Latest Posts

802.11 Wireless Channel Planning

Different Technology

I used to work with Motorola Canopy wireless gear back in the day. It was great ptmp wireless gear. The carrier to interference ratio on this gear was 3 dB, which meant that you could provide extremely reliable wireless links in high RF congested areas. Of course this was proprietary based equipment that didn’t come close to the contention based CDMA/CA 802.11 stuff. I was extremely spoiled when using the Motorola canopy line. It just worked.

802.11 Wireless Channel Planning

Why am I bringing up all this when talking about 802.11 wireless channel planning? Well it’s because of the preconceived notion that using all the 2.4Ghz 802.11 channels may be a good thing (including overlapping channels). At first, I though, just let the AP’s pick the best channel between 1-11 and that I would be good to go. Well that wasn’t the best solution as AP’s were selecting channels 1,3,4,7,10, etc. My thoughts were spurred on by this twitter discussion with wireless guru, Keith Parsons.

Javier S. “What’s better, SNR of 20db between two AP’s on channel 1 or SNR of 20db between AP on channel 1 and AP on channel 3?”
Keith P. “I’d go with the two on the same channel, given a choice. At least they’d ‘Play Nice’ with each other rather than ACI fighting.”
Javier S. “So is it CSMA/CA that works better at detection if interference is on same channel?”

Keith P. “It is the difference between how 802.11 deals with CCI vs ACI.”
Javier S. “So based on CCA, you would rather detect noise and back off rather than face possible data corruption from ACI.?”

The last question wasn’t answered. Basically I needed to do my homework and I would suggest you do the same. Check out the following link:

In the above article Andrew really dives into understanding how CDMA/CA works. What I gathered what that wifi can use carrier sense techniques in order to back off in order to avoid possible frame corruption. Keith’s statement of “AP’s on the same channel will likely play nice with each other” will allow carrier sense to do its job.


Ok, so I started doing some more research which lead me to my safaribooks account and checking out a CWNA (certified wireless network administrator) study guide book. The book defines CCI as co-channel interference or “unnecessary medium contention overhead that occurs because all the AP’s are on the same channel.” (Coleman and Westcott) Basically you have wireless devices following the rules of CDMA/CA.

Now ACI is defined as adjacent channel interference and is what you get when you use channels that overlap with one another. The only non-overlapping channels in 2.4Ghz are 1,6,11. When Keith suggests that he would rather see two AP’s on the same channel instead of two using overlapping channels such as 1 and 3, it’s because the 1 and 3 will give you ACI. ACI will cause re-transmits due to corruption of frames. You will rather want CDMA/CA to work as it should instead of facing re-transmits due to corrupt frames.


Where did this lead me? Well, I turned off the AP’s auto channel feature and went back to only using channels 1, 6, and 11. I hard set the channels myself and performed a site survey. My goal was to try to maximize the SNR between any two AP’s that my client could see that were on the same channel. At the end of the day, I’m seeing better performance especially since we just doubled the number of access points we used to have. I had to also play around with the minimum basic rate and power output levels as well in order to achieve maximum optimization. Hopefully this helps explain why proper channel planning is extremely important.


Here’s a busy, but healthy network using 1,6,11 (Shane, disregard my previous comments on your screenshot using only channels 1, 6, and 11) – Courtesy of Metageek Chanalyzer

Metageek wireless channel planning spectrum image


Healthy 2.4Ghz wireless channel planning. I’m working on 5Ghz as well. – Courtesy of Extreme Networks Oneview.

wireless channel planning 5Ghz building map

Wireless channel planning map

Wireless Channel Planning Resources

CWNA: Certified Wireless Network Administrator Official Study Guide: Exam PW0-105, 3rd Edition by David D. Coleman; David A. Westcott


ICX6610 Brocade Switch – Firmware

Ok, so I’m in the process of configuring our spare icx 6610 brocade switch with the same firmware and configuration of one of our main border WAN icx 6610’s that’s running BGP. If our router fails, then I will have a hot spare ready to go while I wait for an RMA. This requires that the space icx 6610 is running router firmware along with an icx 6610 advanced license. The icx 6610 has the ability to run in layer 2 switching mode only or layer 3 mode when the proper firmware is loaded. By default, I had two code versions loaded on the icx 6610. You can identify which code is which by looking at the flash file name. Running the show flash command will give you the following:

