100 Mbps vs 1 Gbps in a network

Question

I have a network with an older HP 1400-24G un-managed switch. A while back I noticed that backup for a SQL server database took 15 minutes. Using the performance monitor I found the Ethernet connection being the bottle neck. It was in use for 100%, but was only connected at 100 Mbps. It made me wonder why my equipment is not connecting at 1 Gbps. The switch supports auto sensing and has 24 port which can handle 1 Gbps connections.

Ultimately I got a NETGEAR GS305E managed switch (5 ports) + some pre-assembled CAT6 network cables for experimentation. After a bit of fiddling I managed to connect a couple of devices to the NETGEAR switch and they connected at 1 Gpbs. Still if I take one of these PCs and plug the CAT6 cable into the HP switch it negotiates 100 Mbps ... plug it back into the NETGEAR switch -> 1 Gbps ...

It is true that if you have a single device on a un-managed switch that can not handle 1 Gbps per second, but only 100 Mbps that all ports on that switch will use 100 Mbps? On a un-managed switch you cannot have different speeds on different ports? I read that somewhere on the internet, but the source did not seem to reliable and did not provide any explanation as of why ..

I would like to understand why this behavior happens ...

Thanks, Rene

Answer 1

t is true that if you have a single device on a un-managed switch that can not handle 1 Gbps per second, but only 100 Mbps that all ports on that switch will use 100 Mbps?

No. Each port on a switch uses separate Auto Negotiation. It's one of a switch's features, including the ability to change transmission speed between communcation partners. (This was even possible with obsolete, dual-speed repeater hubs, but those used just a two-port bridge between the single-speed collision domains.)

Accordingly, on a 1400-24G you can run any port independently at 1000BASE-T, 100BASE-TX, or 10BASE-T speed, depending on each connected device's capabilities. If a gigabit port only ever links with 100 Mbit/s (with known-good Gigabit partners and with known-good cables) it can be considered broken.

Usually it's the cabling though - not sure about the 1400 series but quite a few devices fall back to two-pair 100BASE-TX when four-pair 1000BASE-T linking fails. If the cables work elsewhere they might not be fitting snugly into the ports and their looseness may make the link fail.

I'd also try whether power cycling the switch changes anything and if it doesn't I'd replace it.

Answer 2

It is true that if you have a single device on a un-managed switch that can not handle 1 Gbps per second, but only 100 Mbps that all ports on that switch will use 100 Mbps? On a un-managed switch you cannot have different speeds on different ports?

Not to my experience. See the comment by Zac67.

Some devices can handle Ethernet pair swapping. Maybe your cable is not correct. I would try with another cable.

Also, if autoneg. fails, it is common to fallback to parallel detection, which is either 10BASE-T (half duplex) of 100BASE-T (half duplex).

Answer 3

If all else fails in a situation like this, you replace the switch. It obviously is not working properly and without any management features, you can't do any more diagnosis beyond a power cycle of the switch, replacing cables and testing with a different switch.

The fact that it works well with a different switch means it is time to replace the failing switch. 48 port managed switches that are capable of 1 Gigabit or even 10 Gigabit on some ports are available on the used market for under $100 (under $50 for some) and unmanaged 1 Gigabit switches are under $50. Easily worth your time to just replace it.