Difference between siaddr/sname and ciaddr/yiaadr in DHCP (DORA Process)

In DHCP packet we have fields

"ciaddr" -> client IP address, "yiaddr"-> Your client IP address

What is difference between the two?

ciaddr : will be filled by client and is used only in BOUND,RENEW and REBINDING state

yiaddr :Filled by server and sent to client in DHCPOFFER and DHCPACK.

Similarly what is difference between "siaddr" :- Next server IP address and "sname" : optional host name ?

siaddr : used in boop protocol and it signifies TFTP server name

sname: optional fields used by clients to inform preference of tftp server for booting purpose.

I have not seen this field set by any client. Let me know who uses this field.

DHCP server puts his own address in "siaddr" by default. If you want to seperate DHCP server and TFTP server use option 66 in Windows 2003 DHCP server to specify the separate TFTP server name.

The DHCP server always use option 54 : DHCP server identifier to declare its own identity and ip address. It should not be confused with "siaddr" field.

Let me know your if you have any comments, on this my email id embsystest@gmail.com or post in comments below.

How to enable option 66 ( Bootp filename) and option 67 (bootp or tftp server name) in tftpd server

I have covered in another post how to enable option 66 and 67 in windows 2003 server. TFTPD is anothe DHCP/TFTP server which can be used for testing. In this you can enable the option by modifying these fields:

Here both DHCP server and tftp server are configured on same TFTPD (same interface/same PC)

  Settings -> Bootfile name -> "imagename"
              -> siaddr (the address of tftp server, its own interface )


But looks like bug is present in this server, if we give these fields and the client requests for ip address with DHCPDISCOVER message the TFTPD server is sending DHCPOFFER with Client IP address set, which it is taking as some junk ip address as 0.0.0.115 ( not sure why) and this value changes with different NIC cards.

So even if the Client sends DHCPREQUEST message it is setting this Client IP address filed to junk ip and "your client ip address" as proper. But then TFTP is not sending back the ACK.

Looks like some bug ...will have to confirm with some other clients.

Letter to Developers from Testers !!!!

Hello Mr/Miss Developer !!

Hope you are doing good. I want to tell you few points so that you can understand our point of view. I hope you take time to understand it properly and give some time to analyze the problems we face in the team and how we can resolve it.

1) When i file a bug in your module , please understand that I am not pointing at your coding capabilities. I am just doing my job.

2) When i say "the bug is not reproducible" , please don't smile at me and mark my bug as "works for me". At least try to spend time in analyzing the bug and understand the scenario. Even i understand how it is difficult to fix not reproducible bugs. But i believe by giving you enough information at least you will have better understanding about the module which can create problem.

3) I know sometimes I am not good in filing bugs and i should read this

"http://www.chiark.greenend.org.uk/~sgtatham/bugs.html" before filing any bug and follow it. But if it is not as per your expectation please reassign me with the

information you want instead of marking it as "invalid"


4) If you think any bug is "Invalid" or "Works as designed" please mention in such a way that i can understand the reason for doing it. If you say in your comment as " works as designed " how i will know what is the expected behavior of the design. Please write explicitly the expectation of the module and how the bug is not valid.

5) If you are fixing any bugs please mention the changes done in the code not only in terms of file names but also in  terms of human readable form. Instead of only giving branch and affected files please mention what exactly you have done in your files.

6) If you have fixed some major bugs please mention what other module it affects or can affect. If you have time to test you can test it or let us know , we will test it no problem.

7) If you are reducing the priority of any bug, please mention the reason for doing it as next time i will be capable enough to understand it what priority should be given to which bug.

Last but not least please don't make any bug as ego issue. If you see from my point of you, i am getting paid to test and break the code. If I am not finding bugs properly i am not doing my job and its immaterial who has written the code. For me bug is more important and not "Who has written the code".

if i miss bug in old build and found the issue in new build, don't blame me for not finding it at first place. If you can understand, it will be like this that every time I go for fishing you ask me why last time you did not get this type of fish even if it is the same sea ? I know the bug has been found late , don't thank me that i have found the issue before customer can find but at least don't blame me for finding it late. Please if you can , go and fix it.

