+ Reply to Thread
Results 1 to 21 of 21
  1. Junior Member
    Join Date
    Jul 2009
    Posts
    10
    #1

    Default Collision Domain Confusion?

    Hi,

    I am bit confused with collision domain topic. I know what is a collision domain but if i look on different network diagrams i can never tell how many collision domains are there in the diagram.

    Actually my concept is not clear. Can some one please explain with some diagrams (if possible) how to find out no. of collision domains//

    I wil be really grateful.

    thanks
    Reply With Quote Quote  


  2. Login/register to remove this advertisement.
  3. Senior Member
    Join Date
    Nov 2003
    Location
    England
    Posts
    178

    Certifications
    CCNA, MCP.
    #2
    Depends on the devices, know what a hub and switch look like.

    Each port off a switch is it's own collision domain. A hub is a physical multi-port repeater, all hosts attatched are part of a single collision domain.

    check out my diagram.
    Attached Images Attached Images
    ICND1 - Passed 25/01/10
    ICND2 - Passed 9/03/10

    Studying CCNA:S
    Reply With Quote Quote  

  4. Last RHCT EVAR!? CiskHo's Avatar
    Join Date
    Feb 2010
    Location
    RTP NC
    Posts
    189

    Certifications
    CCNA:Security RHCT CCENT MCP Net+ A+
    #3
    A port off of a router would be a collision domain as well wouldn't it? In particular, what about the serial link between the two routers in your diagram? I would consider the diagram to show 6 collision domains, 1 being the serial link between the routers. However, I wouldn't think the CCNA or CCENT exams would even give a diagram with multiple routers (too advanced) but I could be wrong.

    Simmzz: I had issues with the same dollision domain counting questions too. Once I looked at it like this I started understanding it:
    Every cable coming off of a hub is part of ONE collision domain (hubs suck so everyone has to share the same domain/wire).
    Last edited by CiskHo; 03-10-2010 at 05:13 PM.
    Reply With Quote Quote  

  5. Junior Member
    Join Date
    Jul 2009
    Posts
    10
    #4
    Quote Originally Posted by hexem View Post
    Depends on the devices, know what a hub and switch look like.

    Each port off a switch is it's own collision domain. A hub is a physical multi-port repeater, all hosts attatched are part of a single collision domain.

    check out my diagram.

    ok so in your diagram how many collision domains are there: i guess 5 in total (4 for switch and 1 for hub). but i saw a very similar diagram to urs where the answer should be 14 but it was 15.. have a look on my example



    the actual answer from on online test website is 15 but whereas if i count is 14. pls let me kno wat do u think
    Reply With Quote Quote  

  6. Went to the dark side.... Moderator networker050184's Avatar
    Join Date
    Jul 2007
    Posts
    9,799

    Certifications
    CCNA, CCNP, CCIP, JNCIA-JUNOS, JNCIS-SP, JNCIP-SP
    #5
    There are 15 links there, which one are you not counting?
    An expert is a man who has made all the mistakes which can be made.
    Reply With Quote Quote  

  7. Junior Member
    Join Date
    Jul 2009
    Posts
    10
    #6
    ok do you count the link between 2 routers as well
    Reply With Quote Quote  

  8. Last RHCT EVAR!? CiskHo's Avatar
    Join Date
    Feb 2010
    Location
    RTP NC
    Posts
    189

    Certifications
    CCNA:Security RHCT CCENT MCP Net+ A+
    #7
    Quote Originally Posted by simzz View Post
    ok do you count the link between 2 routers as well

    I guess I knew more than I thought! The only way you are able to get 15 collision domains out of that diagram is if you count the link between the routers... and seeing that a router is not a hub I don't see why it would not be counted.
    Reply With Quote Quote  

  9. Old Timer thenjduke's Avatar
    Join Date
    Jun 2005
    Posts
    831
    #8
    There is only 5 collision domains in this picture. Every Wan connection works at full duplex so would be no collision there.
    Reply With Quote Quote  

