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New Member

Connecting Cable Modem Through 3560 Switch

I have a 3560 series switch and two comcast cable modems. I connected the modems to them switch via cross over cables and set an OSPF routing on their subnets. I connected my wireless router to another port of the switch and set its gateway IP on the switch port. I can ping the modem with the switch and I can ping the wireless too. But I cannot access to the Internet via the wireless router.

Can anybody help me? Tell me what is the process to accomplish this task. I need load balancing on two cable modems and get a single network connection via the wireless router.

48 REPLIES
New Member

Re: Connecting Cable Modem Through 3560 Switch

Hi,

Here is the scenario as I see it:

Modem-------|

                        |-----------Switch------------- Wireless Router

Modem-------|

You can have 2 default routes on the switch pointing to the Cable Modems, no need for OSPF. If you use multiple ip route 0.0.0.0 0.0.0.0 commands, traffic is load-balanced over the multiple routes:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094374.shtml#route0.0

Remember to have the cable modems on different SVI's or issue the "no switport" command on the interfaces attached to the modems.

Configure the Wireless router to send all traffic to the switch.

In order for OSPF or any other routing protocol to work, you'll need the modems to use that same protocol.

Let me know how things work.

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

Thanks, but i have some problems with this switch. Here is the scenario and what i do:

Modem |-------------------------------|

10.10.10.1 255.255.255.0

                                             |-------------Switch-----------|Wireless Router            

Modem |-------------------------------|                                    10.0.0.14 255.255.255.0

20.20.20.2 255.255.255.0

Switch(config)#ip routing
Switch(config)#int fast0/2
Switch(config-if)#ip address 20.20.20.1 255.255.255.0
Switch(config-if)#^Z
Switch#config t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#int fast0/3
Switch(config-if)#ip address 10.0.0.1 255.255.255.0
Switch(config-if)#int fast0/1
Switch(config-if)#no switchport
Switch(config-if)#ip address 10.10.10.2 255.255.255.0
Switch(config-if)#exit
Switch(config)#ip defa
Switch(config)#ip default-network 20.20.20.2
Switch(config)#ip default-network 10.10.10.1
Switch(config)#exit

But my routing table won't change and I get this (plus I cannot access to the Internet through my wireless router):

Switch#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set  <------------------------------------------------------------------- See!

     20.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       20.20.20.0/24 is directly connected, FastEthernet0/2
S       20.0.0.0/8 [1/0] via 20.20.20.2
     10.0.0.0/24 is subnetted, 1 subnets
C       10.0.0.0 is directly connected, FastEthernet0/3

What am i doing wrong?

New Member

Re: Connecting Cable Modem Through 3560 Switch

Hi,

This is an example of configuring a gateway of last resort using the ip route 0.0.0.0 0.0.0.0 command:

Switch#configure terminal

   Enter configuration commands, one per line. End with CNTL/Z.

   Switch(config)#ip route 0.0.0.0 0.0.0.0 10.10.10.1

   Switch(config)#ip route 0.0.0.0 0.0.0.0 20.20.20.2

   Switch(config)#^Z

   Switch#

Let me know how it works.

Remember to enable "ip routing".

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

now I can ping www.google.com from the switch, but my wireless router is not connected to the internet..!! This should not be this hard, it is driving me nuts!!! What do you think is the problem? My wireless router ip address is 10.0.0.14 and the port on the switch which it is connected to is 10.0.0.1. Also i can ping the wireless router from the switch.

Thanks again for your quick replies.

New Member

Re: Connecting Cable Modem Through 3560 Switch

Any other clue???

New Member

Re: Connecting Cable Modem Through 3560 Switch

Hi,

The configuration on the switch is right, so know, to test it u can attach a computer directly to the switch. Although you may want to check the configuration on the AP, are you using the IP address of the switch as the default gateway for the AP? DG should be 10.0.0.1.

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

The port on the switch which the AP is connected to is on "no switchport" and has this IP: 10.0.0.1 255.255.255.0

So the DG set on the AP is 10.0.0.1 and the AP itself has an IP address in that range.

I can even ping to modem with the wireless router but not the Internet. Do you know why?

New Member

Re: Connecting Cable Modem Through 3560 Switch

Also when I connect my laptop to another port of the switch I have no access to the internet. I have internet access on the switch but when I connect a wireless router to it or my own laptop it drops packets. What should I do?

New Member

Re: Connecting Cable Modem Through 3560 Switch

Are you using the IP address of the switch as your default gateway? Can I see the configuration of the switch?

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

What do you mean by IP address of the switch? Which port's IP address are you referring to?

Here is a full "show run" information:

version 12.2
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname Switch
!
boot-start-marker
boot-end-marker
!
no logging console
enable password admin
!
!
!
no aaa new-model
system mtu routing 1500
ip routing
!


!
spanning-tree mode pvst
spanning-tree extend system-id
!
vlan internal allocation policy ascending
!
!
!
!
interface FastEthernet0/1
no switchport
ip address 10.10.10.2 255.255.255.0
!

interface FastEthernet0/2
no switchport
ip address 20.20.20.1 255.255.255.0
!
interface FastEthernet0/3
no switchport
ip address 10.0.0.1 255.255.255.0
!
interface FastEthernet0/4
!
interface FastEthernet0/5
!
interface FastEthernet0/6
!
interface FastEthernet0/7
no switchport
ip address 30.30.30.1 255.255.255.0
!
interface FastEthernet0/8
!
interface GigabitEthernet0/1
!
interface Vlan1

no ip address
!
ip classless
ip route 0.0.0.0 0.0.0.0 20.20.20.2
ip http server
ip http secure-server
!
!
ip sla enable reaction-alerts
!
!
!
!
line con 0
line vty 0 4
login
line vty 5 15
login
!
end

----------------------

I connected my laptop to FastEthernet 0/7 and gave the IP address to the port.

