Gradual conversion from flat network to VLAN network

Posted on 2014-03-21
Last Modified: 2014-06-23
I need to be able to gradually convert to a non-flat network.  I'm attempting to get the core switches configured to allow the new VLANs while still passing the flat vlan1 traffic to the gateway.

Core Switch: 3com 5500G
Flat Network Gateway: Cisco 3500 router ( main IP -- secondary IP)

[5500G-EI]display ip routing-table
 Routing Table: public net
Destination/Mask   Protocol Pre  Cost        Nexthop         Interface    DIRECT   0    0     Vlan-interface1    DIRECT   0    0        InLoopBack0    DIRECT   0    0     Vlan-interface254    DIRECT   0    0        InLoopBack0        DIRECT   0    0        InLoopBack0       DIRECT   0    0        InLoopBack0      DIRECT   0    0     Vlan-interface1    DIRECT   0    0        InLoopBack0

I've hit a bump in the road early in the process.  I've added VLANs to the 5500G switch and connected my workstation to that switch.  The trunk ports on the 5500G are in trunk mode and set to allow all vlans.

gi1/0/1 on the 5500G switch is an access port on vlan 254.

When connected to gi1/0/1 on my workstation, I set an ip address of with gateway

I can then ping,, and

I can not ping or

From the 5500G switch, I can ping but I can not ping

I was thinking a static route on the 5500G, but my attempts at doing this didn't make a difference.  If there is any easier way to accomplish this please let me know.
Question by:stephenmiller
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Accepted Solution

pergr earned 500 total points
ID: 39947265
The confusion here is because you have not decided on what device you will do the routing between the networks.

I assume you want the to have the 5500G as default gateway for the user networks. Then it will route between these networks.

When you want it to route out to the Cisco, you need a different network between 5500 and Cisco, for example on 5500 and on Cisco.

There should be no address from the user networks on the Cisco. Also, you do not need a trunk to the Cisco. Just a link even without vlan tags will do.

The 5500 should then have a default route with next hop the Cisco

The Cisco should have routes for the user networks, with next hop
LVL 28

Expert Comment

ID: 39951156
I can not ping or
Are there machines that exist with these IP addresses?  And are they connected to the correct VLANs?
LVL 46

Expert Comment

by:Craig Beck
ID: 39951520
pergr is right.

Simply, you need to put the Cisco router on its own subnet.  The 3Com switch can use the Cisco router's IP address on VLAN1 and you'd create a link between the 3Com switch and the Cisco router by just putting a new IP address on the interface which connects to the Cisco router.


1] Configure Vlan-Interface1 with and IP addresses.
2] Create a new VLAN on the 3Com switch for the link to the Cisco router, and put the switchport in that new VLAN.
3] Configure the new Vlan-Interface with an IP address such as / and put on the Cisco router.
4] Configure a default static route on the 3Com switch to point to
5] Configure two static routes on the Cisco router...
     ip route
     ip route

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LVL 28

Expert Comment

ID: 39951521
I think you have 2 different, but related, issues.
1. You said that you had a "secondary: IP address on the 3500 of If you have 2 vlans trunking between the Cisco 3500 and the 5500, then you need to have that address on vlan 254, same as it is on the 5500. You can't use that address as a secondary on Vlan 1.

2. Because the 3500 apparently doesn't know about vlan 254, it needs a route back to the working vlan 254 on the 5500. But this should clear up once you've got vlan 254 correctly configured on the 3500.

The above assumes that you want to use the 3500 as the gateway for both vlans. If you want the 5500 to be the gateway, then you should set it up differently. let me know.

Author Comment

ID: 39951693
Looking at craigbeck's post, I follow except that I want to be sure the default routes on the cisco will not cause a problem.

I'd like the setup to go Workstation > 5500 > 3500 > Internet

And of course eventually Workstation > 5500 #2 > 5500 #1 > 3500 > Internet

Thanks for the replies.
LVL 46

Expert Comment

by:Craig Beck
ID: 39951703
The default route is all traffic not destined for internal subnets.  If the 5500 doesn't have a route to the destination in its routing table (a connected route) it will forward to the Cisco for internet routing.
LVL 28

Expert Comment

ID: 39953072
I don't see a default route on the 5500, based on the routing table you provided.

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