SG300 as L3 and modem for internet not working

[nayef salem]

Hi all

i have a network that am trying to fix , i have 1 switch SG-300 as a layer 3 network and a modem provided by the service provider

see attachment.

vlan 1(192.168.100.1) vlan 2(192.168.101.1)

now my problem is the modem is acting as a gateway and also it has wireless , if i make the setup as the following :

user connect to wireless from modem , get dhcp ip (L3 switch acting as dhcp ) address with default gateway the L3 switch ,

there is interruption and some users have internet some don't.

only when when i make the modem (192.168.100.1) as gateway for clients , things works fine? and then no routing will happen as the modem doesn't support.

how can i overcome this problem?

i want to make the L3 switch as the gateway as it will do routing between the two vlans and also have internet ?

[keglass]

Nayef samel,

I am sorry to hear you are having trouble with your network. I recommend you also post this to the Cisco Support Community for additional feedback and information.

https://supportforums.cisco.com/

I hope this helps. Thank you for participating in the community.

Kelli Glass

Moderator for Cisco Customer Communities

[David Hild]

Hello Nayef.

You need to communicate your plans with the service provider that supports this wireless modem. I suspect that what you are trying to do is not possible for the modem because the one's I have seen only allow wireless traffic to go out the outside interface of the modem, thereby only having internet access and no access to the inside networks. This is a typical guest access scenario. You are obviously trying to do something different. If the modem is capable, you may need to put the DHCP service on it instead of the switch, make the modem the default gateway for the wireless clients only, and configure routes on the modem to the switch VLANs. The service provider should be able to help you with this.

I hope this is helpful.

[nayef salem]

Hi David

thank you for your reply

the problem with this router is that it doesn't support static routes even,

i believe dhcp server can be put anywhere , whether in L3 switch or the  modem itself , the most important thing is the gateway for clients , if i put the L3 switch as a gateway , the scenario of traffic will be :

client    >>     modem   >>   L3   >>  modem >> internet

100.X   >>     100.1      >> 100.2 >> 100.1     >>   internet

i believe this loop is the problem because as soon as i put the default gateway to the modem directly , everything was fine

but with this fixing the problem of instability , the routing between vlan 1 and 2 is no more valid and they can't see each other

as the modem has no static routes configs .and the modem ip address being the gateway to internet and wireless access too

[David Hild]

Hi Nayef.

That is what I thought was happening. I recommend that you do not use the wireless capability on the modem and purchase a separate AP that can be added to the inside network VLANs. This will make the routing much more simple.

I wish you good luck.