As "no of bugs found by tester"cannot be used to measure performance of testers similarly "no of bugs found" in your module should not be treated as your shortcomings. It is one of the matrix but not the major one. The importance should be given to the resolution and fixing of the issue instead of who has missed the bug  and whose module the bug is found.

Please accept me as a part of you. We are equal. We are working for the same goal, to make products better. The more I help you by finding bugs the more product will be stable. The more you help me in finding bugs by giving details of use case, customer scenario etc the more product will be stable.

Please let me know your thoughts on this.

Thanks,
Testers

How to enable tftp server filename and bootp file name in windows 2003 server for Bootp process

In windows 2003 server if you wants to add tftp server file name and bootp file name, we need to add dhcp options 66 and 67 as given below. Remember that the option 66 here does not set "sname" but  "siaddr"

 FIELD      OCTETS       DESCRIPTION
   -----      ------       -----------

   op            1  Message op code / message type.
                    1 = BOOTREQUEST, 2 = BOOTREPLY
   htype         1  Hardware address type, see ARP section in "Assigned
                    Numbers" RFC; e.g., '1' = 10mb ethernet.
   hlen          1  Hardware address length (e.g.  '6' for 10mb
                    ethernet).
   hops          1  Client sets to zero, optionally used by relay agents
                    when booting via a relay agent.
   xid           4  Transaction ID, a random number chosen by the
                    client, used by the client and server to associate
                    messages and responses between a client and a
                    server.
   secs          2  Filled in by client, seconds elapsed since client
                    began address acquisition or renewal process.
   flags         2  Flags (see figure 2).
   ciaddr        4  Client IP address; only filled in if client is in
                    BOUND, RENEW or REBINDING state and can respond
                    to ARP requests.
   yiaddr        4  'your' (client) IP address.
   siaddr        4  IP address of next server to use in bootstrap;
                    returned in DHCPOFFER, DHCPACK by server.
   giaddr        4  Relay agent IP address, used in booting via a
                    relay agent.
   chaddr       16  Client hardware address.
   sname        64  Optional server host name, null terminated string.
   file        128  Boot file name, null terminated string; "generic"
                    name or null in DHCPDISCOVER, fully qualified
                    directory-path name in DHCPOFFER.
   options     var  Optional parameters field.  See the options
                    documents for a list of defined options.

Review OPENKM : Document management Software and installation Problems

My setup is windows XP PC. I  wanted to download OpenKM so i searched and got this link:

http://www.openkm.com/en/download-english.html

If you click on "Only Download" you get the page where you can download the software, but its not working. It downloaded one file which was not working and says only 30Kb. At this time i stopped thinking if the download itself is not working how poorly they must have maintained the software. But i must say i was wrong. I stopped for few days as was busy in some other work.

Again when i searched i got this link for download:

http://sourceforge.net/projects/openkm/files/

This when downloaded it was of 190MB and it was working fine.

We need Java jdk i had already installed jdk-6u26-windows-i586.exe  from


http://www.oracle.com/technetwork/java/javase/downloads/index.html

The OPEN KM installer is thisone :OpenKM-5.1.10_JBoss-4.2.3.GA.exe


Now installation starts :

1) Followed instruction given in

http://wiki.openkm.com/index.php/Quick_Install:_OpenKM_5

a) Uncompress on your file system disk  My installation has xampp. So the default path for me is c:\xampp\htdocs\


b) Open command prompt. Go to C:\xampp\htdocs\jboss-4.2.3.GA\bin and give in command line

      
            run.bat -b 0.0.0.0

c) now click on  http://localhost:8080/OpenKM/.This will open login page with default username as "okmadmin" and password as "admin"

d) login and see how it works.

Issues faced:


1) Once the server started i got error message as "JAVA_Home" not set so to avoid this error message i had set the JAVA_HOME variable in run.bat like this after below lines:

==========================
set RUNJAR=%JBOSS_HOME%\bin\run.jar
if exist "%RUNJAR%" goto FOUND_RUN_JAR
echo Could not locate %RUNJAR%. Please check that you are in the
echo bin directory when running this script.
goto END

:FOUND_RUN_JAR

set JAVA_HOME=C:\Program Files\Java\jdk1.6.0_26
==================================

The issue got resolved.




