I have one flat network with our data center and it is causing as a lot of issues, so i had to design a new network to separate the buildings from the data center, when I designed the new network i was thinking to cut off the old network but unfortunately some changes has been happened and we can't do that so we need to keep our IDF switches connected to the OLD MDF (N7K) that is connect to the DataCenter. Old design\ one flat network building connected the DC" N7K" and IDFs with one big subnet 10.100.x.x/16, the link between N7K and the IDF is trunk. new design\ Core switch connected via routed ports to the buildings MDF "Distribution layer" , And MDF connected trunk to the IDF , each building have there subnets and there is ospf routing enabled between the buildings.

Current situation now it's showing in the picture below. so the issue i am running to is

" I need to use same vlan ID and same subnet with 4 buildings. such as vlan 100,200,300" using the old subnet 10.100.x.x and some pc need to be assigned to these vlans" .enter image description here

  • "causing a lot of issues", "some changes has been happened" are very unspecific, so we won't be able to address those problems.
    – Zac67
    Commented Oct 1, 2020 at 13:46
  • Is there no way to change the IP on the new segments? The horrible option on the N7k is to cable port pairs from vlan-x to vlan-y as access ports (with cdp disabled) to extend the L2 domain into a new vlan ID.
    – cpt_fink
    Commented Oct 4, 2020 at 6:52
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin
    Commented Nov 19, 2022 at 23:28

1 Answer 1


Nexus 7k support VLAN translation, so you could e.g. translate the remote VLANs 100, 200, 300 (from a trunk) to 1100, 1200, 1300 in one zone and 2100, 2200, 2300 in another.

VLID translations can be tricky (esp. with RPVST+ or multiple MSTP instances), so I'd seriously recommend renumbering the VLANs. You can use translations as an interim migration scheme and get rid of them once it's done.

Additionally - or alternatively -, consider migrating to routed links between buildings/zones where no VLANs need to be trunked at all. Even if you use routed links, you should keep VLAN IDs unique at all times, just in case.

btw: Looking at the diagram, it seems your STP root is not your new core switch (looks like it's Switch0, bottom left)- that might be a problem in the diagram only though. You should double-check that the top left 3960 has the lowest bridge priority value = highest priority of all switches. If the diagram is correct, data between Switch3 and the 3960 runs over the old 3650 and Switch0.

  • Hello Zac, Thank you for your advise, if i am going with disconnect all the links between the old MDF and IDFs and keep the old mdf "N7" connect p2p to the new mdf "Core switch", it's L3 switch. is there away to access the old vlans in the old N7k? i know to access vlan we need L2 trunk port but if there is no trunk available is there is away to make these vlans reachable?
    – RR Cisco
    Commented Oct 1, 2020 at 20:01
  • For L2 connectivity you'll need to trunk the VLANs.
    – Zac67
    Commented Oct 1, 2020 at 20:22
  • Zac, when you mentioned to use Vlan Translation, do mean to use OTV between the old and new building and then extend the vlan? Also i didn,t find that much about Mapping vlan in the internet only few and it's not really clear enough for me, when i create a map vlan how the traffic will flow, and for example i have a dhcp for 100 do i need to setup a dhcp for 1100? Also, do i need to configure the mapping vlan in both sides? do you have an example how this is work?
    – RR Cisco
    Commented Oct 2, 2020 at 13:41
  • OTV is something else (it's Cisco's version of IETF's VXLAN - extending a VLAN over L3/L4). VLAN translation works by configuring "VLAN 100 on port 10 is my VLAN 1100". You configure it on one side only, on the boundary between VLAN regions.
    – Zac67
    Commented Oct 2, 2020 at 14:35
  • Zac l, do you have a useful link for the vlan mapping?
    – RR Cisco
    Commented Oct 3, 2020 at 17:31

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