Subnetting confusion 1

[GlenJohnson]

I've gotten the hang of how custom subnetting works, but I've never had the fortune of trying to implement custom subnetting. I realize that with a class b subnet, if I use 255.255.248.0, then I'm taking bits from the users and giving them to the network to allow 32 seperate subnets which will support 2,046 clients on each subnet. I even know how to figure out how to do the math. My question, I've never done this in the real world. I find it hard to believe that in the above situation, you have 32 seperate nics to support each subnet, eacy using 255.255.248.0 with each nic supporting the 2,046 clients. I'm just curious, how does this work in the real world since I've never physically done this? Thanks, just curious about something I've never tried. (I hate book learning, I want to do this on my home network.) Thanks. Enjoy the holiday.

Glen A. Johnson
Johnson Computer Consulting
MCP W2K
glen@johnsoncomputers.us

http://www.johnsoncomputers.us

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[ChrisAC]

<snip>I find it hard to believe that in the above situation, you have 32 seperate nics to support each subnet</snip>

You don't have to use every subnet!! You just have the option to. Of course, in the real world you wouldn't really want 2,046 clients in one subnet so you could subnet that up further.

In the real world you would just choose a subnet mask that suits the size of your network.

Chris.


**********************
Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
**********************

 

[jimbopalmer]

Where I use custom subnet masks most is with my QOS filters. since I put all the subnets of my PBXs together, I can easily raise the 802.1p priority of all traffic from or or those subnets with a single filter. (802.1p is not retained through routers, I need to re-discover that this traffic is special)

If I have PBX gear in 192.168.192.x through 192.168.199.x, I can raise my QOS to priority 6 with one filter on 192.168.192.0 masked as 255.255.248.0, rather than writing a lot of filters for each subnet dedicated to VoIP (then I do not need to put the phones themselves in dedicated subnets, they are promoted because they talk to PBXes)

I tried to remain child-like, all I acheived was childish.

 

[GlenJohnson]

What if I'm supporting a network at GM with thousands of pc's, and I want Engineering on one, Accounting on one, Advertising on one, so on and so forth till I need 32 subnets. I don't need 2,046 clients, but I need that many subnets. Is this done with routers? I still can't see 32 nics. Lets tone it down, say I need at least 10 subnets. How would I do this physically, I don't care about the way to figure out what the subnet number is, just how to connect them to my server. Thanks. (Stupid in Seattle.)


Glen A. Johnson
Johnson Computer Consulting
MCP W2K
glen@johnsoncomputers.us

http://www.johnsoncomputers.us

http://www.icca.org/member/memberpage.asp?id=2165

Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884
&quot;Watson, the game is afoot!&quot;

 

[jimbopalmer]

My servers all see the subnet of the bulding they are in, I pay WAY too much for servers to waste their time being routers. The level 3 switches (hardware routers) handle the 45 VLANS (one per subnet) to keep traffic focused on the building it goes to.

The only reason for me to put multiple NICs in a server is for multi link trunking.

I tried to remain child-like, all I acheived was childish.

 

[GlenJohnson]

So switches are handling your subnetting? So you've got 45 subnets, correct?

Glen A. Johnson
Johnson Computer Consulting
MCP W2K
glen@johnsoncomputers.us

http://www.johnsoncomputers.us

http://www.icca.org/member/memberpage.asp?id=2165

Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884
&quot;Watson, the game is afoot!&quot;

 

[jimbopalmer]

Yes Layer 3 switches are simple hardware routers, I run OSPF on my employers. We are in about 45 buildings, mostly in an area about 2 miles long.

http://www.barrick.com/1_Global_Operations/1_02_04_01_NA_Meikle.asp

I tried to remain child-like, all I acheived was childish.

 

[GlenJohnson]

Ok, so you run Open Shortest Path First, which is about the simplest networking you can do. Are they as easy to configure as my wireless smc router was which uses dhcp? Thanks for the info. It's starting to make sense.

Glen A. Johnson
Johnson Computer Consulting
MCP W2K
glen@johnsoncomputers.us

http://www.johnsoncomputers.us

http://www.icca.org/member/memberpage.asp?id=2165

Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884

 

[jimbopalmer]

we previously had used RIP, but it kept noticing that my 1 meg wireless backup links were 'shorter' than my 1 gig fiberoptic links. OSPF uses the line speed in determining the 'shortest' route, so it never makes such horrible choices. I can leave the wireless links up at all times without traffic going that way unless it is the only link available.

So long as you never change the defaults (which seem sensible), OSPF seems easy to setup on Nortel Accelears. We use 7 of them to manage our LAN in roughly a figure 8.

1 hooks to 2 and 3 gig
1 hooks to 4 wireless 1 meg
2 hooks to 1 and 3 gig
2 hooks to 5 wireless 4 meg
3 hooks to 1, 2,4, and 5 gig
3 hooks to 7 T1 50 miles
4 hooks to 3 gig
4 hooks to 6 100 meg
4 hooks to 1 wireless 1 meg
5 hooks to 3 gig
5 hooks to 6 100 meg
5 hooks to 2 wireless 4 meg
6 hooks to 4 and 5 100 meg
7 hooks to 3 T1 50 miles

the mix of speeds (and media) made RIP difficult to use


I tried to remain child-like, all I acheived was childish.

 

[GlenJohnson]

Thanks, Jimbo. I have no need to do this currently, but seeing how somebody is using this in the real world has helped me understand how it works much better. This is one reason I don't like brain dumps for trying to get certified. Studying to get my MCSA, and I've figured out the way subnetting works, but I really wanted to know the ins and outs of it. I may set up a custom subnet at home just to keep learning. Good luck and thanks again. (Here's a star for you.)

Glen A. Johnson
Johnson Computer Consulting

http://www.johnsoncomputers.us

&quot;The best fire does not flare up the soonest.&quot;
George Eliot (1819-1880); Englist novelist.

Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884