?
Solved

iptables causes connection stall

Posted on 2013-01-16
1
Medium Priority
?
673 Views
Last Modified: 2013-01-16
We are having connection stall issues on many of our http servers. As a test I have created a script that connects to the webserver using curl and tries do download a txt file of about 3mb size.

Every now and then the speed goes down to 0 and the connection hangs.

When I disable iptables the problem resolves and everything works ok.

iptables -vL
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
   28  2080 ACCEPT     all  --  any    any     anywhere             anywhere            state RELATED,ESTABLISHED
    0     0 ACCEPT     icmp --  any    any     anywhere             anywhere
    0     0 ACCEPT     all  --  lo     any     anywhere             anywhere
    0     0 ACCEPT     tcp  --  any    any     anywhere             anywhere            state NEW tcp dpt:ssh
    0     0 ACCEPT     tcp  --  any    any     anywhere             anywhere            state NEW tcp dpt:http
   17  1924 REJECT     all  --  any    any     anywhere             anywhere            reject-with icmp-host-prohibited

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 REJECT     all  --  any    any     anywhere             anywhere            reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT 15 packets, 1564 bytes)
 pkts bytes target     prot opt in     out     source               destination

Open in new window


There is couple of routers and firewalls in between.

Any ideas what this could cause?

Ah. I use Centos 6.3 Kernel 2.6.32-279.19.1.el6.x86_64 Iptables version is: iptables-1.4.7-5.1.el6_2.x86_64
0
Comment
Question by:Chris Sandrini
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
1 Comment
 
LVL 11

Accepted Solution

by:
Chris Sandrini earned 0 total points
ID: 38782063
I found the problem.

By default CentOS had ipv_sack enabled which is a good thing. But somehow on the firewall the packages with SACK were dropped because it did not understand what it is.

So there are 2 solutions:

1. Have a modern firewall that understands and accepts SACK
2. Disable SACK on the server with

sysctl –w sysctl -w net.ipv4.tcp_sack=0

Open in new window

0

Featured Post

Get real performance insights from real users

Key features:
- Total Pages Views and Load times
- Top Pages Viewed and Load Times
- Real Time Site Page Build Performance
- Users’ Browser and Platform Performance
- Geographic User Breakdown
- And more

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction We as admins face situation where we need to redirect websites to another. This may be required as a part of an upgrade keeping the old URL but website should be served from new URL. This document would brief you on different ways ca…
Google Drive is extremely cheap offsite storage, and it's even possible to get extra storage for free for two years.  You can use the free account 15GB, and if you have an Android device..when you install Google Drive for the first time it will give…
Connecting to an Amazon Linux EC2 Instance from Windows Using PuTTY.
If you're a developer or IT admin, you’re probably tasked with managing multiple websites, servers, applications, and levels of security on a daily basis. While this can be extremely time consuming, it can also be frustrating when systems aren't wor…
Suggested Courses
Course of the Month13 days, 6 hours left to enroll

777 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question