2) After some time i started getting these messages, and the web page stopped responding:
==================================
15:02:11,343 ERROR [CoyoteAdapter] An exception or error occurred in the container during the request processing
java.lang.OutOfMemoryError: PermGen space

===================================


This issue is resolved by adding below lines in run.bat


-----------------------------------------------------------
rem JVM memory allocation pool parameters. Modify as appropriate.
set JAVA_OPTS=%JAVA_OPTS% -Xms128m -Xmx512m -XX:PermSize=64m -XX:MaxPermSize=128m -Djava.awt.headless=true--------------------------------------------------------------
The issue got resolved.

3)  After this i logged in the server and created some "userroles" but i was unable to do anything. For this issue to resolve we need to change:

 in openKM.cfg -> change "hibernate.hbm2ddl=create" to "hibernate.hbm2ddl=none"

4)  Suddenly i started getting these messages


HTTP Status 404 - /OpenKM/j_security_check

--------------------------------------------------------------------------------

type Status report

message /OpenKM/j_security_check

description The requested resource (/OpenKM/j_security_check) is not available.
-------------------------------------------------------------------------------





JBossWeb/2.0.1.GA

To resolve this i stopped the server, closed all open browser and restarted the server and browser. The issue got resolved. Still not sure why the issue came.


5) After this i was able to create users and user roles but when i created users with some user roles i was unable to login to the server with that user name. Eg. I created user "A" with user role as "DEPT A" and user "B" with user role as "Dept B" . When i tried to login with user A i got below messages

===============================.HTTP Status 403 - Access to the requested resource has been denied

type Status report

message Access to the requested resource has been denied

description Access to the specified resource (Access to the requested resource has been denied) has been forbidden.
JBossWeb/2.0.1.GA
=======================

To resolve this issue the user has to be part of default "UserRole" group. So i selected user with user roles as "Dept A" and "UserRole" and similarly with user B. And i was able to login with both the accounts

6) Some small issues but which took me time to figure out:

  a) For everything first see right click is giving you some option or not.

  b) In Create folder if we create the folder and try to click anywhere else , after giving name the folder wont get created or sometimes the webpage stops working.  Easy way "right click on "okm:root" create folder , give name and again "right click" immediately the folder gets created.

c) Adding user : It costs me almost half day to find out how to add user. I may be dumb but i tried to follow this

http://wiki.openkm.com/index.php/Create_users_and_roles

and i could not find anywhere how to add users. I guess it was different in previous version and they have not updated the document.

A small + is there in Administration -> users icon.

OK after all this its done. Now i can add users, departments, folders, files , security option for each file which can restrict users or groups. I can checkout and checkin so it has versioning control. I can search with title and user name.

I has these features/issue but still i need to verify and see how it is working

1) Email notification
2) open office integration  for  file preview
3) Need to restart every-time the server so need to write a script to restart automatically.

Will post in another entry after i am done with this. But as of now this looks best.Also all these issues got resolved with the help of friend "Google" and OpenKM Forum friends. Thanks to them for helping me out with these issues.

Career Path for freshers in embedded systems ?

a) How a fresher can enter into embedded systems domain ?

Generally in embedded systems companies there are three types of jobs for fresher :-

• As a developer 
• As a tester
• As a document writer

 b)  What exactly are their job profiles ?

  Developer : Who writes code
  Tester   : Who tests the code
  Document Writer : Who documents the things and prepare User manual etc.

c)  How will be the Salary for these ?

    Developer : Highest
    Tester : Equal or slightly less than developer
    Document Writer :  less than Tester

d) How you can decide which one to join as fresher ?

    It all depends on your written test and Interview. Generally all freshers has to give written test. Prepare well in C and C ++ , chances are if you do well in reasoning and coding section . You will be given priority as a developer.

    If you have talent for writing/communication you can join documentation team. These is less fight there and communication is only criteria, other things you can manage.
   
