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General Hardware General hardware related questions. |
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Hello, and welcome!
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[router] | | | [switch] | | | | | | [NAS]-+ +-[PC] (It is possible to configure the devices on separate IP subnets, or with a managed switch on separate VLANs. Then, the traffic must be routed. You would have had a specific operational need to do this, and the knowledge you were doing it.) Last edited by jggimi; 28th January 2015 at 06:03 PM. Reason: clarity |
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At boot-time, a switch will know nothing about what MAC addresses are attached, so the initial traffic is broadcasted to all active switch ports. As traffic commences, the source & destination addresses within each packet encountered will be looked at, & placed into the switch's ARP table keyed by the switch port attachment. The presence of gigabyte & slower ports should not make any difference.
If you interested in empirically testing, enable logging through the router's packet filter. If the end points are on the same network segment, packets do not need to go through the router at all. No logging will be seen. However, packets can be forced through the router if the switch supports virtual networks or VLAN's. The endpoints would need to reside on different VLAN's, & the router would have to be configured to send packets from one VLAN to the next. In this scenario, the packets would have to traverse the router to reach their destination. This topology is frequently called a "router on a stick". Most consumer switches targeting the home market do not support VLAN's. Last edited by ocicat; 28th January 2015 at 07:46 PM. Reason: Insert missing participle |
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To further beat a dead horse on describing this issue (just kidding, ocicat and jggimi! Great explanations...I'm just OCD about this stuff), the switch cares nothing about what ip address a packet is sent to. It only deals with mac addresses/ethernet frames. In other words, if host A looks in its route table and sees that host B falls within the same subnet as host A, it will send the traffic directly (i.e. the frame with have host Bs mac address and the packet within the frame will contain host Bs ip). If, however, host A notices that host B resides outside of host As subnet (different vlan/subnet/whatever), then it will send the packet as before with host Bs ip, but the containing frame will instead have host As default gateways mac address, with the understanding that host As default gateway will forward the packet down the line (even if that means back to the switch =)
None of this matters if host A and host B are on the same subnet/vlan, though, as the packets/frames will then be forwarded by the switch and not touch the router.
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Linux/Network-Security Engineer by Profession. OpenBSD user by choice. |
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