Using vconfig to set vlan tagged interface with 802.1p CoS priority bits set

tux This is just quick how-to on setting up vlan interface on a Linux system. As this is in lengths described elsewhere I will stick just to the commands and brief explanations.

The first thing to do is to get the “vlan” package as it is not normally installed. The other bit is the 8021q kernel module which is not normally loaded but is present on Debian-based systems by defualt.

Checking the state of the module:

lsmod | grep 8021q

if this will return empty result you must load the module using mordprobe

modprobe 8021q

and verify again with lsmod as before.

Now the system is ready to get new tagged interfaces

vconfig add eth0 X

Where eth0 is your physical interface and X is the VLAN ID you want the new interface to be tagged with. The command will have an output saying that interface eth0.X has been created. This is great but you also must now somehow specify what pbit setting do you want in there as by default egress traffic is by default priority 0. In order to make lets say ping ICMP packets marked with CoS we must create an egress map for the default priority (o) in which we will re-map it to whatever we want.

vconfig set_egress_map eth0.X 0 7

In this example I have re-mapped the default priority 0 to egress priority 7

This setup can be made permanent by adding the module name in /etc/modules and adding the relevant lines in the interfaces file e.g.:

auto eth0.100
iface eth0.100 inet static
vlan-raw-device eth0


Multiple permanent linux interfaces with dhcp allocated addresses

tuxRecently I have been doing some on the HP 5500EI including a port security feature limiting the number of MAC addresses to 8. This is not a difficult configuration at all – in fact it is just one command on the interface itself .

mac-address max-mac-count 5

So now with the limit in place I would like to test it. The first thought was to use Linux alias as a fast and dirty way of doing this but unfortunately I soon found out that tit doesn’t allow for the requirements I had in mind.

  • There have to be 5 or more virtual interfaces on one physical interface
  • Each virtual interface must have its own individual MAC address
  • All virtual interfaces must be getting their own IP addresses from the DHCP server
  • All the virtual interfaces must receive an IP address from the same subnet (as they as plugged into an access port)

The main issue with just aliasing the interface is that it is a L3 interface only (uses the same MAC) and definitely doesn’t allow for DHCP allocations from the same subnet. But fortunately on Linux this is not an issue and this can be done via “ip link” feature which is part of the iproute package in Debian. The usage is rather simple:

ip link add dev intX link eth0 type macvlan
ip link del dev intX link eth0 type macvlan

Where int will be name and X the number of the new interface and eth0 is the physical interface you want to bind to. This can be repeated multiple times and the MAC address will be generated randomly. There is also a way for setting it up to whatever you want by changing the syntax to this:

ip link add dev intX link eth0 address aa:aa:aa:aa:aa:aa type macvlan

If you run this couple times and get some IP addresses on those interfaces from DHCP server you will soon notice the following messages on your switches.

%Jun 7 11:03:01:411 2000 Core1 ARP/5/ARP_DUPLICATE_IPADDR_DETECT: Detected an IP address conflict.
The device with MAC address 6e99-1b38-2b8c connected to Bridge-Aggregation2 in VLAN 100 and the device with MAC address d6b2-1ac8-9bd2 connected to Bridge-Aggregation2 in VLAN 100 are using the same IP address

Quick check will reveal that there are no duplicate addresses assigned nor allocated so what is the system complaining about? The answer is that the defaul behavior of linux kernel is that it will repli to ARP from the first interface in the list (eth0) also it can reply from all interfaces /and or random interface making the Comware go crazy.

Fortunately this default behavior can be adjusted by the following commands:

echo 1 > /proc/sys/net/ipv4/conf/eth0/arp_ignore
echo 8 > /proc/sys/net/ipv4/conf/eth0/arp_announce

There has been a lot of people around the net suggesting the second value should be 5 but that didn’t work for me at all. If you want to make these changes persistent add the line with the values into /etc/sysctl.conf

There is some more explanation of the values above here

PackEth tutorial part II – The Gen-B,Gen-S and PCAP options

PackEthThis is a Second part of an article I have written some time ago about the great tool called PackETH.  This article will be much shorted as it will be focused on the less complicated (but not useful!) modes of the tool.

