CISCO CCNA MAC ARP TABLE

[300392Alis]

great!! XD

[undead287]

Thanks for the training vids. I used these as well as the CCNA manual I got from ciscoccnaforfree com and just passed yesterday. Hope you all have as much luck as me.

[shellaire]

You guys should really take it outside! WOW! Talk about ego.

[eighteenfive]

thanks for posting this video, it helps a lot. I hope more IT professionals will be more willing to share their knowledge.

[sligon00]

Aha, at last you have seen the light...now just apply that light to your comment about the instructors voice and ask what is more important your opinion about his voice or the information that is being provided free of charge...and the fact that the information alone on its own merit may help others...

[sligon00]

and you are annoying because you can't spell

worth beans...lol

[carnage123123123]

lol...this isn't even 1/5 of the explanation. It excluded where system A found systems B IP address, what DNS server it used. How else could it know that the broadcast was intended for system B? First system A must know the IP address/Name of system B, then afterwards only then can it send an ARP broadcast to which then sends a unicast back to system A. Geesh!

[renos24]

sorry man the video is correct

if you are in a LAN enviroment and you want to ping a local pc , then first your pc checks its arp cache for an ip to mac entry , if the arp cache is emty it send a local brodcast so as to find who has the mac of the ip you wanted to ping. Address Resolution Protocol is used to map OSI level 3 IP addreses to OSI level 2 MAC addreses

[carnage123123123]

Sorry, I don't think you are understanding. Without knowing the Computer Name or IP address, how do you think an ARP broadcast will help? The video assumes you know the computer name or IP address from the beginning. I never said the video is "incorrect", just thats is incomplete. Do you want me to provide the full explanation?

[pedrowasabi]

You are right

[renos24]

ok , lets say you sit in a lan , ok?

your lan uses private ip addresses (although you dont have to but it is a good practise)

in a class c network that is 192.168.0.0/24.

lets say you want to ping computer "b" 192.168.0.3,

you are computer "a" , 192.168.0.2

your pc checks its ARP cache for an entry , if it doesnt have one , it sends an arp broadcast

and the pc with ip 192.168.0.3 replies with its MAC address .

[renos24]

in a LAN enviroment Address Resolution Protocol is used to map OSI level 3 IP addreses to OSI level 2 MAC addreses. dont confuse it with dns , dns has to do with out of the lan connection .

[carnage123123123]

renos24, every device speaking TCP/IP needs a MAC address and an IP address to communicate. Every TCP/IP device encapsulates an 802.3 header and trailer MAC, plus the layer 3 IP, plus the transmission protocol (TCP/UDP) blah blah blah. ARP is for IP to MAC address translation. Computer "B" for example might be the name of a web browser on your LAN and you want to communicate with it. For your computer to communicate with it it must first send a DNS request out to translate the "B"(url) into a IP

[carnage123123123]

After it has gotten the IP then it can send out an ARP broadcast, get its MAC address to IP mapping and send out the frame (or send out a ICMP echo PING request)

(in my first reply I meant to say "web server" not "web browser")

[carnage123123123]

The video assumes you know which computer name (you want to communicate with) has which IP because they're on the same subnet and probably using static IP instead of DHCP since they're using names ("A" or "B") to signify who they want to talk too.

[renos24]

if you just wanted to ping an IP and not a domain name , why you should send a dns request?

this video cares about the NETWORKING part , not the application.

[renos24]

anyway it seems you know some stuff what is your problem with this?

it says : CISCO CCNA MAC ARP TABLE

it doesnt say : cisco ccna full internetworking explanation.

it is just i suppose a part of a tutorial so other stuff will be explained elsewere.

or do you think cisco cant explain networking decently?

[carnage123123123]

Okay, lets just leave it at the fact that it depends on which situation. There are other details to fill in, but the video is correct, you are as well. I never said anyone was wrong here did I?

[elpaisitadeoro]

PCs do not keep any kind of ARP cache. It broadcasts ARP requests everytime it wants to establish a connection.

[slimjim6666666666]

type arp -a into ur command line and see

[antikriszt]

@elpaisitadeoro well, this is kinda late to warn you, but PCs DO keep an ARP Cache/table, try the command "arp -a" and you'll see the table. Maybe if you are behind a router, the only line you are going to have is the IP and MAC from that router, because remember that ARP works in layer 2.

[chucknorris687]

If A is pinging B, A I think will send an ARP request to b, then b will send an ARP reply with it's ip address, and A will know how to get to B I think anyways........

[moersenice]

This is easy basic beginner stuff