   Generally fresher has less choice when they have to join in development or testing team. It all depends on your attitude and how to end up in interview. Its always good to revise about your subjects and learn more and more about final year project.

   Generally for freshers the expectation is they should know what they have done in their graduation and programming knowledge of C.

e) Is certifications help in getting jobs?

  YES and NO. It all depends on how much you can talk about them and know them in detail. IF you have lots of certifications but you were not able to answer some basic questions like " name all OSI layers" or "write a simple function to check palindrome" then its of no use. But if you have some basic knowledge and you use certification to gain more knowledge, it will definitely gives you an edge over other candidates.
   



    

Review of opendocman: Document management system (Free software to manage documents)

Opendocman can be downloaded from : http://www.opendocman.com/

The installation is easy it needs a webserver with PHP and MYSQL. I have Xampp with me (http://www.apachefriends.org/en/xampp.html) and i downloaded opendocman. 

After installation these are some important points:

• Added document will be visible to same department all members. If "A" and "B" are in same department, "A" will see all documents uploaded by "B" and have admin rights for the same.
• Admin has all permission for all files
• While uploading the documents we need to select the rights for other departments specifically or we can “Set all department to” only “view” rights. Now other people can see and download it but cannot modify it.
• File versioning is supported. We can see all revisions of file. We need to check out and check in the file with same name.
• Once file is checked out by someone, the status is shown in red with “x” mark.
• The same person has to check-in the file, which has checked out.
• Even if the file is checked out, other people can still download and view the file, but they cannot modify and upload again.
• History of the file will display the modification date and the revision log and previous versions of the file.
• The deleted files are archived and through admin account, can be recovered.
• Files can be searched with name.
• Some file types are not supported but file types can be added through admin account.

  

Some issues

• Sub directories are not supported so all files will be in single page.
• File name with “spaces” are not allowed. Some special characters are not allowed.
• Checked out file status can be seen but “who” has checked out information is not available.
• Search within file is not possible.
• Each document has to be given separate permission to other users/departments. Basically as folder structure is not supported. All documents are individual items. 
• No LDAP authentication

Other features which i have not touched:

• File expiration.
• “Review” process 

Looks like great tool for small organisation who doesn't have many documents. Hopefully i can use it once sub-directories are supported.  

How to disable VLC audio track display pop-up

Oh it was so irritating. To disable it we have to do following.



Go to Tools-> Preferences -> All -> Interfaces -> Main Interfaces -> Qt ->and un-check Notify on track change.

Spanning Tree Protocol : Why BPDU Validation is not done properly in various implementations? ?

In Spanning tree protocol if a root bridge receives a better root BID, it will stop advertising its own values and consider the other bridge as superior and starts advertising the values which it got from new bridge.

Lets say

                 PC1---Switch A----SwitchB----PC2

The one who has better BID will become root bridge lets say A.

Now consider this scenario , i capture one packet in wireshark, modify its BID such that it becomes root bridge and put all invalid timer values as 0x FF FF i.e. 255 for hello timer, forward delay and message age.

So what will happen if i send this packet from PC1 to switch A ?

1) Switch A will not accept this packet .

2) Switch A will accept this packet and become designated bridge?


Well, the answer is even if the BPDU has all the invalid values of timer, still the bridge/switch will not consider it as invalid packet and accept it as it is, and start advertising these invalid values to all other switches.

Why is it so? In 802.1D-1998 standard there is no mandatory validation  for received BPDU. So what is actually happening is, it depends on vendor whether they are applying this validation check or not.

In Linux this validation check is not present and when i raised this question in forum i got two reason for not fixing it:

1) STP is not secure protocol , so it accepts and treats every received  BPDU as valid

2) In linux PC bridges, everything has to be done in CPU , adding all these validations for all protocols will just add  an overhead and waste of CPU cycles.


What will be affect if we don't do these validations:

Any one in small lan who knows about this flaw can insert root bridge and propagate invalid timer values. It results in change in convergence time which can lead in formation of loops.

Who does these validation and who doesn't?