In the previous par I have described how to build your own packet from L2 to L4 but what if you need something else ? maybe not a single packet but a burst of packets? or what is you need to send multiple streams of various frames ? Well then you need to use the Gen-S and Gen-B modes.


The name stands for Generate burst. The necessary prerequisite for using this mode is for you to have a ready and valid packet loaded in the Builder mode. Once you have that you can run the burst generation. This is how the GUI looks like:


The “Number of packets” field is I think rather self-explanatory. The second is more interesting and deserves our attention as it can be used for buffer testing. The “Delay between packets” field is actually referring to what is correctly called the Inter Frame Gap (IFG) which is a delay between end of one frame and beginning of the next one. The physical media has a limitation of how fast you can the frames be send. Then the “max speed” check box is in effect it means you will send all the frames with minimal IFG. This situation is also be known as back-to-back scenario.  Under normal circumstances the frames would not be played out from the buffer like this unless the buffer would be full. So you are asking what is this good for ? Well the traffic can be very bursty and the software on your network equipment might not be able to handle it very well so testing this behavior before you introduce new equipment into your network is highly recommended (and is actually standardized as part of RFC 2544 test suite).

The other interesting thing you can do in Gen-B mode is to change the frame’s content on fly (from the original you’ve build in the Builder mode). The things you can do with it are quite wild. let’s have a look at the options and what they do:

  • do nothing  – will result in sending the same frame you have in Builder mode with no changes
  • MAC set random source address – rather self explanatory – good for testing L2 paths and load balancing mechanisms
  • IP set random source address – rather self explanatory – good for testing L3 paths and load balancing mechanisms
  • RTP options – this allows to simulate a more real RTP stream
  • Change Byte X and Y values – probably quite good for protocol developers


This is a Stream generator as there is quite often a need to play different types of traffic. For example you want to try a nice voice traffic stream you have captured or build in combination with various bursty types of traffic and see how your network will be dealing with it? Well that is why you can select up to 10 packets in pcap format and give them some basic parameters (as seen below).


You can also run these stream in cycles so the traffic pattern will repeat itself up to infinity. You can also enable/disable the stream on the fly to alter the traffic mix.


The PCAP’s only function is to open a packet in pcap format (not pcapng!) and load is into the builder once it is selected. On the other hand this can be achieved using the load button from the Builder as well so I am bit unsure what is supposed to be the extra feature here.

The Summary & a small testimonial

Well what to say at the end – I hope I was able to describe PackETH’s features with few minor hints what they can be useful for. I will most likely include PackETH in some of my other articles as a method of testing thing while playing with various LAB scenarios. The truth is that it cannot replace a proper Ethernet tester but taking in account its flexibility,stability and the fact it is free  I must say I can only rate it as high as possible.

Before I will really end this article I wanted to write one more thing a small testimonial – I successfully used PackETH over period of about three years for various testing ranging from proving equipment behavior for L2 broadcasting/multicasting, faking ARP and ICMP messages to invoking network behaviors so as proving equipment’s dealing with QinQ and it has aways been a tool in my software toolbox I could and can completely rely on. There aren’t many pieces software like this one and I would recommend to anyone anytime for both  training and troubleshooting purposes.

PackEth tutorial part I – The Inetrface and The Packet Builder

PackEthIn my previous post I have mentioned ingenious piece of software called PackEth and I have also promised that will write up a separate article about it as I just think this amazing tool deserves as much attention as I can give it.  So what this software do?  Well let me quote the author ” PackETH is GUI and CLI packet generator tool for Ethernet…It allows you to create and send any possible packet or sequence of packets on the Ethernet link.” I would add that that it is the only tool I have found that actually allows you to assemble Ethernet frames and a IP packets that actually does what you would expect it to do while being multi-platform and incredibly stable. I think I have never seen it crashing which speaks for itself.  This article will focus around version 1.6 as that is the one that has both Linux and Windows versions available. The drawback is that the L3 IPv6 support is not included.


