Simple SOHO setup difficulties with 2821 Router and 2960 switch

[chriscavallo6]

HI my name is Chris and I am currently getting ready to take my CCENT. One issue I have had with my home lab is the lack of communication between my test network (cisco switch and one router interface) and my private network from my DSL Router. Here is a bit of setup information below.

I am using a Motorola NVG589 router on Private network 192.168.1.0, My routers IP address is 192.168.1.254 subnet 255.255.255.0

My Cisco 2821 router has 2 ports G0/0 and G0/1

 On router interface G0/0 I am using DHCP to be assigned an ip address of 192.168.1.79 (255.255.255.0)

 -Now at this point, i have no difficulty. I can ping and translate websites without issue and everything is okay.

I now want to create a DHCP pool for my network that will be used on the G0/1 interface going to a Cisco 2960 Switch on its G0/1 interface

I use the following commands

-int G0/1, Ip address 192.168.50.1 255.255.255.0, no shutdown

-Ip dhcp exlcude address 192.168.50.1 192.168.50.10

-Ip dhcp pool (name)

-network 192.168.50.0 255.255.255.0

-default router 192.168.50.1 (heres where im a litte confused, You need to point to the interface that connects the router to the switch correct? Making sure its in the same network? My other thought process is the default router may need to be 192.168.1.79)

-Dns server (again, not sure if it should be 192.168.50.1 or 192.168.1.79 or even 192.168.1.254 since that would actually be doing the page translation)

This is where im being hung up. If I continue configuration by either connecting a host(laptop) directly, I can be assigned an IP address and ping up to the 192.168.1.79 network, but i cannot ping 192.168.1.254. The confusion lies in if i can reach 192.168.1.79, why can I not reach 192.168.1.254 if they are on the same network? Also. in the cisco routers routing table, I can see all the connected devices including 192.168.1.254. If i go into my laptops ARP table though, I cannot see an entry for 192.168.1.79 even though I can ping it.

Im sure there is a step or two I am missing on the router side to get the 192.168.1.0 and 192.168.50.0 networks to communicate. I understand if this has been confusing and please let me know if any other information is needed. This has really got me stumped and This place is my last resort, Thank you in advance for any help.

[Jon Marshall]

You cannot ping 192.168.1.254 because that is a different L3 device and it has no knowledge of your 192.168.50.0/24 subnet.

You need to add a route to the Motorola router telling it how to get to 192.168.50.0/24 ie. in Cisco syntax it would be -

"ip route 192.168.50.0 255.255.255.0 192.168.1.79"

although you may want to exclude that from DHCP and assign it statically. 

To reach the internet from 192.168.50.0/24 you also need to NAT those IPs and if your Motorola router allows this you can set it up there.

If it can't do this then you can use NAT on the Cisco router, let me know if you need help with that.

Finally DNS settings are whatever DNS you have on clients that work in your existing subnet.

Jon

[chriscavallo6]

Hi Jon,

That was a great Response and I appreciate the answers. I do have a couple other questions.

I was able to add the second network by doing what my router calls a cascaded router and it allowed me to add the 192.168.50.0 network and I can now ping 192.168.1.254 from my switch.

I enabled NAT inside command on the G0/1 interface going to my switch. I still cannot translate webpages or even ping outside of the network (IE ping 8.8.8.8) I suspect there is more to enabling NAT and im reading through the ICND1 book as we speak but would appreciate a walk through if possible. I cannot use my Motorola router for NAT.

Once NAT is enabled, Does this mean i should be able to ping 8.8.8.8 without a DNS server?

-My understanding of NAT is translating your Private IP address to your Public ISP assigned IP address, so if pinging an IP directly(out of your network) do you need to use a DNS server(or better question, is it used?)

Also, Based on this configuration, Can I use a DNS server such as 8.8.8.8 or does the Motorola Home Router need to act as the DNS server? I understand what a DNS server does in theory but have a tough time grasping where it needs to be in a network.

Thank you once again, it was such a simple answer and I think i was getting too caught up in the Cisco learning side of everything. I believe that simple answer can help me a TON throughout my networking career, so Cheers!

