connecting my Switch to Internet Modem

[otb]

Dears

I’m facing a problem in configuring a cisco switch with Internet Modem

Here is my case

I have 1 Cisco 3850 switch and 3 linkses Modem for internet each modem is providing

Users with it’s DHCP

Modem 1 IP’s is 192.168.10.X

Modem 2 IP’s is 192.168.11.X

Modem 3 IP’s is 192.168.12X

I have 30 users and I need 10 users to take IP’s from modem 1 and 10 users from modem 2 and 10 users from modem 3

And I need all this user can communicate with each other

I make 3 Vlan and it work fine but the PROBLEM is users can’t communicate with each other.

Thank you,

[Deepak Kumar]

Hi,

There are a few things to consider:

1. InterVLAN Routing: Enable L3 routing on the Cisco 3850 Switch with using the command: "IP Routing"

2. Assign IP address on all three VLANs as

Interface VLAN 2

IP address 192.168.2.2 255.255.255.0

3. Assign Routes on your Modems as (I am not sure which is your modem and Where is an option for routing)

Destination Subnet: 192.168.1.0 Destination Mask: 255.255.255.0 Destination Gateway: 192.168.2.2

Destination Subnet: 192.168.2.0 Destination Mask: 255.255.255.0 Destination Gateway: 192.168.2.2

Same must be repeated for all VLANs and but routing statement will change.

If there is no option to configure the routing then you have to configure PBR on 3850.

Regards,

Deepak Kumar

[otb]

Hi Deepak Kumar

thank you for your replay,

i need to check your suggestion but before that i will enplane more about the case
my 30 users with get IP and GW from MODEM (each 10 users i need them to go through 1 modem)
i did 3 VLAN
VLAN 1 will have MODEM 1 with IP 192.168.10.1 and users with get IP's within 192.168.10.X now if i make interface VLAN 1 with 192.168.10.2
it will give me messages for duplication with 192.168.10.1 which is the MODEM IP

the problem that MODEM will give the users IP and GW 192.168.10.1
i cant make SVI and make it GW for USERS in order to have comunication between users .

thank you

[balaji.bandi]

Make sure there is not other device have same IP 192.168.10.2 in the network. check ip arp table in the modem ?

[Deepak Kumar]

Hi,

I know there are more limitations with modems, So I asked you that is it possible to configure Route on the Modem? Is it possible to change Default gateway in DHCP server configuration (DHCP Skope) on the modem?

If you are not sure then share your modem Model number.

Regards,

Deepak Kumar 

[Richard Burts]

Can we get a better understanding of the topology from the original poster. We have been told about 3 modems, 1 switch and 30 users. How are devices connected? Does each modem connect to a switch port? Is the switch port connecting to each modem in a separate vlan?

If we knew more about the topology we might be able to make better suggestions. But based on what we have been told so far I believe that there is a fundamental problem. If each modem is using DHCP to assign IP addresses to users and if it assigns the default gateway for the user as the modem IP address then when a user in the first vlan wants to communicate with a user in the second vlan then the packet from the first user will be sent to its gateway on the modem. Unless there is a way to configure some routes on the modems it will be difficult to route between the subnets.

HTH

Rick