Getting the package is quite simple as it is a a project hosted on sourceforge. There are versions available fro r Windows Linux and MacOS. But if you are using Linux then there is a good chance that the package will be in your repository (is present in Debian stable and most likely in Ubuntu). Installation is simple – in windows just unpack the .zip file and run packeth.exe – And yes it is completely standalone software so no installation no garbage in registry etc. the installation has all libraries included so the folder after unpacking has about 18MB which I think is very reasonable. I would recommend using Linux version as along with Packeth you will be most likely using WireShark as well and that has some issues on L2 in windows. If you are happy with L3 testing only then the OS choice is irrelevant.

The Gui will open in the builder mode which is probably the most useful and most interesting mode of all the ones that are offered. Switching between the mode you can on the top left part of the menu.


In the middle section you can save and load configuration you have made in the past for repeated testing. In the interface button you will have a selection of interface you can use for PackETH – in Linux it is simple ethX interface. Under windows it is bit more complicated as PackETH doesn’t use the “human readable” name a.k.a. local network 1 or similar but instead it uses the system name which looks like this


If you are wondering where is that name coming from it is an ID from WinPcap library and there is no simple way how to find out which ID is which interface but as normally you want to use just one – you can just disable all the others and read the ID in PackETH. The most important thing is – if you are not a superuser (or have permitted access to network cards on the machine) the interface list will be empty.

The send button is simply sending the frame/stream from the interface. The stop button us useful only when you are running continuous streams as in all other cases.

Builder mode

Is the basic and most interesting for me personally as it allows for complete buildup of a L2 frame/ L3 packet / L4 datagram. It has multiple options and parts which make it incredibly handy.

Data Link Layer

Before going into Data Link Layer of the builder – just a small reminder of how ethernet frame looks like:

ethernet frame

In the Link layer section you can choose which standard of Ethernet you want to use for your frame. The majority of Ethernet traffic in networks nowadays is Ethernet Version II (Also known as DIX). In the last data I’ve read about this topic about 5 years ago were showing that Ethernet II is about 95% of all Ethernet traffic. This should be taken in account when you build your frames as the NIC in your PC might not even be able to build 802.3 frame due to driver restrictions. I have seen this on multiple PCs. Also the receiving party might be dropping this type of frames as despite the attempted compatibility not many vendors actually care about this at all.


If you chose the Ethernet version II frame format the ethertype field (also known as DIX type) will become available. This field identifies what protocol is encapsulated in the frame. The current options are:

  • IPv4  – 0800
  • IPv6 – 86DD
  • ARP – 0806
  • User defined – whatever number you can fit in two octets

Be aware that there is no internal logic of PackETH stopping you from selecting let’s say IPv4 DIX type and then building and ARP packet on higher layer which is incredible advantage if you want to test behavior of equipment to invalid types of traffic, but is easy to overlook when you are not after such specialty.

When we’re in the Data Link layer the next after ethertype is 802.1Q and (in)famous QinQ.

As you can see in the  picture of the Ethernet frame the first field in the 802.1Q shim is the TPID which identifies the following data as part of the shim rather than Ethertype. This fields is followed by  PCP (Priority code point) which is defined in 802.1p and is used for CoS. The priority can be selected from the menu – it also tells the standard meaning of the p-bit in question. But be aware that the numeric value actually means nothing as long as the devices passing this traffic are p-bits aware. Also the mapping is based on standard’s recommendations so in every network it can be used as seen fit by the network admins.


