Monthly Archives: May 2015

ICND1 100-101 Study Progress 2

I have reached page 682 of the Odem book which is where I am going to stop. Now I am going finish typing up my notes. Next I will use the attached CD to quiz myself to figure out what areas I need to brush up on in the coming weeks.

CHAP19 Subnet Design p533
– count the bits know the powers of 2
– 2^10 is 1024 and that is easy to remember

CHAP20 VLSM p561
– Old routing protocol doesn’t support vlsm (RIP)
– no additional config to get this to work
– be able to find overlap of networks to troubleshoot

CHAP21 Route Summarization p577
– strategy used for performance to lower the size of routing tables
– subnet design should have summarization in mind
Steps to finding the best summary route
1. list all decimal subnets in order
2. note low and high points
3. pick the shortest prefix length mask and subnet -1
4. calculate new potential network mask summary

CHAP22 Basic ACLs p599
– ACLs most common use is a packet filter
– can match source and/or destination
– match packets for QoS
– to filter a packet you must enable acl on the interface either enter or exit
– NAT uses ACL permits
– when processing ACL list router uses first match logic
– ex command: access-list 1 permit
– To figure out wildcard, get mask and subtract

*know where the best place to put the ACL is and on what router in the path

CHAP23 Advanced ACLs p623

ACLs are numbered or named
– to make a change to the list, must delete the whole list and reconfigure
– extended ACLs allow for more packet headers to be searched
– example command: access-list 101 permit protocol SIP wildcard DIP wildcard
– example command: access-list 101 deny tcp any gt 1023 host eq 23
– keywords can be used instead of port #s (HTTP instead of 80)

Named ACLs, differences
– easier to remember
– subcommands not global
– allows single line deletion

numbered ACLs allow for new style of command

config t
do show ip access-list 24

– use the “enable secret” command
– username secrets if external auth not available
– disable telnet
– avoid using simple password checking
– disable unused services
– use ACLs to secure SSH
– extended ACLs close to source
– Standard ACLs close to destination
– Specific ACLs early in list

enable secret myPass
-this sets the password of myPass to reach enable mode

CHAP24 NAT p653
– CIDR route summarization
– classless interdomain routing
– inside local: local ip assigned to host
– inside global: what the internet knows your network as. address used to represent inside host as packet hits internet
– outside global: public ip outside enterprise (the ip of the URL you are trying to access)

PAT is port address translation
pic on p664-uses source port to return traffic to proper client
NAT troubleshooting
-don’t mix up ip nat inside and ip nat outside addresses
-don’t mix up local and global addresses in this command: ip nat inside source static
-dynamic NAT uses ACLs, check these
-PAT uses the overload command on ip nat inside source command


I took a couple 10 question tests from the CD. The idea was hit some chapters that I struggled with which were, WANs, ACLs and NAT. I got 6 out of 10 questions right which isn’t all the great.

Next I took a test of the first 5 chapters of the book. I scored 8 out of 10 right which is passing for the book test. The only concept I wasn’t sure on was crossover cable pin numbers and when to use a straight through and crossover cable. I knew like devices use crossover cables but that alone didn’t help me get the two questions right. I may memorize this table for the test.

routers Hubs
pcs Switches
1,2 3,6
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Posted by on May 30, 2015 in Network Admin


ICND1 100-101 Study Progress


I’m starting to see the fruits of an aggressive study plan. Here we are, May 23rd, roughly two weeks until test time and I am nearly on track.

Part I: Networking Fundamentals
Part II: Ethernet LANs and Switches
Part III: Version 4 Addressing and Subnetting (Be done by May 11th and practice subnetting)
Part IV: Implementing IP Version 4 (Be done by May 18th and practice show commands)
Part V: Advanced IPv4 Addressing Concepts
Part VI: IPv4 Services (Be done by May 26th, decide if I want to skip IPv6, Review OSPF and practice more advanced subnetting)
Part VII: IP Version 6
Part VIII: Final Review (Be here by June 1st and have taken a practice exam to decide what areas to review)

I got off to a rocky start with an older 2008 version of the book. Fortunately my study buddy had purchased the correct book instead of borrowing an old one. I had gotten two chapters into the old book and before I started to really get into the newer edition that took a week to recieve. I decided to take a practice test early on. The test is very configurable. I chose study mode for 45 questions and limited myself to 90 minutes with a small chunk of whiteboard. I also decided to exclude any IPv6 questions from this first stab.

