A set of questions downloaded from a web site proclaim that VLANs create separate broadcast domains and VLANs do NOT create separate collision domains. This appears to conflict with data details learned elsewhere. VLANs are a level 2 switching function. If they create separate broadcast domains, we can just toss the routers, really simplify this CCNA exam! Is the information above just wrong or am I missing something?
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Colliding broadcasts...
- Thread starter k0mbachi
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each VLAN has its own broadcast domain ,and collisions for that VLAN is limited only to that VLAN alone.
Each switch port is its own collision domain, but they share the same broadcast domain. If VLANs would be created, then that VLAN would have its own broadcast domain. To be able to communicate between VLANs, that's the time where the router comes in. The router would route the data's between VLANs. the process is called ISL routing.
Each switch port is its own collision domain, but they share the same broadcast domain. If VLANs would be created, then that VLAN would have its own broadcast domain. To be able to communicate between VLANs, that's the time where the router comes in. The router would route the data's between VLANs. the process is called ISL routing.
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I've just reviewed VLANs in Odom's book and concur that you are indeed correct. There may be qualifications (Odom warns) and other questions to ask but I'm not yet smart enough to ask them. Every place where broadcasts were mentioned it seems the broadcast referenced was initiated from within the VLAN and that broadcast was not shared outside the VLAN. What about broadcasts initiated from outside the VLAN, where the destination isn't in any of the switch or router tables? Probably the way to do this right is to acquire at least two switches and do some serious experimenting. Alas, not today, but maybe later.
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The thing to remember about ALL switches is they are a layer 2 device. They build SAT tables that map a MAC address to a particular port. As ecafracs stated, each switch port is its own collision domain. But, when a layer 2 broadcast enters a port, the switch cannot make a determination as to which port it needs to go - therefore it sends it out all of the other ports. In a nutshell, a broadcast storm is just an extremely large number of broadcasts that a switch cannot filter. That should answer your last question.
SOME switches also have the capability to create VLANs. VLANs allow us to assign individual ports to a common group. That group acts as a broadcast domain (similar to a router) with all the rights and responsibilities
of a broadcast domain. That means layer 2 and layer 3 broadcasts are limited to that VLAN. And like ecafracs said, to communicate from one VLAN to another, you must use a router and some trunking protocol (ISL or 802.1Q).
About broadcasts outside of a VLAN?? If a broadcast is initiated in VLAN 1, it will not be seen in any other VLAN. Remember, VLANs created broadcast domains just like routers. If broadcasts could transend broadcast domains, the Internet would be a very congested place.
SOME switches also have the capability to create VLANs. VLANs allow us to assign individual ports to a common group. That group acts as a broadcast domain (similar to a router) with all the rights and responsibilities
of a broadcast domain. That means layer 2 and layer 3 broadcasts are limited to that VLAN. And like ecafracs said, to communicate from one VLAN to another, you must use a router and some trunking protocol (ISL or 802.1Q).About broadcasts outside of a VLAN?? If a broadcast is initiated in VLAN 1, it will not be seen in any other VLAN. Remember, VLANs created broadcast domains just like routers. If broadcasts could transend broadcast domains, the Internet would be a very congested place.
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wahooguy:
Thanks for the enlightenment. Odom's definition of a VLAN explains it all:
"A virtual LAN (VLAN) is a broadcast domain created by one or more switches."
I'm not familiar with the term "SAT table"; a search leads me to believe that SAT is an acronym for Source Address Table.
Thanks for the enlightenment. Odom's definition of a VLAN explains it all:
"A virtual LAN (VLAN) is a broadcast domain created by one or more switches."
I'm not familiar with the term "SAT table"; a search leads me to believe that SAT is an acronym for Source Address Table.
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