Redundant links best way?

Sone · 6 Apr 2012 at 11:50

Not done networking for a loooong time.

I have a small building about 50m away which has 2 cat5s coming across. Currently has 2 unmanaged switches and redundcy plan is basically for someone to swap out cables.

Other end has 1 unmanaged switch and a router.

If i wanted to do STP or similar do i need to swap out all 3 switches or could i get away with just the 2 in the remote building. Or am i looking at this wrong, is there a better way of doing this than STP?

Thanks in advance

Skidilliplop · 6 Apr 2012 at 23:59

To do STP you'd need the switches on each end of the redundant link replaced. If they were managed you could also use LACP or similar to load balance the links with failover built in.

You can also have redundancy at layer3 but you'd need a router at either end that supports links state dynamic routing protocols, E.G OSPF or ISIS

Sone · 7 Apr 2012 at 09:13

thanks Skidilliplop.

It just a link for remote telemetry over satellite so don't need layer 3 (router is customers kit anyway) or any link aggregation just fail over.

Phemo · 7 Apr 2012 at 10:29

What he means is that if you used the two links in LACP you would get redundancy from that since if one link fails the other link would still remain up. Easier than messing about with STP in this scenario. However it'd still require new switches no matter what you do.

ecksmen · 7 Apr 2012 at 11:14

Do the cables follow the same physical path? I'm just wondering what you think you are protecting against if the cables are dug up, but they're next to each other... Or if one cable naturally degrades, then wouldn't the other as well.

Unless through put is required, I'd be tempted to look at another redundant solution if its that important where you couldn't just refresh the cable (50m cables are cheap as...)

Skidilliplop · 7 Apr 2012 at 15:28

Sone said:
thanks Skidilliplop.

It just a link for remote telemetry over satellite so don't need layer 3 (router is customers kit anyway) or any link aggregation just fail over.

I suggested LACP because it's simpler to configure, hence more reliable than STP for a single pair of links on the same switch. The load balancing would just be a bonus ontop.

If you're creating a "Ring" through 3 switches, you'd need STP or similar, and all 3 switches would need to support it.

Though for the same affect most managed switches also support static laod balancing which offers the same only you can usually define a preferred link that it'll fill first and overflow/failover to the second link.
Some switches do offer the option to select "fail over only" as a trunk group type.
On Extreme networks kit they have "software redundant ports" as a feature which does exactly that.

There's lots of ways to do it. But whichever way you choose you'll need at least two new managed switches to do it. (I'm amazed people still install unmanaged switches in business environments anyway)

Sone · 7 Apr 2012 at 16:44

its an industrial environment.

Its a second instrument kiosk they had to install. Need to do a site visit told its cat5e but normally would use armoured TP and a westermo DSL converter. Din rail 24v managed atex switchs are expensive so normally unmanaged are used. Also they have to be easily swapped by random C&I 'engineers' so simple is usually best.

Skidilliplop · 10 Apr 2012 at 11:14

Well the first step is going to be to ID the cabling and find out if it's Cat5 or not. If there's not an end to end ethernet connection you'll struggle to get it working with STP or link aggregation and will need to look at layer 3. I.e you want to do this at the lowest common communication layer.