Detailed Wireless Client Stats with collectd

collectd has always been able to grab interface traffic statistics from Linux. But what if we want to collect data about individual WiFi clients that connect to it? How much bandwidth is each of the clients using?

That information is already being recorded by the wireless driver; all we need to do is to query it. Turns out you can do that with the wl utility. This is Broadcom’s proprietary tool to control and query the wireless interfaces.

To do this, first use wl to get associated stations:

wl -i eth2 assoclist

Given a particular MAC address that is associated to the AP, query its info using sta_info:

# wl -i eth2 sta_info d4:a3:00:aa:bb:cc
 STA d4:a3:00:aa:bb:cc:
     rateset [ 6 9 12 18 24 36 48 54 ]
     idle 0 seconds
     in network 16 seconds
     flags 0x11e03b: BRCM WME N_CAP VHT_CAP AMPDU AMSDU
     HT caps 0x6f: LDPC 40MHz SGI20 SGI40
     VHT caps 0x43: LDPC SGI80 SU-BFE
     tx data pkts: 663916
     tx data bytes: 68730715
     tx ucast pkts: 155
     tx ucast bytes: 42699
     tx mcast/bcast pkts: 663761
     tx mcast/bcast bytes: 68688016
     tx failures: 0
     rx data pkts: 234
     rx data bytes: 73557
     rx ucast pkts: 192
     rx ucast bytes: 62971
     rx mcast/bcast pkts: 42
     rx mcast/bcast bytes: 10586
     rate of last tx pkt: 866667 kbps
     rate of last rx pkt: 780000 kbps
     rx decrypt succeeds: 195
     rx decrypt failures: 1
     tx data pkts retried: 19
     tx data pkts retry exhausted: 0
     per antenna rssi of last rx data frame: -61 -56 -59 0
     per antenna average rssi of rx data frames: -61 -56 -57 0
     per antenna noise floor: -104 -98 -98 0

The “easy way” is probably to write a shell script, invoked via the Exec plugin that calls wl multiple times (once per interface, and once for each WiFi client) and uses grep or awk to get the information we need. This won’t be performant, of course.

wl itself does have quite a fair bit of overhead. It does some verification of the provided interface name. It checks for the Broadcom driver magic to ensure that the interface is a Broadcom device. It then needs to convert the MAC address from the argument string to binary, and vice-versa. Sure, that’s not really much “these days”, but we can definitely do better.

Instead, let’s short-circuit the process and write a plugin that directly collects the data, without going through wl. This way, we avoid creating several new processes for every query.

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Cross-compiling collectd for ASUSWRT

I have been using collectd on my server to monitor traffic (inbound, outbound and to/from the Internet), as well as disk stats because it’s being used as a NAS. So far it has been helpful, observing various graphs to understand patterns, and detecting problems when they happen.

I’m also recording video from a WiFi camera, so I can constantly see traffic that comes into the server. But without visibility on the router itself, I am unable to determine whether the traffic is from the 5 GHz or 2.4 GHz band, or the guest network.

By getting a collectd instance onto the router, we can get those detailed interface statistics separately.

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Extending ASUSWRT Functionality, Part 2

Following up from my earlier post, Asus has released faster and beefier routers. But perhaps the more important change here is that they have moved from MIPS in the RT-N56U to ARM in newer routers. I have also upgraded to the RT-AC68U for better reception and hopefully to fix the poor battery life experienced by my Android tablet.

the Asus N56U and AC68U routers, side by side

After upgrading, I noticed that the method I described back then no longer works. Someone also noticed this, as they translated key portions of my post into Chinese, while pointing out some of the steps that didn’t work.

In this post, I’ll summarize the key changes required to get it working again.

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Hacking Functionality into ASUSWRT Routers

This weekend, I spent some time to replace my aged Linksys WRT54G wireless router, which is running DD-WRT. The WRT54G is slow by today’s wireless standards and since I sync my iOS devices wirelessly, the speed was getting quite unbearable. When I bought my Macbook Pro in 2007, it already has draft 802.11n support and fast-forward to 2012, my iPad (1st generation) and iPhone 5 both support the 5GHz band.

The ASUS RT-N56U wireless router ranks up there on wireless performance, and the “feature” I was really after was a router that can run an alternative firmware such as Tomato or DD-WRT. The really good news is, I figured out how to get the functionality I wanted while still using the official ASUS firmware.

ASUS router photo

For proper reviews and better photos, you might want to check out these other reviews:

Read on to find my short review, as well as how you can run your own programs on the router without using a third-party firmware.

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