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Gradual conversion from flat network to VLAN network

Posted on 2014-03-21
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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 (172.16.0.1 main IP -- 10.254.254.2 secondary IP)

[5500G-EI]display ip routing-table
 Routing Table: public net
Destination/Mask   Protocol Pre  Cost        Nexthop         Interface
10.254.253.0/24    DIRECT   0    0           10.254.253.1    Vlan-interface1
10.254.253.1/32    DIRECT   0    0           127.0.0.1       InLoopBack0
10.254.254.0/24    DIRECT   0    0           10.254.254.1    Vlan-interface254
10.254.254.1/32    DIRECT   0    0           127.0.0.1       InLoopBack0
127.0.0.0/8        DIRECT   0    0           127.0.0.1       InLoopBack0
127.0.0.1/32       DIRECT   0    0           127.0.0.1       InLoopBack0
172.16.0.0/20      DIRECT   0    0           172.16.0.252    Vlan-interface1
172.16.0.252/32    DIRECT   0    0           127.0.0.1       InLoopBack0
[5500G-EI]

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 10.254.254.20/24 with gateway 10.254.254.1

I can then ping 10.254.254.1, 10.254.253.1, and 172.16.0.252.

I can not ping 172.16.0.1 or 10.254.254.2

From the 5500G switch, I can ping 172.16.0.1 but I can not ping 10.254.254.2

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.
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Question by:stephenmiller
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pergr earned 500 total points
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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 10.10.10.1/30 on 5500 and 10.10.10.2/30 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 10.10.10.2.

The Cisco should have routes for the user networks, with next hop 10.10.10.1.
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by:asavener
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I can not ping 172.16.0.1 or 10.254.254.2
Are there machines that exist with these IP addresses?  And are they connected to the correct VLANs?
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by:Craig Beck
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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.

So...

1] Configure Vlan-Interface1 with 172.16.0.1 and 10.254.254.2 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 192.168.0.2 / 255.255.255.252 and put 192.168.0.1 on the Cisco router.
4] Configure a default static route on the 3Com switch to point to 192.168.0.1
5] Configure two static routes on the Cisco router...
     ip route 10.0.0.0 255.0.0.0 192.168.0.2
     ip route 172.16.0.0 255.240.0.0 192.168.0.2


Done.
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by:mikebernhardt
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I think you have 2 different, but related, issues.
1. You said that you had a "secondary: IP address on the 3500 of 10.254.254.2. 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.
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by:stephenmiller
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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.
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by:Craig Beck
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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.
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by:asavener
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I don't see a default route on the 5500, based on the routing table you provided.
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