#show flash
Stack unit 1:
Compressed Pri Code size = 7189206, Version:07.4.00cT7f3 (FCXR07400c.bin)
Compressed Sec Code size = 8874046, Version:08.0.00aT7f3 (FCXR08000a.bin)
Compressed Boot-Monitor Image size = 370733, Version:07.3.03T7f5
Code Flash Free Space = 49020928

You want to look at the character after FCX in parentheses, I have (FCXR07400c.bin) and (FCXR08000a.bin). The fourth character is an R, which is for routing. If the letter was an S, then that would represent switching only. Right now, I have two different routing versions. Since this is a major rev., there was also a new boot code as well (07.3.03T7f5). Unfortunately, there’s not two slots in the flash to have two different boot codes. If I try to boot back to the 7.4 code, I won’t have the proper boot code that I had before. I will therefore copy another version 8 code to the primary flash space. To do that I will run the following command:

#copy tftp flash <ip-of-tftp-server> <flash-image> primary

In order to boot to the new flash (assuming you don’t need a new boot code), you can then run the following command:

#boot system flash <primary | secondary>

HINT: The default boot is set to boot from the primary location, so if you reboot again without running another command, it will boot back to the default location. If you want to always boot from the secondary flash location, run the following command in config t mode:

(config)#boot system flash secondary

Don’t forget to write mem.


Raspberry Pi network monitoring wifi Smokeping

I finally deployed my wireless raspberry pi network monitoring device at the edge of our wireless network. I installed the smokeping app on the raspberry pi with wheezy via apt-get. I already had a smokeping running on a Linux server, so I setup the raspberry pi to run smokeping in client mode.

Client mode allows the raspberry pi to pull the config from the smokeping server in order to know what tests to run. I setup some fping, DNS, and tcpping tests. This is a great way to test the client’s wireless experience (latency) on the other side of campus. I stuck the raspberry pi behind a bundle of cables to provide for additional attenuation to simulate a user in a worse case scenario. The AP was a few rooms away on a different floor as well. Here are some of the smokeping graphs:

raspberryPi Smokeping monitoring wifi latency

The line with the higher latency is the raspberry pi to google and the lower line is the latency from the smokeping server to google via fping in the picture above.

Here’s a longer term graph painted vi rrdtool by smokeping. There’s some packet loss going on over the wireless interface on the raspberry pi. I may have to move it to a better spot and see how the graphs look afterward. I also want to install iperf and maybe tshark as well.

RaspberryPi smokeping long term wifi latency

Here’s the command to get the raspberry pi running in client mode:

/usr/sbin/smokeping –master-url= –cache-dir=/var/smokeping/ –shared-secret=/var/smokeping/secret.txt

I also had to modify the permissions in the /tmp/smokeping-ms/data/ folder on the server in order to allow the rrds to be modified by apache.

If you’re looking for a small free solution or larger scale paid solution, take a look at I would recommend giving their NetBeez free tier model a try.


Another round of great IT web resources

Check out the new list of great IT web resources below. I’ve also started to use twitter to get involved with the network/wifi community. I don’t really like how twitter works, but that’s where lots of tech enthusiasts are going. The user interface on my nexus 4 android is not very intuitive, but once you figure it out, it’s a great resource. The good thing is that there’s not too much to figure out.

The hardest thing is getting followers, but hey, start posting worthy comments and you might catch a few followers.


IT Resource list: Chicago Network Operators Group You can find some great podcasts here. There’s an extensive list of tools in the armory section. Great info on SDN. Purdue Prof, great insight. Shane blogs very often. Worth the visit. A great wifi gem.

