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[TCP]: MTU probing

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Implementation of packetization layer path mtu discovery for TCP, based on
the internet-draft currently found at
<http://www.ietf.org/internet-drafts/draft-ietf-pmtud-method-05.txt>.

Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
John Heffner 2006-03-20 17:53:41 -08:00 • committed by David S. Miller
parent 1d60290f27
commit 5d424d5a67
9 changed files with 326 additions and 37 deletions
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36
net/ipv4/tcp_timer.c
View file

@ -119,8 +119,10 @@ static int tcp_orphan_retries(struct sock *sk, int alive)
/* A write timeout has occurred. Process the after effects. */
static int tcp_write_timeout(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int retry_until;
int mss;
if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
if (icsk->icsk_retransmits)
@ -128,25 +130,19 @@ static int tcp_write_timeout(struct sock *sk)
retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
} else {
if (icsk->icsk_retransmits >= sysctl_tcp_retries1) {
/* NOTE. draft-ietf-tcpimpl-pmtud-01.txt requires pmtu black
hole detection. :-(
It is place to make it. It is not made. I do not want
to make it. It is disgusting. It does not work in any
case. Let me to cite the same draft, which requires for
us to implement this:
"The one security concern raised by this memo is that ICMP black holes
are often caused by over-zealous security administrators who block
all ICMP messages. It is vitally important that those who design and
deploy security systems understand the impact of strict filtering on
upper-layer protocols. The safest web site in the world is worthless
if most TCP implementations cannot transfer data from it. It would
be far nicer to have all of the black holes fixed rather than fixing
all of the TCP implementations."
Golden words :-).
*/
/* Black hole detection */
if (sysctl_tcp_mtu_probing) {
if (!icsk->icsk_mtup.enabled) {
icsk->icsk_mtup.enabled = 1;
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
} else {
mss = min(sysctl_tcp_base_mss,
tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)/2);
mss = max(mss, 68 - tp->tcp_header_len);
icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
}
}
dst_negative_advice(&sk->sk_dst_cache);
}