Network resilience 1

[bigcaesar]

Hi there,
Hopefully someone can answer my question. I will give you some background first.
I currently have a Cisco 3508 backbone switch. I have 6 Cisco switches connected to the 3508 using fibre. As i said in the subject I want to build in some resilience to the network. I have a spare fibre run to each of the switches which i can use as well.
My question is - would it really be as simple as to introduce a second 3508 to the network and double up on the correct fibre modules and cables to connect all the switches to the second 3508 switch or am I being far too simplistic?
Thanks in the meantime

JT

 

[burtsbees]

No, you have it right.

Burt

 

[burtsbees]

Forgot to mention---you'll want to enable HSRP so that the redundant switch will take over seamlessly in case of a hardware failure. Remember to configure it to preempt.

Burt

 

[BuckWeet]

Make sure you have spanning tree configured for your layer 2 domain!!

 

[burtsbees]

Oh yeah...nobody likes a broadcast storm...lol

Burt

 

[ADB100]

Nobody has bothered to point out the flaw in all this....

Catalyst 3508XL has been end-of-sale since 2005 and is end of support in 2010. The 3508 is an old switch and only offers layer-2 features, even then it is pretty poor compared to todays standards.

http://www.cisco.com/en/US/prod/col.../prod_end-of-life_notice0900aecd8021a948.html

If you must stick with 'stackables' in your core/distribution layer then upgrade to something like a pair of 3750G-12S and introduce some layer-3 functionality to slim down your broadcast domains.

HTH

Andy

 

[bigcaesar]

Thanks to everyone so far that have taken the time to respond. Looks like I need to read up on Spanning Tree and
HSRP. Andy, I understand your comments. I know that the 3508 is old tech but the fact that I have to come to a forum like tek-tips for help speaks volumes for the size of budget I have for this project. Believe me I would love to buy some new kit but....
I take it both spanning tree and HSRP are enabled on both 3508s?

 

[ADB100]

What is the point of HSRP with the 3508? It is purely layer-2 so won't get involved in any routing. I think you can configure it on the single SVI that is used to manage it but this is purely due to the IOS porting, enabling HSRP does not achieve anything on this platform (maybe the daft clustering management thing, but really don't go there it's terrible).
STP is enabled by default and it runs PVST (Per VLAN Spanning Tree) which is compatible with STP. Unless you manually disable it, each VLAN will be running STP. You might want to change the priorities so you can dicate where the STP roots are and therefore which ports will be forwarding and which will be blocking. Introducing the 2nd 3508XL will create loops and STP will (should...) block on some redundant links.

HTH

Andy

 

[bigcaesar]

Thanks again Andy for your comments. You seem to know what you are talking about so I bow to your superior knowledge. I must admit to only scratching the surface of Cisco Networking.
Our 3508 "network" is not doing anything special. We are using Cisco mostly because of its reputation for reliability.
Thats not to say we won't try setting up vlans etc. in the future though. Forgetting for a moment the age of the kit I am dealing with here, can I ask you what your next step would be to make this network more resilient? As I said at the start my initial idea was to buy a second 3508 and one at a time gradually build it up to duplicate the first 3508.

JT

 

[ADB100]

I am assuming here this is just a flat, single VLAN network? If you want to deply VLANs that's fine however you would need an external router or Layer-3 switch to route between them as the 3508 is just Layer-2.
If that is the case then if there is a spare Gig port on the existing 3508 connec this to the 'new' 3508 (it won't be new as you can't actually buy them anymore....). Then on the remote switches connect the 2nd Gig uplink back to the new switch, that's it really. You would probably want to set the STP priority on the 3508's to make sure one was the root and if it failed the other takes over. I assume you are just using the default VLAN:

!main 3508
spanning-tree vlan 1 priority 24000
!2nd 3508
spanning-tree vlan 1 priority 24010

I am not sure if the IOS in the 3500XL series supports the command 'spanning-tree vlan 1 root primary & secondary' as this will also achieve the same result.
From each of the remote switches only one uplink will be active - one will be STP Forwarding the other should be STP Blocking. If an uplink or one of the 3508's failed the other path would go forwarding.

Seriously though I wouldn't do any mileage with these old switches, if you are working on a budget use another vendors switches or if you are a charity etc approach Cisco and see what they can do for you?

HTH

Andy

 

[bigcaesar]

Unfortunately, although I feel like a charity case occasionally, the company I work for are just tight when it comes to IT spend
Andy, you definitely have thrown some light on the subject so thank you for that. I will go away and try to convince the powers that be to part with some more money to do this thing properly. Wish me luck.