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Re: RedBoot sequencenumber generation
>>>>> Roland =?iso-8859-15?q?Ca=DFebohm?= writes:
> Hello Mark,
> thanks for helping.
> In most cases it works, but if the initial sequencenumber, which
> is now a pseudo random number, is anyhow in the window of the
> TIME_WAIT connections of the host I get the old problem.
> The SYN packet don't get a responce and will be retransmitted
> on and on with the same sequencenumber.
Retransmitting the same seqnum with the SYN is okay. Interestingly,
the RFCs state that while in the TIME_WAIT state, the server refuses
connection requests using the same tcp socket pair. In the tcpdump
you sent, the second connection uses a different socket pair (port
7800 vs 7801). Some BSD stacks are more stringent and refuse to reuse
the local port number while in TIME_WAIT. It looks like this is the
problem you are running into.
However, there is hope. Most BSD implementations allow a new
connection in TIME_WAIT iff the new seqnum is greater than the
final seqnum of the connection in TIME_WAIT. So, here's the same
patch, but with an extra manipulation of initial_seqnum when an
active close FIN is received from the server.
--Mark
Index: redboot/current/src/net/tcp.c
===================================================================
RCS file: /cvs/ecos/ecos/packages/redboot/current/src/net/tcp.c,v
retrieving revision 1.11
diff -u -p -5 -r1.11 tcp.c
--- redboot/current/src/net/tcp.c 21 Dec 2003 13:17:52 -0000 1.11
+++ redboot/current/src/net/tcp.c 16 Mar 2004 17:02:20 -0000
@@ -58,10 +58,12 @@
#include <cyg/hal/hal_if.h>
#define MAX_TCP_SEGMENT (ETH_MAX_PKTLEN - (sizeof(eth_header_t) + sizeof(ip_header_t)))
#define MAX_TCP_DATA (MAX_TCP_SEGMENT - sizeof(tcp_header_t))
+/* setting this to 1 is technically wrong, but BSD does it too... */
+static int initial_seqnum = 1;
/* sequence number comparison macros */
#define SEQ_LT(a,b) ((int)((a)-(b)) < 0)
#define SEQ_LE(a,b) ((int)((a)-(b)) <= 0)
#define SEQ_GT(a,b) ((int)((a)-(b)) > 0)
@@ -479,10 +481,11 @@ __tcp_handler(pktbuf_t *pkt, ip_route_t
return;
}
s->state = _ESTABLISHED;
s->ack = ntohl(tcp->seqnum) + 1;
s->seq = ntohl(tcp->acknum);
+ initial_seqnum += 64000;
__timer_cancel(&s->timer);
send_ack(s);
break;
case _LISTEN:
@@ -523,10 +526,11 @@ __tcp_handler(pktbuf_t *pkt, ip_route_t
} else if ((tcp->flags & TCP_FLAG_ACK) &&
ntohl(tcp->acknum) == (s->seq + 1)) {
/* we've established the connection */
s->state = _ESTABLISHED;
s->seq++;
+ initial_seqnum += 64000;
BSPLOG(bsp_log("ACK received - connection established\n"));
}
break;
@@ -543,10 +547,12 @@ __tcp_handler(pktbuf_t *pkt, ip_route_t
BSPLOG(bsp_log("FIN received - going to _CLOSE_WAIT\n"));
s->ack++;
s->state = _CLOSE_WAIT;
+
+ initial_seqnum = ntohl(tcp->seqnum) + 64000;
}
/*
* Send an ack if neccessary.
*/
if (s->ack != ack || pkt->pkt_bytes > (tcp->hdr_len << 2))
@@ -643,10 +649,13 @@ void
__tcp_poll(void)
{
__enet_poll();
MS_TICKS_DELAY();
__timer_poll();
+
+ /* rfc793 says this should be incremented approx. once per 4ms */
+ initial_seqnum += 1000 / 4;
}
int
__tcp_listen(tcp_socket_t *s, word port)
@@ -890,11 +899,11 @@ __tcp_open(tcp_socket_t *s, struct socka
s->his_port = host->sin_port;
s->pkt.buf = (word *)s->pktbuf;
s->pkt.bufsize = ETH_MAX_PKTLEN;
s->pkt.ip_hdr = (ip_header_t *)s->pkt.buf;
s->pkt.tcp_hdr = (tcp_header_t *)(s->pkt.ip_hdr + 1);
- s->seq = (port << 16) | 0xDE77;
+ s->seq = initial_seqnum;
s->ack = 0;
if (__arp_lookup((ip_addr_t *)&host->sin_addr, &s->his_addr) < 0) {
diag_printf("%s: Can't find address of server\n", __FUNCTION__);
return -1;
}
--
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