I have tested in Linux, Cisco, Netgear and Dlink switches. I wont give model no and version as this is only for information purposes. Cisco has all type of validations so it wont accept the BPDU. Linux, Netgear and DLink all are not doing any validation. So if you are in testing team of any of these, please raise it as a bug and see if gets fixed, even if they say native OS has this issue. Let me know if you could get this bug fixed so that eventually it comes to Linux.

Brocade switches does these validation, as i came to know but not tested on it.

If you are working on any other make of switch/ bridge let me know this issue is fixed or not in your platform.

Free Knowledge base management system | Free tools to manage documents | Document management system review

Completely free tools to manage documents :

1)Project-Open :  http://www.project-open.com/

This is basically project management software which has option for file storage.

2) Opendocman: http://www.opendocman.com/

Very easy to use with one page setting. Major drawback we cannot create sub-directories.

3) Twiki : http://twiki.org/

Very comprehensive suite with emphasis on web page format.

4) OpenKM :http://www.openkm.com/en/

 Another good one.

I have installed all the above , now i have to experiment on each one and see.Lets see which will be a better tool to use as document management system.

Free Video tools to capture screen of computer, record Video !!!

Sometimes bugs are not reproducible.  We need to spend constant effort and time to reproduce these issues. Or sometimes developers just refuse to acknowledge that the bug exists in the system. At those times its always good to record the screen and show them exact steps when the issue came.

Some of the free tool which can be used to capture computer activity are:

1) Camstudio:  A great tool : http://camstudio.org/

2) Jing : http://www.techsmith.com/download/jing/

3) Debut video capture software: Free for personal use:

http://www.nchsoftware.com/capture/index.html

How to do spelling checks for webpages ? , How to test spellings for webpages?

We have two ways:

1) Manual : right click on web page-> view source -> copy, paste in Microsoft word and do spell check.

2) Firefox addon-> Add spell-check addon

https://addons.mozilla.org/en-US/firefox/addon/spell-checker/

click on each page and do spell check with this addon.

Routing and Bridging conformance sample test cases

This link has many test cases including  routing and bridging like RIP, VLAN, Spanning tree, BGP, OSPF etc.

https://www.iol.unh.edu/services/testing/

How to add Plus and minus symbol in Microsoft word ( Special symbol + _ how to write in microsoft word)

If we have to write 45 plus minus 3 , we have to use + symbol with - below it. I was searching for it and came across two ways to make it:

1) Microsoft word-> Insert-> Symbol -> Select "±"

2) Another way Write +, select it and underline it using ctrl+u like this ->+

Both ways are proper but second way has more clarity and both symbols are not joined so looks better..

eg. 56 ± 5

     56 + 5

You decide which one you want to use.

How to add delete static routes in Windows XP

To add Static route in windows XP the  command is:

route add "network-address" mask "mask-of-network" "gateway

eg.

route add 10.0.0.0 mask 255.0.0.0 192.193.192.1


To delete Static route in windows XP the  command is:

route delete 10.0.0.0 mask 255.0.0.0 192.193.192.1

How to test Spanning tree Protocol : Spanning tree protocol Test Cases

Spanning tree test cases written by me.Please add/update other test cases which will be useful to test this protocol. Please post in comments.

Setup:                               link2
                      |-----------HUB-------|
           PC1----Root/Switch1---------Switch2-----PC2

HUB is connected so that redundent link when goes down, the tcn bpdu can be captured.

1) Verify the configuration BPDU : Capture the packets using wireshark on PC1,verify following fields in Spanning tree protocol frame.

   Expected : It should have following fields with values as set in Root

bridge:
 
               protocol id :0 (2byte)
               Version :0  (1 byte)
               BPDU Type: 0 (1 byte)
               BPDU Flags: 0 (1 byte)
               Root Identifier : (8 bytes)
                       Root bridge priority : 32768
                       Root bridge system ID extension: 0
                       Root bridge System ID: MAC address

               Root path cost : 0 ( for root bridge) 4 bytes
               Bridge Identifier : (8 bytes)
                       Bridge priority : 32768
                       Bridge system ID extension: 0
                       Bridge System ID: MAC address
               Port Identifier : 0x8001 ( 2byte)
               Message Age : 0
               Max age: 20
               Hello Time :2
               Forward Delay :15

Veirfy in ethernet-II header the destination mac address is 01:80:c2:00:00:00


 2) Make link down between hub and switch 2, observe the TCN BPDU and  verify following fields:

     Spanning tree protocol :
               Protocol id :0 (2byte)
               Version :0  (1 byte)
               BPDU Type: 0x80 (1 byte)

3)  Verify STP can be enabled or disabled.

