Cable modem to 3750

[gunnermike53]

I have Cox Cable with a DHCP IP address. I want to connect my cable modem to my 3750. I have fa1/0/1 connected to the modem. I have a few other devices I would like to connect to the rest.

I can get an IP from Cox on fa1/0/1. My switch will pass out IP's to the devices that connect to it. NONE of those devices can connect to the internet.

What am I doing wrong?

mikeroswitch#sho run
Building configuration...

Current configuration : 3786 bytes
!
! Last configuration change at 06:07:35 UTC Thu Jan 22 2015
! NVRAM config last updated at 06:07:39 UTC Thu Jan 22 2015
!
version 12.2
no service pad
service timestamps debug uptime
service timestamps log uptime
service password-encryption
!
hostname mikeroswitch
!
no logging console
enable secret 5 $1$OCX1$xPVzdxIbA1dzoEhNaNiE/1
!
no aaa new-model
switch 1 provision ws-c3750-48p
ip subnet-zero
ip dhcp excluded-address 10.10.17.1
!
ip dhcp pool HOME
import all
network 10.10.17.0 255.255.255.0
default-router 10.10.17.1
!
!
no file verify auto
spanning-tree mode pvst
spanning-tree extend system-id
!
!
!
vlan internal allocation policy ascending
!
!
interface FastEthernet1/0/1
no switchport
ip address dhcp
!
interface FastEthernet1/0/2
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/3
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/4
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/5
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/6
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/7
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/8
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/9
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/10
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/11
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/12
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/13
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/14
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/15
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/16
switchport access vlan 10
switchport mode access
!
interface FastEthernet1/0/17
shutdown
!
interface FastEthernet1/0/18
shutdown
!
interface FastEthernet1/0/19
shutdown
!
interface FastEthernet1/0/20
shutdown
!
interface FastEthernet1/0/21
shutdown
!
interface FastEthernet1/0/22
shutdown
!
interface FastEthernet1/0/23
shutdown
!
interface FastEthernet1/0/24
shutdown
!
interface FastEthernet1/0/25
shutdown
!
interface FastEthernet1/0/26
shutdown
!
interface FastEthernet1/0/27
shutdown
!
interface FastEthernet1/0/28
shutdown
!
interface FastEthernet1/0/29
shutdown
!
interface FastEthernet1/0/30
shutdown
!
interface FastEthernet1/0/31
shutdown
!
interface FastEthernet1/0/32
shutdown
!
interface FastEthernet1/0/33
shutdown
!
interface FastEthernet1/0/34
shutdown
!
interface FastEthernet1/0/35
shutdown
!
interface FastEthernet1/0/36
shutdown
!
interface FastEthernet1/0/37
shutdown
!
interface FastEthernet1/0/38
shutdown
!
interface FastEthernet1/0/39
shutdown
!
interface FastEthernet1/0/40
shutdown
!
interface FastEthernet1/0/41
shutdown
!
interface FastEthernet1/0/42
shutdown
!
interface FastEthernet1/0/43
shutdown
!
interface FastEthernet1/0/44
shutdown
!
interface FastEthernet1/0/45
shutdown
!
interface FastEthernet1/0/46
shutdown
!
interface FastEthernet1/0/47
shutdown
!
interface FastEthernet1/0/48
shutdown
!
interface GigabitEthernet1/0/1
!
interface GigabitEthernet1/0/2
!
interface GigabitEthernet1/0/3
!
interface GigabitEthernet1/0/4
!
interface Vlan1
no ip address
shutdown
!
interface Vlan10
ip address 10.10.17.1 255.255.255.0
!
ip classless
ip route 0.0.0.0 0.0.0.0 FastEthernet1/0/1
ip http server
!
!
!
!
!
control-plane
!
banner motd ^C Mi^C
!
line con 0
password 7 1214121443535F50
login
speed 115200
line vty 0 4
password 7 1214121443535F50
no login
line vty 5 15
password 7 0009040555035852
no login
!
!
end

 

[brshoemak]

Get a router and put it between your cable modem and 3750. It can be SOHO grade or a Cisco router if you're doing it to learn - just make sure it can handle whatever throughput (internet speed) you're working with.

The problem is you don't have any NAT statements to translate your internal IP addresses to a public IP address.

When you are trying to contact something on the internet without NAT, the request comes with a source address of (in your case) of 10.10.17.X /24 (/24 = 255.255.255.0). Because those addresses are part of an established standard for private IP addresses, routers on the internet not route those packets and they will be dropped.

You need NAT and the Cisco 3750 does not support NAT in any way, I think the lowest switch that supports NAT are the 6500 series which are big and expensive. Routers are designed to route between networks, switches are designed to direct packets to the correct nodes on a network.

 

[JackMDS]

Maybe this can Help.

http://www.howtogeek.com/99001/htg-explains-routers-and-switches/

 

[gunnermike53]

Maybe this can Help.

http://www.howtogeek.com/99001/htg-explains-routers-and-switches/

I appreciate that however I understand how routers and switches work. The 3750 is a layer 3 switch which means it is capable of switching between subnets. I am pretty sure there is a way to do it.

 

[dave_the_nerd]

I appreciate that however I understand how routers and switches work. The 3750 is a layer 3 switch which means it is capable of switching between subnets. I am pretty sure there is a way to do it.

http://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/29283-166.html

Says there's not NAT support on the 3750.

:shrug:

If you're interested in this stuff, I'd encourage you to take a class or two at a local community college - it really helped me.

 

[brshoemak]

I appreciate that however I understand how routers and switches work. The 3750 is a layer 3 switch which means it is capable of switching between subnets. I am pretty sure there is a way to do it.

L3 switches like the 3750 are indeed able to route between networks. However, this is not an issue of routing between networks, it's an issue of NAT and source IP addresses.

The IP addresses of your internal clients are part of a range of IP addresses designated by RFC1918 that are non-routable on the internet. Any packet with a source IP address that falls in that range of IP addresses will be dropped and not routed any further on the routers/switches that make up the internet.

Without NAT, your data will appear with a source IP address of the client, which has a non-routable IP address (10.10.17.X) - it will be dropped. You need a function that can rewrite the source IP address to be one that is routable on the internet, like the IP address of your cable modem for instance. But it would also need to keep track of what clients sent what data since they would all share that same IP address (the cable modems address). That's what NAT is for.

Now, if you have a block of routable IP addresses then you can assign one of those to each of your clients to your hearts content and they will have internet access, because the source IP will be a routable address that can route directly back to the IP address it originated from.