There are 24 ports on a 1900 switch, one AUI port and 2 fast Ethernet ports, right? Now each of these port are separate collision domains right? If you split the 24 ports into 3 VLANs, with 8 ports each, you would have 3 collision domains right? Is it true that no matter what, the 1900 switch is still one broadcast domain, or are each of the 3 Vlans separate broadcast, and collision domain. Now if you want these three Vlans with 8 ports each to speak to each other you must connect all three VLAN to a router because, Layer 3 transactions can not occur with out a router.
What does port 25 AUI (Attachment unit interface) do? I know that it is a RJ-45 connector, or is this wrong.
Are ports 26 and 27, like a send and return to the router or just for Trucking Vlans? Could some one clear this up.

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Hi,

My understanding is that each switch port defines a collision domain, no matter how many VLANs you create. That is collision on port 1 will not affect port 2 and vice versa.

Each VLAN (port based) will define 1 broadcast domain, i.e all ports being to 1 VLAN will see all the broadcast packets unless you do up filtering.

I believe when you meant layer 3 transaction, you only meant "routing". Note that layer 3 switching to a certain extent, examines layer 3 information yet does up switching only in switches, not routers.

AUI were for 10 Base5 if I am right, in this case, may be relevant to interconnect to 10 Base5 LANs or backbone. However, you could always purchase a transciver to convert it to 10 BaseT.

Port 26& 27 really depends on you network or needs, you may trunk them to distribution or core switches or, I believe a connection to a server is possible.

Hope that helps..

Debarros



[This message has been edited by debarros (edited 01-05-2001).]

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There are 24 ports on a 1900 switch, one AUI port and 2 fast Ethernet ports, right? Now each of these port are separate collision domains right? If you split the 24 ports into 3 VLANs, with 8 ports each, you would have 3 collision domains right?

No, you now have 3 broadcast domains. VLAN's do not change the number of collision domains.

Is it true that no matter what, the 1900 switch is still one broadcast domain, or are each of the 3 Vlans separate broadcast, and collision domain.

Neither. The 3 VLAN's give you 3 broadcast domains. The number of collision domains is not changed when you configure multiple VLAN's.

Now if you want these three Vlans with 8 ports each to speak to each other you must connect all three VLAN to a router because, Layer 3 transactions can not occur with out a router.

1. The "router" could be a Route Switch Module (RSM) in the higher-end switches; basically this is a router that sits in a switch chassis. You need an external router for the Catalyst 1900.

2. You can use VLAN trunking to connect all 3 VLAN's to one router interface with one switch port, and route between the VLAN's.(Cisco calls this a "router on a stick.") This is a way to "connect all 3 VLAN's to a router" using one physical connection instead of 3. Trunking can also be used to connect switches. Depending on the VLAN trunking protocol you use, you can also buy hardware and/or software to enable a server to be trunked as well.

HTH,
doctorcisco

------------------
Silicon is made from sand; nothing made from sand is allowed to wreck my day!

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24 10BaseT (that would be a Catalyst 1924), one AUI and 2 100BaseT, that gives you 27 ports, for a grand total of 27 collision domains. Before you start creating your VLANs, all 27 ports are in in the management VLAN (VLAN 1). That's one broadcast domain, still 27 collision domains.

Now you create 3 VLANs: VLAN 2 (ports 1 through 8), VLAN 3 (ports 9 through 16) and VLAN 4 (ports 17 through 24). Note that ports 25 (the AUI), 26 and 27 (the FastEthernets) are still in VLAN 1. You have know 4 broadcast domains, and still 27 collision domains.

Makes sense, so far?

You're right regarding VLAN communication (inter-VLAN routing): you need a router to do that.

You can use ports 25, 26 and 27 as regular ports, including assigning them to one of your VLANs. However, if you want to have VLANS than span multiple switches you'll need to use trunk links and VTP. You may use only the FastEthernets (ports 26 and 27) for trunk links.

I hope I'm clarifying, not adding to the confusion.

An extra note about Catalysts 1900 (and 2820, they're one family): you can use so called "bridge groups" on these switches. Bridge groups and VLANs are mutually exclusive: you use either one, or the other, but not both at the same time. I don't you need to know about bridge groups for CCNA, but it never hurts to know something extra.

Cheers!

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Thanks for the help guys, more questions to come, promise
sea*******out*********

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Just a thought,, no one else on the forum is from houston.

If possible, maybe we could meet and throw a cold one down. ooooh,,, does this sound like the makings of a date????? j/kidding.

seriously, if you think you may want to talk shop about cisco, let me know. I'm trying to learn all that i can and all input is considered.,,,,,,,,,,,,,silky,,,,,,,

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Silk, I would like to tag with some one from Houston, to talk about what we have learned and what we need to learn.
e-mail
seadragon2@earthlink.net

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