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Connecting Cable Modem to Catalyst 3500

Posted on 2006-05-15
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Last Modified: 2013-11-30
Is there a way to configure a catalyst 3500 switch to connect through a normal cable internet modem?  I have tried configuring the IP for the VLAN to the static IP given by the ISP along with the GW and DHCP server.  When I connect the cable modem to the switch I cannot see past the switch, I cannot even ping th GW.  Any ideas?

Thanks in advance.
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Question by:nakoz69
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by:mikefalcone
ID: 16684783
The device that has the assigned IP has to be the gateway on all the other devices to get thwough it to the internet.


Did you assing the IP to VLAN0?
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by:nakoz69
ID: 16684914
So basically lets say the following was the IP address settings for my Cable modem

IP: 192.168.1.1
GW: 192.168.1.254
DNS: 192.168.2.1
DNS: 192.168.2.2

and I have two cisco 3500 switches.

The 3500s would have to be configured for VLAN 1 with the IP address of 192.168.1.2 and 192.168.1.3 and both would have the GW of 192.168.1.1 (IP of cable modem)?

Is this correct?
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by:mikefalcone
ID: 16685269
Correct

The computers that need to access the internet would also have a gateway of 192.168.1.1.
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by:nakoz69
ID: 16685387
I have tried that already, and yet still no dice.  The way I have them configured now is the one cisco 3500 switch is configured with the 192.168.1.1 IP address for VLAN1 with a GW of 192.168.1.254.  The other switch is 192.168.1.2 IP for VLAN 1 and a GW of 192.168.1.254.  The two switches are communicating with each other just fine over telnet using their IPs but I cannot see the cable modem and it is hooked to int fa0/1 on the 192.168.1.1 switch.  
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by:mikefalcone
ID: 16685552
is the cable modem 192.168.1.254
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by:mikefalcone
ID: 16685596
For some reason I'm thinking the default VLAN is VLAN0. check to see if there is a VLAN0 on those switches
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by:nakoz69
ID: 16685907
The cable modem is 192.168.1.1 and the default VLAN for the switches is VLAN 1.  The gateway for the cable modem is 192.168.1.254.
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plemieux72 earned 400 total points
ID: 16686565
So your cable modem is also a router?  

If not, you have to get a router that can do NAT (or PAT).  The 3500XL switches are layer 2 only.  This is why you need a router or some kind of layer 3 device as well.

But, once you get a router attached to your cable modem, if its inside interface is 192.168.1.1/24, here is how you'd configure your 3500XL without using VLAN 1 (the native VLAN):

vlan database
vlan 100
exit
conf t
int vlan 100
 ip addr 192.168.1.5 255.255.255.0
 no shut
int fa0/1
 desc TO ROUTER
 switchport mode access
 switchport access vlan 100
 no shut
int vlan1
 no ip addr
 shut
 exit
copy run start

Then make sure the router is connected to port 1.  This config makes your switch management IP 192.168.1.5.  Then, you can assign the remaining ports you want to use to VLAN 100 and no shut them and connect clients to them.

Don't forget to verify port 1 for errors (there should be none):

sh int fa0/1

If you see input errors, that means you have a speed/duplex mismatch.  Hardcode both speed and duplex on the router and port 1 on the switch or ensure both are set to auto.  Clear counters fa0/1 and then check for errors again.
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by:Jaedub
ID: 16687452
Quite simple....Enable the VLAN

Int vlan1
no shut
exit
Write mem
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