4) Verify by changing configurable parameters in Switch and verifying that updated value is reflected in BPDU

5) Verify that bridge with lowest bridge id ( same bridge priority lower

mac) becomes the root of LAN.

6) Verify by changing the bridge priority, the lowest bridge priority

bridge becomes the root bridge.

7) Verify in above two scenarios the bridge is converging. Verify all state of ports.

8) Make another loop between bridge 1 and 2 using hub. Verify the STP is converging  properly.

9) By changing the port path cost try to change the blocking port to forwarding and vice versa.

 In this test case the path cost of the upstream bridge is to be modified.

    Bridge1(root)------------Bridge 2 --------   blocking---Bridge 3
                                |                             |          
                                --------HUB------fwd----------
  
To make blocking port of bridge 3 in to fwd mode modify in bridge 2 , connected path cost to less number like 19 to 0.Immediately the blocking port should go into discarding/listening/learning/fwd mode and the other port should change into blocking.

10) Repeat same by changing port priority as above. Observe the convergence time for both the cases.

11) Root bridge down scenario:

In 3 bridge scenario make another loop  between bridge 3 and bridge 1


Bridge1(root)------------Bridge 2 --------   blocking---Bridge 3
       |                         |                             |          
        -------------------------HUB--------------fwd----------
  
Observe it converged and note down all the ports designations (root/designation, root bridge, designated bridge). Connect two pcs between non root bridge and ping between them. Lets say set such a way that root bridge is bridge 2 and ping is going between bridge 3 and bridge 1 PC.

Now make bridge 2 down and see the topology is converging properly with new bridge selection and note down the convergence time.

12) Link down scenario:

 When the topology has converged make forwarding port down of non root bridge and see if the blocking port mode is changed to forwading mode.

13) In 3 bridge scenario, after converging disable STP in one non -root bridge. Observe the topology is converging is not and note down the time taken.

14) Change parameters of Spanning tree root bridge like hello timer, max age and forward delay. Verify on non-root bridge the updated parameters are getting propagated properly in BPDU.

15) Add new root

  With two bridges converge STP, now add another bridge with bridge priority less than the original root bridge. Verify if the STP reconverges.

16) Add another bridge with lower priority than root bridge in existing network, verify STP re converges properly.

17) In all above where topology is getting changed verify TCN BPDU and corresponding TCN ack in BPDU from root bridge. Verify in sniffer.

18) Verify by entering non acceptable values in parameters and verify if it is accepting the values (negative test case)

19) Verify BPDU in 3rd bridge the Message Age is incremented to 2.

20) After the STP converges, disable the STP on forwarding port of non-root bridge and verify the topology re converges properly.


21) TCN retransmit timer: STP converged, now change hello time in non-root bridge. Make this non-root bridge link up and down, capture the TCN and verify the retransmission timer for TCN is the hello time configured on this switch.

22)  4 bridge setup : Verify that TCN are sent upstream and TCN-ACK in BPDU are sent downstream direction. TCN generated by 3rd bridge should not be seen by 4rth bridge but TCN-ACK BPDU should be observed at bridge 4 also.



References: 802.1D-2004
           

Myth of testing : Article from BjRollison ( Main purpose of Testing)

I came across this very nice article from Bj Rollison, the Myth of testing.

http://newsweaver.ie/qualtech/e_article001048143.cfm?x=b11,0,w


I completely agree with him and i recommend everyone to read this article  whether you are  in senior or junior positions in QA or testing.

It explains few very good points:


What is the main purpose of testing ?

a) Testing is to find bugs.

b) To ensure quality.

c) To give information about the product.


