IP routing process question

borumas

I am just wanting a little clarification on this since in the books I only see this:
hostA

---

router

---

hostB

but on practice test I have seen this:
hostA

---

switchA

---

router

---

switchB

---

hostB

Question is like this:
host A sends a ping to host B
what is the destination ip and mac from between host A and switchA, switchA and router, router and switchB, and switchB and hostB?

From what I understand hostA will determine if hostB is on the local network and if not then it will send it to the default gateway. Since hostB is not local, hostA will create a packet with a destination IP of hostB, a source IP of hostA, and frame the packet with the mac address of the interface of the router port it connects to and it will have a source mac of hostA. The switch operates at layer 2 so it will just look at the hardware destination and push it out the interface going to the router, not making any changes to the frame or packet. The router then takes the frame, strips the packet from it and trashes the frame, then the packet is given to the protocol listed in the type field (IP in this case). IP on the router then takes the packet and checks the destination IP address. Since the router has an entry for the network address it sends it to the interface of that entry, now that buffer finds the hardware address of hostB (because it has the destination IP of hostB it does an ARP or checks the ARP cache) and sends the info to the data link layer. The data link layer then frames the packet with a destination address of the mac of hostB, source mac address of the router (is this correct?-- this is what I'm iffy on), and type field. SwitchB just checks the hardware destination address and forwards it out to hostB.

Now I know this is long but I'm wondering if I am correct in thinking this is the way it all works since in most examples I have seen they never have switches in between the hosts and the router.

Thanks in advance for reading that stuff and giving an answer, lol.

EdTheLad

borumas wrote:

The data link layer then frames the packet with a destination address of the mac of hostB, source mac address of the router (is this correct?-- this is what I'm iffy on), and type field. SwitchB just checks the hardware destination address and forwards it out to hostB.

Why are u iffy on this? HostB to respond to the ping, must use the dest mac address of the router,so of course the frame leaving the router must be encapsulated with the routers mac address,otherwise hostb would have to waste time doing an unnecessary arp
So yes you are correct, so now what happens when cef is enabled

borumas

Thanks for the reply. What's cef though?

EdTheLad

Cisco Express Forwarding, read about it on cisco.com, just speeds up the forwarding process.

tech-airman

EdTheLad wrote:

borumas wrote:

The data link layer then frames the packet with a destination address of the mac of hostB, source mac address of the router (is this correct?-- this is what I'm iffy on), and type field. SwitchB just checks the hardware destination address and forwards it out to hostB.

Why are u iffy on this? HostB to respond to the ping, must use the dest mac address of the router,so of course the frame leaving the router must be encapsulated with the routers mac address,otherwise hostb would have to waste time doing an unnecessary arp
So yes you are correct, so now what happens when cef is enabled

EdTheLad,

CEF is beyond the scope of the current CCNA exam material.

Netstudent

True, but there is no scope to learning. There is never a limit to gaining knowledge. People should be trying to learn as much as they can, and pick up the certs along the way. Not do only what is covered on some certification just to get the letters.

networker050184

Netstudent wrote:

True, but there is no scope to learning. There is never a limit to gaining knowledge. People should be trying to learn as much as they can, and pick up the certs along the way. Not do only what is covered on some certification just to get the letters.

Couldn't agree more. If you just learn the objectives for CCNA you are gonna have a hard time in a real network. When you look at the config it will make your head spin! Almost every network has mls in it anyway.

rossonieri#1

come on guys,

give us - noobs - a break will you
does the word "foundation" on any curriculum mean nothing anymore?
hmmmm.... people will take the portion they can take.

no offense guys

cheers.

networker050184

I'm not saying you have to be an expert, just don't learn to test. Learn to have the knowledge to use it for real even if that means going beyond the exam objectives.

Netstudent

rossonieri#1 wrote:

come on guys,

give us - noobs - a break will you
does the word "foundation" on any curriculum mean nothing anymore?
hmmmm.... people will take the portion they can take.

no offense guys

cheers.

None Taken. I understand where you are coming from actually. For someone just learning the foundation, things can get slighly overwhelming. I just wanted to state the fact that you don't have to learn only CCNA objectives. If you are studying and a concept takes you beyond CCNA depth of that concept, don't be afraid to read on and try to understand it as a whole. When I was studying for the CCNA just recently, I couldn't help but go beyond the scope of CCNA just because I wanted to know. Wanted to know why and how. I guess I just have a different outlook on certifications and learning.

I hear a lot of people out there asking "What do I need to know to pass the CCNA". These people just want to learn the bare minimum just to pass the test, but aren't serious about learning all that they can.

gabrielbtoledo

I guess it all depends on what you want.
If you want just a few letters to put in your resume to get your foot at the door, then just learn the essential to pass the exam. However I am almost 100% sure that in your trial, they will submit you to a technical test and you will probably fail or show weakness in some areas, and other candidates that chose to learn more than the scope will get the opening.

Now, if you want to rock your interview and once starting to work show them that you have more than just what they required, then learn as much as you can and get your salary raise in no time or even a promotion.