Cisco ASA 5505


I was recently asked by a friend to help out with a config for a cisco ASA 5505. An additional network and VLAN had been added on the ASA 5505 and we needed anyconnect VPN users to be able to access devices on that new network. I’m used to working with checkpoint firewalls, but most firewalls function in a similar fashion. I first logged onto the ASA using the ASDM gui. I checked the firewall rules and access looked to be permitted between the vpn network and the new network. I was a little stumped because it seemed that I needed a little more than just a firewall rule to allow both networks to communicate. I then consoled into the ASA and looked at the routing table. All looked good there. The ASA management interface was able to communicate with devices on both networks, so something else was missing. I then looked at the log files in the ASDM gui and was receiving the following message when trying to rdp into a server after connecting to the VPN:

Asymmetric NAT rules matched for forward and reverse denied due to NAT reverse path failure. An attempt to connect to a mapped host using its actual address was rejected.

I searched cisco for a solution and found a few vague possible solutions. I then pinged Network guru Shane to see if he could point me in the right direction. He hinted that I might have needed a “no nat statement”. Bingo, that worked. Here’s the command that I needed:

Nat(vlan1) 0 access-list vlan1_nat0_outbound

In the ASDM gui, its called a nat exempt statement. This rule makes sure that the internal traffic from the new network going to the VPN network would not get nat’d on its way out.

Since then, I opened up my safari books account back up for $9.99 a month which includes 5 book slots a month. The first thing I checked out was a Cisco Press ASA book. Safari books is a great resource for low cost e-learning. I highly recommend you give it a try. They don’t really advertise the $9.99 subscription, but if you sign up for a free trial, you can still choose the $9.99 pricing. I’m not 100 percent sure if they are still offering this to new users, but its worth checking out. As a network administrator, its important to know the fundamentals. Don’t get stuck in the, “I only know cisco or juniper” mode. If you know the fundamentals, then learning a new syntax and a few different config parameters is not the end of the world. After all you don’t want to limit yourself by putting a vendor name in front of your title, i.e. Cisco Network Administrator or Brocade Network Administrator. Be (emphasis added) the “Network Administrator”.



IPplan – IPAM (IP address management)

For those of you looking to track your IP space in something other than a shared excel sheet, take a look at open source IPplan. All you need is a linux box with apache and a few other components. Installation is not too hard. I would recommend that you use https to access your build that way your authentication is encrypted. If you were using excel, format your columns to the correct format that IP plan will take and export your excel sheet to a tab delimited file. You can then import that file into IPPlan.

IP-plan ip address management

You can easily select multiple addresses to make bulk changes as shown above. You have all the fields you need. There’s even a MAC field that’s visible when you click on the IP link. I like how the change field is updated with a time stamp after a modification. This way you can see who made the latest change.

ipplan request

Another nice feature is the request an IP address page. You can point all your internal clients to this page in order to submit a request for a static IP if you don’t have a ticketing system. You can then be emailed. You can manage DNS as well, but I haven’t dug into that. NMAP can also be implemented into the system to check which IP’s are being used. You can also have the system email you when ip subnets exceed a certain utilization level.

If your interested in a fully supported paid IPAM platform, check out infoblox. You can try out their IPAM software for free. Its highly limited compared to IPPlan, but if your looking to expand your DDI (DNS,DHCP, IPAM) services and you have a budget, this may be a better option for you.

FreeRadius multiple domains

We use freeradius to 802.1x auth our wireless users. We need to authenticate users that may be on one of two domains. We have an issue with trying to authenticate to the global catalog because we have duplicate user account names that have been created on each domain. That wasn’t my idea and it can’t be fixed, so I have to work around the issue. One way to fix the issue is to have the user append the domain when they authenticate, but we don’t want to make things harder for end users.

With freeRadius, I was able to use some freeRadius unlang. I wanted to share some of the config with you. I’m assuming you have most of your freeradius running at a point where you can authenticate against one domain via mschap. Basically my config tries to auth the user by specifying one of the domains in one mschap module and specifies the other domain in a new mschap module. If the user fails on authentication to the first domain, then the second mschap module fires off with the second domain specified.

