Decode CDP or LLDP packets with tcpdump

If you don’t have LLPDd available you may use tcpdump to get all LLDP information. Bellow are a few examples on how you can do it.CDP

## This will often show you the Cisco chassis switch, then use your firms asset management software to find the upstream switch.
## -s 1500 capture 1500 bytes of the packet (typical MTU size)
## ether[20:2] == 0x2000 – Capture only packets that are starting at byte 20, and have a 2 byte value of hex 2000

interface=eth0 ; tcpdump -i ${interface}-v -s 1500 -c 1 'ether[20:2] == 0x2000'


## Switch:

interface=eth0 ; tcpdump -i ${interface} -s 1500 -XX -c 1 'ether proto 0x88cc'

## Port and CDP Neighbor Info:

interface=eth0 ; tcpdump -i ${interface} -v -s 1500 -c 1 '(ether[12:2]=0x88cc or ether[20:2]'

If you need more info about CDP or LLDP have a look on the links bellow.
CDP stands for Cisco Discovery Protocol, which is a layer 2 protocol and is used to share information about other directly connected Cisco equipment (WikiPedia). LLDP stands for Link Layer Discovery Protocol and replaces CDP. LLDP is a vendor-neutral Data Link Layer protocol used by network devices for advertising of their identity, capabilities and neighbours (WikiPedia).This is useful to find out what VLAN your network interface is connected to (assuming that your using tagged VLANS), or what port am I plugged into on which switch.


digiKam – Facebook export

I use digiKam as my primary photo manager, it’s a great professional tool for those work with media. Maybe you are one of these and you didn’t even noticed, look at your mobile phone probably you have hundreds (maybe even thousands) of pictures on it. If you sum the ones you take with your camera it will be even more, so after a few years some of us may have more than 100.000 pictures.


This is why you need a photo manager and I would strongly recommend digiKam. I’ve been using it for years and I love it.

One part of taking pictures is be able to share them, digiKam supports exports to several social media web sites; Facebook, Igmur, Twitter, Flickr, etc.

Nevertheless the integration with Facebook is not working properly, and I doubt that the digiKam developers can do something here as it looks more of a Facebook issue. I’ve came out with a workaround that may help go around this issue if want to use the Facebook export function. Just follow these easy steps (I’ve done this with digiKam v5, but it will also work on v4):

  1. With your default browser log in to Facebook.
  2. Open digiKam from a console, just type digiKam on the command line.
  3. Inside digiKam go to menu export, choose export to Facebook.
  4. On the export dialog press change account.
  5. You’ll see that in the browser it just states success, nevertheless you don’t see the authentication link that you need to use to paste into the plugin dialogue.
  6. On the console where you started digiKam you have some of the debugging info of what is happening
    1. digiKam uses OAuth to authenticate with Facebook so look for a line like:
      • OAuth URL: QUrl(“
  7. Copy the content of that line starting on “https://…token” (without the quotes)
  8. Enable debug mode on your browser (I use Firefox CTRL+SHIFT+C or F12)
  9. On the debug window select network and persistent, see selected options on image bellow:Spectacle.V19137
  10. Paste the URL that you got on this list step 7 on the browser
  11. On the debug window you should be able to see an entry like the one bellow, with a right click choose copy locationSpectacle.V19190
  12. Go to the digiKam Facebook export plugin window and just paste.

Now you can share all those pictures to world 🙂

Just select the pictures you want, use the export plugin, choose your Facebook album (or create a new one within digiKam), choose to resize (or not the images). If you create a new album be careful with the the permissions you wish for the album, on the Add Album option you’ll be able to select who do you wish to share your pictures. By default all your friends will be able too see it, but this may not be right for all the albums so just choose careful your options, usually I choose only me and then on Facebook page I add who I want to share it with.

More about digiKam

  • A professional digital photo management application for KDE (it will work on Linux, Windows and MacOS), which makes importing and organizing digital photos a “snap”. The photos are organized in albums which can be sorted chronologically, by folder layout or by custom collections
  • Powerful, fast and automated tagging
  • An easy-to-use interface is provided that enables you to connect your camera directly and preview, download and/or delete your images
  • A Light Table function is provided. This tool assists artists and photographers with reviewing their work ensuring the highest quality only
  • Common filters are available out of the box, with side by side previews
  • Extensible by the use of plugins and recipes

Hope you enjoy this tool as much as I do.

Have fun,

Pedro Oliveira


udev – Change network card label


Several time I’ve been asked how to rename a network card label on a Linux system, this can be achieve by following the steps mentioned bellow.

