Refer to RFC2012, tcpAttemptFails is defined as following:
tcpAttemptFails OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times TCP connections have made a direct
transition to the CLOSED state from either the SYN-SENT
state or the SYN-RCVD state, plus the number of times TCP
connections have made a direct transition to the LISTEN
state from the SYN-RCVD state."
::= { tcp 7 }
State changes of SYN-RCVD to CLOSED, SYN-SENT to CLOSED and SYN-RCVD to
LISTEN should be counted to TCP_MIB_ATTEMPTFAILS.
Following state changes does not be counted to TCP_MIB_ATTEMPTFAILS by
the kernel.
SYN-SENT state => CLOSED
TCP A TCP B
1. LISTEN CLOSED
2. <-- <SEQ=Z><CTL=SYN> --> SYN-SENT
3. --> SEQ=X><ACK=Z+1><CTL=RST> --> CLOSED
SYN-RECEIVED state(came from SYN-SENT state) => CLOSED
TCP A TCP B
1. LISTEN CLOSED
2. <-- <SEQ=Z><CTL=SYN> --> SYN-SENT
3. --> <SEQ=X><ACK=Z+1><CTL=SYN> SYN-SENT
4. <-- <SEQ=Z+1><ACK=X+1><CTL=ACK> --> SYN-RECEIVED
3. --> <SEQ=X+1><ACK=Z+2><CTL=RST> --> CLOSED
SYN-RECEIVED state(came from SYN-SENT state) => CLOSED
TCP A TCP B
1. LISTEN CLOSED
2. <-- <SEQ=Z><CTL=SYN> --> SYN-SENT
3. --> <SEQ=X><ACK=Z+1><CTL=SYN> SYN-SENT
4. <-- <SEQ=Z+1><ACK=X+1><CTL=ACK> --> SYN-RECEIVED
3. --> <SEQ=X+1><ACK=Z+2><CTL=SYN> --> CLOSED
SYN-RECEIVED state => LISTEN
TCP A TCP B
1. LISTEN LISTEN
2. ... <SEQ=Z><CTL=SYN> --> SYN-RECEIVED
3. (??) <-- <SEQ=X><ACK=Z+1><CTL=SYN,ACK> <-- SYN-RECEIVED
4. --> <SEQ=Z+1><CTL=RST> --> (return to
LISTEN!)
5. LISTEN LISTEN
SYN-RECEIVED state => LISTEN
TCP A TCP B
1. LISTEN LISTEN
2. ... <SEQ=Z><CTL=SYN> --> SYN-RECEIVED
3. (??) <-- <SEQ=X><ACK=Z+1><CTL=SYN,ACK> <-- SYN-RECEIVED
4. --> <SEQ=Z+1><CTL=SYN> --> (return to
LISTEN!)
5. LISTEN LISTEN
Patch to kernel 2.6.15.4 as following:
diff -Nur a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
--- a/net/ipv4/tcp_input.c 2006-02-23 09:20:24.659262056 +0900
+++ b/net/ipv4/tcp_input.c 2006-02-23 09:28:50.772321176 +0900
@@ -4003,6 +4003,7 @@
*/
if (th->rst) {
+ TCP_INC_STATS_BH(TCP_MIB_ATTEMPTFAILS);
tcp_reset(sk);
goto discard;
}
@@ -4290,6 +4291,8 @@
/* step 2: check RST bit */
if(th->rst) {
+ if(sk->sk_state == TCP_SYN_RECV)
+ TCP_INC_STATS_BH(TCP_MIB_ATTEMPTFAILS);
tcp_reset(sk);
goto discard;
}
@@ -4303,6 +4306,8 @@
* Check for a SYN in window.
*/
if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
+ if(sk->sk_state == TCP_SYN_RECV)
+ TCP_INC_STATS_BH(TCP_MIB_ATTEMPTFAILS);
NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
tcp_reset(sk);
return 1;
diff -Nur a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
--- a/net/ipv4/tcp_minisocks.c 2006-02-23 09:20:24.660261904 +0900
+++ b/net/ipv4/tcp_minisocks.c 2006-02-23 09:26:07.432152656 +0900
@@ -591,8 +591,10 @@
/* RFC793: "second check the RST bit" and
* "fourth, check the SYN bit"
*/
- if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN))
+ if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) {
+ TCP_INC_STATS_BH(TCP_MIB_ATTEMPTFAILS);
goto embryonic_reset;
+ }
/* ACK sequence verified above, just make sure ACK is
* set. If ACK not set, just silently drop the packet.
-
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