Business Networking. Switch load balancing? (multiple cat links to a switch?)

zeegy · 14 Jul 2014 at 14:36

Afternoon All,

I have a little network conundrum that I would like answering.
At present, all of our network is running on unmanaged switches. We have now had a few instances where people have plugged in patch cables to multiple switches causing loops and bombing out our network.

Obviously, this cant happen and as a result we are looking to upgrade the switches. STP will of course ensure that we no longer have any loops, furthermore we can add additional lines, and they can exist for resilience purposes.

That said, I want more. Ideally, I would like more than a 1Gbps connection linking up multiple switches to try and avoid bottleknecking.

For instance, I would like 3 Patch cables going from one switch to the other to serve as a backbone. What protocols should I be looking in to that would support this technology (so I know what switches to purchase)

BattFink · 14 Jul 2014 at 14:55

You'll be looking for something with Link Aggregation (LACP), have seen this referred to as Trunk linking

Although personally I'd try finding a switch with a dedicated uplink/daisy chain.

I'm running a pair of Netgear GSM7352v2's on my home network & would seem to tick all the boxes you require

Ploppy2k3 · 14 Jul 2014 at 15:00

you are looking LACP or Link Aggregation Control Protocol.

if you are serious about speed though binding more and more 1gbs coper connection will bottom out as you then run into IOPS not throughput. then you are into the land of fibre.

you may be better of getting 10GB GBIC for your switches rather than just aggregating copper.

Chief Wiggum · 14 Jul 2014 at 15:02

It's not true link load balancing (or capacity) though, so be careful on this, it's done per traffic flow, usually from a hash of the source MAC address.
If you're going to use multiple links, always use multiples of 2, so 2/4/6/8 not 3/5/7 - The hash uses a 0/1 algorithm, so odd numbers of links don't factor into that very well.

Ploppy2k3 · 14 Jul 2014 at 15:07

Chief Wiggum said:
It's not true link load balancing (or capacity) though, so be careful on this, it's done per traffic flow, usually from a hash of the source MAC address.
If you're going to use multiple links, always use multiples of 2, so 2/4/6/8 not 3/5/7 - The hash uses a 0/1 algorithm, so odd numbers of links don't factor into that very well.

it amazes me that switches will allow you to configure them as odd. I can see why they fail over to odd numbers but why you can configure 3 or 5 in a lacp team is a mystery. maybe someone will pop up with a reason.

zeegy · 14 Jul 2014 at 15:39

Ploppy2k3 said:
it amazes me that switches will allow you to configure them as odd. I can see why they fail over to odd numbers but why you can configure 3 or 5 in a lacp team is a mystery. maybe someone will pop up with a reason.

Thanks for the heads up guys. I was thinking 3 so I can get the performance of 2, plus resillience. 2bh, 2 lines should be fine.

chris6273 · 14 Jul 2014 at 21:33

zeegy said:
Afternoon All,

I have a little network conundrum that I would like answering.
At present, all of our network is running on unmanaged switches. We have now had a few instances where people have plugged in patch cables to multiple switches causing loops and bombing out our network.

Obviously, this cant happen and as a result we are looking to upgrade the switches. STP will of course ensure that we no longer have any loops, furthermore we can add additional lines, and they can exist for resilience purposes.

That said, I want more. Ideally, I would like more than a 1Gbps connection linking up multiple switches to try and avoid bottleknecking.

For instance, I would like 3 Patch cables going from one switch to the other to serve as a backbone. What protocols should I be looking in to that would support this technology (so I know what switches to purchase)

If I were you I'd get Gigabit Managed switches with the usual Gigabit ports but with a few 10GbE GBIC slots on each allowing you to:

1. Enable link aggregation for end users so they can trunk connections
2. Have the capacity to link the switches together easily and with plenty of capacity

The technology you're looking for is LACP (Link Aggregation Control Protocol) for allowing connections to be trunked.