almost passed today

gotbyu

Just took the 640-801 today and got a 821 Really bummed out as I thought I was going to pass. I had 4 sims and got about 5 questions on ARP which threw me off as I didn't even really study this stuff. Does anyone know of some reading material on this as I'm not too familair with how ARP works. What is displayed in the ARP table and how a computer uses it.

Looking to take the test again next week.

thanks

binarysoul

I'm not too familair with how ARP works.

Wow, you were lucky then. You must understand this protocol, just google it, I'm sure you will find a lot of info on it. here is one:

http://www.mcmcse.com/cisco/guides/arp.shtml

The good news is you're not too far from passing, BUT....

Be careful you're not taken off guard on another topic next week and end up with same score. Go throw official exam objectives and make sure you [religiously] understand each item in the objectives.

gotbyu

thanks for the quick reply.

what happens if a computer has this in it's ARP table.

192.168.1.1 (mac address) type dynamic

is this were the address of say the router and I ping it how does arp come into play? also, if I were to ping say www.yahoo.com what happens to the ARP table then?

thanks

steve-o87

In computer networking, the Address Resolution Protocol (ARP) is the method for finding a host's hardware address when only its IP address is known. Due to the overwhelming prevalence of IPv4 and Ethernet, ARP is primarily used to translate Ethernet MAC addresses from IP addresses. It can, however, easily be used for IP over ATM or FDDI.

http://en.wikipedia.org/wiki/Address_Resolution_Protocol

http://www.erg.abdn.ac.uk/users/gorry/course/inet-pages/arp.html

what happens if a computer has this in it's ARP table.

192.168.1.1 (mac address) type dynamic

This means that your pc sent out an arp request and found that the mac was linked to the IP address.

Simply put ARP is used to resolve a MAC address to an IP address

Dont beat yourself up
Good luck on your next try

!30

Just be prepared next time and give one more shoot Good luck !

marlon23

this link provide nice course to ARP:


http://www.learntosubnet.com/License_arp.htm


(only in Internet Explorer)

slaj

What type of SIMs have you encountered? You have to perfect these SIMs if you want to pass. Otherwise you have to cross your fingers.

Ching01

Oh, I remember my first intro exam regarding ARP and I failed not focusing on this section. Anyway just to give you a hint about what is ARP.



Example.


pc1

---

r1

---

pc2

PC1 want to communicate to pc2 so he send a ping
R1 receive the packet with the info:

source ip address : PC1
destination ip address : PC2
MAC source : PC1 :
MAC destination : MAC address of R1 which is the ethernet address.

If r1 already knows how to get to pc2 by then it will send its packet to pc2. IF NOT then issue an ARP request to know the mac address of PC2.

hope this help, read SYBEX 5th edition.

EdTheLad

Ching01 wrote:

Example.

pc1

---

r1

---

pc2

PC1 want to communicate to pc2 so he send a ping
R1 receive the packet with the info:

source ip address : PC1
destination ip address : PC2
MAC source : PC1 :
MAC destination : MAC address of R1 which is the ethernet address.

If r1 already knows how to get to pc2 by then it will send its packet to pc2. IF NOT then issue an ARP request to know the mac address of PC2.

hope this help, read SYBEX 5th edition.

Or maybe better..
If PC1 wants to talk to PC2, it will realise the destination IP address is on a different IP network.It has a default gateway configured that is the IP address of r1 so it checks its route cache for a mapping of r1 IP address to MAC address.After examination of the route cache no MAC address entry is present for r1 so PC1 sends an ARP request which has a destination mac address FF.FF.FF and destination IP address of r1, r1 along with all other devices on the ethernet segment will receive the ARP frame as its addressed to the broadcast address, the frame will get thrown up to layer 3 which will only match to r1 i.e. same ip address and r1 will reply with a frame which includes its MAC address in the SA field.
When PC1 receives the frame it will enter the MAC and IP address into the route cache so all other communication off the local segment will be addressed to the default gateways mac address located in the arp cache.