Packet delivery process

[CSCO12531324]

Hi,

 I understand standard packet delivery process host-to-host through the router or a switch but following question puzzles me.

HOST A (192.168.0.1) ------->HOST B (192.168.0.2) ------->HOST C (192.168.0.3) ------->HOST D(192.168.0.4) 

Question:

Host A is sending a packet to Host D. What will be SRC IP, DST IP, MAC DST and MAC SRC in the packet at each link between A-->B, B-->C,

C-->D and in whole process in reverse?

Is it similar to if instead of Host B and Host C we used routers or differ?

Thank You

[Gregory Leeson]

It looks like your example is all on the same subnet.  So all 4 hosts would be connected to the same LAN.  In that scenario, since you're not going through a router, there wouldn't be any changes to the source and destination MAC addresses.

Host A would send the frame to the switch and the switch would send it out to Host D.

Does that make sense?

[CSCO12531324]

But this setup doesn't have a switch or a router. Each computer let's say two port NiC cards. 

Will the host b forward ARP request with broadcast DST address or drop the packet? Will host b route the packet further if it doesn't know of existence of host d?

Its confusing or maybe just not enough information in the question itself

[Gregory Leeson]

 I guess I'm not sure what you're doing here.  So there are no routers or switches involved at all, is that correct?  You want to daisy chain a bunch of PCs together, each with two network cards?

 If that's the case, they would need to be set up like routers with static routes between them all so they would know which way to go with traffic.

[Gregory Leeson]

Here's how to add a static route in Win 7

https://technet.microsoft.com/en-us/library/cc757323(v=ws.10).aspx

[Gregory Leeson]

Also, a couple other things to consider :

 You'll need to make the connections between the PCs using crossover cables.

 You'll need to change the IP addresses on the NICs and set them up like Point to Point connections.  For Example :

PC1, NIC 1 would be 192.168.0.1/30

PC2, NIC 1 would be 192.168.0.2/30

PC2, NIC 2 would be 192.168.0.5/30

PC3, NIC 1 would be 192.168.0.6/30

Or maybe do it like, 192.168.1.0/24 for the PC1->PC2 connection, then use 192.168.2.0/24 for the PC2->PC3 connection.

Does that make sense?

I've never tried this before, but I imagine it would work.  Might be kind of fun.  It'd sort of be like building your own routers.  Maybe you can get them to run a routing protocol or something.  That'd be cool.

 Or.... you could use GNS3 on each of the computers and use bridged connections with virtual links and route your traffic that way.  Might be kinda cool.  : 

http://www.smartpctricks.com/2014/06/connecting-gns3-real-networks.html

[Gregory Leeson]

A good way to think about the two different addresses (Layer 2 and Layer 3) is this :

Imagine you want to travel from your home in Portland, Maine to Starbucks in Seattle, Washington.  You have no idea how to get there, but your roommate might know.  He's downstairs.  You know how to get downstairs, at least.  

 So right off the bat you have two destinations, your longterm destination of Seattle's Starbucks and your shortterm destination of downstairs.  So you go downstairs and ask your roommate how to get to Seattle.  He says, "No clue, dude, but the chick at AAA knows how to get everywhere, ask her.  AAA is down two blocks to Main St, take a left and it's another block down."

 So now you have two destinations again, your longterm destination of Seattle's Starbucks and your shortterm destination of AAA. (Triple A is a travel advisory place in the USA.)

 And this keeps repeating over and over.  The lady at AAA tells you to take an airplane and gives you directions to the airport, the airport gets you to Seattle, etc., etc.

 If someone asks you at the airport where you came from, you can give two different answers.  You can say, "I came from my bedroom in Bangor, ME." (your source IP address) or you can say, "I came from the AAA on Main St." (your source layer 2 address - MAC address or DLCI or whatever)

 Just think, once you get there and you get your double macha-locha-crapa-supremo-latte, you need to figure out how to get back home.... so you follow the same process but with a reverse destination and source.  And you might not take the same route home.  Maybe your airplane has a layover in Dallas, TX.

Does that make sense?