0

I have a project assignment that consists of 3 routers, the ISP, and 2 company routers, the ISP can address a network /24 IPv4.

I delegated a /25 to DNS servers and a /26 to one company and 2*/30 to the second company and the other goes to the VPCS that represents the "internet".

On the company server, I was trying to subnet the /26 into 3 networks for each department but looks like I'm doing something wrong.

F1/1 is connected to the ISP with an IPv4 of 212.199.4.130/26

I thought that I could set the other interfaces as

F0/1: 212.199.4.129/27
F0/0: 212.199.4.160/28
F0/1: 212.199.4.176/28

But I was wrong, if try, it tells me that there's an overlapping error.

Im not sure what I'm doing wrong here, any help would be appreciated

enter image description here

3
  • Classroom scenarios are unfortunately off-topic.
    – TDurden
    Feb 3 at 17:39
  • I will add a single appliance cannot have an interface with a mask which overlaps with another interface. Another way to view this is- you cannot have subnet on an interface which overlaps with a subnet on another interface on the same device. Check your IP ranges.
    – TDurden
    Feb 3 at 17:41
  • @TDurden I think I understand it now, so I just need to divide the /24 network and assign it to each department according to the needs of each one, and I need to make sure that they don't overlap, by using /30 or /31 as pointed by Ron. Also, do you know an appropriate place to ask questions about this? Note that I'm not looking for anyone to solve my project, I just needed to ask a few questions, I'm allowed to research to complete this assignment, I'm just not allowed to copy from someone else, but that's not my intention Feb 3 at 18:08

2 Answers 2

2

The interface on F1/1 needs to be a different subnet than the other interfaces. Try using a smaller subnet (only needs to be a /30 or /31).

0

F1/1 is connected to the ISP with an IPv4 of 212.199.4.130/26

If the ISP expects all IP addresses from that /26 to be 'on link' then that's what it's going to be. You need to either put a switch in front of the router and connect the public-IP devices there (you'll need a transparent/L2 firewall in front of or besides the switch as well), or let your router respond to all those addresses and map the desired servers using destination/reverse NAT.

Normally you'd get a /30 or /31 address for the router to enable you to put the public subnet somewhere else.

I thought that I could set the other interfaces as

F0/1: 212.199.4.129/27
F0/0: 212.199.4.160/28
F0/1: 212.199.4.176/28

That doesn't work. As Ron has already pointed out, those subnets overlap with the one configured on the router's uplink. Using a smaller subnet for the uplink (just your ISP's default gateway and your router) may work but it won't if your ISP expects a normal /26 subnet 'on link'.

You should talk to your ISP on what options you've got or use the destination NAT method above.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.