Adding a secondary IP address won't affect the number of broadcast domains.
Secondary IP addressing is a network-layer configuration. Broadcasts are a
physical and data-link layer issue. All stations in a LAN hear each others
broadcasts because they either share a cable, are connected via hubs which
forward all bits, or are connected via switches which forward all broadcasts.
Here's an analogy:
You live on First Street. One afternoon, instead of cursing at your
routers, you take out your frustration by yelling out your window, "Hey
neighbors, I think you're all ugly." Now let's say that some of your
neighbors decide to rename their side of the street from First Street to
Main Street. When you yell out the window, won't they still hear you?
Renaming their street would be like giving them IP addresses in a different
subnet.
Now, who can follow up with a VLAN example??! &;-)
Priscilla
At 10:48 AM 2/20/01, Tony Chen wrote:
>Follow up question to the secondary IP address on the ethernet interface:
>
>When you add secondary IP address to an ethernet interface, does that
>create multiple broadcast domains, or still one broadcast domain?
>
>Tony
>
> >>> Priscilla Oppenheimer <[EMAIL PROTECTED]> 02/19/01 09:33PM >>>
>At 04:47 PM 2/19/01, Chris Wornell wrote:
> >Hello,
> >
> >I've found out you can't create multiple interfaces on an ethernet port
> >apparently. I was wondering why this is exactly? I know you can accomplish
> >the same on serial lines using pvc's but it seems odd you can't do it on
> >ethernet.
>
>Why do you want to create multiple interfaces on your Ethernet port?
>Ethernet was designed as a connectionless, packet-switched shared network.
>Serial links, on the other hand, are more often used for
>connection-oriented virtual circuits. Subinterfaces let you associate a
>single physical link with multiple virtual circuits.
>
> > I know there are ethernet only networks and the ip secondary
> >command doesn't seem right compared to creating a new interface.
>
>Sure there are Ethernet-only networks. Each physical Ethernet port on a
>router is usually associated with an IP subnet. If you happen to have two
>IP subnets on the LAN to which a physical port is attached, you could use a
>secondary IP address as a workaround to this problem. Traffic between
>subnets would still go through the router usually.
>
>If you're using your Ethernet port as a "trunk port," and you use ISL or
>802.1q VLAN encapsulation, then you can configure subinterfaces. In this
>case, subinterfaces let you associate a single physical link with multiple
>VLANs. Inter-Switch Link (ISL) and IEEE 802.1q maintain VLAN identification
>information as traffic travels between connected switches.
>
>Maybe you can give us a better idea of what you are trying to accomplish
>and we can provide more tailored information, but I hope this info was
>somewhat useful.
>
>Priscilla
>
>
>
> >Chris Wornell
> >Technical Support
> >MM Internet http://mminternet.com
> >888-654-4971
> >CCNA, CCDA, CSE
> >
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