d/freebsd-dev
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Fix an unnecessarily aggressive behavior where mtu clamping begins on first

Browse Source 
retransmission timeout (rto) when blackhole detection is enabled.  Make
sure it only happens when the second attempt to send the same segment also fails
with rto.

Also make sure that each mtu probing stage (usually 1448 -> 1188 -> 524) follows
the same pattern and gets 2 chances (rto) before further clamping down.

Note: RFC4821 doesn't specify implementation details on how this situation
should be handled.

Differential Revision:	https://reviews.freebsd.org/D3434
Reviewed by:	sbruno, gnn (previous version)
MFC after:	2 weeks
Sponsored by:	Limelight Networks
This commit is contained in:
Hiren Panchasara 2015-10-14 06:57:28 +00:00
parent add9ac4043
commit adf43a9279
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=289293
1 changed files with 10 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
sys/netinet/tcp_timer.c
View File

@ -664,9 +664,15 @@ tcp_timer_rexmt(void * xtp)
int isipv6;
#endif
/*
* Idea here is that at each stage of mtu probe (usually, 1448
* -> 1188 -> 524) should be given 2 chances to recover before
* further clamping down. 'tp->t_rxtshift % 2 == 0' should
* take care of that.
*/
if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) ==
(TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) &&
(tp->t_rxtshift <= 2)) {
(tp->t_rxtshift >= 2 && tp->t_rxtshift % 2 == 0)) {
/*
* Enter Path MTU Black-hole Detection mechanism:
* - Disable Path MTU Discovery (IP "DF" bit).
@ -734,9 +740,11 @@ tcp_timer_rexmt(void * xtp)
* with a lowered MTU, maybe this isn't a blackhole and
* we restore the previous MSS and blackhole detection
* flags.
* The limit '6' is determined by giving each probe
* stage (1448, 1188, 524) 2 chances to recover.
*/
if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) &&
(tp->t_rxtshift > 4)) {
(tp->t_rxtshift > 6)) {
tp->t_flags2 |= TF2_PLPMTU_PMTUD;
tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE;
optlen = tp->t_maxopd - tp->t_maxseg;