Campus Design Question

[gerard.gallagher]

Hi,

I currently have a flat L2 network of mostly 3548 switches connected with fibre to a 6509. Ip addressing scheme is 10.2.x.x/16. Because this net has grown there are now too many devices and performance is suffering. Also there is little redundancy. I am looking at VLANS as an option, with an additional 6509 in the core linked to original by etherchannel. I would then have redundant link from each closet to each 6509.

Is L2 the way to go here? If so would a'VLAN per cabinet be ok? (there is no need for vlans to see other vlans). If this is the case I wouldn't need to trunk the VLANS?. The servers would be in a server farm with redundant NICS, and I'm also wondering how this would work with STP.

Any ideas would be greatly appreciated. There are approx 600 devices on the network.

Finally, the 7-device rule with STP - does that just count end to end ir just from end device to core?

Many thanks - I can post additional info if required.

[dbellazetin]

Could you post a visio diagram of your proposed solution.

The diameter of 7 on STP is for layer 2 hops starting from the root of the STP.

Daniel

[gerard.gallagher]

Daniel,

Thanks for the post. A diagram will be posted within 24hrs

[milan.kulik]

Hi,

if you want to segment your flat L2 network, don't forget one basic problem:

You need to change your IP address scheme. There is strongly not recommended to use the same IP address range in two different VLANs, it could bring you to a BIG trouble. One IP subnet for each VLAN is a standard. So you will need to readdress all (or most) your PCs, change default gateway address in their configuration and subnet mask probably.

(Easiest way for this change is using DHCP server with multiple address scopes for particular VLANs, if not used already.)

Then you can use a VLAN per cabinet, e.g. I'd also recommend to put your servers to another VLAN than users.

But you'll need some router (or L3 module) to provide interVLAN routin then.

It's possible to connect your cabinets via access ports (no trunks necessary) and to use a trunk only to connect your router (if an external router would be used). But it's recommended to use a separate VLAN for your switches management, so I'd connect the cabinets via trunks.

See http://www.cisco.com/warp/customer/473/103.html for Best practices.

To the server NIC redundancy:

I've never seen it working correctly.

We have tested NIC teaming several years ago. The basic idea was: Two NICs, each having it's MAC address (physically), using one common "virtual" MAC address assigned to the active NIC (and one IP address). In the case of a link failure, the NIC driver should move the virtual MAC address to the backup NIC. But in reality the result was a "blue screen of death" on Windows server. So we gave it up. But nowadays drivers might work correctly.

Also don't forget that moving servers to another (routed) VLAN could bring you problems especially in "Microsoft world". So broadcast-based services (MS network neighborhood, e.g.) might stop working.

Generally: segmenting a flat network is not an easy task.

To your final question:

"Diameter of the STP domain (dia): this is the maximum number of bridges between any two points of attachment of end stations. The IEEE considers a maximum diameter of seven bridges."

See http://www.cisco.com/warp/public/473/122.pdf.

So the STP diameter is the maximum number of hops (switches) between any two devices in your L2 network (VLAN in PVSTP case).

You can find some helpful documents on Cisco STP support page:

http://www.cisco.com/cgi-bin/Support/browse/psp_view.pl?p=Technologies:Spanning_Tree&viewall=true

Regards,

Milan

[milan.kulik]

Hi,

if you want to segment your flat L2 network, don't forget one basic problem:

You need to change your IP address scheme. There is strongly not recommended to use the same IP address range in two different VLANs, it could bring you to a BIG trouble. One IP subnet for each VLAN is a standard. So you will need to readdress all (or most) your PCs, change default gateway address in their configuration and subnet mask probably.

(Easiest way for this change is using DHCP server with multiple address scopes for particular VLANs, if not used already.)

Then you can use a VLAN per cabinet, e.g. I'd also recommend to put your servers to another VLAN than users.

But you'll need some router (or L3 module) to provide interVLAN routin then.

It's possible to connect your cabinets via access ports (no trunks necessary) and to use a trunk only to connect your router (if an external router would be used). But it's recommended to use a separate VLAN for your switches management, so I'd connect the cabinets via trunks.

See http://www.cisco.com/warp/customer/473/103.html for Best practices.

To the server NIC redundancy:

I've never seen it working correctly.

We have tested NIC teaming several years ago. The basic idea was: Two NICs, each having it's MAC address (physically), using one common "virtual" MAC address assigned to the active NIC (and one IP address). In the case of a link failure, the NIC driver should move the virtual MAC address to the backup NIC. But in reality the result was a "blue screen of death" on Windows server. So we gave it up. But nowadays drivers might work correctly.

Also don't forget that moving servers to another (routed) VLAN could bring you problems especially in "Microsoft world". So broadcast-based services (MS network neighborhood, e.g.) might stop working.

Generally: segmenting a flat network is not an easy task.

To your final question:

"Diameter of the STP domain (dia): this is the maximum number of bridges between any two points of attachment of end stations. The IEEE considers a maximum diameter of seven bridges."

See http://www.cisco.com/warp/public/473/122.pdf.

So the STP diameter is the maximum number of hops (switches) between any two devices in your L2 network (VLAN in PVSTP case).

You can find some helpful documents on Cisco STP support page:

http://www.cisco.com/cgi-bin/Support/browse/psp_view.pl?p=Technologies:Spanning_Tree&viewall=true

Regards,

Milan