Switch redundancy question 1

[peterve]

Hi,

I'm about to buy 4 Cisco switches, that will be interconnected by using Gigabit fiber uplinks.
Every switch has 2 fiber connections :
-------switch1-------
| |
switch2 switch4
| |
-------switch3--------

The 4 switches need to be configured in a closed fiber loop, but what I'm trying to figure out is :
Will this scenario offer some redundancy; i.e. when one of the fiber links is broken, will all traffic be sent over the links that are still up ?
We need to configure this in such a way that the clients will not suffer any performance issues because of the configuration used.
The plan is to buy 2950x switches, but I'm not sure if they are capable of doing this .. if not, what type of switches should I use.
Some other features need to be : support for 4 VLAN's (I'm pretty sure this won't be a problem, I just want to verify this)

thanks

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[pmesjar]

Yes, 2950 will be able to hadle this. And what you need to do is to dig a liitle deeper into operation of Spanning-Tree Protocol and more specifically Per-VLAN STP that Cisco uses on 2950. Problem is that by default if one of your links go down, some VLANs might notice about 50 second timeout. Check out this:

http://www.cisco.com/warp/public/473/15.html

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/1219ea1/scg/swstpopt.htm

Hope this helps

Peter Mesjar
CCNP, A+ certified
pmesjar@centrum.sk

"The only true wisdom is in knowing you know nothing.

 

[ccmuser]

Why are you going to loop these?
Why are you going to create 4 vlans?

Are you creating one vlan per switch?

 

[peterve]

Loop : to maximize the redundancy... If one uplink is broken, then all clients will still have full network access

VLAN's : I have 4 different types of networks, that need to go into 4 different firewall interfaces behind the central switch

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[ccmuser]

not really... do you have Multi entry point FW setup.. are all your servers multi-homed or do they have redundant links into more than one switch?

I am assuming all your important device and FW are local to each other. You still have that as a singe point of failure regardless of how you "wire" this network.

Unless you have some nice cash flow to thow at this the star is usually a better choice.

 

[peterve]

don't worry about the firewall - I have that one covered
I need to figure out how to solve the 4 switch scenario, and making the network as redundant as possible, with only those 4 switches and their fiber Gigabit uplinks...
so I'm afraid a ring is the only way to make it happen... unless I'm missing the point here

any comments or ideas ?


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[ccmuser]

I guess the point I am trying to make is that making a network more redundant is not really a good goal.. Atleast when you put a money factor into it..

Look at what services you require to be redundant. running a fiber loop if all file access and applications are sitting in one data center(for other economic reasons that usually is the case in most small to med buss) really does nothing for you.

I am not saying a ring never needed.. Just in so many installations today they do not in any way eliminate a single point of failure problem and intoduce problems that your otherwise would never have to deal with.

 

[peterve]

Look at it from this angle - the fibers are already in place; (so it doesn't cost any money to implement the cabling for the ring structure) but the older equipment doesn't support a closed ring. (Which of course doesn't give us a lot of redundancy... when the cable is interrupted somewhere, we need to walk over to the place where the ring was left open, and someone needs to close the ring (by connecting the two endpoint switches with a uplink ethernet patch cable)


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[Dlweeksjr]

Peter,
You should look at the STP Thread. Look at my configuration for the 2950. I get less than 1 sec failover using Rapid Spanning Tree with Port Fast and uplinkfast. In the config shown, I have two 2950's hooked together but eventually, I will have 4 hooked up just as you are suggesting. I however, do not have 4 vlans. Eventually, I will have to test the configuration that you are trying and I need to stay under 1 sec.
Don

 

[peterve]

Cool - thanks

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