  10. Went to the dark side.... Moderator networker050184's Avatar
    Join Date
    Jul 2007
    Posts
    9,799

    Certifications
    CCNA, CCNP, CCIP, JNCIA-JUNOS, JNCIS-SP, JNCIP-SP
    #9
    Quote Originally Posted by thenjduke View Post
    There is only 5 collision domains in this picture. Every Wan connection works at full duplex so would be no collision there.
    Say what?
    An expert is a man who has made all the mistakes which can be made.
    Reply With Quote Quote  

  11. Last RHCT EVAR!? CiskHo's Avatar
    Join Date
    Feb 2010
    Location
    RTP NC
    Posts
    189

    Certifications
    CCNA:Security RHCT CCENT MCP Net+ A+
    #10
    Quote Originally Posted by networker050184 View Post
    Say what?
    +1 Not sure what he was trying to say there.....

    Quote Originally Posted by thenjduke View Post
    Every Wan connection works at full duplex so would be no collision there.
    Which is exactly why it is its own collision domain

    Top diagram would have 6 collision domains.
    Next diagram would have 15 collision domains.

    Per Wiki:
    "If a group of Ethernet or Fast Ethernet devices in a CSMA LAN are connected by repeaters they will compete for access on the network. This situation is typically found in a hub environment where each host segment connects to a hub that represents only one collision domain and only one broadcast domain. Only one device in the collision domain may transmit at any one time, and the other devices in the domain listen to the network in order to avoid data collisions."
    *Keep in mind that a hub is just a multiport repeater.
    Last edited by CiskHo; 03-10-2010 at 06:57 PM.
    Reply With Quote Quote  

  12. Senior Member
    Join Date
    Oct 2004
    Location
    New zealand
    Posts
    226

    Certifications
    Diploma Network Engineering (CCNA, CCNP Academy) Pursuing Degree in BEngTech(Networking)
    #11
    guys isn't there 21 collision domains since each ports its own collision domain
    Reply With Quote Quote  

  13. Old Timer thenjduke's Avatar
    Join Date
    Jun 2005
    Posts
    831
    #12
    Quote Originally Posted by networker050184 View Post
    Say what?
    Oops I apologize it is collision domain. I meant to say that. I was talking to buddy of mine since I was finishing up
    Reply With Quote Quote  

  14. Old Timer thenjduke's Avatar
    Join Date
    Jun 2005
    Posts
    831
    #13
    Quote Originally Posted by CiskHo View Post
    +1 Not sure what he was trying to say there.....


    Which is exactly why it is its own collision domain

    Top diagram would have 6 collision domains.
    Next diagram would have 15 collision domains.

    Per Wiki:
    "If a group of Ethernet or Fast Ethernet devices in a CSMA LAN are connected by repeaters they will compete for access on the network. This situation is typically found in a hub environment where each host segment connects to a hub that represents only one collision domain and only one broadcast domain. Only one device in the collision domain may transmit at any one time, and the other devices in the domain listen to the network in order to avoid data collisions."
    *Keep in mind that a hub is just a multiport repeater.
    I meant it was collision domain. I was talking to buddy and not thinking
    Reply With Quote Quote  

  15. Last RHCT EVAR!? CiskHo's Avatar
    Join Date
    Feb 2010
    Location
    RTP NC
    Posts
    189

    Certifications
    CCNA:Security RHCT CCENT MCP Net+ A+
    #14
    Quote Originally Posted by moss12 View Post
    guys isn't there 21 collision domains since each non-hub port is its own collision domain
    Yes.
    *Edited for accuracy/clarification. Even though the hub in the 1st diagram has multiple ports every connection to that hub/repeater would be part of the same (1) collision domain.
    Reply With Quote Quote  

  16. Senior Member
    Join Date
    Nov 2003
    Location
    England
    Posts
    178

    Certifications
    CCNA, MCP.
    #15
    Quote Originally Posted by simzz View Post
    ok so in your diagram how many collision domains are there: i guess 5 in total (4 for switch and 1 for hub). but i saw a very similar diagram to urs where the answer should be 14 but it was 15.. have a look on my example



    the actual answer from on online test website is 15 but whereas if i count is 14. pls let me kno wat do u think
    If the two router's were connected via cross-over cable through fastehernet or ethernet port then i'd say there was 15..however over a serial link no, csma/cd is specified in 802.3 ethernet standards.

    i think he's confused about how effectively collisions are eliminated through the use of full-duplex, so maybe he thinks they are no longer a collision domain at all.


