Broadcast Loop when connected SFP module

[password1234]

Quick Question

 

School we support have 2 Data sites both on the same estate connected via Fibre to both buildings

 

Have some broadcast loop somewhere

 

Building 1 has 3 switches

Unifi (Has SFP Port connected back to Fibre Panel which links the other building)

Netgear 1

Netgear 2

 

so its daisy changed as below:

Router link to Netgear 1

Netgear 1 to Netgear 2

Netgear 2 to Unifi

 

 

If we plug the SFP into the Unfi Switch it takes down the entire network cant ping router and everything goes down including internet, disconnect the SFP and everything works fine

 

Only thing i can think of possibly is a dodgy switch at Building 2 which also has a similar setup as above (Not had a chance to fully check out Building 2 today but hoping so tomorrow)

 

Could this be the issue you think? or possibly something else?

[DavR]

It could be so many things tbh. I would start by unplugging everything bar one device on a static IP in each unifi switch, plug in the SFP port, and see if you can ping device to device over that fibre link, as that appears to be what's introducing the loop.

 

If that works out fine, then re-connect switches and devices bit by bit until you find the one that causes the loop.

 

Could there already be a link between the two Unifi switches or cabs, such as a copper link you don't know about?

 

Just a personal preference, but I quit using daisychain to connect my switches long ago. I use star config with my best switch in each cab as the centre. It's a lot easier to troubleshoot as well when things like this kick off.

[password1234]

It could be so many things tbh. I would start by unplugging everything bar one device on a static IP in each unifi switch, plug in the SFP port, and see if you can ping device to device over that fibre link, as that appears to be what's introducing the loop.

 

If that works out fine, then re-connect switches and devices bit by bit until you find the one that causes the loop.

 

Could there already be a link between the two Unifi switches or cabs, such as a copper link you don't know about?

 

Just a personal preference, but I quit using daisychain to connect my switches long ago. I use star config with my best switch in each cab as the centre. It's a lot easier to troubleshoot as well when things like this kick off.

 

Hey thanks for your reply

 

Here is a topology of how its basically set up currently

 

 

 

So basically when we disconnect the SFP Module completely everything seems to be working fine

Plug it back in to the unifi switch then we get all sorts with router not being able to ping, not internet access etc

[DavR]

OK - assuming that you're running a flat network with no VLANS, and no link aggregation, you have too many ethernet links between your switches. Can't tell you why the SFP link sets it off, but the loop looks to be in your switches.

 

Each switch should only have one route to other switches, including any routes it may take through a switch. Eg, currently Netgear2 can reach Unify via a direct link, or pass through Netgear1 - a classic loop.

 

Remove either the ethernet between Unify and Netgear2, or, ethernet between Netgear1 and Netgear2, and that should resolve the situation.

[password1234]

OK - assuming that you're running a flat network with no VLANS, and no link aggregation, you have too many ethernet links between your switches. Can't tell you why the SFP link sets it off, but the loop looks to be in your switches.

 

Each switch should only have one route to other switches, including any routes it may take through a switch. Eg, currently Netgear2 can reach Unify via a direct link, or pass through Netgear1 - a classic loop.

 

Remove either the ethernet between Unify and Netgear2, or, ethernet between Netgear1 and Netgear2, and that should resolve the situation.

Thanks! Will give that a go tomorrow

 

Just one of these schools we have inherited unfortunately from a previous provider so just trying to get our head around things

 

Yup everything is as flat single network !

[Glenn22]

Curious if you got this resolved or not? I have had an issue with the latest firmware on Ubiquiti switches when using SFP modules. I downgraded the switches affected to firmware version 5.64.8.13083 and the problem went away.

[DGardiner]

Curious if you got this resolved or not? I have had an issue with the latest firmware on Ubiquiti switches when using SFP modules. I downgraded the switches affected to firmware version 5.64.8.13083 and the problem went away.

 

which gen switches do you have? were having a few issues at one site on the latest too - We ordered a full set of unifi sfps in the meantime

[Oaktech]

Hey thanks for your reply

 

Here is a topology of how its basically set up currently

 

[ATTACH=CONFIG]63672[/ATTACH]

 

 

So basically when we disconnect the SFP Module completely everything seems to be working fine

Plug it back in to the unifi switch then we get all sorts with router not being able to ping, not internet access etc

 

Unless those extra links are LACP or configured static trunks then you are creating a loop and I imagine the addition of the SFP becomes more than the loopback protection or STP mitigations can cope with.

[Glenn22]

which gen switches do you have? were having a few issues at one site on the latest too - We ordered a full set of unifi sfps in the meantime

 

The latest generation whichever that is, the switches are nearly brand new.

[password1234]

Curious if you got this resolved or not? I have had an issue with the latest firmware on Ubiquiti switches when using SFP modules. I downgraded the switches affected to firmware version 5.64.8.13083 and the problem went away.

 

Got it sorted in the end! The problem was that one of the teachers decided to start messing about with stuff and found some old ancient knock off Hub stashed away in a cupboard and decided to start to connect multiple PCs to this hub causing loops!

[DavR]

Teachers. Every blummin time!

 

Glad to hear you worked it out.

[Davit2005]

Got it sorted in the end! The problem was that one of the teachers decided to start messing about with stuff and found some old ancient knock off Hub stashed away in a cupboard and decided to start to connect multiple PCs to this hub causing loops!

 

One of our academics thought they were being smart by connecting a router giving out the same ip address range but different gateway. We spent 2 weeks as the issue was intermittent when only certain devices would not connect to our AD and network. We've since rolled out dhcp snooping on switches as it was not the first time.

 

Lets jus say we weren't pleased.