After two chapters and a couple videos on subnetting I was able to get a 600 which is 200 points away from passing. This was on the practice test that came on the CD in the book. The higher layer concepts I did quite well on where as the lower layer concepts such as Routing, WANs, ACLs and any kind of IOS commands and configuration questions I did very poorly on. Subnetting seems to get a lot of attention either directly, or indirectly and I was sitting at about 50% or less on that.

What is subnetting?

Don’t listen to me, I’m not an expert, but I don’t think there are many good explanations of this out there. A lot of people go way deep and off on tangents to frequently. Here is my overview of what I understand are important subnetting concepts for ICND1.

IP Address = 32 bits = 4 Octects = 4 bytes

Each byte can store 256 possible combinations of 1s and 0s. So lets represent in binary, 00001001.00000000.00000000.00000001

See, that is 32 bits in an IP address.

The second concept we need to understand is the netmask. Picture a mask you might put on your face. A very thick mask you won’t be able to see much. A thin mask you might be able to see a lot.

Take that concept and apply it to this very common netmask, or 11111111.11111111.11111111.00000000

Out of all the possible combinations that is a pretty thick mask so I can only see a small number of hosts with that mask. If you combine the IP & netmask, you will be able to see IP address from or 256 possible hosts.

And there you have it, networking. Wait, what was I talking about? Ah yes, SUBnetting.

Subnetting takes those 256 possible hosts and divides them into smaller networks. If I needed several separate networks and only 18 hosts per network I could split that network into smaller chunks. If I want to see fewer hosts in my network I need a thicker, or higher number mask.

Pulling up the /24 mask again, 11111111.11111111.11111111.00000000 you will see it is /24 because there are 24 1s or network bits and 8 0s or host bits.

In our problem, we need at least 18 IP address options for hosts. For this we will use 0s. How many 0s will we need? Less than 8 for sure because that gave me 256 options. But how many less?

The powers of 2 come in handy for any binary math. There are 2 possible values for each bit, 0 or 1. With 2 bits there are 4 possible values, 00, 11, 10, 01. That isn’t going to get me to at least 18 hosts. This could take a while and for the ICND1 test you need to subnet in 15 seconds. Yikes!

In comes the cheat sheet.


Memorize this formula to go with the table: Possible hosts on a network = 2^h – 2

Each network supports 2^h ip addresses, however 1 ip address is used for the network id and another is used for the broadcast address, hence the minus 2 part.

I don’t suggest just memorizing the table. I would suggest understanding how to generate the table. Start from the top right and do your powers of 2 up to 128. 2^0 = 1, 2^1 =2 2^2=4 … 2^7=128

Next is the second row, the decimal mask. Take 256 – the h row to get the decimal mask row.

Next is the last 2 octets of cidr notation. This is simply a count of 1s in the binary representation of the mask. Remember 1s are the network bits and 0s are the host bits.

Once we have this table we can solve our problem, subnet in a way that supports at least 5 networks and at least 18 hosts in each network.

Start this question with the important number h, or 18.

Go to the table and find the h value that supports at least 18 hosts, which is 32.

Go down to the decimal notation .224 and we know that we can support at least 18 hosts with a decimal mask of

Next we can list the network IDs that this mask could possibly create

To figure this out mathematically take 2^n where n = the number of network bits. There are 3 network bits or 1s in the octect we subnetted. We can make 8 networks which is greater than 5 required by the problem. BOOM CAKE!


For the remainder of this post I will be simply typing up my notes from the Wendell Odom Cisco Press Book and some other notes I took watching YouTube videos from a variety of authors which I will link to.