Stop networking

service networking stop

The network kernel module needs to be removed, but first you need to identify the right kernel module

sudo lspci -k | grep -i -A4

ethernet 04:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 07) Subsystem: Sony Corporation Device 9099
Kernel driver in use: r8169
Kernel modules: r8169

Reload rules

udevadm control –reload-rules

Edit udev rules by editing the /etc/udev/rules.d/*persistent-net.rules, in the example bellow we will set previous eth0 to eth5

# PCI device 0x10ec:0x8168 (r8169)

SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”d4:3d:7e:xx:xx:xx”, ATTR{dev_id}==”0x0″, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth5″


Remove the module in question

rmmod r8169

I’m using an realtek chip on my Vaio laptop, you should replace r8169 with the module in your system
Request device events from the kernel

udevadm trigger

Start network

service network restart

Et voila! You should have now a network card named eth5 on your system.
If you want to learn more about udev and udevadm check the info here or just type man udevadm on the command line.

Have fun,

Pedro Oliveira

Testing BTRFS – Performance comparison on a high performance SSD (BTRfs vs Ext4)

Today I was reading about btrfs and as never used it before I thought in giving it a try.
On my laptop I have a ssd with 256GB, there I created 2 LVM2 volumes to use and test btrfs.
It’s not the ideal solution because there’s a LVM layer but I’m not in the mood for backup,erasing,installing,erasing and installing. So the tests I’m going to do are just on the FS itself, not on all the layers that btrfs supports. A good thing in using a ssd card is that the access time is equal for all the block device and the data position on the block device is not accountable, so this is a very good opportunity to have measurements both on ext4 and btrfs.
Here’s the benchmark architecture, tools and setup:


Linux MartiniMan-LAP 2.6.38-31-desktop #1 SMP PREEMPT 2011-04-06 09:01:38 +0200 x86_64 x86_64 x86_64 GNU/Linux

LVM lv creation command:

lvcreate -L 20G -n TestingBTRfs /dev/mapper/system
lvcreate -L 20G -n TestingExt4fs /dev/mapper/system

LVM lvdisplay output:

--- Logical volume ---
LV Name /dev/system/TestingBTRfs
VG Name system
LV UUID zBYf0d-metk-VC9U-YkjE-z1Ts-NMLb-HzYmrJ
LV Write Access read/write
LV Status available
LV Size 20.00 GiB
Current LE 5120
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:3

--- Logical volume ---
LV Name /dev/system/TestingExt4fs
VG Name system
LV UUID FJEfiv-Hs9W-zGuV-sJIo-3INN-gh52-YgmsVl
LV Write Access read/write
LV Status available
LV Size 20.00 GiB
Current LE 5120
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:4

FS creation command:

mkfs.ext4 /dev/system/TestingExt4fs
mkfs.btrfs /dev/system/TestingBTRfs


model name : Intel(R) Core(TM)2 CPU T7200 @ 2.00GHz



Mount command (as you can see I didn’t do any optimizations, noatime, etc):

/dev/mapper/system-TestingBTRfs on /mnt/btrf type btrfs (rw)
/dev/mapper/system-TestingExt4fs on /mnt/ext4 type ext4 (rw)

Test software:

'Iozone' Filesystem Benchmark Program

Version $Revision: 3.373 $
Compiled for 64 bit mode.

Command line for the tests:
Command line used:

 ./iozone -Ra -r4k -r8k -r16k -r32k -r64k -r128 -r1024 -r4096k -r16384k -s1g

This command was used in the btrfs and the ext4 volumes.
The options mean:
-R excel/

office compatible format.
-a auto test
-r the record size (you can see I used several (4k,8k…))
-s size of test file (I used 1GB)

Here’s the test results:

And the charts (The scale is logarithmic):

(you may download the data here: [download id=”1″])


As you can see on the charts for sequential reading/writing there’s a performance gain  in BTRfs with the smaller record sizes but the inverse is also true, EXT4 has more performance on larger record sizes.

If you look to the random data access while reading or writing you’ll see that EXT4 is far faster that BTRfs, and this is according to my daily usage pattern would be 70% of the access to my hard drive. To be sincere I’m a bit surprised on such a difference. I know I didn’t tune any of the file systems and the purpose of this benchmark is not having to, just playing with the defaults as most of the installations out there.

Another conclusion that is really simple to understand is that bigger record sizes mean best performance.

For now I think I’ll stick to EXT4 and LVM, who knows if I’ll sometime soon I’ll change to BTRFS, I’ll let it grow and advise you to do the same.


Pedro Oliveira