The CFI (canonical format identifier) has been deprecated and re-used drop eligibility but generally it can be just ignored as most equipment just ignores it anyway. The filed of interest is the VID which defines the VLAN ID. The problem with it is that it must be written in hexadecimal digits which is not exactly user friendly but should be no big problem.

The biggest topic in this part is the QinQ. Let’s start with the definition of what is QinQ. As the name suggest it is abbreviation for all sorts of nested VLANs (aka 802.1Q in 8021Q). This practice started as totally non-standard behavior and as a result it has been implemented in many different ways before a standard has been written. The major issue is that the standard is fairly new and mos of network vendors actually doesn’t support the standardized version. Fortunately PackETH support all versions that exist plus some more as you can define whatever you want. So what are our options in the TPID field for QinQ for the outer/SP tag ?


  • 0x8100 – the common vlan – as most vendors even nowadays support and do the original 802.1Q in 802.1Q – extremely common – default almost everywhere
  • 0x9100,0x9200 (and missing 0x9300) – proprietary outer/SP tags used by vendors like Cisco an Juniper and is fairly common on decent equipment
  • 0x8a88 – 802.1ad format that almost no-one supports

So the outer tag we must select from a drop-down list and the TPID for the inner/C tag is  always 0x8100 (that is why the filed is grayed out). So the only thing to do is fill in the VIDs for outer tag and the inner-one. The only next step is to select what is the next layer protocol as L2 configuration is finished.

Network Layer

In the network layer you can chose between ARP and IPv4 (ind IPv6 in the newer version) and user defined payload. All of these are quite simple.

This is how IPv4 setup looks like:


Let’s go through the header fields:

  • Version – should be always set to 4 (that’s why it’s called IPv4)
  • Header length – IPv4 has a variable header length due to existence of “options” field at the least significant position (this causes a lot of issues with L3 aware devices and was important driver in IPv6 development) The header length is in increments of 4 Bytes so the most common value of 20 Bytes would be equal to the default value of 5. This field uses hexadecimal numbers so the allowed values are from 1 to F
  • ToS field as originally defined in RFC2474 Is no longer used as ToS (Type of Service) in about 99% of networks and is deprecated in favor of DSCP (Differentiated Services Code Points) and these are options available:

ToS  and DSCP options

As I have never really used ToS for anything I will not really dive into explaining the variables on this place. I might do that in article I am preparing about QoS theory and its implementation in some equipment types.

  • Total length – calculates the total length of the packet and unless you want to check behavior for runt packets keep it on auto so you will generate valid packets
  • Identification – this is completely useless field no 99% cases as it is only used for reassembly of fragmented packets
  • Flags – very important as it allows/disallows fragmentation of the frame – the best practice here is for the packet to be set to 2 (do not fragment), the other option is “more fragments”  anyway this seems to be broken in the 1.6 windows version and all three values are always zeroes


  • Fragment offset – again in my testing I have found no use for playing with fragmented packets
  • TTL – Time to live – number which is decreasing while the packet is being processed through L3 device might get very handy when you need to prove how many hops away your receiver is
  • Protocol – code informing about what higher-level protocol is encapsulated in the IP packet (options ate TCP,UDP,ICMP and IGMP) again this is just a number in the header of the packet and doesn’t prevent mixup with different protocol actually being configured in upper layer.
  • Header checksum – does exactly what you would expect and again – Unless you are testing runts there is no need to uncheck the tick-box that calculates the checksum for you
  • Source and destination addresses – These do not need any comment
  • Options – a barely used field – I don’t think I ever seen it used and I have never used it myself as far as I remember

If you think – that the IPv4 was pretty simple then ARP will look like a piece of cake. I have to say I like the possibility to send fake ARPs around the network as you can easily populate various tables (specifically APR and switching tables on L2/L3 devices) without having the real source in the network. This allows you to see behavior of elements of your network that would be difficult to observe otherwise. Well there is not much to say about it and here is the screen-shot:


As you probably know ARP has been deprecated in IPv6 and it is now a component of the IP protocol itself and is know as neighbor solicitation.

