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I am using Cisco Packet Tracer to simulate a network of two routers each connected to a switch and two hosts per switch. The network is setup as so: Current configuration

I'm using a default subnet mask of 255.255.255.0. Between router to router, they can ping each other successfully. Between computers on the same switch, they can ping each other successfully. However, when I try to ping PC7 to PC1 for instance, or vice versa, the requests time out. The IP Address of the Seattle Router is 23.12.0.1/24 and Van Nuys is 23.12.0.2/24. I think it might have something to do with the ip route command, but I feel like I've tried everything and still won't work.

Any ideas?

  • You can't have the same network on different sides of the routers. Routers route between network, and a directly connected network takes precedence over any other network. Traffic destined to the 23.12.0.0/24 network that originates on that network will never go through the router. – Ron Maupin Apr 20 '17 at 19:49
  • @RonMaupin but when I change the IP to that, I get this error message % 23.12.0.0 overlaps with FastEthernet0/0 – mangoHero1 Apr 20 '17 at 19:55
  • What I am telling you is that each network segment must be a unique network. If you have the 23.12.0.0/24 network in Seattle, you must have a different network in Van Nuys. Then, you can configure routes in your routers to get to the other network. You cannot route from a network to the same network. – Ron Maupin Apr 20 '17 at 20:00
  • Oh okay, because when I was trying to divide 23.12.0.0 into four subnets, I got one of the network IDs to 23.12.0.192 ... I suppose that means it's telling me it's still on the same network. Isn't this IP considered class A? I've only been subnetting class C networks before... – mangoHero1 Apr 20 '17 at 20:09
  • Network classes are dead; forget about them. What you need to do is learn how to subnet. You can subnet the 23.12.0.0/24 network into four equal subnets. See this question and the excellent answer for how to do this. You really must learn subnetting (become an expert) before you try routing. – Ron Maupin Apr 20 '17 at 20:16
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Based on you comments, it seems that you first problem is that you don't know how to subnet, and you need to divide your 23.12.0.0/24 network into four subnets. You can do this by using /26 networks.

Assign a different /26 network to each of the sites, and you will need a network different than the site-assigned networks for you router-to-router link. Usually, you will use a /30 or /31 network for a point-to-point link like you have between the routers.

Once you have the networks correctly assigned, you can set up your routing. Each router will inherently know about the networks directly connected to it, but the router will need to be told about the networks on the other side of the other router. You can do this with static routes (this doesn't scale well), or you can run a common routing protocol between the routers that will automatically tell each router about the networks connected to to the other router.

  • Interesting, I will try to grasp this concept further! Also for router-to-router, is the /30 notation a rule of thumb? Or is there some math behind that? – mangoHero1 Apr 20 '17 at 20:41
  • The /30 network is the most commonly used for point-to-point links because that gives you four addresses, but you mest reserve the network and broadcast addresses, giving you two usable addresses. In 2000, RFC 3021 was published, letting you use /31 networks (two addresses) for point-to-point links. Some vendors have never supported this, but Cisco does. Also, many people still think it is an invalid network. It does not waste half the network addresses like /30 does. – Ron Maupin Apr 20 '17 at 20:44
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enter image description here

as shown in figure. your Network Model contains 3 Network as shown in figure. each network individually called as LAN Network. one pc can able to ping other pc which is in the same LAN Network. that's why you are able to successfully ping Between computers on the same switch. nut when you try to ping computers like PC0 to PC7 they are not able to ping others because they are in the different LAN Network. if you want to ping pc0 to pc7 then you have to run routing protocol on your both router. to learn about routing protocol click on below link: http://study-ccna.com/eigrp-configuration/

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