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New Member

secondary ip on cisco 3745


i am having cisco 3745 router with 2 ethernet ; want to create 4 diffrent subnet on one of the ethernet port for VLAN. Is it possible? let me know....

Also what will be other way to create diffrenet subnet on one interface.I dont have any other module with me and dont have much time to get one as need to setup the LAn with in 2 days.....

you can refer the attached LAN connectivty diag. where user on pc should able to access server on subnet same with other floor users..

( ip in diagram are dummy ip)


Hall of Fame Super Silver

Re: secondary ip on cisco 3745


There are two ways to accomplish what your drawing seems to show. I say seems to show because the drawing is ambiguous about the connection of the switch to the 3745. If that connection is a trunk carrying multiple VLANs then you want to configure subinterfaces on the 3745 interface to accomodate the VLANs and to provide inter-VLAN routing. But when the drawing shows it as an unmanaged switch I wonder if the connection could possibly be a trunk.

If the connection is not a trunk then all of the ports are in a single broadcast domain (single VLAN or whatever terminology that you want to use). The solution would be to use secondary addressing on the Ethernet of the 3745. While the configuration would look like you have separate subnets and the benefits that different subnets have (limiting broadcasts, etc) the reality is that all the devices are in the same broadcast domain. Every machine will see all the broadcasts from every other machine. Every PC can potentially ARP for any other PC and they could communicate directly, without needing the router.

The drawing suggests that you are attempting to isolate the traffic of each floor. But the choice of unmanaged switches does not support that.



New Member

Re: secondary ip on cisco 3745

Thanks rick;

So you mean to say i need mangedswitch to create trunk between router and that switch... then create vlan

other way around is to give secondary ip and create only two diffrenent subnetbut it will be under same Broadcast domain......

hope i got you right....