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Network running slow, where do I start?

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14 replies

by oskar

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I recently took over a network that is a hybrid of Microsoft and Linux. After upgrading from DSL to a T-1 line the whole system started to bog down. Internet Imap emails and folder access have all but given up. Where would I begin looking for a bottle neck in my system? What tools are available? Any suggestions would be great.

thanx

14 replies

by robo_dev

Such as a duplicate IP address, incorrect gateway, interface set to 10MBs when other side is set to 100MBS.

Look for silly things like faulty patch cables, or my favorite...TWO uplinks from one switch to another switch (creating a topology loop).

What devices changed with T-1 install? Router?

I would start with the router. Load up WireShark protocol analyzer (free) and start sniffing packets. This should give you some clues very quickly.

If you don't find anything obviously

by dumphrey

on the network, once again with wireshark. A T1 line has more upload bandwidth, but less download bandwidth then DSL (usually), so and trffic thats only download heavy will be slower.

Are you mail and file servers located on the LAN? And are you using samba for file services? Samba does not always play nice with M$ depending on versions.

Also, I would check disk usage and queu on servers to see if its the network or servers.
With out any other info, I would first check email server and file server performance, then check network performance between hosts and servers (ping, trace route), sniff some traffic on the wires in various places, check cables, and then look at WAN, ISP issues. The ISP will always say its your fault right off the bat, so you need to have eliminated any issue at your end first.

[edit should be reply to OP not robo_dev]

by oskar

The reason for the T-1 upgrade was to handle the new digital phone system. Now I did have a problem when the phone tech plugged the unit into my switch and it started to hand out addresses (yup, DHCP was enabled on the PBX). So the only thing that really changed was that I unplugged the DSL line from my firewall and plugged in the T-1.

by ---tk---

I don't know much about PBX boxes, but I do know that two DHCP servers on one network is a real bad idea... that will take down your network. Also you might want to purge your DNS Cache.... so it has the updated information from the ISP...

I guess a better question would be, what kind of servers do you have in your network? What was handling your DHCP before?

by jdclyde

How many concurrent calls does the system handle?

How much is each call set for (encoding)?

Keep in mind, on top of the packet size you have to add your normal network overhead.

If you turn off the phone, I bet everything would work just fine.

This T1 goes to another location, right?

by dumphrey

ONE DHCP server, and if more then 1 DNS server, they are replicating. That much broadcast can make alot of chatter, and confuse workstations.

Also, voip will eat your bandwidth if you do not have QOS set. Are all your lines/switches at least 100Mbps? Gig would be better...

by jlmorris

Sounds silly, but always best to start at the bottom, but since you changed ISP's I assume that updated the appropriate DNS settings? I forgot to change DNS servers on time after swapping to a new ISP and my network slowed to a crawl.

by robo_dev

then what else did he break?

Did he leave a DNS server enabled?

by oskar

I had to disable DHCP myself. You would think paying a small countries yearly budget on an over-priced Nortel system (then finding out they are filing Bankruptcy) and having QWEST install it, I could get something that actually works. I am pretty sure that all my protocols are correct. I may have a "Dirty" connection through my T-1 because it sounds like I am talking on a cell phone while driving through a canyon on my new system.

by ---tk---

if it sounds like that then somewhere there are packets being dropped...

I would try running traceroute and see where the hold up is...

by oskar

I did have to purge the dns cache out of all my workstations because my samba server is taking care of handing out addresses. I am wondering if perhaps just running my phone system on the Integrated T-1 and all other internet traffic will go back on DSL if that would improve performance. Again, my network was flying before QWEST got their hands on it (Let's not go there today because I WILL go Postal).

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