    Now shall we play how many broadcast domains? who wan't to say 3? lol!
    Last edited by hexem; 03-10-2010 at 07:05 PM.
    ICND1 - Passed 25/01/10
    ICND2 - Passed 9/03/10

    Studying CCNA:S
    Reply With Quote Quote  

  17. Senior Member ConstantlyLearning's Avatar
    Join Date
    Dec 2006
    Location
    Dublin, Ireland
    Posts
    445

    Certifications
    JNCIA-JunOS, CCNP, CCNA-Security, CCNA, CCENT, CWNA, JNCIA-FWV, Security+, Network+, A+, MCP, MCSA, ITIL Foundation V3
    #16
    Quote Originally Posted by moss12 View Post
    guys isn't there 21 collision domains since each ports its own collision domain
    That used to trip me up.

    I think of it as every 'link' is a CD.

    Link between a switch or router and a hub (including all the other links off the hub) - 1 CD
    Link between two switches - 1 CD
    Link between two routers - 1 CD
    Link between a switch and a router - 1 CD
    Link between a switch and an end device - 1 CD
    Link between a router and an end device - 1 CD
    Reply With Quote Quote  

  18. Junior Member
    Join Date
    Jul 2009
    Posts
    10
    #17
    Quote Originally Posted by ConstantlyLearning View Post
    That used to trip me up.

    I think of it as every 'link' is a CD.

    Link between a switch or router and a hub (including all the other links off the hub) - 1 CD
    Link between two switches - 1 CD
    Link between two routers - 1 CD
    Link between a switch and a router - 1 CD
    Link between a switch and an end device - 1 CD
    Link between a router and an end device - 1 CD

    thanks for the answer matey and ending the confused discussion
    Reply With Quote Quote  

  19. Member websponge's Avatar
    Join Date
    Aug 2008
    Posts
    88

    Certifications
    A+, Network +, MCP, CCENT, CCNA, CCNA Security, CCNP
    #18
    Quote Originally Posted by thenjduke View Post
    There is only 5 collision domains in this picture. Every Wan connection works at full duplex so would be no collision there.

    ?? where did you get 5 from? there are 9 PCs connected to 3 switchs, thats at least 9 collision domains? they arent hubs are they?
    CCNP Next!
    Reply With Quote Quote  

  20. Senior Member
    Join Date
    Sep 2009
    Location
    Wales, UK
    Posts
    411

    Certifications
    CCENT, CCNA, CCNA Voice, CCNA Security, ITIL V3 Foundation, MCP, MCTS
    #19
    Quote Originally Posted by websponge View Post
    ?? where did you get 5 from? there are 9 PCs connected to 3 switchs, thats at least 9 collision domains? they arent hubs are they?
    Don't worry there has been two different topologies discussed in this thread, the original one had 6 collision domains, the second had 15.
    Blog : http://www.caerffili.co.uk/

    Previous : Passed Configuring Microsoft Office SharePoint Server 2007 (70-630)
    Currently : EIGRP & OSPF
    Next : CCNP Route
    Reply With Quote Quote  

  21. Old Timer thenjduke's Avatar
    Join Date
    Jun 2005
    Posts
    831
    #20
    The first topology has six collision domains. I was not talking about the 2nd one.
    Reply With Quote Quote  

  22. Senior Member bcall64's Avatar
    Join Date
    Dec 2009
    Location
    Morrisville, NC
    Posts
    156

    Certifications
    CCENT
    #21
    I know this doesn't answer your question but what really helped me with topics like this was CBTNuggets. It clarified the three way handshake with tcp/ip, switch configuration, collision and broadcast domains. With that and Odom's book I was pretty solid across the board. It was almost like being in a classroom.
    Reply With Quote Quote  

+ Reply to Thread

Social Networking & Bookmarks