java - Intermittent failures connecting to 127.0.0.1, no failures when connecting to IP (eth0) -

java - Intermittent failures connecting to 127.0.0.1, no failures when connecting to IP (eth0) -

i have servlet based application running on tomcat(7.0.53), oracle jvm (1.7.x) , centos(6.5). there script peridically "sainity checks" application issuing get request (every 10sec).

i encountering next issue:

when under normal (moderate) load (~4k parallel connections), of sanity checks fail connect timeout (approximately every 10th 20th request fails). connection timeout configured on client 120s. happning only when connecting 127.0.0.1 (loopback), connecting <ip> of real lan interface (eth0) not have issue*. so:

curl <args> http://127.0.0.1:<port> fails,

curl <args> http://1.2.3.4:<port> not fail.

running tcpdump show server side not send syn-ack in failed cases.

note: out of curiosity, disabled ipv6 back upwards (net.ipv6.conf.all.disable_ipv6 = 1) , issue dissapeared. before, ipv6 not used, ipv6 loopback (lo) interface initialized , application bound available interfaces (127.0.0.1, ::1 , <ip>). on eth interface ipv6 not initialized @ all.

what possilbe reasons kind of behaviour?

any ideas furthure troubleshooting issue?

java linux tcp network-programming ip