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Can two legs of a router be configured to be in the same subnet?

I am a newbie in networking and is experimenting with CISCO Packet Tracer 5.0. I found that in Packet Tracer I cannot configure two legs of a router to be in the same subnet. In that software one simply can't configure a network card to be in the same subnet as an already configured card. However, I found that I can configure the two NICs in my PC to be in the same subnet, and can still get through to the Internet. I know that a router loses most of its role if both of its legs are configured to be in the same subnet, but theoretically are there an rules forbiding such practice?

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Yes, the route table won't like the same subnet on two interfaces. I'm not sure if this would work if you didn't have "ip routing" configured... you could try turning off "ip cef" too... but i've never been able to do this on a real router.

Other option on a real router is to put both interfaces in "bridge" mode, or configure the second interface to clone the details from the first... although i've only ever done this with Dialer interfaces before.

So I guess the answer is yes... the router wants to put the route to the subnet in its route table (show ip route) and if you have two interfaces both with the same subnet, the route-path costs would be equal and identical... which is a huge issue in a networking environment.

Your PC doesn't care... it's not really routing. It's quite common to do this with a PC for the purposes of doubling bandwidth, load balancing, or having redundant links. (on the switch you would need to configure a "port-channel" to bond two ports together.)

Cheers!

Posted on Feb 05, 2009

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I have set my Asus RT-N12 to repeater mode, have captured the WiFi source signal, have connected my Client router with CAT5 cable but can't get internet from the Client router.


can you provide a diagram similar to this
I am doing CNNA so this was created with Cisco Packet tracer which is only available to Cisco Students


25880832-z0b4ejwdpu00bf4gywjxw3j2-2-0.png

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What collaboration capabilities are available on the new Cisco 2900 and 3900 Series routers?


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Jun 25, 2014 | Computers & Internet

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I have tried connecting Cisco linksys router but it gives ERROR 322 NEW ROUTER OR GATEWAY NOT DETECTED...How can I solve this problem please advice


Use an Ethernet cable to connect from the network-port on your computer to one of the LAN ports on the router.
Click Start
Click Run
Type CMD
Press Enter
Type IPCONFIG
Press Enter
You should see output like:
IP Address. . . . . . . . . . . . : 192.168.1.100
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.1.1

if the router has self-configured, and is ready for "wired" usage.

Then, start Internet Explorer.
Type http://192.168.1.1
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Login to the web-server "inside" the router
Click to run the "Wireless Networking Setup Wizard" to configure it for "wireless" usage.

Feb 21, 2011 | Cisco Linksys Wireless N Home Router...

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Dhcp setup on a Cisco 2851 router


Let's look at how to configure basic DHCP on an IOS-based router. For this example, we'll start off with the default configuration on a Cisco 2611 router running IOS 12.2. (The configuration should be the same—or very similar—on all IOS-based routers).
To begin, connect the router's Ethernet port to a switch, and connect the switch to a laptop, which will serve as the DHCP client.
To configure Cisco IOS DHCP, follow these steps, which include sample commands:
1.Configure an IP address on the router's Ethernet port, and bring up the interface. (On an existing router, you would have already done this.)
Router(config)# interface ethernet0/0
Router(config-if)#ip address 1.1.1.1 255.0.0.0
Router(config-if)# no shutdown2.Create a DHCP IP address pool for the IP addresses you want to use.
Router(config)# ip dhcp pool mypool3.Specify the network and subnet for the addresses you want to use from the pool.
Router(dhcp-config)# network 1.1.1.0 /8 4.Specify the DNS domain name for the clients.
Router(dhcp-config)#domain-name mydomain.com5.Specify the primary and secondary DNS servers.
Router(dhcp-config)#dns-server 1.1.1.10 1.1.1.116.Specify the default router (i.e., default gateway).
Router(dhcp-config)#default-router 1.1.1.17.Specify the lease duration for the addresses you're using from the pool.
Router(dhcp-config)#lease 78.Exit Pool Configuration Mode.
Router(dhcp-config)#exit

I hope this is helpfull for you.

Thanks

Vikrant

Oct 26, 2009 | Computers & Internet

3 Answers

Configuration


That is a very good question, but that would take way more space than this forum offers. A good router tutorial, which covers the configuration from the IOS command-line interface can also be found here.

You should check out Cisco's page on EIGRP (link) or Petri's Blog about configuring EIGRP (link), but if routing protocols are in general a new thing for you, you will be better advised to get a book that covers all protocols, otherwise this might not make any sense to you.
Look for this:
CCNA - Cisco Certified Network Associate Study Guide by Todd Lammle, Publisher: Sybex
You can get it at amazon and it costs you only 20$ (used) or 30$ new including shipping. Here is a link.