1. Physical – wiring standards, physical topology, bandwidth usage, syncronizing bits
2. DataLink – MAC, Flow Control standards
3. Network – IP, IPX, Switching, Route Discovery, TTL
4. Transport – TCP, UDP, windowing, buffering
5. Session – Netbui
6. Presentation – jpg, encryption, data formatting(ascii, ebcidic)
7. Application – http, smb, smtp, service advertisement, dns

IP Addressing

First Octects
CLASS A – 1-127
CLASS B – 128-191
CLASS C – 192-223

Hub – layer 1 device that simply spams all ports with frames

Rember these things in this order
SEGMENT – includes the tcp ports
PACKET – includes the IP
FRAME – the whole stinking thing with headers and trailers

Encapsulation – IP Packet is a Layer 3 PDU

CHAP2: Fundamentals of Ethernet Lans

UTP – unshielded twisted pair

crossover cable

like devices need crossover cable to switch transmit and receive pins

MAC – 48bits – 24 for OUI

FCS – frame check sequence is at the end of the frame to ensure proper delivery


leased line , service provider
CPE – customer premises equipment
CSU/DSU – channel service unit, data service unit usually on prem and RJ-48
Router-Router communication can occur on serial cables
HDLC – high level data link control
——way of encapsulating frames over WAN
PPP – point to point protocol
MPLS – multi protocol label switching

CHAP4: IPv4 Addressing and Routing

Routing uses L3PDUs
Layer 2 are called frames

IPv4 headers are 20 bytes and include SIP,DIP,Len,offset,chksum,ttl,etc…

CLASS A: 126 networks and 16,777,214 hosts per network
CLASS B: 16,384 networks and 65,534 hosts per network
CLASS C: 2,097,152 networks and 254 hosts per network

Router FWD logic
1. uses FCS to make sure no errors
2. discard old frame header and trailer
3. compare DIP to routing table and find next hop
4. encapsulate

CHAP 5: fundamentals of TCP/IP transport applications

UDP – connectionless

Connection establishment
SYN —->

Connection termination

shutdown – command that turns a port down/down
no shutdown – turns a port up/up (the second up is if the protocol works)

CHAP 8: configuring Ethernet Switching

enable secret mYpass
show history
no shutdown

port security
1. switchport mode access (access or trunk)
2. switchport port-security (enables port security)
3. switchport port-security maximum 2 (allowed macs on port)
4. switchport port-security violation shutdown (action to take)
5. switchport port-security mac-address AAAA:AAAA:AAAA (specifiy allowed macs)
6. switchport port-security mac-address sticky (dynamic learned mac addresses)

CHAP 9: implementing VLANs

ISL = OLD protocol

12bits for VLANID (this is a “shim” in the frame)
how many vlans? 2^12 or 4096
vlanid 1 is default

router on a stick – one physical link to a router instead of two

show vlan brief

(allow port 4 to communicate on vlan id 10)
1. enable
2. configure terminal
3. interface FastEthernet0/4
4. switchport access vlan 10

Layer3 switch does routing …but can’t do this in packettracer :[

Reasons switch prevents VLAN traffic from crossing a trunk
1. removed from allow list
2. vlan doesn’t exist in show config
3. vlan doesn’t exist, been disabled

and some other less important reasons

CHAP 10 Troubleshooting

show cdp neighbors
show interfaces status

“administratively down” means shutdown command was run
err-disabled means port security

vlan troubleshooting
1. identify all access interfaces and their vlans
2. do vlans exist and are they active
3. check allowed vlan list on both ends of the trunk
4. check for trunk/no trunk neighbors

show vlan brief


IPv4 subnetting

One subnet for every:
1. vlan
2. ppp serial link
4. frame relay

VLSM – variable length subnet mask


CHAP 12 analyzing classful IPv4 Networks
CHAP 13 analyzing subnet masks
CHAP 14: analyzing existing subnets

CHAP 15: Operating Cisco routers

Installation steps
1. connect lan ports
2. connect CSU/DSu external
3. connect CSU/DSU internal
4. connect console port to pc using a rollover cable
5. connect power
6. power on

show ip route

show mac address-table

status layer 1/status layer 2
down/down : has not been shutdown but physical layer problem

