Troubleshooting Your Local Area Network

Posted on January 2nd, 2017

Troubleshooting Your Local Area Network

Router port settings

Today's Ethernet chips Auto sync with too many variables. It's best to turn Auto OFF and fix the port facing Fiber Internet Center (FIC) to 100 Full Duplex. With different manufacturers of chips there is no RFC they follow to determine a match up ((3 different speeds x 2 Duplex settings) x 2 cables , straight or cross over). When left in Auto devices can flip to a mismatch even if not rebooted. Auto setting is the main cause of slowness. A compatibility problem often arises even amongst the same products of a single manufacturer. This is also true in your LAN as well as facing the FIC gateway. In the LAN the most common points are firewall to switch , switch to another, switch wireless router, switch to desktops....etc. A $50 switch or $100 firewall often designed for DSL, does not allow manual settings of the port. This setting is something you should be aware of befoee you buy it. We have also seen IT engineers use a $100 firewall designed for DSL with a 5 meg/sec throughput when the firewall is enabled. Sometimes they clearly state that it's only good for a 5 person office, but the words DSL alone should be an indicator that it will limit your fiber Internet experience. It's best for the device facing FIC to have a manual setting and be able to display RX and TX port errors. These errors are true indications of repeat packets and cause of slowness. Usually, one side sees the other in the half duplex mode.

Firewall Settings

Often have Virtual Private Networks (VPN), State full Packet Inspection (SPI), or other taxing features turned on. Firewalls have complex code and power cycling a once operational firewall will often clear up any problems. However, noticing how busy a VPN has become or number of VPNs operational can be an indication of the CPU can't handle the throughput. Throughput is the amount of traffic that can pass through after the firewall has processed it. VPNs must have every packet leaving encrypted and every packet arrived decrypted. SPI feature checks every packet leaving or entering your LAN. Together these two features alone often bring a firewall to it's knees. Check your firewalls tech specs, not the marketing hype specs.

Wireless office routers or access points

The fact that wireless works at a satisfying level at all is amazing in a large office. Never, think your network is slow as a result of a wireless issue always check perform ping and trace routes using a physical connection. If your thinking your internet access is slow using a wireless laptop, think again. Multiple wireless devices often interfere with each other on the same frequencies. Channels are not the same as Frequencies. What can be Channel 1 for one N-router is another devices 1-4 on a G devices. You may only notice it when both are active at the same time. You can't see the packets traveling in the air - so you don't know, it's not the device, just because it hasn't been in the past. You must RF sweep the area. It could be someone's new wireless phone using a harmonic frequency. Never, think your network is slow as a result of a wireless issue always check perform ping and trace routes using a physical connection.

Infected Computers , bit-torrent and other peer-to-peer issues

Check your bandwidth utilization graphs. Viruses, worms, malware and peer-to-peer applications are often hidden and difficult to detect. Sometimes the person's machine with the issue is the last to detect a slowness problem. Check internal network for unusual traffic that may indicate such infection. Often the problem is local, isolated to the LAN's NATed ip address space. Other times it may be happening through the Internet. We have seen complex issues such as; Firewall allows all packets to leave the LAN, a cracked machine makes a request to remote site. The site begins downloading something requested by the machine. That same machine may become a reflector and repeat the download to many others. The real complex ones are when it happens occasionally.

Domain Name Service (DNS) Hammering

Avoid hammering DNS. DNS is often performed by your NAT device in your LAN. It is best to configure a seperate machine in the network to perfrom this function. Since it is easy to make any computer preform DNS services for your LAN, it's best not to pile on this taks to your firewall and NAT devices. Viruses or Microsoft bugs attempting continuous record zone transfers and record updates are a common cause of slowness. You notice it when you tell your browser to go to a new site. It seems to take a long time before the site begins to load. This is often an indication that something is hammering your DNS. DNS is often performed by your NAT device in your LAN. Either situation will create a feeling of slowness for every domain name lookup.

Running Internet Speed Tests

Let's get real for a minute. Here's how this really works.

You found a link on the net to test your connection. It tests your DSL at home just fine at 9PM. It tells you that it sees a nice 1.2 megabits/per second and your DSL is only 1.5 megabits. After all no server outside of the LAN itself can give a more accurate reading through router hops.

That speed test server may have a 100 meg/second port on a network that has 10 other machines all connected to a DS3 or 100 meg/sec connection. So measuring your DLS line together with 15 others isn't very difficult for that server. That's only 20 meg/sec. If the other machines on that server's network are not running traffic, it has enough bandwidht to test.

Now lets say it's 5 cable users and 10 DSL users , the cable users are at 6 meg/sec, that equals 30 meg/sec of cable + 15 meg/sec of DSL users that would normally top out a DS3 circuit. However, the server cpu and memory have been exceeded and it's doing page swapping. So the the top speed the server measures is now just 30 meg/sec. How do you think the readings of those running the tests are effected. That's right the get a lower result.

FIC runs a speedtest server at . The server has a GigE port, connected to a router with almost 10 gigabits/sec of internet access. The server can't go that fast. Since most test machines are only connected on 100 meg FastE ports, you can imagine that a server with that much Internet and a GigE connection becomes a very popular destination to test. So, it too can get loaded.

How to report Slowness

Fiber Internet Center has abundance of bandwidth and Internet paths. More than 300 BGP sessions in many locations, connected all over the world, so you should not be experiencing slowness over our network. Do not be confused that network slowness equals the slow responce of a single site. That site you are accessing could have a network issue of it's own. Or it's internet provider may have a temporary issue that will correct itself. Therefore try several sites before looking into your LAN or contacting FIC.

The Network Tools page will allow you to test outside your network to a specific site. It will let you compare the results from inside your network.

Before reporting slowness, check your LAN. If that looks fine we will check the port facing your network for RX and TX errors, CRC and fragmented packets. If we see no errors, there's a 98% chance it's inside your network.

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