Session Layer

The session layer provides you with following options : UDP, TCP, ICMP ang IGMP. I will cover all of them briefly as I most of the time do not work with L4. Also IGMP and RTP will be covered in greater detail in an upcoming article about multicasting.


Is the most common protocol I am using as most of the data I am normally dealing with are various voice frames. The Protocol itself is minimalistic and so is the possible setup as you can see below:


The one thing I would like to point out is the option to apply some specific patter of your choice (so ti is not random. This is etremely useful if you have a suspicion that a specific frame with (or within) a specific patter inside is causing some troubles in your network.


TCP is unlike UDP statefull so it must have way more options included to accommodate the windowing mechanism and 3 way handshake and some other minor things. There is a very nice article on Wikipedia about TCP and as I normally do not care much about L4 in testing I will not elaborate on the details here. This is hw the GUI looks like with all the options it has:



This is probably the most interesting of all the L4 protocols as you can actually invoke some actions from the network nodes. The main two options are echo request and echo reply which allows you to send ping to specific nodes (which is not that special) but also fake reply which I have found very useful in the past. The other option is to send network unreachable datagram with all the messages but unless you do testing of L4 aware network (like some firewalls) then it is not of  much interest.



The Internet Group Management Protocol is a predominantly last mile protocol used for membership in various multicast groups. IT is widely used for multimedia delivery specifically – IPTV. It exists in 3 versions and V2 is most widely used (at least to my knowledge).  IGMP is rather simple as it has basically only two types of messages – Query (from router) and Report (from client). As you can see all of those are available to you which is ideal when troubleshooting both ends of the multicast network as combined with Wireshark you can emulate the required response.



The other three parts –  Gen-B mode, Gen-S mode and PCAP will be discussed separately in a follow up article as I must try keeping the length on a readable level.

How to capture, analyze, create and replay ethernet traffic

I have decided to write up new article after long time of silence as I think this is a topic that many engineers are facing on fairly regular basis but finding solutions to the simple and interconnected questions is rather time consuming and not exactly simple. Let me stress at the beginning that most of the tools mentioned below are free or cheap and all of them are easily available. So enough talk and let me start with the first chapter

Part 1 – Capturing the traffic – software

There are various situation in which you might need this and various ways how to achieve it. So let me start with software which will allow you to capture the traffic on a PC.

Wireshark LogoWireshark – the Alpha and Omega

I think the first software anyone always encounters is Wireshark – it is absolutely incredible and flexible piece of software with so many functions and features it is difficult to believe it is free. The software itself uses libpcap (or its windows variant Winpcap) and is multi-platform (Windows/LINUX/MacOS). I will not write about Wireshark’s functions and features on this spot as it has been done many times and I might do it in separate article anyway. But I will point out few thing that are a must-to-know when working with this amazing software.

  • Captures made in Windows OS will never have 802.1q tags as the drivers of most network cards will just strip them (might be also fault of libpcap – never found complete answer to this)
  • If capturing large amounts of data the default behavior is to display the captured data in real time on screen which is causing crashes (as the PC is usually unable to cope with this amount of calculation)
  • Alway use the latest stable version as the developers of this software make huge improvements every release

It is needles to say that Wireshark is great for small amount of traffic but generally for capturing of data it must be tweaked and is less stable than the second option I will talk about.


This is a Linux only tool – at least as far as I know which is exclusively used from command line interface. This might seem to be like quite a drawback as many people for different reasons don’t have or cannot have Linux PC. Well think again – there is huge amount of network equipment that is based on either Linux (Checkpoint SPLAT) or BSD (Juniper,Nokia IPSO) so you can still use it. The syntax is really simple :

$ tcpdump -i etho  – will set the interface on which we listen to eth0
$ tcpdump -w filename.pcap  –  will save the captured packets in file in pcap format so you can later read them either with tcpdump or Wireshark
$ tcpdump -d – display the captured frames on the active console

I have listed only these three as those you would normally use the most there is a whole bunch of commands this software can do out of which the interesting one is that it understands regular expressions so you can filter while capturing. For the complete list check this manpage.

