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The Cisco Topic used only by Goomba and Cheatar
« on: October 02, 2012, 10:05:39 pm »

So...yeah.

I have this big skills final thing next Monday. We are given 2 end user computers, router, and switch. My instructor will give us an IP address (class A B or C) and we have to subnet it to the best possible (not VLM or whatever it's called). We will be subnetting into 2 separate networks, and my instructor will give us the number of hosts in each subnet. We are given 45min to do all of that and make sure they can ping each other.

I know the wiring closet like the back of my hand, but when it comes to subnetting, I'm still nervous.   It's a pass/fail Final!

SIDE NOTE:
   There's this Cisco book that has nothing but router commands....do you know what that is called? I was told about it, but not the name of it.  Are You Asking For A CHALLENGE!!!!
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #1 on: October 02, 2012, 10:18:50 pm »

<a href="http://www.youtube.com/v/6PuWDUsQvBg?version=3&amp;amp" target="_blank">http://www.youtube.com/v/6PuWDUsQvBg?version=3&amp;amp</a>
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #2 on: October 03, 2012, 08:17:46 am »

So...yeah.

I have this big skills final thing next Monday. We are given 2 end user computers, router, and switch. My instructor will give us an IP address (class A B or C) and we have to subnet it to the best possible (not VLM or whatever it's called). We will be subnetting into 2 separate networks, and my instructor will give us the number of hosts in each subnet. We are given 45min to do all of that and make sure they can ping each other.

I know the wiring closet like the back of my hand, but when it comes to subnetting, I'm still nervous.   It's a pass/fail Final!

SIDE NOTE:
   There's this Cisco book that has nothing but router commands....do you know what that is called? I was told about it, but not the name of it.  Are You Asking For A CHALLENGE!!!!

I'll write some subnet stuff up after class, but as far as the cisco book goes:

http://www.amazon.ca/Portable-Command-Guide-Scott-Empson/dp/1587201933

Another helpful thing that they didn't tell us about right away with commands is using Tab and ?. Doing a command like:
Code:
Router# show ?
will provide a list of commands that can follow show. Tab will also complete commands that you have started typing:
Code:
Router# copy ru
then hitting tab will often finish it up with
Code:
Router# copy running-config
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #3 on: October 03, 2012, 02:22:08 pm »

Below I'm going to write out a bunch of different topics related to subnetting. I'll make another post after this with an example of how to subnet.

Classful Networking
Note: N represents network bits and H represents host bits.

Class A uses the following octets N.H.H.H meaning the first octet determines the network you're on, if two people were given class A addresses they couldn't have the same first octect. So one person might get 1.H.H.H and the other person might 2.H.H.H. The other 3 octets are used for hosts (which in this case means anything that gets an IP including routers, not just actual end users).

Class B uses N.N.H.H which means they use the first 2 octets to determine the network and the second 2 octets are used for host IPs.

Class C is more common when networking for smaller networks and it is N.N.N.H meaning it can only use the last octet for host IPs.

There were also some rules about what the first octet of each class could be.
Class A 0.#.#.# - 127.#.#.#
Class B 128.#.#.# - 191.#.#.#
Class C 192.#.#.# - 223.#.#.#



Subnet/CIDR Mask
When you assign an IP address to a router's interface or an end device you need to give it a subnet mask (192.168.1.0 255.255.255.127) this can also be represented with what is called a CIDR mask (192.168.1.0 /23). These masks tell the device what size of subnet it is in.

IPv4 addresses are split up into 4 octets, they are called octets because each can hold 8 bits.
The address 0.0.0.0 when converted to binary looks like 00000000.00000000.00000000.00000000
The address 255.255.255.255 when converted to binary looks like 11111111 11111111 11111111 11111111
Because these are made up of all 0s and then all 1s, these 2 addresses are the first possible and last possible address respectively.

