intro to networking question

[elevationzero]

I'm just starting to learn about networking and have a basic question, a picture is worth a thousand words so here's the picture http://www.gangtf.org/gatewayquestion.JPG

Im sure I'll have about a thousand noob questions, any help given is greatly appreciated. If this is not really an appropriate forum for these types of questions just let me know and I wont post too many of them.

Tia

 

[Changlinn]

The switch or the router can check the subnet mask, really depends, are you running seperate masks on each switch or one across the whole lan? Subnetting really isnt my strong suit however, but I am pretty sure it is done at the switch and at the router, for example an internet/extranet bound packet would hit the switch which would go that ain't on my ports or on the switch I am cascading too, it would then be sent to the router which would look at it and go thats on the internet/extranet and send it out.

 

[catrats]

I'm a little confused about the comparison you mention being made between the IP address and the subnet mask. If you're asking where the decision is made as to whether to keep the "frame" inside your network or to send it to another network (in this case, the Internet), then I'm pretty certain this decision is made at the computer. If it recognizes that it's an IP address within its own subnet, it will just send it to the switch to find the correct destination host. Otherwise, it will be sent to the default gateway?in this case, your router. Hopefully, that is the question your asking. 😉

 

[syco83]

A layer 2 device looks at mac address.
A layer 3 device looks at ip addresses.
So the router will look at ip address because it is layer3
A layer2 switch looks at mac address
The router compares ip and subnet addresses but if both host are on same subnet router is not needed.

 

[WPFossil]

The info about the IP address/subnet is already in the packet when it is sent - so you could say the host sets it.

This kind of information won't help you with either certifications or with understanding networks - it's more along the lines of trivia... 🙂

 

[nweaver]

the comparison is made on the PC (It's called bitwise anding) to determine if the host is remote or local. If the bitwise anding results in local, it sends it direct. If it is remote, it sends it to it's default gateway...



Bitwise anding (it's been a while, bear with me) is where you take the IP address and break it down to binary numbers


128.128.128.128 becomes
10000000.10000000.10000000.10000000

subnet mask
255.255.0.0
11111111.11111111.00000000.00000000

so you add them

10000000.10000000.10000000.10000000
11111111.11111111.00000000.00000000
__________________________________
10000000.10000000.00000000.00000000


in bitwise anding, 1+1=1, 1+0=0, 0+0=0

if the results of bitwise anding it's own address and bitwise anding the other computers address is the same, the host is local. If the results are different, it's remote, and the request is forwarded to the default gateway.


Make sense?

 

[lansalot]

In your diagram, you have a link from switch-switch, and also a route (I would hope) via your router. That's a bit wasteful 🙂

 

[RedCOMET]

he said dragons in his picture.

LMAO

 

[Changlinn]

Originally posted by: lansalot
In your diagram, you have a link from switch-switch, and also a route (I would hope) via your router. That's a bit wasteful 🙂

Not nessesarily if he/she needs 200+mb of bandwidth between the switches.

 

[Smitdog]

Dude, the link-VD ain't no good.
🙂