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How can I make two different network segment can talk to each other

Posted on 2008-10-07
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Last Modified: 2008-10-08
Here is the laundry list:
- Two server that each one has two NIC.
- Two different network segments: 192.168.1.1 and .2.1
- 5 Linksys SRW2048 switches
- 1 Linksys RV042 router 192.168.2.1)
- 1 Cisco 1841 router (192.168.1.1)

I connected all the SRW2048 through their uplink, implementing LAG and trunk them too.

Because I divided the network in two I can't make a computer from segment .1.1 to access a computer on .2.1 segment.

So I wonder how can I over come this. I have tried the vlan, but I'm not sure that I'm doing the right thing because I either loss connection between the ones in the same segment or nothing happened.

I trunk the ports between the switches.
I selected two computers, one from each network.
I port trunk them.
I set the port to vlan to the right vlan

I can't ping between them so I their I'm doing something wrong or my approach is not quite right

For those that wonder about two segments, well I run out of ip address also I move the iPhone and personal laptop to the DHCP in the .2.1 segment.

Thanks,
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Question by:prologue
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11 Comments
 
LVL 3

Expert Comment

by:keno44
ID: 22663299
Need more info. Are you using both routers and if so through which ports are they connected to the other router and switches? Even though you have these devices in the same VLAN, their different network masks are preventing them from communicating.

By default, most switches do not route packets from one network to another network. You have to have a switch that supports routing or utilze your router's ethernet interfaces.  
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Expert Comment

by:tismetoo
ID: 22663440
As Keno suggests - you need a route between the 2. It's OK physically connecting the LANs but there has to be a router to readdress the packets for the destination required. Choose one of the routers or one of the servers, give them an IP address on each subnet and configure it to route traffic. Ideally do this on whatever is your default gateway device, especially if it's the same for both subnets ( but suspect not ). If you don't do this on the default gateway the default gateway needs a route defined for the device with the routes specified, or all the clients need the route adding ( you can use DHCP for this ).

Hope this helps.
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Accepted Solution

by:
aleghart earned 125 total points
ID: 22664429
You can't ping between two computers on different sub nets without a router.

If you're trying to run two subnets only because you need more IP addresses, that is your problem.

Flatten the network.  Instead of two /24 networks, use one /23.

Change your subnet mask:

192.168.1.1 , mask=255.255.254.0

gives you 192.168.0.0 - 192.168.1.254

Should be room for 510 hosts.

http://www.aboutmyip.com/AboutMyXApp/SubnetCalculator.jsp?ipAddress=192.168.1.0&cidr=23
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Expert Comment

by:aleghart
ID: 22664469
http://www.solarwinds.com/products/freetools/free_subnet_calculator.aspx

Cool free tool for calculating sub-nets.

Also useful for generating IP address lists for a given network.
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Author Comment

by:prologue
ID: 22664546
Hi Keno44,

Yes, I'm using both routers. The two routers are connected to a switch, because the COVAD wireless provides a 10baseT connection and 5 IP addresses.

I wonder about your line "You have to have a switch that supports routing or utilze your router's ethernet interfaces." Will a Bridge Multicast function on the Linksys SRW2048 will do it? or if I create two virtual interface on the Cisco 1841 router, could that handle the job?

Hi Tismetoo,

I have one gateway and the two routers address it.

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Expert Comment

by:aleghart
ID: 22665188
@prologue: is there a reason you're trying to run two LANs on your physical network?  I didn't see a reason listed in your OP.

If you don't need two separate networks, you can eliminate the routing problems by having only one subnet on the LAN.  You can remove a router and dispense with the VLANs.

Running out of IP addresses is just an addressing issue.  No need to complicate things by adding routes and routers.
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Assisted Solution

by:lrmoore
lrmoore earned 125 total points
ID: 22665211
you could use the 1841 router. Create a trunk port on the switch and plug the 1841 into the trunk port.
Create 2 vlan subinterfaces on the router and give these interfaces IP addresses. Set the PC's on each vlan to point to this router's IP address as their default gateway.

Example:
interface Fast 0/0
 no ip address
interface Fast 0/0.1
 encap dot1q 2  <== where "2" is the vlan number
 ip address 192.168.1.1 255.255.255.0
interface Fast 0/0.2
 encap dot1q 3
 ip address 192.168.2.2 255.255.255.0

Which router (RV02 or 1841) is your Internet connection?
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Expert Comment

by:keno44
ID: 22668688
Prologue,

Irmoore has explained how to route between VLANs with a switch that does not support routing. Trunk the switch port into sub-interfaces on the router.
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Author Comment

by:prologue
ID: 22671166
Hi,

Thank you all, I'm going to use two of the solution that I was giving a one from aleghat and the one from Irmoore.

Because I can expand my network and also create a trunk port on the cisco router, but one more question for Irmoore because I will use it sometime in the future which will entitle to change all the sub netmask of every computer that is running on static ip address:

Could I use the following:
interface Fast 0/0
 no ip address
interface Fast 0/0.1
 encap dot1q 2  <== where "2" is the vlan number
 ip address 192.168.1.0 255.255.254.0
interface Fast 0/0.2
 encap dot1q 3
 ip address 192.168.2.2 255.255.255.0

Thanks you all again.

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LVL 79

Expert Comment

by:lrmoore
ID: 22674927
I would not use mask 255.255.254.0 with 192.168.1.x
This actually constitutes a "super"net and not a subnet mask.
We strongly suggest that no single vlan or broadcast domain includes more than the 250+ hosts available in the 255.255.255.0 subnet mask.
If you need more hosts, create more vlans and keep each vlan to a max 250 hosts
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Author Comment

by:prologue
ID: 22675850
I will take that in consideration, thanks for your invaluable input.
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