Cisco SG90D-08 Unmanaged Switches "blocking network signal from another switches"

[bvn63]

Hello,

I have a few Cisco unmanaged switches (SG90D-08) and they have a problem "blocking network signal from another switches" when using the ethernet cable has 6 wires (3 pairs) for network and 2 wires (1 pair) for phone line.

For Example :

Juniper / Cisco Switch ---> the ethernet cable has 6 wires ---> Cisco unmanaged switch (SG90D-80) ----> PC : Led status is off and it doesn't work
Juniper / Cisco Switch ---> the ethernet cable has 6 wires ---> Tenda,Dlink, others unmanaged switch ----> PC : Led status is on (green) and it works

Perhaps this cisco unmanaged switch doesn't enough power to work. Anyone know why it's not working?

Thanks you.

[pieterh]

first, try to use the SG90D stand-alone, if the PC-LED is still off, then your cable may be faulty (or the whole switch)
you may not get an IP-address because there is no DHCP-server but the PC should continue trying! and the LED should burn/flash

second, the PC may be set to "fixed speed" -> check if you can set to speed-auto / duplex-auto

third, even unmanaged switches support the spanning-tree protocol (to prevent loops in the network)
the Cisco STP version may not be compatible with the Juniper, as the Cisco is unmanaged, you need to look into the Juniper config

fourth,  I'm surprised about the 6 wires between Juniper and Cisco
using 6 wires (and 2 separate for phone) is an unusual combination, i would expect 4 and 4 ( or even 4 and 2 and 2)
- Fast-ethernet (100Mbps) uses 4 wires/ 2 pairs pins 1/2 + 3/6
- GigabitEthernet uses all 8 wires (4 pairs)

your SG90D is a gigabit switch (my guess is the others are not ?) it prefers to use all 8 wires, it may fall back to 100Mbps when using 4 wires, and it could be it throws an error when using 6 wires

[bvn63]

Hello pieterh,

Sorry for the late reply to your message. Thank you for the information.

1) Try to use the SG90D stand-alone : Please see below

2) the PC may be set to "fixed speed" : I already set it to speed-auto

3) STP on Juniper/Cisco/Meraki : I have turned it off

4) your SG90D is a gigabit switch (my guess is the others are not ?) : I combin SG90D and TL-SG1008D (tplink, 1000 Mbps)

I have tried the following:

+ It doesn't work for case a -> c (Cisco SG90D-08 - the indicator light is off)

a) Juniper/Cisco/Meraki <-- 4 or 6 wires ---> Cisco SG90D <--8 wires --> Tplink (TL-SG1008D) <--- 8 wires ---> PC

b) Juniper/Cisco/Meraki <-- 4 or 6 wires ---> Cisco SG90D <--8 wires --> PC
c) Juniper/Cisco/Meraki <-- 4 or 6 wires ---> Cisco SG90D 

+ It works for case d -> g (Cisco SG90D - the indicator light is on)

d) Juniper/Cisco/Meraki <-- 4/6 wires ---> Tplink (TL-SG1008D) <--- 8 wires ---> PC

e) Juniper/Cisco/Meraki <-- 4 or 6 wires ---> Tplink (TL-SG1008D) <-- 8 wires --> Cisco SG90D <--8 wires --> PC

f) Juniper/Cisco/Meraki <-- 8 wires ---> Tplink (TL-SG1008D) <-- 4 or 6 wires --> Cisco SG90D <--8 wires --> PC

g) Juniper/Cisco/Meraki <-- 8 wires ---> Cisco SG90D

I think there is an issue between Juniper EX3300, EX2200/Cisco SW 2960S/Meraki SW and Cisco SG90D when using 4 0r 6 wires. I don't see any warning/error in logs of the switches.

Please help and advice me on this issue.

Thanks.

Sang.

[pieterh · Accepted solution]

>>> I think there is an issue between Juniper EX3300, EX2200/Cisco SW 2960S/Meraki SW and Cisco SG90D when using 4 0r 6 wires.<<<
-> agree: I allready mentioned 6 wires is an unusual situation I expect it won't work, 4wires MIGHT work, but apparently does not

in the original design of RJ45-ethernet devices either have a MDI or an MDI-X port, and you needed different cables to connect
- a crossed cable to connect two switches  MDI-X - MDI-X 
   (unless the switch has a special uplink port wired as MDI then you can use a straight cable)
- a straight cable to connect pc to switch MDI-X - MDI
- a straight cable to connect router to switch MDI-MDI-X 
- a crossed cable to connect two routers
nowadays most is handled by auto MDI-MDIX detection on modern devices, but maybe this causes a problem in your situation

if possible you may do a last test with a 4-wire crossed cable

[bvn63]

Hello pieterh,

I think maybe this is a solution for my case, I will check and test according to your requirements and update the results soon. Thank you very much.

Sang.