Geek question
Jun. 14th, 2004 08:18 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
ciphergothAbout network switches. Can you join two cheapo (Dabs Value) 100BASE-T switches with a crossover cable?
One friend argues "no" on the grounds that before any switch will send a packet to the other, it would have to know of an address at the other end, but neither switch will know of any addresses on the other switch until some packets have been exchanged. (Is that right?) This makes sense, but it occurs to me that if switches broadcast any packets they don't know how to route then all will be well. I don't know if they do though.
I also have no idea what to do if I can't connect them this way! Possibly buy another PCMCIA Ethernet card for the laptop that's also the gateway, but they are costly.
Advice gratefully received...
One friend argues "no" on the grounds that before any switch will send a packet to the other, it would have to know of an address at the other end, but neither switch will know of any addresses on the other switch until some packets have been exchanged. (Is that right?) This makes sense, but it occurs to me that if switches broadcast any packets they don't know how to route then all will be well. I don't know if they do though.
I also have no idea what to do if I can't connect them this way! Possibly buy another PCMCIA Ethernet card for the laptop that's also the gateway, but they are costly.
Advice gratefully received...
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no subject
Date: 2004-06-14 02:37 pm (UTC)Don't get too creative with hanging many switches off many switches and don't go over a few tens of hosts and it should be fine.
Oh, and don't create any loops in your network, or it'll all go to ratshit really fast.
(in detail: each switch will learn what is on each port of it when it sees a packet from that host. If it sees packets from more than one host it'll just think more than one host is connected to that port.
Ditto for the other switch, so each switch thinks there's one port with a whole lot of hosts on it and doesn't see the other switch.
There's a table in the switch of which host is on which port, which limits how many hosts can be on the ethernet that the switch is in. It's at least tens, and is thousands on any decent switch. However the switches do assume that each host is only reachable by one port - if you make a loop, the switches can forward packets to each other ad infinitum and there's enough delay in the network that you do get feedback. So Don't Do That.
Also don't make the chain of switches between any host too long, or the delay can be too long for collision detection to work right. You need several switches in a chain for that to happen so as long as you haven't got delusions of grandeur you'll be fine.)