Any reason to set a lower speed on a switchport?

Morty3

As the topic says, is there any reason to lower my switchports speed to 10mbps when I got a 10mbps NIC? I mean, the speed is autonegotiated, but maybe it is any improvement to set the portspeed to the same as the nics?

Also, if I got a mate with a 100mbps NIC transferring data to my computer with a 10mbps NIC, is there any risk my switch will be flooded (store n' forward)?

I'm just starting to learn switches now in my Cisco-career

Netwurk

You sometimes need to manually set the speeds to match. The Cisco interfaces are usually very reliable, but the NIC you connect to might not autonegotiate very well.

For instance, when I hook up my XP Asus rig to my 2950, I set both ends of the link to 100 Full. Despite being 10/100/1000 auto, the built-in NIC on the mobo doesn't play nice with 10/100 auto ports (Cisco or otherwise).

Morty3

I'll just set the speed to 10 mbps on the hosts and 100 on the wanlink. Doesnt matter anyhow, I just like doing configs on my switch (Catalyst 2916)

Netwurk

Morty3 wrote: »

I'll just set the speed to 10 mbps on the hosts and 100 on the wanlink. Doesnt matter anyhow, I just like doing configs on my switch (Catalyst 2916)

You should either leave them on auto or set them both to 10 Half (although there are some 10Mbps NICs that can do 10 Full).

Believe me, speed mismatches are not good.

Morty3

At the moment I'm going with 10 full. Can reach internet with out any problems, although I'm at this moment the only host. What happends when you got speed mismatches? Can't be any worse then I've got to change it back to half?

Netwurk

I'm guessing your WAN link connects to your ISL connection. I would leave that on auto for both ends. You'll most likey end up with a 100 Full link, depending on your ISL's equipment.

For connecting your switch to your PC, you can experiment all you want since it's your own equipment (plus the PC is likely very old if it has a 10Mbps NIC).

famosbrown

I always use a rule of thumb to always have complete control when I need to. If a device will always be connected to a port with no reason to move...i.e. a server or other enterprise piece of hardware, I will set both ends to what it should be without letting it decide for me. For things that I don't have control over or changes frequently, or whatever, I let the autonegotiate take control...

But yeah...it's your lab, so do what you want with it and have fun .

Netwurk

At some point you might even want to use portfast on the link to the PC. Optimizing that slow a link might seem odd, but keep in mind that your throughput to your ISL is probably only 3Mbps (if you're lucky). That's a lot slower than 10Mbps, so your efforts won't be wasted.

Morty3

Portfast is for STP? To make it skip listening and learning mode? :O

Netwurk

You can safely set portfast on a host, as it does not need to participate in STP

LBC90805

Netwurk wrote: »

You can safely set portfast on a host, as it does not need to participate in STP

OK then, how would you do that in XP; set portfast that is?

kalebksp

I think Netwurk meant you can safely set portfast on a port connecting to a host, not on the host itself.

Morty3

Yeah, but since I dont use STP on my switch, the "learning" and "Listening" modes does not exist anyhow!

But of course portfast should be used to hosts, theres nothin about the net to learn on a host-port.

kalebksp

You disabled STP? Any particular reason why?

Morty3

Was playing around! Now I reseted the switch, so now it's enabled again, and i've set portfast.

EDIT: did not copy run start

miller811

I have experienced issues on the job where older laser printers on the network would connect at 100/half when the switches were set to auto. In those cases we would hard code the ports to 10/half and they would run fine.

Also as a CBT fan Jeremy is quoted as saying "if it is auto, you AWGHT TO NOT DO IT"

Morty3

miller811 wrote: »

Also as a CBT fan Jeremy is quoted as saying "if it is auto, you AWGHT TO NOT DO IT"

Yeah, everything "Auto", "Negotiaite" etc aint not good :P

Netwurk

So Morty, are you going for the CCENT or just trying to get a handle on Cisco equipment?

tech-airman

Morty3 wrote: »

As the topic says, is there any reason to lower my switchports speed to 10mbps when I got a 10mbps NIC? I mean, the speed is autonegotiated, but maybe it is any improvement to set the portspeed to the same as the nics?

Also, if I got a mate with a 100mbps NIC transferring data to my computer with a 10mbps NIC, is there any risk my switch will be flooded (store n' forward)?

I'm just starting to learn switches now in my Cisco-career

Morty3,

It depends. One of the factors of your decisionmaking process to manually configure a switchport to 10 Mbps is if you know or don't know the speed of the NIC or networking device that will be plugged into the other end of the network cabling. If it's somehow known that the switch port will be plugged into a 10 Mbps Ethernet NIC on a host, then feel free to manually configure the switchport to operate at 10 Mbps. Please remember to document your decision to manually configure the switchport to 10 Mbps to at least remind yourself why you manually configured the switchport speed.

Another reason to manually configure a switch port to operate at 10 Mbps is if there's a known upstream bandwidth bottleneck where allowing all downstream switchports to operate at 100 Mbps may overwhelm a single 1 Gbps upstream link. Especially if the hosts connected to the switch use host-intensive applications instead of network-intensive applications.

Does my post help you?

Morty3

Above, the best post. Thanks a lot!


Answer to question above, yes, I'm going for CCENT. Scheduled 31/3.