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ip/tcp: only calculae mss from interface mtu when directly reachable for v6

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we currently do not implement path mtu discovery so for
destinations that are not directly reachable assume the
minimum mtu of 1280 bytes.
This commit is contained in:
cinap_lenrek 2016-11-15 20:28:45 +01:00
parent fdc8187038
commit 1f628ef132
1 changed files with 24 additions and 20 deletions
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44
sys/src/9/ip/tcp.c
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@ -47,7 +47,7 @@ enum
MSL2 = 10,
MSPTICK = 50, /* Milliseconds per timer tick */
DEF_MSS = 1460, /* Default maximum segment */
DEF_MSS6 = 1280, /* Default maximum segment (min) for v6 */
DEF_MSS6 = 1220, /* Default maximum segment (min) for v6 */
DEF_RTT = 500, /* Default round trip */
DEF_KAT = 120000, /* Default time (ms) between keep alives */
TCP_LISTEN = 0, /* Listen connection */
@ -846,32 +846,36 @@ localclose(Conv *s, char *reason) /* called with tcb locked */
/* mtu (- TCP + IP hdr len) of 1st hop */
static int
tcpmtu(Proto *tcp, uchar *addr, int version, uint *scale)
tcpmtu(Route *r, int version, uint *scale)
{
Ipifc *ifc;
int mtu;
ifc = findipifc(tcp->f, addr, 0);
switch(version){
default:
case V4:
mtu = DEF_MSS;
if(ifc != nil)
mtu = ifc->maxtu - ifc->m->hsize - (TCP4_PKT + TCP4_HDRSIZE);
break;
case V6:
mtu = DEF_MSS6;
if(ifc != nil)
mtu = ifc->maxtu - ifc->m->hsize - (TCP6_PKT + TCP6_HDRSIZE);
break;
}
/*
* set the ws. it doesn't commit us to anything.
* ws is the ultimate limit to the bandwidth-delay product.
*/
*scale = Defadvscale;
return mtu;
/*
* currently we do not implement path MTU discovery
* so use interface MTU *only* if directly reachable
* or when we use V4 which allows routers to fragment.
* otherwise, we use the default MSS which assumes a
* safe minimum MTU of 1280 bytes for V6.
*/
if(r != nil && (version == V4 || (r->type & (Rifc|Runi)) != 0)){
ifc = r->ifc;
mtu = ifc->maxtu - ifc->m->hsize;
if(version == V6)
return mtu - (TCP6_PKT + TCP6_HDRSIZE);
else
return mtu - (TCP4_PKT + TCP4_HDRSIZE);
}
if(version == V6)
return DEF_MSS6;
else
return DEF_MSS;
}
static void
@ -1309,7 +1313,7 @@ tcpsndsyn(Conv *s, Tcpctl *tcb)
tcb->sndsyntime = NOW;
/* set desired mss and scale */
tcb->mss = tcpmtu(s->p, s->laddr, s->ipversion, &tcb->scale);
tcb->mss = tcpmtu(v6lookup(s->p->f, s->raddr, s), s->ipversion, &tcb->scale);
tpriv = s->p->priv;
tpriv->stats[Mss] = tcb->mss;
}
@ -1487,7 +1491,7 @@ sndsynack(Proto *tcp, Limbo *lp)
seg.ack = lp->irs+1;
seg.flags = SYN|ACK;
seg.urg = 0;
seg.mss = tcpmtu(tcp, lp->laddr, lp->version, &scale);
seg.mss = tcpmtu(v6lookup(tcp->f, lp->raddr, nil), lp->version, &scale);
seg.wnd = QMAX;
/* if the other side set scale, we should too */
@ -1763,7 +1767,7 @@ tcpincoming(Conv *s, Tcp *segp, uchar *src, uchar *dst, uchar version)
tcb->flags |= SYNACK;
/* set desired mss and scale */
tcb->mss = tcpmtu(s->p, dst, s->ipversion, &tcb->scale);
tcb->mss = tcpmtu(v6lookup(s->p->f, src, s), version, &tcb->scale);
/* our sending max segment size cannot be bigger than what he asked for */
if(lp->mss != 0 && lp->mss < tcb->mss)