broadcast domain

hi tom thanx! jus wanna double check

switches reduce the size of collision domains, how does this happen?

with vlans....broadcast domains are reduced in size...and so are the collision domains right.

the number of collision domains have increased or fallen with vlan?
what about the number of broadcast doamins...they have increased right.

I don't understand what your asking here. As you mention, there is one collision domain on a switch port. If you have a 4 port hub, there is one collision domain, with a 4 port switch there is 4 collision domains (1 for each port).

With VLANs, you are correct. Both domains are reduced in size. The number collision domains will go up. Again, realize that the VLANS work from a switch, so each port is it's own collision domain.

The number of broadcast domains will also go up with a VLAN. Remember, each VLAN segment is really a subnet and to get to another subnet you have to route. Routers reduce broadcast domains, therefore the number of broadcast domains will go up.

hi tom
thx i get it now:)
as long as the no of collision n broadcast domains have increased...
the size has decreased...right?

i have one more qn...its on WAN
there is a WAN link between the cisco main office at A and the cisco remote office at B.
a cisco router that was providing frame relay connectivity at the A site has been replaced with a different vendor's frame relay router. connectivity is now down between the A and B site.
whats the most likely cause?
the ans is mismatched LMI type...
but i think its mismatched encapsulation....coz routers only deal with encapsulation right? and LMI is betwn router n switch...

thanx again:)

Mm I think you need to review your WAN protocols section. LMI is 'local management interface' and its what lets the router talk to the frame-relay network.

You have to ensure the LMI types match..
Use the command
[code:1]
frame-relay lmi type <type>
[/code:1]

Where <type> will be either 'cisco' 'ansi' or 'q9331' (I don't know if there are any other supported types. Use ? to check).

Hmm..if both the end of the frame relay you are using CISCO router..
lmi type can be used as CISCO..or with differnt vendor router...better to use ANSI

Thnx

In the real world, you will ask your ISP for the LMI type. Cisco devices with IOS 11.2 and newer will auto sense the LMI type, BUT it is best practice to ask the ISP and manually configure the LMI type.

As for the switches questions; assuming I remember my CCNA questions properly, a switch increases the number of collision domains compared to a hub, but a switch (with no vlans configured) is one broadcast domain. VLANS are broadcast domains. VLANS cannot be configured on a hub, so a hub is forever one large collision domain and one large broadcast domain.