Part 2 – Capturing the traffic – hardware

Now when we have something to capture the traffic with we must somehow direct the flow of the traffic to our endpoint. Most people go for the easy approach and just unplug whatever equipment is in the path of the traffic they want to intercept and run the analyzer. But this is fundamentally flawed method unless you are in control of the traffic transmitter (i.e. in lab environment) – in live networks or when investigating some protocol-related issues this is just not possible as the traffic will either die out on some timers or will just not arrive at all as the upper protocols will notice that their counterpart is no longer there. Well fortunately there are ways how to achieve the traffic diversion or transparent interception.


Hub is the first thing that will come to mind – it is a simple L1 device and the main thing is it sends everything everywhere. Of course this is a simplification but it does the job – or not – The problem here is that you will not be able to buy a hub nowadays as switches are so cheap that there is really no reason for hubs to be manufactured anymore. The other limitation is that there are no hub with gigabit Ethernet ports as the have never been built.

You might have luck on e-bay but even there most people are selling switches and even routers as “hubs” so it is unlikely to get one of those. Also there is a big limitation of a hub and that is that you can actually listen only to maximum of 1/2 speed of what its declared speed is. The reason is obvious – as you listen to both part of conversation on your link from the hub, it will be limited to max of 100mpbs or more typically 10mbps. So if you will  think about a composite, equal, bidirectional stream directed to your end point the maximum of the down link which is 100mbps (or 10mbps) which will be shared as 50Mbps conversation from A->B and 50Mbps from B->A.

Despite this limitation hubs are great especially for small lab environments but unfortunately they are almost impossible to get nowadays.

Port mirroring / Span port / Tap port

This is usually the most available way of diverting traffic from live network and is present on all equipment that has a cli (ok almost – but definitely on all decent, recent equipment). The configuration is usually very simple you just must identify the port to mirror and a port you want to direct your traffic to (in Cisco catalyst switches it can be also vlan). Here is a sample config:

Switch(config)# no monitor session 1
Switch(config)# monitor session 1 source interface fastEthernet1/0/1
Switch(config)# monitor session 1 destination interface fastEthernet1/0/24
and for verification
Switch# show monitor session 1

This is a very fast thing to configure but it has she same drawbacks

  • malformed frames will never be processed by the ASICS as they will be dropped on inbound of the source interface
  • even though most vendors swear that this is capturing fully transparent there will be protocols being filtered out so the trace is never complete

Port mirroring is excellent for protocol related problems but for lower layer problem it always must be combined with interrogation of the source interface and this might be rather tricky in busy networks.

tuxLinux bridge

I will add this only as a last resort thing as it has so many drawbacks and so narrow utilization that I’ve never seen it used in real life. In linux if you have two interface cards you can bind them in a bridge group using bridge control utilities and command brctl. This will create a L2 bridge on which you can listen to traffic but this is a classic bridge with all its disadvantages of being full L2 device. Also please note that the bridge would have spanning tree turned on by default ! The example below shows how to configure the bridge group and disables the stp.

