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Router <-> Switch Question

Tags:
  • Routers
  • Switch
  • Cisco
  • Networking
Last response: in Networking
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October 12, 2013 5:23:06 AM

I have my Cisco router connected to my Cisco switch via each of their first ports (both gigabit, switch is full gigabit 24-port). Question: The router's port is the gateway to the Inet but if one machine on the switch wants to send data to and from another machine on that same switch, does the router come into play (which would cause a slowdown?). In other words, does the router have to be involved in machine to machine communication on the same switch after the router has assigned IP addresses to each machine via DHCP? The router is acting as the DHCP device also, if that matters. Thanks!

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October 12, 2013 5:34:36 AM

routers connect networks. If the data is all on the same network, the router does not come into play. The switch will handle all traffic.
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October 12, 2013 5:36:47 AM

The router ip is your gateway ip and that means it is only used, if the destination ip is not on the same network as the source pc. Traffic on the network is handled by the switch.
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October 12, 2013 8:57:56 AM

So, if the router is at 192.168.1.1 and one of its four gigabit ports is connected to my 24-port gbit switch which I told the router to statically (always) recognize as 192.168.1.242 (do not DHCP it), the router will give out via DHCP IP addresses (as needed) to machines that come online on the switch. A server is on that switch. So, when a machine needs data, the switch has a "maintained IP list" (internally?) and only goes between say 192.168.1.102 and 192.168.1.105 without having to refer to the router? It is that "referring to the router" that had me concerned. If packets had to "check with the router" to learn which switch port was the destination, I would then ask if not using DHCP on the router but rather using DHCP on the switch would be a better (higher performance) solution. Thanks again for a bit of further clarification. I truly appreciate it. Lastly, when a machine goes for say 55.66.33.44, the switch says "don't know that one!" so it sends the packet(s) to the 192.168.1.1 (router/gateway), right?
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October 12, 2013 9:02:34 AM

Switches don't use IP addresses. They use mac addresses.
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October 12, 2013 11:08:18 AM

nocona_xeon said:
So, if the router is at 192.168.1.1 and one of its four gigabit ports is connected to my 24-port gbit switch which I told the router to statically (always) recognize as 192.168.1.242 (do not DHCP it), the router will give out via DHCP IP addresses (as needed) to machines that come online on the switch. A server is on that switch. So, when a machine needs data, the switch has a "maintained IP list" (internally?) and only goes between say 192.168.1.102 and 192.168.1.105 without having to refer to the router? It is that "referring to the router" that had me concerned. If packets had to "check with the router" to learn which switch port was the destination, I would then ask if not using DHCP on the router but rather using DHCP on the switch would be a better (higher performance) solution. Thanks again for a bit of further clarification. I truly appreciate it. Lastly, when a machine goes for say 55.66.33.44, the switch says "don't know that one!" so it sends the packet(s) to the 192.168.1.1 (router/gateway), right?

You have basically the right idea how it works. The switch uses it's mac address table top learn witch device is connected to witch port. The ip address of the switch is only used for the web interface. an unmanaged switch doesn't have an ip address.
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