Connecting two separate Networks through separate VLANs so they can talk to each other - HP Procurve


- I am using an HP E5406z switch
- I have 2 VLANs:
VLAN A: uses network on 10.1.10.X / / GW
VLAN B: uses network on 172.95.16.X / / GW

on my VLAN A I have devices that need to talk to a DNS & NTP Server on VLAN B

We have been struggling on making these two VLANs to talk to each other. We tried to do IP Routing but I still cant ping nodes on A from B and viceversa.


- How can we make this happen?
- Should the VLANs have a static IP address assigned to them? this is confusing us as well.

Any help or guidance is greatly appreciated!
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Wylie BayesNetwork Technician IIICommented:
If you need the vlans to route to each other they each need an IP interface assigned on the switch.  So vlan A would need, and vlan B would need (or whatever IPs you choose).

The devices on vlan A would either need to use (or which ever IP you setup on the switch) as their Default Gateway address, or implement a static route for -> on the devices.

Also leave IP routing enabled as it will need that as well.
Matthew BorrussoCommented:
to continue with what Wylie is saying:

you should have entries like so: adjust accordingly)

ip router-id x.x.x.x (recommend this if doing a routing protocol)
ip routing
vlan 100 (lets call this A)
   name "meh1"
   untagged (native interfaces
   tagged (trunks, converged ports, etc)
   ip address
   ip helper-address (may need )if DHCP on different subnet)
vlan 101 (lets call this B)
   name "meh2"
   untagged (same story as above)
   tagged (same story as above)
   ip address
   ip helper-address (may need )if DHCP on different subnet)
spanning-tree (dont forget to make sure spanning tree is enabled on the switch).

With the above config, if your clients are pointed to the addresses above as their default gateway, then by rights you should be able to communicate across the subnets without issue.

Good luck,
ArgieITAuthor Commented:
Thank you Wyllie for the answer and Matt for providing very useful details. My question based on the solution is:

- On the network connected to VLAN A I already have default gateway of with its own DHCP Server while the network connected in VLAN B I have GW of with its own DHCP Server... I've been using other IP Addresses in these VLANs such as and do you see any issue with this? ( I am asking this as Matt mentioned if your clients are pointed to the addresses above as their default gateway, then by rights you should be able to communicate across the subnets without issue.)
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Wylie BayesNetwork Technician IIICommented:
What device holds and if not the switch?

(Lol Matt, "Meh1", "Meh2" )
Matthew BorrussoCommented:
Ok, let me understand your topology.
Please correct me if I am wrong.
1. you have two subnets.
2. each of these subnets has their own Dhcp server.
3. you already have a device that is the default gateway for each subnet. which is the existing .1 address.
4. your goal is to interconnect these two subnets without changing the clients or?
5. based on your goals, you want to use the switch to route between these networks?

Let me know if I am correct. If I am, then I can provide some direction.
ArgieITAuthor Commented:
Absolutely correct Matt. Goal is to have Device in A (with already assigned IP In that subnet) contact a Device in B (with an already assigned IP in that subnet)

Wyllie, My HP Switch is connected through another switch to the ISP Router so the gateway comes from the router not the switch. I have a SBS12 serving as the DHCP Server on this same network.

I put together a quick rough topology drawing for you. Hope this clarifies it. Thanks for the help and patience guys.
Zacharia KurianAdministrator- Data Center & NetworkCommented:
VLAN A: uses network on 10.1.10.X / / GW
VLAN B: uses network on 172.95.16.X / / GW

Just for a test purpose; What if if make your VLANB same network class of VLAN A ?

For Example. VLAN A:  10.1.1..0 /24 GW:
                         VLAN B:  GB
Matthew BorrussoCommented:
By the drawing, I believe that you have vlan B downstream from "vlan A" and the ISP gateway is on vlan A on the upstream switch.

If this is correct, then you need to do the following.

Build the switch as a router just like the config above. The vlan B keep the .1 gateway, and you can keep .16 address.

no you will need to create a default route on the switch, which points to this will tell the router to send all unknown traffic to the ISP gateway. now here is the rub, you need to put a route on the ISP gateway. the route needs to point to the once these are in, you should be able to ping at least to the other side of the switch.

Let me know if this does not make sense.
Also, you may need to allow this new subnet (subnetB) permissions to pass through the gateway, IE outbound policys, NAT, etc.. but at minimum, to start, you should be able to route.

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ArgieITAuthor Commented:
Hi everyone,

I was finally able to fix it by adding a route to the HP Switch, enabling spanning tree and making sure the VLAN's can talk to each other. Moreover, I had to create manual routes to the clients as I did not have access to the main ISP router. Thanks for your help.
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