On what basis the performance of testers can be evaluated?

a) On numbers of bug he/she can found while testing.

b) Numbers of bug caught in his/her module once software is in field.

c) On new scenarios he/she can test



If you are a testing manager/director do you recommend

a) more salary for developers than testers

b) more salary for testers than developers

c) recommend same salary structure for both tester and developer


Who should be held responsible if many issues are caught in field in one module lets say XYZ module:

a) Testes who tested it.

b) Developer who developed it

c) Product managament team for not providing enough use case scenarios to testing and developement teams.


How software success can be measured ?

1) Smiley faces on customer surveys.
2) No bugs in field.
3) Customer and decision maker expectation meets.


State true and false:

1) Testing can eliminate all defects.

2) 100 % tested software means no defects exists in system .

3) Finding bugs in sowftware is finding fish in ocean.


Which is correct role of tester information provider or bug finder?


Read below link for answers

http://newsweaver.ie/qualtech/e_article001048143.cfm?x=b11,0,w


if you are into testing please respect your profession and respect fellow testers. One problem in this profession is we don't value this profession.

If you, yourself not give enough credit, no body else will....

Testing Zindabad !!!!

Ethernet Format decided by two byte field in Ethernet Header

In Ethernet header we have different type of Ethernet headers like Ethernet-II, 802.3, 802.3 with 802.2 LLc,

802.3 with 802.2 and SNAP etc. To decide which format it is following the two byte field is checked after

Destination and source address of 802.3 header. If the value lies in range of 0x0000-0x05DC (1500 in

decimal) the value indicated length other wise if it is greater than 0x05DC it is Ethertype for Ethernet-II frame.

Like STP frames has length field in format : 802.3 (length) +LLC+STP

Normal ICMP frames has: Ethernet-II (ethertype-0800)+IP+ICMP

Default gateway in Bridging and Routing Answers

Consider below two scenarios:


1) Bridged network

                          193.192.192.1                        193.192.192.2                                                 193.192.192.3
                     PC1----------Switch------------------------DUT(acting as Bridge)------------------------------Router-----------Internet
                                         |
               PC2 ----------- --|




To reach Internet what gateway IP address should be set in PC1 and PC2 ?

Answer : The gateway will be 193.192.192.3

2) Routed network

                                      193.192.192.1               193.192.192.2                            193.192.192.3
                     
               PC1----------Router------------------------DUT(acting as Bridge)----------------------------------------Router-----------Internet
                                     |
               PC2 -----------|





To reach Internet what gateway IP address should be set in PC1 and PC2 ?

Answer : The gateway will be first router ip address 192.192.192.1

What will happen if you connect different subnet PC with Switch ?

Consider following scenario:

1)   PC1-----------------------L2 Switch ---------PC2

  192.193.193.1/24                                  192.193.192.1/24


Try to ping from PC1 to PC2, will they ping?  Why?

Answer: They will ping but we need to do something...

2) What you should do to make them ping ?

Answers Here

How Default Gateway should be configured ? What default gateway we should give in Router or Switch Networks?

Consider below two scenarios:


1) Bridged network

                          193.192.192.1               193.192.192.2                            193.192.192.3
                     
               PC1----------Switch------------------------DUT(acting as Bridge)------------------------------Router-----------Internet
                                 |
               PC2 -----------|




To reach Internet what gateway IP address should be set in PC1 and PC2 ?


2) Routed network

                                      193.192.192.1               193.192.192.2                            193.192.192.3
                     
               PC1----------Router------------------------DUT(acting as Bridge)----------------------------------------Router-----------Internet
                                 |
               PC2 -----------|




To reach Internet what gateway IP address should be set in PC1 and PC2 ?

Please post in comments.

Answers Here 

How to add additional columns in Wireshark like Protocol , Packet length etc

Do you know in Wireshark we can add additional columns to view specific fields like : src port, dst port, protocol, packet length, relative time etc.

To do this go to Edit-> Preferences ->Columns -> Add

Add the new column with required parameter.  As shown below

Now the new column will also be displayed when you start the capture.