CHAP 16: configurating IPv4 addresses and routes

1. choose to process frame
-proper mac (is its destination me?)
-no errors (FCS)
2. de-encapsulate packet
3. compare DIP to routing table
-this identifies outgoing interface
4. encapsulate
5. transmit

routers should ignore switch floods not intended for it

large routing tables can cause performance problems

cisco express forwarding
-uses organized tree and other tables to help speed up routing

adding routes can be done via:

1. connected routes
2. static routes
3. routing protocols

cisco will add routes if the interface is IP’d and UP

ROAS 802.1Q trunk


commands to turn on

router ospf 1
network area 0

ospf – open shortest path first – uses link state
OSPFv2 is for IPv4

routing protocol – set of messages, rules and algorithms (RIP, EIGRP,OSPF,BGP)

routed & routable protocol – defines packet structure and addressing (IPv4)

1. learn routing information about ipsubnets from neighboring routers
2. advertise this info
3. if more than 1 route exists, pick best
4. if topology changes, advertise current best route (convergence)

Interior gateway protocol – designed for use inside a single autonomous system
exterior gateawy protocol – BGP

routing algorthims use
1. distance vector
2. advanced distance vector
3. link state (ospf uses this)

RIP is old
IGRP is a little less old

RIP-2 uses hop count and is also old with slow convergence
OSPF is a cost based protocol
EIRGP – cisco proprietary and uses bandwidth and latency
IS-IS – uses link state

0 connected
1 static
20 BGP E
110 OSPF
115 IS-IS
120 RIP
200 BGPI

this will show the database of link state advertisements(LSAs)
show ip ospf database

routers must agree to be neighbors

configuration, this will turn on for any interface that matches 10.0.* because of the wildcards in network command

router ospf
network area 0


Discover – TO FROM

ip helper-address {dhcp server ip} – command for router that enables DCHP servers to sit outside of the subnet by changing SIP&DIP ( Thanks /u/Sprockle )

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Posted by on May 23, 2015 in Network Admin


Gearing up for another exam ICND1 100-101

The more I learn about networks, the less I tend to blame the network.

It was almost 20 years ago that I set a static IP address on my sisters computer and connected a cross over cable to my computer so we could play a game called Quake. She wasn’t that interested so I ran back and forth between the rooms and played by myself. This loneliness was resolved a few years later with a device that looked something like this


Point is, I’ve been doing this for a long time and I still don’t know jack. I don’t like to fail tests, so signing up for a test is going to help me learn. I would like to become a more well rounded datacenter administrator.


ICND1 100-101 is the first half of a valuable certification CCNA. I now have the book in hand and about 5 weeks to prepare. Normally, I would allow myself about 3 months with a book this size but opportunity has struck and I need to accelerate my pace.

Like Microsoft, Cisco is very open with their exam topics.

1.0 Operation of IP Data Networks 6%
2.0 LAN Switching Technologies 21%
3.0 IP addressing (IPv4/IPv6) 11%
4.0 IP Routing Technologies 26%
5.0 IP Services 8%
6.0 Network Device Security 15%
7.0 Troubleshooting 13%

These do not line up that nicely to the book topics. But I am going to attempt to cruise through the book which I have given myself some milestones below.

Part I: Networking Fundamentals
Part II: Ethernet LANs and Switches
Part III: Version 4 Addressing and Subnetting (Be done by May 11th and practice subnetting)
Part IV: Implementing IP Version 4 (Be done by May 18th and practice show commands)
Part V: Advanced IPv4 Addressing Concepts
Part VI: IPv4 Services (Be done by May 26th, decide if I want to skip IPv6, Review OSPF and practice more advanced subnetting)
Part VII: IP Version 6
Part VIII: Final Review (Be here by June 1st and have taken a practice exam to decide what areas to review)

The schedule is set, plans are in place, now it is time for me to do some reading.

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Posted by on May 9, 2015 in Network Admin