Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Community Member

VLANs or Routing Table

I have 30 sites I need to setup with fiber between them trunking(3550's). What are the pros and cons of using a VLAN for each site and then using one 3550 to route between all vlans or to put a route table into each switch?

10 REPLIES

Re: VLANs or Routing Table

If you use option 1, traffic from vlan 1 on switch 1 to vlan 2 on switch 2, will take a trip from switch 1 to the 3550 that routes between the vlans, and then from there back to switch 2. You definitely dont want a traffic pattern like this. All 3550s are layer 3 capable. If you have SMI, you can run RIP. But if you have EMI you can run EIGRP or OSPF which is a better option.

Community Member

Re: VLANs or Routing Table

Let me ask this then. If I set them up using OSPF it is still possible to use VLANs too to seperate certain traffic? If so, does that mean that I need to specify what VLANs OSPF will run on?

Community Member

Re: VLANs or Routing Table

Yes your can use OSPF and VLANs. You will specify what VLANs OSPF is active on by using the command:

network [network ID] [wildcard mask] area [area ID]

this command is used uner the router ospf configuration context. Don't forget that the wildcard mask is the inverse of a subnet mask.

So if your VLAN 12 has an ip address of 10.30.250.1 255.255.255.192 then your corresponding OSPF command would be "network 10.30.250.0 0.0.0.63 area 0"

Community Member

Re: VLANs or Routing Table

This might be a stupid question but what if someone puts two address schemes that overlap each other on different vlans. Wont that cause a problem with routing?

Purple

Re: VLANs or Routing Table

Yes it will , and I think the router will bitch about to if you try to do that .

Community Member

Re: VLANs or Routing Table

The router or layer 3 switch will not let you assign overlapping address ranges on different interfaces. Give it a try. Here is a sample output:

Test1(config-if)#ip address 10.10.0.1 255.255.0.0

10.10.0.0 overlaps with Vlan20

Community Member

Re: VLANs or Routing Table

If I specify VLAN 1 and 2 to use OSPF they will only route in the VLAN right? So VLAN 1 shouldn't be able to reach VLAN 2. I think you would need to use intervlan routing to accomplish this.

Also right now I use SVI and when I issue "ip routing" my VLAN1 on that switch goes down but not on VLAN 2. Any suggestions?

Re: VLANs or Routing Table

Yes, it will only route between vlan 1 and 2. Do you have any host connected in Vlan 1.Does it only happen when you enable IP routing ?. Paste the switch config and also the output of " show int vlan1 " before and after ip routing is enabled on the switch.

regards,

amit singh

Community Member

Re: VLANs or Routing Table

Yes there are hosts throughout the 30 3550's. The only change in the config is IP Routing. The configs are here http://whitneysolutions.com/config.htm

I am trying to do this with minimal interuption, is this possible?

Community Member

Re: VLANs or Routing Table

Let me make sure I have this down. Create 30 VLANS for the 30 sites all with different IP addresses. Each site will have all ports enabled on the VLAN for that site (IE site 1 all VLAN1, site 2 all VLAN2). Enable OSPF on all 30 VLANS. Is this right? Now it will create its own routing tables and route between all VLAN/networks? Also say I have 60 VLANS can I create 30 on OSPF 1 and 30 on OSPF 2 so that they will not route between each other.

Also the config is above from when I enable IP Routing VlAN 1 shuts down.

332
Views
0
Helpful
10
Replies
CreatePlease to create content