If you have a class C network as mentioned above you can only use the last octet for host IPs. So if your class C network is 192.168.1.0 the host address range is the following :
11000000 10101000 00000000 00000000 which is 192.168.1.0 to
11000000 10101000 00000000 11111111 which is 192.168.1.255
But the actual number of usable hosts is not 256, the first address of a subnet is used as the network address so 192.168.1.0 in this case, the last address is used as the broadcast address so 192.168.1.255 in this case. You must always subtract 2 hosts from your total number of available IPs to find your number of usable host IPs (teachers like to try and catch you with this)

A subnet mask is determined by putting a 1 in every bit you are using for your network address, a class C network would have the first 24 bits as 1s.
A is 11111111 00000000 00000000 00000000 = 255.0.0.0
B is 11111111 11111111 00000000 00000000 = 255.255.0.0
C is 11111111 11111111 11111111 00000000 = 255.255.255.0

If you have a subnet like /26 you simply need to make the first 26 bits 1s
/26 is 11111111 11111111 11111111 11000000 = 255.255.255.192

A CIDR mask is used to show how large a subnet is by giving the number of bits that are used for the network part of the IP. If your subnet is a whole class C address then you have /24 as your CIDR mask because you are using 24 bits for the network part.
11000000 10101000 00000000 00000000 is the binary for 192.168.1.0, as you can see 8*3=24 bits used for the network so this is a /24. This leaves 8 bits left for the hosts which offers 2^8 address (256) but remember you have to subtract 2 so 254 usable IPs in a /24 network.

Point to point links (like a serial connection between 2 routers) will often use a /30 address. This means that you have 30 bits used for your network and 2 leftover for your hosts. 2^2 hosts is 4, but subtract 2 and you are left with 2 usable IPs, one for each end of the link.


Subnetting without VLSM
Subnetting the "best possible" way as far as I can remember (since I mostly just use the VLSM way now) is splitting up one of your classful networks into smaller networks of the same size, this way you don't waste any addresses. So a /24 network of 256 host IPs can be split up into 2 /25's of 128 IPs each, or 4 /26's of 64 IPs each, or 8 /27s of 32 IPs each, etc. The reason you can do this is because you are taking some host bits and adding them to the network bits to make new network segments.

The /24 into 4 /26's example using 192.168.0.0/24 (red as network, green as host)
11000000 10101000 00000000 00000000 = 192.168.0.0/24 with hosts 192.168.0.0-192.168.0.256
11000000 10101000 00000000 00 000000 = 192.168.0.0/26 with hosts 192.168.0.0-192.168.0.63
11000000 10101000 00000000 01 000000 = 192.168.0.64/26 with hosts 192.168.0.64-192.168.0.127
11000000 10101000 00000000 10 000000 = 192.168.0.128/26 with hosts 192.168.0.128-192.168.0.223
11000000 10101000 00000000 11 000000 = 192.168.0.224/26 with hosts 192.168.0.224-192.168.0.256

« Last Edit: October 03, 2012, 04:32:59 pm by Goombazoid » Logged

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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #4 on: October 03, 2012, 04:31:12 pm »

Subnetting Example 1 (NO VLSM):

You have 2 host PCs, 1 router and 1 switch.

You have a Class C network of 192.168.16.0/24 to use.

You have 2 floors in an office to network, each floor will have its own subnet for management purpose.

Floor 1 has 64 users and Floor 2 only has 45 users.


Ignore the coloured lights, just didn't want to setup things in packet tracer  Tongue.

So this is a trick I've seen some teachers do where one subnet will have a number of hosts that is a power of 2 (64 in this case). This leads some people to believe they need to split up the /24 256 host network into 4 /26 64 host subnets. But you have to remember that each subnet needs the first and last address for network address and broadcast address. So in this case you'd have to use 2 /25 addresses each with 128 host addresses and 126 usable ones.

So I would give floor 1 192.168.16.0/25 and floor 2 192.168.16.128/25.

Now as far as IPs on the hosts and devices, the switch doesn't need an IP since it is operating at OSI layer 2 which uses MAC addresses, but both hosts will need an IP address and both interfaces on the router will need an IP address from the respective subnet.

