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On 10-12-2014 10:34, Marcelo Ricardo Leitner wrote:
On 09-12-2014 21:37, Julian Anastasov wrote:
Hello,
On Mon, 8 Dec 2014, Marcelo Ricardo Leitner wrote:
Signed-off-by: Marcelo Ricardo Leitner <mleitner@xxxxxxxxxx>
---
Notes:
Hi,
We have a report that not doing so may cause poor load balacing if
applications reuse src port. With a patch like this, it would make
new SYNs on a given connection to drop the old one and start a new
one.
People complained about UDP, such as RADIUS, etc.
I guess, for TCP it is some local client that can benefit
from balancing, it can be also a local testing tool.
So it's a new type of issue, ok. I don't have info on what their application
is, just that it ends up reusing port numbers.
One could say that this reuse can be done on purpose and carefully
as a way to cause poor load balancing to cause a DoS.
Thing is, I'm unsure if we really should do this, as it may end up
doing more harm than good.
WDYT? And if we do additional checks, like at least validating seq
number, would it be better?
I think, checking of SEQ will not help, tw_recycle
works by checking the timestamp option, SEQ of SYN is
arbitrary.
I thought for time wait assassination it would have to use a bigger seq
together with the timestamps. But anyway, Windows (since Vista, even 8)
doesn't use timestamps by default, unfortunately. Windows is not really
involved, it's just to have that in mind, as by relying on timestamps we would
be limiting the solution.
Also, not all connections can be expired, for
example controlling conns (FTP CTL), i.e. our attempt
to expire conn will not succeed if FTP DATA is still in
progress (cp->n_control != 0 check) or in some FW/TW state.
Interesting. I hadn't thought about this case.
Thanks,
Marcelo
net/netfilter/ipvs/ip_vs_core.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index
990decba1fe418e36e59a1f081fcf0e47188da29..e81a9ac3c7e4e25fb14953b7faa4ace054f51274
100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -1036,6 +1036,14 @@ static inline bool is_new_conn(const struct sk_buff
*skb,
}
}
+static inline bool is_new_conn_expected(const struct ip_vs_conn *cp)
+{
+ if (cp->protocol != IPPROTO_TCP)
+ return false;
+ return (cp->state == IP_VS_TCP_S_TIME_WAIT) ||
+ (cp->state == IP_VS_TCP_S_FIN_WAIT);
For conns with cp->flags & IP_VS_CONN_F_NOOUTPUT the
FIN_WAIT state is problematic, we see only packets from
client (eg. DR method) and can not tell if server has sent its
FIN packet. I.e. diverting large transfer from one real to
another will lead to sending of FIN+ACKs from client to
new place.
So, I'm not sure if we should restrict the FW state, eg:
return (cp->state == IP_VS_TCP_S_TIME_WAIT) ||
(cp->state == IP_VS_TCP_S_FIN_WAIT &&
(cp->flags & IP_VS_CONN_F_NOOUTPUT) &&
time_after_eq(jiffies + cp->timeout,
cp->timer.expires + 1 * HZ));
I.e. for INPUT+OUTPUT IP_VS_TCP_S_FIN_WAIT is
not expired because only one side sent FIN. For
And when the other side send it too, it will be in TIME_WAIT then. Ok.
INPUT-ONLY we can allow expiration in IP_VS_TCP_S_FIN_WAIT,
for example, when FIN+ACK was not seen recently, say in
last second?
That's interesting.
If such checks look dangerous we can try to expire
only in IP_VS_TCP_S_TIME_WAIT.
Or only enable it within some sysctl, like we have expire_nodest_conn? We
could have a "(tcp_)rebalance_on_port_reuse" or something like that.
Actually, I'm more for this tunable than a timeout, as it would allow one to
easily rebalance the cluster when one add new nodes. More like:
return (cp->state == IP_VS_TCP_S_TIME_WAIT) ||
(sysctl_tcp_reschedule_on_syn &&
cp->state == IP_VS_TCP_S_FIN_WAIT &&
(cp->flags & IP_VS_CONN_F_NOOUTPUT));
Then we play safe, leave that sysctl_tcp_reschedule_on_syn off by default, but
one may use it when applicable. WDYT?
Marcelo
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