Is a router/switch aware of static IP devices on the network?

Question

If I have a device programmed with a static ip address in the proper network range, what happens when I plug this device into the network? Is there some low level communication that occurs between the device and the router that makes the router aware of the device? If not, how does the router direct packets to this device?

Answer 1

Since you asked...

When a device talks on a network, it uses an Address Resolution Protocol (ARP) request to determine the MAC address of the destination on the network. So, you plug your router in and if the router needs to talk to anything, it first needs to broadcast out to ask for that MAC address. It'll say something on the wire to the fact that "Who has IP 192.168.0.1..., tell 1020:3050:5060." This is sent to the broadcast address of FFFF:FFFF:FFFF. What this does is ask the network who has that IP address and to tell it to the router. This happens all of the time, especially to find the default gateway.

The router and other computers store this information in their respective MAC Address table or ARP table for a period of time. If during that period of time, it needs to communicate with that device, it looks in the cache, pulls out the MAC and talks to it. If it doesn't know the address, it queries for it.

Managed switches use Bridge Protocol Data Units (BPDU's) to find other switches on the network to send packets to and to prevent bridging loops. They are linked below (tired of typing).

WG

Answer 2

Well, if all we are concerned about is the router and/or switch, you should be OK ... if you have a DHCP server, that is a bit more complicated. Your router will learn about your statically assigned machine through a mechanism known as ARP (Address Resolution Protocol). ARP basically ties a Layer 3 address to a Layer 2 address, that is a bit of an oversimplification - but if you would like to learn more, visit this link: http://www.tcpipguide.com/free/t_ARPOverviewStandardsandHistory.htm
The switch doesn't need to know anything about your IP Address anyway - it is a Layer 2 device (typically) and is more concerned therefore with the Link Layer addressing, or your MAC address.

If you have a DHCP server doling out addresses to other hosts on this network, then you may need to consider that you now have a static address and you do NOT want the DHCP server to dynamically hand out that address. There are two ways I know around this, but I am not a sysadmin so there may be more. First you could create an exclusion to the scope - so lets pretend you are handing out 10.10.10.0/24 addresses and your range available is 10.10.10.2 - 10.10.10.254 ... your static host is 10.10.10.100 so you exclude that from the scope - how you do that is rather up to the DHCP server you are using. The other (and this works better long term) is to reserve a set number of addresses for static and not even add them into the pool. So if you are still using 10.10.10.0/24 you might make the range of your pool 10.10.10.10 - 10.10.10.254 and leave .1 - .9 available for static addresses.

Hope this helps.

Answer 3

If you have a router with DHCP enable for a specified range and you connect a device in the same subnet/ip scheme within or outside of range you will be able to communicate between devices/pcs. As long as the device's gateway is pointed to the router the device can go online or do whatever.
If the IP is in range of the DHCP range of the router may try and give out the IP to a different computer because it wasn't leased out by the router in the first place and you'd have a conflict.

Answer 4

Yes,
As you suspect routers and switches will initially communicate with your machine using a lower level communiction, at the MAC address level.

Not all switches operate the same way, but in general they communicate with the attached machine(s) purely by MAC address(no IP address involved at all) but maintain a routing table to direct traffic through the proper port.

With routers, generally the communication is "end to end" IP addressing which is a bit different because it fundamentally routes traffic from one IP network to another, so it's a combination of MAC addresses and entries into the router's routing table.

Answer 5

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ELfaGeek
0
If you mean on your home LAN, the router should see it when connected, if not, ad the static IP in your router settings. RTFM.

Answer 6

If you mean on your home LAN, the router should see it when connected, if not, ad the static IP in your router settings. RTFM.

Answer 7

Normally they dont, they resolve the table dynamically with they want to communicate. if you want you can always make a manual entry on the Router/Switch Table...

Answer 8

yes