broadcast domain

indebluez · Posted: Fri Jan 09, 2004 2:27 pm Post subject: broadcast domain

hi everyone...i have a qn on broadcast domains...

!) how do we identify a broadcast and collision domain?
like if we have 3 stations connected to router and
a server connected to the router.
where 3 more stations are connected to the server....
there are 4 broadcast and i think4 collsion domains....why?

2)any rules on how we connect usinf a crossover cable? like do we use cross over only for similar devices? like router to router...?

mil thanx in advance.... Smile

tfs · Posted: Fri Jan 09, 2004 5:57 pm Post subject:

Bridges and switches segment your collision domains and routers segment your broadcast domains.

You didn't say how you are connected to the router or server. If your router is also a switch (with 4 ports, for example), each port is it's own collision domain (4 of them), but one broadcast domain.

On the crossover, there is an excellent tutorial under the network section.

indebluez · Posted: Fri Jan 09, 2004 6:41 pm Post subject:

hi thomas....
the qn in the book looked like....the router has 4 ports...
and each of the 3 ports has a computer stationed...
and on the last port...a server is connected....and 3 more computers are connected to the server....

could u plz explain how u got 4 collision domains n 4 broadcast domains?

thanx again:)

tfs · Posted: Fri Jan 09, 2004 8:45 pm Post subject:

You need to re-read what I said.

I said "if" you have a router that is also a switch, which many of the low cost routers (linksys, dlink, etc) are, then you have 1 broadcast domain (not 4) and 4 collision domains (each port on a switch is its own collision domain).

If, however, you are talking about a router that has 4 ports (interfaces) then you have 4 broadcast domains.

In this case, as I mentioned above you have 4 broadcast domains (one for each interface). There are 3 workstations off of the server, but you don't say whether they are connected to the server by a hub or switch. If they are connected by a hub - you have 1 collision domain. If they are connected by a switch, you have 3 collision domains.

Take a look at the following page and it might help you understand the difference. Has pictures and everything ( pictures always help me see it ).

http://www.firewall.cx/hubs.php
_________________
Thanks,

Tom

indebluez · Posted: Tue Jan 27, 2004 9:48 am Post subject:

hi guys...one of the qns from the exam was about
(1)whether switches reduce the size of collision domain..
i know on a switch...each port is its own collision domain....but does it reduce the size of collision domain?

(2)same 4 bridges right?

(3)whats if a VLAN is implemented....are the broadcast domains reduced in size? what about the collision doamins...i noe the collision domains have increased in number but have they increased in size?

hmm help?thanx

tfs · Posted: Tue Jan 27, 2004 8:09 pm Post subject:

1) Yes. A switch reduces the size of a collision domain. The fact that each port, as you correctly mention, is one collision domain - does not mean that there is only one computer involved. If you were to add a hub onto the port you would still have 1 collision domain at the port, but you may have 5 computers on that 1 collision domain.

2) Yes. Remember that a bridge is a multiport bridge.

3) If you implement a VLAN, you introducing routing into your scheme (which reduces broadcast domain). When you reduce your broadcast domain, you also reduce your collision domain. Increasing the number of collision domains is not a problem, the size of a collision domain is what you care about.

Hope this is what you were looking for.
_________________
Thanks,

Tom

indebluez · Posted: Wed Jan 28, 2004 3:38 am Post subject:

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.

tfs · Posted: Wed Jan 28, 2004 5:02 am Post subject:

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.
_________________
Thanks,

Tom

indebluez · Posted: Wed Jan 28, 2004 7:25 am Post subject:

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:)

sahirh · Posted: Wed Jan 28, 2004 8:35 am Post subject:

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