Networking: What is the broadcast ip?
 

I've worked with networks for what seems like years...

I know this:

1. each nic has its own ip address
2. each nic has a subnet mask (which dictates what ips it can see?)
3. each nic can route to a different DNS server
4. what dns servers do and how to set one up
5. an nic can get it's settings from a DHCP server


My Questions:

1. What does NIC stand for?
2. What does the broadcast IP do?! (Please, as much information as possible)
3. I'm setting up a small business network on linux, what are some good rules to practice?

Thanks alot! (in advance)

1. Network Interface Card
2. dur...
3. Learn about ipchains or iptables (for security/ router purposes), and how to manage networking using samba (to interact with windows), and nfs (mountable linux-to-linux filesharing network, very useful)

2. dur...?

That doesn't help much...

3. ...

I know about ip chains, I know about samba (although we don't plan on having any windows networking at all) and I know about NFS...

Cheers anyway

....

What I

2. as the name suggests, broadcast ip is generally used to broadcast the ip packet to all hosts connected in any network domain
take an example, if ur n/w id is 192.168.0.0 and subnet mask is 255.255.255.0 (Class C n/w ), then generally ur broadcast address will be 192.168.0.255
one main application of broadcast ip is in ARP(Address Resolution Protocol) to get the mapping between IP address and corresponding NIC address

3. well this depends on ur business needs actually

i didnt know about two, so i wasnt about to spit out some false information :)

hey, man, i did what i could, and it seems like you already know the basics of running a good network

Just to add a bit, a "broadcast" is a packet sent to every host on the subnet. So any packet sent to, say, 192.168.1.255 gets sent to every host on the 192.168.1.0 subnet. A number of protocols use broadcasts to get the information they need to fulfill their function. As mentioned, ARP is one of these. ARP resolves IP addresses to MAC addresses. For a packet to reach its final destination, it must know the MAC address of the destination. An ARP broadcast is kind of like shouting on a network "If your IP address is x.x.x.x, would you tell me what your MAC address is?"

Another protocol that uses broadcasts is DHCP. In the "Discover" phase of the DHCP process, a broadcast is sent out to all hosts on the network asking, in effect "Hey, are any of you DHCP servers? If so, offer to supply me with an IP address."

thanks alot you guys!

linux 1, windows 0

again, I really appriciate the knowledge, I've learnt more about operating systems by upgrading my works computers to linux in one week, than I did under windows for 1 year!

can someone tell me the command for editing the broadcate ip? i cant find it in this 1000 + redhat9 bible...

thanks

:D
[root@TFHS root]# ifconfig --help
Usage:
ifconfig [-a] [-i] [-v] [-s] <interface> [[<AF>] <address>]
[add <address>[/<prefixlen>]]
[del <address>[/<prefixlen>]]
[[-]broadcast [<address>]] [[-]pointopoint [<address>]]
[netmask <address>] [dstaddr <address>] [tunnel <address>]
[outfill <NN>] [keepalive <NN>]
[hw <HW> <address>] [metric <NN>] [mtu <NN>]
[[-]trailers] [[-]arp] [[-]allmulti]
[multicast] [[-]promisc]
[mem_start <NN>] [io_addr <NN>] [irq <NN>] [media <type>]
[txqueuelen <NN>]
[[-]dynamic]
[up|down] ...

That's the command line way. If you want an easier approach (like a gui) try "netconfig" as root.

-twantrd

Like I've preached ALOT thru my years on linux....learn to do it on the command line first....then you can (if you want) to learn it on the GUI. Once you learn to do it on the command line you won't need to use a gui.

seabass: cheers dude, I think you're right

Today I started editing the IPTables...

Should have really done this straight away :P

again, thanks you guys!

>2. each nic has a subnet mask (which dictates what ips it can see?)
It dictates what ip's it can send packets to directly on it's local
thernet segment. Packets addressed to outside the subnet are
sent to a gateway address instead of directly

>For a packet to reach its final destination, it must know the MAC address of the destination.
or the MAC of the defalut gateway that routes traffic to the final destination.

>3. each nic can route to a different DNS server
It could be set up that way but it dosn't have to be.

Normally when a computer wants to talk to one of the dns servers
it knows about, it will look at it's routing table to descided
where to send a packet addresses to the dns server. If the
route to all the dns servers the machine knows about is through
one NIC then that is where all the name lookup traffic will go.

>4. what dns servers do and how to set one up

A dns server translates a name eg yahoo.com into an ip address.

Sometimes they also translate ip addresses into domain names but
most people arn't concerned with that, read up on it yourself if
you want to know about that.

Most people use send domainname->ip querys to resolving dns
servers provided by their isp.
A resolvign nameserver talks to the root nameservers, the
nameservers for top-level-domains like .com and the servers for
individual sites.

To set one up you run software such as bind or djbdns on a
machine with port 53 tcp and udp accessible from the
machines that are going to contact it.


Setup depends if you want a server to resolve any internet domain
name (e.g yahoo.com) or you want a server that tells people
the ip of your-personal-domain-name.com


>5. an nic can get it's settings from a DHCP server
Yes, a dhcp server can set the ip address, default route,
nameservers, maybe other stuff.

One more note. Your broadcast address (and gateway) is dictated by your netmask. This is called subnetting and is somewhat complicated to explain.

Quick eg. Your ip 192.168.2.129, netmask 255.255.255.240. Therefore your broadcast is 192.168.2.143 and you have ips 192.168.2.[128-143] minus 1 ip on each end for broadcast and network.

I usually recommend using a calculator for this:
http://www.cotse.com/networkcalculator.html

How difficult is it to setup IPv6? i dunno if it's called that exactly.. when you use the subnet mask 255.0.0.0/24 .. I know how it works, I just dont know how to set it up