Solved

Checking for half open connections

Posted on 2004-08-08
8
2,153 Views
Last Modified: 2007-12-19
Hi,

This is really an extension of my previous post. I managed to track down the issue behind high cpu utilization, which was indeed caused by a worm. The worm caused a lot of hosts to open and terminate connections to our servers, leaving them in the TIME_WAIT state. Some hosts had opened thousands of connections to the servers.

How do I track down these half-closed connections on the firewall? A "show conn " gives out a lot of detail. What do I need to look for?

Second question.

While I was trying to track down the infected hosts using a sniffer, a vendor suggested that I use the MSFC on the core switch as a source and filter it on the specific VLAN. How is this different from port mirroring?

The commands I used were

MSFC sniffing ----> set span (msfc) (destination port) filter (vlan_number)
Port sniffing   ----> set span (vlan_number) (destination port)

Each of these methods threw up a completely different set of statistics. What is the difference?
0
Comment
Question by:fullerms
[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
  • 3
  • 2
8 Comments
 
LVL 51

Accepted Solution

by:
ahoffmann earned 20 total points
ID: 11750291
any statefull inspection firewall should manage this automatically, or better give some options like timeouts to close them.
On the other side, it depends on the implementation of your TCP/IP stack on the effected server how it handles such sockets, most likely the OS provides a timeout for such sockets in TIME_WAIT state too.
0
 
LVL 6

Author Comment

by:fullerms
ID: 11750479
Agreed. The firewall does have timeouts values for half open connections.

My question is, how do I check for half open connections on the firewall? At any given point of time, the firewall is handling 3 times the normal number of connections. We need information on half open connections to track down the offending IPs. How do I go about this?
0
 
LVL 51

Expert Comment

by:ahoffmann
ID: 11751154
> ..  how do I check for half open connections on the firewall?
read your docs of the firewall. There is no general answer, it's specific to your firewall.
0
Raise the IQ of Your IT Alerts

From IT major incidents to manufacturing line slowdowns, every business process generates insights that need to reach the people required to take action. You need a platform that integrates with your business tools to create fully enabled DevOps toolchains.

You need xMatters.

 
LVL 6

Author Comment

by:fullerms
ID: 11751563
The firewall is a Cisco Pix v 6.3(3).
0
 
LVL 6

Author Comment

by:fullerms
ID: 15898269
I wouldn't like to be called a miser, but I feel that a refund would be more appropriate. I did not get the answer that could have helped me.
0
 
LVL 20

Expert Comment

by:Venabili
ID: 15898337
You were pointed in the right direction what to read. You never said if you checked your documentation...
0

Featured Post

Retailers - Is your network secure?

With the prevalence of social media & networking tools, for retailers, reputation is critical. Have you considered the impact your network security could have in your customer's experience? Learn more in our Retail Security Resource Kit Today!

Question has a verified solution.

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

Wikipedia defines 'Script Kiddies' in this informal way: "In hacker culture, a script kiddie, occasionally script bunny, skiddie, script kitty, script-running juvenile (SRJ), or similar, is a derogatory term used to describe those who use scripts or…
Do you have a windows based Checkpoint SmartCenter for centralized Checkpoint management?  Have you ever backed up the firewall policy residing on the SmartCenter?  If you have then you know the hassles of connecting to the server, doing an upgrade_…
This is a high-level webinar that covers the history of enterprise open source database use. It addresses both the advantages companies see in using open source database technologies, as well as the fears and reservations they might have. In this…
Monitoring a network: why having a policy is the best policy? Michael Kulchisky, MCSE, MCSA, MCP, VTSP, VSP, CCSP outlines the enormous benefits of having a policy-based approach when monitoring medium and large networks. Software utilized in this v…

696 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