$ brctl addbr “bridgename
$brctl addif bridgename (i.e. eth0)
$brctl stp bridgename off
$ brctl show  – shows tall bridges on system)
$ brctl showstp bridgename – shows current status of spanning tree on the bridge in question

Linux bridging is very useful thing to know and understand especially for building VPNs and when you do some virtualization. For configuration details see the tutorial on linux foundation.

dualcomm logoHardware tap

This is probably the most expensive option out of all the ones mentioned here but it is my personal favorite. The network tap is a L1 device that basically can work as a smart hub bun on gigabit speed. You can either sniff one direction or the other or both at once (with the limitation of the dow-nlink speed of course). I was looking for device that would be able to do this and wouldn’t cost thousands of dollars (and I was actually considering building one myself). But then I have found Dualcomm and specifically Etap-2306 . It is a very nice piece of equipment – very simple has two different modes for capturing and you can even inject some traffic if you want. But my favorite feature was that it has SFPs as the equipment I work with is 99% fiber only this was a huge bonus. The other great thing is that is is USB povered so you can run it off your laptop without any need of additional power supply.  The device costs about $670 so it is not the first choice if you have strained budget but after using it on several occasions I have to say it was worth of every penny spent.

There is one not so obvious drawback when you start capturing data on speeds of hundreds of megabits – it is the speed of the HDD you are capturing to. Normally you would do this in field with only your laptop – but the throughput of your laptops HDD is actually always below 400mbps (more likely to be close to 200mbps). This will obviously differ between older laptops and newer ones with SSD drives but it will be a bottleneck in most cases. There are ways how to improve the capturing so this will not be such a  big problem but eliminating this issue is very difficult in field conditions – in lab you just use PC with fast drives and plenty of RAM and it will do the trick.

Part 3 – Replaying captured traffic

This might seem like a bit of a useless thing to do – why would you want to do this if you can see the whole stream in the Wireshark analyzer ? Well this is extremely useful for replication of problem in lab where you can monitor the equipment more closely and also can change configuration while the problematic event is happening. Replaying the pcap files is very common feature on testing equipment but that cost thousands and tens of thousands dollars. There is also quite a few pieces of software that do it as one of their functions but I have found those usually have some problems either with timing or sending the packets in different way than they have been received originally. After quite some research I have found Playcap which ideally matched my requirements.

playcap Signal11 logoPlaycap

Playcap is the software of choice for replaying the pcap files from your PC – it is extremely simplistic and has Windows and Linux version. The most important thing about this software is that is rigorously follows the timing of the packets in the pcap files which most of the other pcap players don’t do.

Part 4 – Creating your own traffic

If you need to prove a theory there might raise a need to actually send a frame of specific type (i.e. multicast frame) or with specific payload without having an equipment that can do it. This is a difficult problem even for small testing equipment as it is not primarily ,meant to do these thing. With big testers you usually can do this but must pay a special license not talking about impossibility getting such a device anywhere close to field (or even other lab in the same building). After rather long and unfruitful search I have found project called packeth which actually does quite a few of the above mentioned.


The project can be found on sourceforge and is just great. I am using it for about 3 years now and performed so many tricks with it ! Have no equipment to generate QinQ, igmp, L2 muticast, want to verify unknown unicast want to send fake ARPs test IPv6 ? Yes all of those (and more) you can actually do in Packeth – as with wireshark this is absolutely fabulous piece of software which runs on both Windows and Linux. As there are very specific thing you can do with this software I will most likely write a separate article just about it.

Part 5 Traffic analyzing

The whole exercise of getting the traffic (or even the creation of it) is being done so you one can easily troubleshoot and replicate issues in lab or in live network. but once the data are on a PC the only step must follow – the packet trace analysis. There is only one name I can say about this – Wireshark. IT is the ultimate tool for traffic analysis. I will not write how to use Wireshark as it is a topic for stand alone book. But there is one thing I will say – if you want to call yourself a network engineer understanding the basics of this software is just a must. If you can write decen exptressions and know where to look to find the flows or converstaions between endpoints – it will make your life much easier. As mentioned above multiple times – I will most likely write an article on “how to” for some scenarions that are interesting from my point of view – but the documentation and community around Wireshark is huge so if you want to know anything – just go to the project’s wikipage where you’ll find plenty of useful stuff (including some sample captures or protocols).

This is the end of this first article after a long time but I will try to write follow-ups soon as I should have more time and more interesting things to write about.