100baseTX on Gigabit NIC, why?



  • In pfsense I just got a new setup running and functional, but the gigabit NIC is negotiated at 100baseTX (full-duplex). Why would that be? I've honestly never paid much attention to them before as the network has always been fast enough for what I need. I'm more curious than anything. Will it negotiate a slower speed if there is another component in the network that only supports 100baseTX? For example, a switch or wireless router?



  • Assume:  Modem(NIC1) –-> (NIC2)WAN PF.

    NIC2 negotiates to 100TX because that's what Modem TOLD it can handle.  If you have a service that >100 mbit, then you need to ask the ISP to give you another modem, of buy one yourself if you are using your own modem.

    The negotiation between NIC1 and NIC2 is LOCAL, meaning is a negotiation between them two and no one else, they don't know, have no idea, or care what the rest of the network are doing.



  • @Live4soccer7:

    In pfsense I just got a new setup running and functional, but the gigabit NIC is negotiated at 100baseTX (full-duplex). Why would that be? I've honestly never paid much attention to them before as the network has always been fast enough for what I need. I'm more curious than anything. Will it negotiate a slower speed if there is another component in the network that only supports 100baseTX? For example, a switch or wireless router?

    When two devices autonegotiate, they will connect at the best rate both devices can handle.  So, while one may be Gb, if the other is 100 Mb or 10 Mb, then that's the best they'll connect at.  Please note this only applies for the devices directly connected via cable.  Devices on the other side of a switch will not affect this.  So, if you have device A, capable of Gb, connected to a Gb switch and then device B, capable of 100 Mb, then A will connect to the switch at 1 Gb and B will connect at 100 Mb.  Available bandwidth will depend on the slowest device involved.  So, if you're sending traffic between A and B, the bottleneck will be B, limiting the transfer to 100 Mb.  This is one of the benefits of a switch, compared to the hubs that were commonly used 20 years ago,  A switch can mix devices, but hubs didn't.



  • I think my switch may be 100TX and it connects directly to the LAN on PFsense, so that would explain why pfsense is showing my LAN being negotiated at 100TX. Correct???



  • Correct.

    While different network components maybe running at different speeds but NICs directly connected to each other must run at the same speed, and since the gigabit NIC can't force the 100 NIC go to faster, the link falls back to the least common denominator.



  • @Live4soccer7:

    I think my switch may be 100TX and it connects directly to the LAN on PFsense, so that would explain why pfsense is showing my LAN being negotiated at 100TX. Correct???

    That is my situation here.  All my NICs are Gb, but my switch is only 100 Mb, so everything connects to it at 100 Mb.  If I connect through a small Gb switch or directly, I get Gb.  It is my main switch that limits.



  • Perhaps that'll be the next upgrade! Really 100tx is plenty for most.



  • @Live4soccer7:

    Perhaps that'll be the next upgrade! Really 100tx is plenty for most.

    Actually, there's a Cisco 8 port managed gigabit switch I've been thinking about, but given my Internet connection is only 60/10 (actually closer to mid 70s down & 11 up), it wouldn't make much difference to me.



  • While Ciscos are great (probably SG300 or 350 series?) they aren't cheap.
    Some users here like these D-Link DGS-1100-08 GBit switches.
    Compared to the Cisco SG300/350 they are smart switches "only" and not fully managed.


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