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Question Regarding Router With Network Modules (Cisco 3845)

Abunai1200Abunai1200 Registered Users Posts: 2 ■□□□□□□□□□
in CCNA & CCENT
Hi. This is a very "newbie" question.
If there is a forum better suited to this type of question, I'm sure someone will let me know.

The Cisco 3845 router has four HWIC ports for the WAN interfaces and four ports for network modules.

How are the network modules used?
Would a network module populated with Ethernet ports simply be a layer 2 switch?
To what network (WAN) interface would the connected equipment belong?
Is that configurable?
Can you describe a common use case for a router with one or more network modules?
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    networker050184networker050184 Mod Posts: 11,962 Mod
    Abunai1200 wrote: »
    How are the network modules used?

    They give the router additional interfaces.
    Abunai1200 wrote: »
    Would a network module populated with Ethernet ports simply be a layer 2 switch?

    They are usually L3 ports, but you can also get switch modules as well.
    Abunai1200 wrote: »
    To what network (WAN) interface would the connected equipment belong?

    When the module is connected the corresponding interfaces are created in the routers configuration.
    Abunai1200 wrote: »
    Is that configurable?

    Yep!
    Abunai1200 wrote: »
    Can you describe a common use case for a router with one or more network modules?

    If you need more interfaces you use more modules. Say for instance a router needs to connect to five other routers. You need more ports!
    An expert is a man who has made all the mistakes which can be made.
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    it_consultantit_consultant Member Posts: 1,903
    I have a 3825 with an additional WIC. I have 2 connections from my ISP, so that eats two connections right there. Then one connection to the dirty switch and one connection to the firewall.

    Say you are bonding to T1 connections together, you will need 2 T1 cards to term the ISP connections.

    Many routers which are CPE have only one module (assuming you are not bonding the connections) since you only need one int for the customer and the int on the ISP side. If you ever go to an ISP POP, you will see routers with lots of ports. In fact, you will see things that look a lot like switches (icon_smile.gif) because the ISP needs port dense routing. All of Brocade's routers are in switch chassis', which makes sense since a "router" is really just a piece of software - no need to change chassis because one is a "router" and another is a "switch".
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    Abunai1200Abunai1200 Registered Users Posts: 2 ■□□□□□□□□□
    Thanks for the feedback, all.

    It's helpful to know that these routers can provide routing to more than 4 networks.

    I did a bit more reading and investigating.

    In my theoretical case, I am only routing between 2-4 networks and I accomplish that routing via the HWIC interfaces.

    I have additional network devices that belong to one or more of those networks.

    Instead of purchasing an additional switch, I'm assuming that I can use a Cisco NME-XD-48ES-2S-P "EtherSwitch Service Module" (extended-double-wide) in two of the network module slots to provide the layer-2 switching for those network devices. (I can have two of these double-wide modules, given the four available network module slots.)

    Is my assumption correct? And if so, would all of the 48 ports on a single EtherSwitch module necessarily belong to the same network (broadcast domain)?
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    sratakhinsratakhin Member Posts: 818
    A CCNA-level switch will cost much less than the module you are referring to :)
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