Author Topic: Help with gigabit network...  (Read 2185 times)

jondecker76

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Help with gigabit network...
« on: February 02, 2008, 01:03:29 pm »
I have my core set up finally, now on to the network...

Right now, all PC's in the house as well as the core all have gigabit ethernet cards. I picked up a cheap 8-port gigabit switch - but as I've always just had normal routers, i'm not familiar with how to hook it up (at least nothing has worked that I have tried so far)

For one, normally every router i've used has an Uplink port. The gigabit switch however does not have this. It just has 8 ports. So does my internal ethernet card on my core just go to any port?  How does the switch know what port is hosting the DHCP services of the network?

I have connected the core directly to the switch (on port 1), but upon plugging anything else into the port - there is no DHCP to be found and the computer has no network connection.

Is there something I'm doing wrong, or something I'm not understanding? Do I need a switch with some sort of "uplink" port?

fibres

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Re: Help with gigabit network...
« Reply #1 on: February 02, 2008, 02:13:50 pm »
No upling is only for linking 2 hubs/switches/routers together. Its pretty much legacy now as most kit can autodetect and witch any port to uplink if needed.
Do you have 2 network cards in your core?
If so can the core access the internet. You could have the network interfaces the wrong way round in the core.

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Matthew

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Re: Help with gigabit network...
« Reply #2 on: February 02, 2008, 04:50:10 pm »
There's nothing special about gigabit switches, except they usually don't have "uplink" ports, as every port can now autodetect whether it's connected to a simple host or to another switch. The rest of your question is probably answered in the wiki article Network Settings and those linked from it.

In short, the LMCE Core's inside LAN segment gets the LMCE DHCP server and its UPNP configs. Its outside LAN segment doesn't serve DHCP, but has a DHCP client that gets DHCP info from the existing LAN's DHCP server (just for routing the the Core and its LAN to the rest of the outside LAN and the Internet).

tschak909

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Re: Help with gigabit network...
« Reply #3 on: February 02, 2008, 06:28:21 pm »
also, you're going to find that cheap gigabit ethernet switches lack a lot of muscle, once you start scaling past a few machines.

-Thom

colinjones

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Re: Help with gigabit network...
« Reply #4 on: February 03, 2008, 04:12:07 am »
jondecker76 - I don't think anybody explicitly answered your question about how the switch knows which is providing DHCP services. The answer is, it doesn't and doesn't need to - all the switch does is look at layer 2 addresses (ethernet MAC addresses) remembers which addresses are outside each port that is connected to something. Then as ethernet frames come in, the destination MAC address on the frame gets looked at by the switch - if it can find an entry in its CAM table matching that address, it switches the frame to the port that it saw that address out of. That is the long and the short of switching! And Thom is right, if the core/backplane of your switch is not non-blocking running at at least 8Gbps (ie 1Gbps per port) then if you have a lot of data flowing, this will be a throttle point, but probably not a big deal unless you are running lots of HDTV sessions at the same time, or you are running any VoIP phones - then you will probably need a switch that can do QoS as well.

When a DHCP client asks for an IP address lease, it broadcasts on the ethernet broadcast address - all switches an NICs recognise that address. NICs assume that they should ingest and process any ethernet frame with that address as if it were directed at them in a normal unicast frame. Switches do not look up this address in their CAM table, they just switch the frame out of ALL ports. Thus your switch doesn't need to know where the DHCP sever is, the client broadcasts, the switch sends this to all ports, and the DHCP server hears the frame, then unicasts the response back using the source MAC address that the client broadcast from.

Col.