Network Design

[wrwiii122]

I need some opinions from some people. I have 30 sites each have a 3550 and are connected with fiber to create a loop. I do not have them setup as routing to a single gateway. They run at layer two VLANS and if I ever need to I will route between VLANS. Is this the wrong approach? Should they all be on their own subnet and route to a gateway to get where they are going?

[thisisshanky]

Your 3550s are layer 3 capable, so why not use it. You can use static routes when you want to route (By using static routing, note that you will have an administrative overhead to maintain routes for 30+ networks)

Even if you plan to create more vlans per switch (per site) you can route between them using that switch. If you dont need to route traffic between two sites, you can do that by not having a static route on the switch for that site.

Keeping a vlan per switch per site, will prevent broadcast traffic from traversing switch to switch for that vlan. By keeping each switch in a separate vlan you also help identify which network a particular traffic is coming from based on the source subnet.

There are many advantages of enabling routing in your network. Even convergence might be faster as each switch in your network will have two links (upstream and downstream) so definitely one link is blocked by STP. Unless you have enabled Uplinkfast or something similar, your convergence times right now will rely on STP which is <50s. You can have faster convergence by running a routing protocol for which you will have to enable routing on all the switches.

[wrwiii122]

All sites need to be able to talk to each other. So it is correct in saying that I would have to have 30 static routes to each site. Also on the 3550 how do you make it so that it is acting as a layer 3 device. I enabled IP routing and gave each device and IP but they all see each other still. Do I have to create each site in its own VLAN and route between them?

[bhatia.sachin]

As suggested earlier,it would be better to make the switches run at L3 and enable a routing protocol on them.Create the required vlans on them and assign each vlan an ip for routing.Between the switches u can enable trunking.The config can be:

switch1

int vlan 10

ip add 10.10.10.1 255.255.255.0

int vlan 20

ip add 10.10.20.1 255.255.255.0

int g0/1-----------connceted to switch2

switchport mode trunk

int g0/2-----------connected to switch3

switchport mode trunk

int range fa0/1 - 12

switchport access vlan 10

int range fa0/13 - 24

switchport access vlan 20

router ospf 1

no passive-interface G0/1

no passive-interface G0/2

network 10.10.10.0 0.0.0.255 area 0

network 10.10.20.0 0.0.0.255 area 0

switch2

int vlan 30

ip address 10.10.30.1 255.255.255.0

int vlan 40

ip addres 10.10.40.1 255.255.255.0

int g0/1-----------connceted to switch4

switchport mode trunk

int g0/2-----------connected to switch1

switchport mode trunk

int range fa0/1 - 12

switchport access vlan 30

int range fa0/13 - 24

switchport access vlan 40

router ospf 1

no passive-interface G0/1

no passive-interface G0/2

network 10.10.30 0.0.0.255 area 0

network 10.10.40 0.0.0.255 area 0

Between 10.10.10.0 & 10.10.20.0 the switch will take care of and between 10.10.10.0 & 10.10.30.0 the routing protocol would do the job.

Hope this helps....

[wrwiii122]

Wow this is going to be fun, thanks so much for the great info!!! So what if I need a VLAN that is seperated from the routing scheme that you proposed. I put that on say VLAN 100, will it be isolated from the rest of the VLAN routing or will it automatically be part of the routing?

[thisisshanky]

If you run routing protocols, you could very well filter networks using distribute-lists and thus prevent the subnet for vlan 100 from being listed in the routing tables of other switches.