First, I modified my mschap module found in the following directory: /etc/raddb/modules/mschap

ntlm_auth = “/usr/bin/ntlm_auth –configfile=/etc/samba/smb.conf –request-nt-key –username=%{%{Stripped-User-Name}:-%{%{User-Name}:-None}} –domain=YourFirstDomainName –challenge=%{%{mschap:Challenge}:-00} –nt-response=%{%{mschap:NT-Response}:-00}”

I then created another mschap module instance by editing radius.conf found in the following directory: /etc/raddb/radius.conf

add the following:

mschap NameOfNewModule {
with_ntdomain_hack = yes
ntlm_auth = “/usr/bin/ntlm_auth –configfile=/etc/samba/smb.conf –request-nt-key –username=%{%{Stripped-User-Name}:-%{%{User-Name}:-None}} –domain =YourSecondDomainName –challenge=%{mschap:Challenge:-00} –nt-response=%{mschap:NT-Response:-00}”

Modify your inner-tunnel file with some freeRadius unlang found in /etc/raddb/sites-available/inner-tunnel
Add the following in the authorize { section:


Then add the following unlang in the authenticate { section:


Auth-Type MS-CHAP {
mschap {
reject = 2
if (reject) {

Show me your dashboard…

Zenoss Core open source dashboard

network admin zenoss dashboard

We use zenoss core (open source) to monitor our devices. We have tried zabbix, nagios, and cacti, but Zenoss seems to be the easiest to manage and maintain. I can create custom snmp templates with thresholds that can overlay our rrd graphs. Zenoss also allows you to create email notification triggers based on the severity and threshold set on each graph template. You can see two of these custom graphs in the zenoss dashboard image above. I’m monitoring our wireless dhcp pools and each of the Enterasys Extreme N7 chassis slot CPU’s.

I also have weathermap installed on our linux server that’s also hosting zenoss and the link to the PNG file is placed on the zenoss dashboard. Weathermap is a nice open source network visualization tool. You can create a custom network map that will draw link speeds and colors based on rrd files. I set the weathermap config to point to the zenoss rrd files that can be located under each sub folder in the /opt/zenoss/perf/Devices main directory.

Useful Network Administrator Tools

My boss asked me to submit a list of “inexpensive” network admin tools that would be of value to assist us in managing and maintaining the wired and wireless network on campus. Here are a few tools that would be nice to have:

Throwing star (passive ethernet) LAN tap admin tool

Check out the throwing star
The design allows for inline tapping at 10/100 speeds only. Capacitors within the circuit force the speed down to 100Mbps. Wireshark, here I come.

Cheap 2.4Ghz/5Ghz wireless CPE w/spectrum analyzer

nanostation wifi bridge/analyzer
The ubiquiti nanostation AP/Client wireless device will provide you with a full blown spectrum analyzer. You would have to create your own POE battery pack to be mobile, but the price is right, its cheap. Remember, you pay for what you get. If you can afford something more expensive, try metageek’s wifi chanalyzer pro software. These spectrum analyzers can help identify issues with wireless channel planning and possible wirless interference.

Raspberry Pi Remote Wifi Network Monitoring

wifi admin tool
Buy yourself a raspberry pi from adafruit. It comes with everything you need to deploy a remote monitoring agent. Load up smokeping and put it in client mode. Connect it back to your smokeping server and monitor stats like DNS,web, mail, and a host of other services. You could also load tshark and use your throwing star tap for a remote packet capturing device. You can also use the included wifi adapter to and test your wifi network in remote buildings. iPerf can also be installed to perform wired and wireless speed tests. This would make for a great wifi admin tool.

x86 based tablet

Everyone loves tablets, but in order to run wireshark effectively and a host of other applications natively, you need an x86 device running windows. There are a few nice tablet options out there. The MS surface pro 2 comes in at $899 plus the cost of the keyboard. The base model includes an i5, 64gb ssd, and 4gb ram coming in at 2lbs. HP just released the HP Pro x2 410 G1 tablet which comes in at $999 and includes a keyboard. You get the i5, 4gb ram, but a larger 128gb SSD. The weight without the keyboard comes in at 1.81lbs. The only downside is that your limited to 4gb of ram. I wish apple would come out with a tablet MacBook already. I would prefer apple because you can easily capture raw 802.11 frames without doing much work along with UNIX under the hood. Apple also gives you the ability to boot camp windows as well. They are just a tad bit expensive. We will most likely end up going with HP, as its our vendor of choice. Oh and don’t forget to buy an ethernet dongle as well.

1 2 3 4 5 6