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i have a computer named (PC A) connected to this trunking vlan 100 which containing multiple subnets for example:

  1. 60.60.x.x/16
  2. 70.70.x.x/16
  3. 80.80.x.x/16

I want to do some routing using this trunking vlan (VLAN 100) to access vlans (VLAN 200,300,400) using Cisco switches/routers which is connected to computers (PC B,C,D) on the other side:

  • 60.60.x.x/16 (VLAN 200)
  • 70.70.x.x/16 (VLAN 300)
  • 80.80.x.x/16 (VLAN 400)

What is the best approach to route these subnets (FROM VLAN 100 to VLAN 200,300,400)

  • if the VLAN number on both sides cannot be changed due to network infrastructure
  • if the ip address on both sides computers cannot be changed due to security concerns

i am using cisco layer 3 switches to achieve this task. Please do not give suggestions like changing VLAN number and ip addresses.

user1771844
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1 Answers1

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That won't work. You can't use the same IP network addresses on two different sides of a router. You could use a bridge but that may not be what you want.

You can route 60.60.0.0/16 destinations over a subnet using 70.70.0.0/16 (or anything) but the bound ports cannot reside in that subnet. If PC A requires local IPs from each 60.60.0.0/16, 70.70.0.0/16, and 80.80.0.0/16 subnet then you need to connect it with each VLAN you've set up to transport these subnets.

If you have a VLAN ID or IP address collision when connecting two network your best choice is renumbering. Working around the problem is possible but usually creates a mess that is hard to manage and may produce unexpected problems.

Zac67
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  • Thank you for the help. I am trying to merge internal vlans(VLAN 200,300,400) at my user side on both ends into a common vlan(VLAN 100) which is a bridge to connect them together due to limitation number of vlans. So is it possible in this case? – user1771844 Jan 09 '18 at 14:16
  • If you bridge those VLANs they effectively become a single one. You should describe your goal because usually you divide your traffic into separate VLANs not bridge them together. – Zac67 Jan 09 '18 at 17:41