SG108E does not play well with routers

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SG108E does not play well with routers

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SG108E does not play well with routers
SG108E does not play well with routers
2018-03-31 21:46:29
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Hello, our home has three buildings and I'm using 802.1q on SG108E's to connect over fiber between buildings. This has worked very well for about six months. The reason for the smart switches is that we run two subnets/VLAN's, one for my wife's business devices and the other for Internet devices, Smart TV, Nest, Roku, etc.

The main SG108E connects to a Sagemcom Fast 5260 router from Spectrum cable. About two weeks ago the Sagemcom failed. Spectrum came out and swapped the router. I subsequently discovered that the bad router also took out the switch. So I swapped out the switch with a known good one from another building.

The issue is that when I connect the SG108E to the Sagecom, the link light flashes at a very high rate and it seems to "flood" the router which subsequently locks up. As soon as I unhook the cable, the router goes back to normal operation. I've tried other patch cables and also tried slowing down the port on the SG108E to even 10Mbps with no effect..

So I tried swapping out the Sagemcom with an Archer C900 router, the same thing seems to happen. Interestingly, I use a Linksys router for the second subnet/VLAN and it is working fine with the SG108E.

Thoughts? Thanks in advance!
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#1
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Re:SG108E does not play well with routers
2018-04-02 14:47:11
If the link light flashes at a very high rate all the time, it means that there is broadcast storm and it should be caused by the loop. I think you should check whether your network has the loop.
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#2
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re: SG108E and routers
2018-04-03 05:31:48
Thanks for the reply, you are probably correct. After I posted I noticed that if I unplug the fiber media converter then the issue stops.
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#3
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Re:SG108E does not play well with routers
2020-02-06 19:17:47

@alansc9 

It sounds like there is some loop happening, but it also sounds like there is another compatibility issue.

 

When you connect networks on different subnets, they need to be connected to your internet gateway the same way but with different metrics.

 

EG.

If I have a network with several routers cascaded behind my main router, they cannot have the same set of addresses to hand out, even with NAT turned off.  If one of them is on a class A, 10.0.0.x, the others can have a class B or C, C being the most common: 192.168.y.x, but the y value in their networking cannot be the same unless the masking of their x value actually allows for it--the subnet mask would look like: 255.255.255.x, where x is any value other than 0 or 255.  You can have several subnets in this manner, all of which sit behind a main outer router (say that 4 times fast), and they can be either private internal nets--which only access the internet and their own resources, or subnetted by purpose--I can have a subnet for printers, a net for video devices, a net for gaming, a net for computers, a net for security devices of specific types.

 

It sounds like what you've done is try to connect routers to the smart switch in a very odd way.

 

First, you would need two switches with their own subnets, SA and SB, both at the main network hub where the inside net gets connected to the outside.  These can act as routers for your networks, or as switches, but each needs to be on it's own LAN network metric.  Each needs to have routing internal or have a router connected to hand out addresses, or you can go static and forego this, but they need to have some kind of GATEWAY point (internal or external) that is then connected to the main outer router (your internet gateway).  In fact, one of them can use your main outside router, but the other should use something else, and have that as a gateway.  You will lose speed with double NAT, leave it or don't, up to you, I usually remove it from the second network at the very least.  Both SA and SB have fiber, so I send two fibers across, to SC, another switch with two fiber ports and VLAN capability.  I then use TRUNC to use the wiring for both networks, getting half the ports.  Now here is the kicker, and it's very important.  I use AP wall plugs and switches to separate the networks for Wifi and netting.  I set up the plugs at the main hub, where SA and SB are sitting.  I give the AP's static adresses, and dupelicate this setting in the DHCP of the network they will extend.  When I then plug them in on the other side, they extend only that network, allowing you to connect other devices to them, and have your DHCP carry over.  If you want to have the networks talk to each other, you can set up static routes in the far building to point to the switch, SC, as the first hop, and in the near building, the main router for that network.  On each main router for each network, you then set a static route to the other router, sometimes this will be the outer router, which means you will set one up for that router first, other times the outer router will be the only one you need since it carries the network you wish to talk to.

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