Please tell me what am i doing wrong?

New Member

Re: Connecting Cable Modem Through 3560 Switch

Any ideas?

New Member

Re: Connecting Cable Modem Through 3560 Switch

Hi,

Yes, I do see what we are missing:

1-      We still need one more default static route to the other modem.

2-      We need a NAT configuration.

Here is how you should do it:

!

interface FastEthernet0/1

no switchport

ip address 10.10.10.2 255.255.255.0

ip nat outside

!

interface FastEthernet0/2

no switchport

ip address 20.20.20.1 255.255.255.0

ip nat outside

!

interface FastEthernet0/3

no switchport

ip address 10.0.0.1 255.255.255.0

ip nat inside

!

access-list 1 permit 10.0.0.0 0.0.0.255

ip nat inside source list 1 FastEthernet0/1 overload

ip nat inside source list 1 FastEthernet0/2 overload

!

ip route 0.0.0.0 0.0.0.0 10.10.10.1

!

This should solve the problem, sorry for the late response.

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

Well the switch that I am using is a 3560 serie, so I do not think it supports NAT commands. Is there anyway to go around it and maybe use some other configurations? It is odd that the switch itself can ping 4.2.2.2 and my laptop or the wireless router which are connected to it can't! Also another wierd thing is that when I used Fast0/2 as a trunk port, my laptop seemed to be connected (the icon under there said i have access to the internet) but I could not ping 4.2.2.2!!!

So what do you think?

New Member

Re: Connecting Cable Modem Through 3560 Switch

I do see it doesn't support NAT, my bad!

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a008011c629.shtml

Both modems are only going to route for the 10.10.10.0 and 20.20.20.0 address. So maybe we can include the computer or the AP on the same VLAN (creating a VLAN for each modem) with the modems but that is not going to load balance at all.

Let me reproduce this on my LAB and see what woraround I can find.

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

Oh thanks a lot man. So i will wait for your reply

again i appreciate it

New Member

Re: Connecting Cable Modem Through 3560 Switch

Also, do you think it is possible to use the comcast modem to do the NAT? It

has a 1-NAT-1 feature.

Thanks again in advance

New Member

Re: Connecting Cable Modem Through 3560 Switch

Hi,

After testing in the lab, I see no workaround. Maybe we should try with a different device. I have consulted other engineers and we came to the same conclusion, use a different device, do you have a router we can configure?

The modem will only do NAT for the addresses configured in the LAN segment.

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

I am very grateful for your help so far.

Well I can buy one. But how much are we talking here? And also are you sure that a router that does NAT will be an answer to this task and the load balancing will be done fine?

Thanks,

New Member

Re: Connecting Cable Modem Through 3560 Switch

Any specific model comes to mind? And also can we use the router and the switch together and get the results we want?

Hall of Fame Super Gold

Re: Connecting Cable Modem Through 3560 Switch

You can use, eg a 2901 that has three ethernet routed ports.

New Member

Re: Connecting Cable Modem Through 3560 Switch

Hi,

To better recommend a model, here are some basic questions I may need to be answered:

How many users?

Besides NAT, what other features do you need? (Security, Firewall, encryption)

Traffic load? (estimated)

Any VoIP?

Any other input you can give me regarding the network.

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

Well there are usually 20 to 25 users directly and almost same amount remotely.

There should be a DMZ and firewall which I think we can use the Comcast itself.

About traffic load we have some high traffic days but the load balancing between these two i think will cover it.

There are several virtual servers which each has its own public IPs that needs to be NATed and some physical servers that must have NATing process on them as well.

The thing that makes me wonder is that how is it that I can have access to the Internet through the switch itself but can't have access through another port of the switch. Are you sure there are no ways to accomplish this with current equipments? Is NAT the only way to do this? No other way around?

New Member

Re: Connecting Cable Modem Through 3560 Switch

Anything comes to mind?

New Member

Re: Connecting Cable Modem Through 3560 Switch

Hi,

First of all, let me apologize for the late response as I was out of the office. Now, to answer your question, the only reazon why the switch is able to access the internet is because it has an IP address on the range that is covered by both modems, different to the other devices that have an address on a different range.

Now, regarding the router, we can use a 2811 router, which is powerfull enough to cover the needs of the network and provide the requested features. We are going to need to add an extra card to connect to the LAN as both integrated 10/100 Fast Ethernet ports are going to be connected each to a different modem.


NAT is a feature that we are going to need for this design.

Let me know if I can be of further help.

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

If you are going to buy a device why not look at the ASA5505 series. It provides 8 ethernet connections and does NAT. You would need to look at the different bundels to make sure it will provide a backup ethernet connecton for your secondary cable connection.

New Member

Re: Connecting Cable Modem Through 3560 Switch

So what is the best way to choose which model i need? It is important that it does the load balancing without any issues. I have Cisco 1941, Cisco 2811 and ASA 5505. Which one should i choose according to my needs?

New Member

Re: Connecting Cable Modem Through 3560 Switch

Hi,

As far as my understanding the ASA5505 will not load balance and NAT on different subnets at the same time, it will do it with 2 different IP's on the same segment, although not as what the customer is looking for.

Cheers,

Yanil

New Member

Re: Connecting Cable Modem Through 3560 Switch

How about 1941 or 2811? Does it do load balancing? Also I am going to need different VLANs so i need to be able to route in different subnets.

New Member

Re: Connecting Cable Modem Through 3560 Switch

Hi,

Both routers will do the job, I have a lot of experience with the 2811 so I can recommend you that one as it is very stable. On the other hand the 1941 is a new router that comes with support to new hardware, although for your needs we should go with the 2811!

Let me know if you need anything else.

Cheers,

Yanil

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