For the router the IP you give each interface will be the host's default gateway, I generally like to use the last usable host IP for the gateway IP but you can really use any IP in the subnet.

So for the left port on the router (assume Fa0/1) I would give it an IP of 192.168.16.126 and a subnet mask of 255.255.255.128.
The right port on the router (assume Fa0/2) I would give it an IP of 192.168.16.254 and the same subnet mask 255.255.255.128.
These 2 IPs are the last usable ones of each subnet.

Now the hosts can be any other usable IPs in the subnet, to make it easy I would just use the first available ones
PC1 would have an IP of 192.168.16.1 and a subnet mask of 255.255.255.128
PC2 would have an IP of 192.168.16.129 and the same subnet mask of 255.255.255.128



When I was first starting my networking classes on tests and lab exams I would always quickly write out the CIDR masks and number of hosts from /30 to /24, so the top corner or my first page or scrap sheet would look like
/30 4
/29 8
/28 16
/27 32
/26 64
/25 128
/24 256

Just to use it as quick reference if I was subnetting, also you still have to remember to subtract 2.

So I don't know if this was too basic or too advanced for you, but if you have any questions feel free to ask.
« Last Edit: October 03, 2012, 04:36:35 pm by Goombazoid » Logged

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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #5 on: October 03, 2012, 07:41:50 pm »

The f***?
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #6 on: October 03, 2012, 09:56:48 pm »

The f***?
internets

And this is just the very basics Cheesy
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #7 on: October 04, 2012, 11:04:25 am »

Nerds
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #8 on: October 05, 2012, 12:34:03 am »

Thanks Goomba. I really appreciate it. I understand it a little better now and I think I should do fine on the test now. We did a practice test of it yesterday and I remembered everything (subnetting/wiring/router commands). I completely forgot how to get into these to set a console password and a telnet password. I remember now though. It's Router1(config)# line console 0 and Router1(config)#line vty 0 4

Nerds

Hahahahaha I know I am.
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #9 on: October 05, 2012, 07:36:08 am »

Yeah I'm sure you'll do great. Just want to mention again how useful "?" is after commands you can only remember part of.
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #10 on: October 09, 2012, 10:09:24 pm »

I passed!!!!!!!!  Grin Grin Grin

Thanks again for the help Goomba!
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #11 on: October 09, 2012, 11:46:18 pm »

Congrats! Not sure how much of what I wrote was useful, but I'm glad to have helped.
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #12 on: October 15, 2012, 11:06:50 am »

Since I passed that test, I passed the class. The new class started today. This new class is mainly about routers.

Next year I have a class about switches, and one about security (these are all CISCO). Apparently I graduate next semester as well, so idk what I'll do afterward.
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #13 on: December 10, 2012, 10:04:56 am »

I had another skills final today. It was an EIGRP skill assessment where you have to use 3 routers and connect 6 PCs. They all have to ping each other and there is a loopback that you have to set as the redistribute static.

Here's hoping I did well. I messed up on my IP addressing a bit, but I got everything to ping by changing the number from the 192.168.158.0 to 192.168.160.0 place.
It was a pass/fail final exam, but I did get everything to ping. My professor said he would take that into consideration.

Next class is Switching! Cheesy ONLY PROTOCOLS! Cheesy
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Re: The Cisco Topic used only by Goomba and Cheatar
« Reply #14 on: December 12, 2012, 09:28:17 pm »

Congrats man! I have my CCNP: Troubleshooting final exam tomorrow. Also I got the mark back for the skills based assessment from that class today (60% I had some real trouble). Not looking forward to this exam, covers troubleshooting of various topics inlcuding:

layer 3 routing (ospf, eigrp, redistribution, bgp)
layer 2 switching (spanning tree protocol, vlans, etherchannel)
security
network performance
ipv6
other stuff  like hot standby routing protocol

All in the span of 2.5 hours, but it is one of the last major networking courses in my program so I should probably be prepared  Tongue
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