[Jon Marshall]

You would usually use NAT to translate private to public IPs and if you have internet access for your 192.168.1.0/24 subnet your Motorola router will be doing that but it sounds like you cannot add another subnet ie. some devices only do NAT for directly connected networks.

You may want to check again because it must be doing NAT for your existing subnet but if you can't find anything then you can NAT all 192.168.50.x IPs to the outside interface IP of your Cisco device ie. 192.168.1.79 and because this is already being translated it should work.

So if you have added "ip nat inside" to gi0/1 you need to add "ip nat outside" to gi0/0 then add this to your configuration -

"access-list 101 permit ip 192.168.50.0 0.0.0.255 any"

"ip nat inside source list 101 interface gi0/0 overload"

then you should be able to ping 8.8.8.8 (no DNS needed).

As for DNS if you want to use web page names then you just need to give your clients DNS servers on the internet if you don't have an internal DNS server.

For a home setup you usually don't have your own DNS server.

Try the above and let me know how you get on.

Jon

[chriscavallo6]

Once Again I cannot thank you enough. I have done everything you said and I am connected to the internet through my private network!!!

I now plan to subnet that network 192.168.50.0 to a /27 which should give me 8 subnets and 30 host's per network. Then I will Implement router on a stick and create multiple vlans on my switch and put different devices on them and get them to communicate.

Let me know if you have any tips on creating multiple dhcp pools per subnet or anything else that may be useful in the above setup. I appreciate the tips.

Now thanks to you I have a much deeper understanding of how NAT and DNS are completely different things and yet when troubleshooting internet access issues, can be so closely related. I was having trouble understanding where NAT ended and DNS began, thats why i was intrested to know you can test NAT connectivity by pinging a websites IP to confirm you can access the actual internet. I was having NAT and DNS issues but didnt understand NAT is needed first to have any issue with DNS.(edit: please correct me, im not sure if this statement is correct since a DNS server could be on a local network and NAT would be used after)

My goal for all this is to experiment Implementing a small office environment with multiple "sections" using vlans like you would normally see in an office(ie Accounting, Sales etc) and get them to communicate with each other.

I feel all this troubleshooting will be very valueable in a real world setting. I have no previous IT experience but lots of computer and some networking experience. If you have any suggestions to modify my plan that my be better suited for real world experience, I would appreciate them.

Thank you once again, I truly appreciate your insight.

[Jon Marshall]

Just seen your edit.

Yes if you had a DNS server in your network that clients used then DNS would happen before NAT.

But bear in mind for internet resolution your internal DNS server would need to query an external one so you would still need NAT to be setup.

The two as you say are not directly related as such but you need them both to be working for internet access assuming you are using private IPs.

Jon

[Jon Marshall]

No problem glad to hear you got it working.

One suggestion is as I currently understand it you have an IP subnet in use between the two routers and it's not clear what the default gateway of the devices is although presumably not the Cisco device.

If you want to communicate between that subnet and the others you are creating it may make sense to move that subnet to the same interface as all the others using subinterfaces as you say.

This would be more like a real world setup where there is simply a P2P link between the two routers and all your internal vlans are behind the Cisco router.

Doesn't mean you have to do it that way though, just a suggestion.

As for setting it up it is a case of creating the vlans on the switch, using a trunk link to the router and using subinterfaces on the router together with a DHCP pool per subnet and exclude the router's IP address per subnet.

One last point, you have a 2960 switch and with the right software it is capable of acting as a L3 switch so you could route between all your vlans on there if you have the correct feature set.

Then you don't need subinterfaces on your router.

This would be even more like something you would see in a production environment but don't worry too much if you can't, using subinterfaces on the router you will still learn a lot.

Lastly any problems etc. you get with it feel free to post on these forums, that's what they are for and there are lots of people who can help out.

Jon

[Jon Marshall]

Just a quick point.

If you do use NAT on the Cisco device for your 192.168.50.0/24 subnet then you don't need the route you added because again all IPs are translated to the outside interface IP of your Cisco device.

Any other queries etc. feel free to ask.

Jon