, struct ip *);
register int hlen;
register struct icmp *icp;
struct route ro;
#ifdef _IP_VHL
hlen = IP_VHL_HL(ip->ip_vhl) << 2;
#else
hlen = ip->ip_hl << 2;
#endif
m->m_data += hlen;
m->m_len -= hlen;
icp = mtod(m, struct icmp *);
icp->icmp_cksum = 0;
icp->icmp_cksum = in_cksum(m, ip->ip_len - hlen);
m->m_data -= hlen;
m->m_len += hlen;
#ifdef ICMPPRINTFS
if (icmpprintfs) {
char buf[4 * sizeof "123"];
strcpy(buf, inet_ntoa(ip->ip_dst));
printf("icmp_send dst %s src %s\n",
buf, inet_ntoa(ip->ip_src));
}
#endif
bzero(&ro, sizeof ro);
(void) ip_output(m, opts, &ro, 0, NULL);
if (ro.ro_rt)
RTFREE(ro.ro_rt);
}
n_time
iptime()
{
struct timeval atv;
u_long t;
microtime(&atv);
t = (atv.tv_sec % (24L*60L*60L)) * 1000L + atv.tv_usec / 1000L;
return (htonl(t));
}
/*
* Return the next larger or smaller MTU plateau (table from RFC 1191)
* given current value MTU. If DIR is less than zero, a larger plateau
* is returned; otherwise, a smaller value is returned.
*/
int
ip_next_mtu(mtu, dir)
int mtu;
int dir;
{
static int mtutab[] = {
65535, 32000, 17914, 8166, 4352, 2002, 1492, 1280, 1006, 508,
296, 68, 0
};
int i;
for (i = 0; i < (sizeof mtutab) / (sizeof mtutab[0]); i++) {
if (mtu >= mtutab[i])
break;
}
if (dir < 0) {
if (i == 0) {
return 0;
} else {
return mtutab[i - 1];
}
} else {
if (mtutab[i] == 0) {
return 0;
} else if(mtu > mtutab[i]) {
return mtutab[i];
} else {
return mtutab[i + 1];
}
}
}