If you have specific questions, I'm happy to help, but in the book it's already more than 60 pages on IRGP/EIGRP alone, so I don't really want to type that all up, plus you would need some general information as well.

May 21, 2009 | Cisco (1841) Router (cisco1841)

1 Answer

Unable to connect 2 routers need help!


Hi,

Do you have any funky subnets for your Cisco router? Do not connect the wireless router to your network yet, as it may have the same IP address as your other router.

Basically the easiest way to do this is to set a dedicated IP for the 2Wire router on the Cisoo router. Then make them stay on the same subnet, but give an IP range for your Cisco router, like 1-50 or something. If you give the 2Wire router IP .51 for instance, then give the Wifi users on the 2Wire IP range from .52-75 or something.

Make the 2Wire router only use wifi and not serve DHCP addresses. Then you setup the 2Wire router to get its info from the Cisco router.

I searched and there is no howto out there for doing this with a Cisco router. However, here is one I used to setup a similar scenario with a Netgear router. It worked. If you are able to translate a bit, it might work for you:

http://kbserver.netgear.com/inquira/default.asp?ui_mode=answer&prior_transaction_id=306896&action_code=5&highlight_info=16778323,235,239&turl=http%3A%2F%2Fkbserver.netgear.com%2Fkb_web_files%2Fn101236.asp&answer_id=6056802#__highlight

Here is another article:
http://kbserver.netgear.com/inquira/default.asp?ui_mode=answer&prior_transaction_id=306896&action_code=5&highlight_info=16777285,246,260&turl=http%3A%2F%2Fkbserver.netgear.com%2Fkb_web_files%2FN101496.asp&answer_id=6056800#__highlight

Let me know if you are able to work through this. You need to give the 2wire router a static IP and you need to NOT use it for wired connections, and not use it to serve DHCP settings.

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Hi,

The issue may be due to the existence of two (2) DHCP servers; 1 in the Cisco 675 and the 2nd in the DLink DI-524. You need to disable the Cisco's DHCP server function and assign static IP add & config to the DLink WAN config. This way it will only be the DLink handing out IP adds to the network.

The workaround. Install your original configuration/setting without the DLink DI-524 - PC direct to the Cisco 675 (I am assuming through Ethernet ports). Verify that indeed you are connected to the Internet and can surf the net, check e-mails, etc. Check your Networking Connection Status. Log down your PC's IP Add, Subnet Mask, Default Gateway, DNS. For purposes of discussion, let's call this "N1".

After your Internet connection has been verified with your PC directly connected to the Cisco, remove the direct connection and connect the DLink DI-524 in between the Cisco router and your PC.

Log in to the DLink and modify WAN parameters using the "N1" configurations/settings.

It might be of help to disable any security (WEP WPA, MAC etc) at least while configuring.

Hope this be of help/idea. Pls post back how things turned out or should you need additional information.

Good luck and kind regards.

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Jan 15, 2008 | Actiontec GT704WG Wireless Router...

1 Answer

Netgear router


I'm not sure this is the issue but it is worthy of review. Routers are designed to separate networks or more properly subnets assuming you have the wan side of one router connected to the ISP and the wan side of the other router connected to the first router. You have two subnets in your house and they cannot be addressed the same. If the lan side of each router is addressed as 192.168.0.1 you have a duplicate IP address confusing situation that could well cause the devices to completely shutdown as you indicate. The first step of the resolution is fairly simple configure the LAN side of the second router to have 192.168.2.1 as its address. Assuming further that both subnets have masks of 255.255.255.0. The first router's subnet is 192.168.0 and the second router's subnet is 192.168.2 -- they are different and that is correct. The WAN side of the first router is configured correctly or it would not have worked with the satellite. The WAN side of the second router needs an address in the first routers subnet such as 192.168.0.2 if you wish to statically assign it. However this can successfully be defaulted to a dynamic IP address too. Configured in the stated manner the routers should work successfully. They can both have DHCP enabled for their own subnets. Computers hooked to the second subnet could still fail to access the internet if they lack suitable DNS addresses either provided by the router or statically configured in the wireless adapter configuration.

A second alternative would be to have a lan port on the second router attached to a lan port of the first router. now you have a single subnet and have effectively dumbed down the second router to being either a switch or a hub not bad. However there are issues here too. If you did not shutdown DHCP services on the second router you could have two routers competing to assign duplicate addresses to machines as they join the network which will make for unreliable and somewhat random failures of the networks to service attached machines -- so turn off DHCP on the second router. Should the second router have a static IP address on the wan side make sure it is unique and not in the first router's subnet. The lan side of the second router should be assigned a unique address in the first routers subnet although it will not really be used for anything.

If you have any questions please respond with a comment to this problem.

Dec 18, 2007 | NetGear WGT624 Wireless Router

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