my 3614 was purring along smoothly, i was tasked with making it work nice with our nortel contivity firewall, and a web filter called bess... bess was a dog, a real dog for the filter company owner... bess was loyal, faithful and true and she didn't allow our users to go to unsavory sites any longer... of course her filtering caused processing overhead... and the contivity (a great firewall, but i didn't like the fruit inspired filtering icons) also took its toll on performance... toss in dns, dhcp and possibly a packet filter... "geez the internet seems slow today"... "seems fine to me"... "it was faster yesterday"... the empirical evidence was overwhelming and always based on feelings... "it just feels slow is all"... "can you ping?"... "yes, but what is that REALLY telling me?"... in a word, EVERYTHING...
packet internet groper has a way of restoring your sanity by way of proving network connectivty... but feelings are more reliable as far as management is concerned... "the internet just doesn't seem right to day"... here's a picture; try squeezing a ton of users through a garden hose at the same time... what do you get? an embittered user community and a busy help desk phone... there was this thing once called a cache engine... stick it in the router and it will save url's for visited websites on our side of the fire wall and distribute them from inside the network... nice idea... didn't work very well..
what does work? more frigging bandwidth... you've got 100 M behind the firewall for hosts, now let's shove them through a five meg pipe to the isp...
how do you feel about your network today?
network cisco ccna gns3 certification arteq
a network runs through it
Monday, October 31, 2011
nibbles and bits
nibbles and bits...
the configuration register of a router is represented by a hex number, or 0x... it is a sixteen
bit number read from left to right starting from 15, and ending with 0, sixteen numbers total...
cisco loves the number sixteen because it is difficult to add sixteens... quick what is 16 plus
forty eight? 128 plus 16? how many 16's in 192? 16 x 4 is 64 which goes into 192 3 times... 3 x
four is 12... what is 12 hex?
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256
0x2102 means load start from nvram if found
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
8 4 2 1 8 4 2 1 8 4 2 1 8 4 2 1
15 to 0 are place positions
each group of 4 bits is a nibble
count the nibbles and bits
don't look at me... i didn't make this shit up
0010 0001 0000 0010 = 0x2102
try to think of all three number systems at once.. here is a great site that groups all three...
http://easycalculation.com/decimal-converter.php
decimal 20
is 14 in hex because 16 goes into 20 once with a remainder of 4
the binary value is 0001 0100 because 16 + 4 is twenty:
128 64 32 16 8 4 2 1
0 0 0 1 0 1 0 0
back to 192, the beginning of the class C range of private adresses
16 goes into 192 12 times
12 = C in hex so 192 = C0 hex
192 = 11000000 because 128 + 64 + 0 + 0 + 0 + 0 + 0 + 0 = one hundred and 92
remember 128 64 32 16 8 4 2 1
8 4 2 1 binary = 15 decimal = F hex
what is decimal 42 in hex? 2A
binary? 00101010
10 = A = 1010
sixteen goes into 42 twice remainder 10
the configuration register of a router is represented by a hex number, or 0x... it is a sixteen
bit number read from left to right starting from 15, and ending with 0, sixteen numbers total...
cisco loves the number sixteen because it is difficult to add sixteens... quick what is 16 plus
forty eight? 128 plus 16? how many 16's in 192? 16 x 4 is 64 which goes into 192 3 times... 3 x
four is 12... what is 12 hex?
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256
0x2102 means load start from nvram if found
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
8 4 2 1 8 4 2 1 8 4 2 1 8 4 2 1
15 to 0 are place positions
each group of 4 bits is a nibble
count the nibbles and bits
don't look at me... i didn't make this shit up
0010 0001 0000 0010 = 0x2102
try to think of all three number systems at once.. here is a great site that groups all three...
http://easycalculation.com/decimal-converter.php
decimal 20
is 14 in hex because 16 goes into 20 once with a remainder of 4
the binary value is 0001 0100 because 16 + 4 is twenty:
128 64 32 16 8 4 2 1
0 0 0 1 0 1 0 0
back to 192, the beginning of the class C range of private adresses
16 goes into 192 12 times
12 = C in hex so 192 = C0 hex
192 = 11000000 because 128 + 64 + 0 + 0 + 0 + 0 + 0 + 0 = one hundred and 92
remember 128 64 32 16 8 4 2 1
8 4 2 1 binary = 15 decimal = F hex
what is decimal 42 in hex? 2A
binary? 00101010
10 = A = 1010
sixteen goes into 42 twice remainder 10
Saturday, October 29, 2011
the forward/filter conundrum...
given:
the three functions of switching:
1) learning: switches and bridges remember the hardware address of each incoming frame on an interface and update the mac database with this information. the mac database is also known as a forward/filter table
2) forward/filter: upon receiving a frame the switch examines the destination hardware address, finds the exit interface in the mac database and forwards the frame out that corresponding interface
3) avoiding loops : in a redundant network, STP is used to stop network loops while not impeding that redundancy
this is good until...
The following list provides a quick review of the basic logic a switch uses:
1.A frame is received.
2.If the destination is a broadcast or multicast, forward on all ports except the port on which the frame was received.
3.If the destination is a unicast, and the address is not in the address table, forward on all ports except the port on which the frame was received.
4.If the destination is a unicast, and the address is in the address table, and if the associated interface is not the interface on which the frame arrived, forward the frame out the one correct port.
5.Otherwise, filter (do not forward) the frame.
this from http://ciscotests.org/ccna.php?part=3&page=2 odom, lammele, et al
according to odom:
paraphrase liberty alert
frame came in port E0, filter because destination is on port E0...
frame came in port E0, forward because destination is off port E1
filtering happens when the frame gets dropped, and forwarding happens when the frame is shipped to a port besides the one on which the frame was received...
switch happens...
the three functions of switching:
1) learning: switches and bridges remember the hardware address of each incoming frame on an interface and update the mac database with this information. the mac database is also known as a forward/filter table
2) forward/filter: upon receiving a frame the switch examines the destination hardware address, finds the exit interface in the mac database and forwards the frame out that corresponding interface
3) avoiding loops : in a redundant network, STP is used to stop network loops while not impeding that redundancy
this is good until...
The following list provides a quick review of the basic logic a switch uses:
1.A frame is received.
2.If the destination is a broadcast or multicast, forward on all ports except the port on which the frame was received.
3.If the destination is a unicast, and the address is not in the address table, forward on all ports except the port on which the frame was received.
4.If the destination is a unicast, and the address is in the address table, and if the associated interface is not the interface on which the frame arrived, forward the frame out the one correct port.
5.Otherwise, filter (do not forward) the frame.
this from http://ciscotests.org/ccna.php?part=3&page=2 odom, lammele, et al
according to odom:
paraphrase liberty alert
frame came in port E0, filter because destination is on port E0...
frame came in port E0, forward because destination is off port E1
filtering happens when the frame gets dropped, and forwarding happens when the frame is shipped to a port besides the one on which the frame was received...
switch happens...
Friday, October 28, 2011
the present is a gift... GNS3
why did it take so long and why wasn't it around back when i was struggling with second rate router and switch sims (network simulators... you know who you are) spent a fortune on that garbage and while many of the labs and exercises were useful, they were not ios based, the command sets were horribly lacking and they were cobbled together... gave me a bad case of yuck mouth...
a few months ago i stumbled upon http://www.gns3.net/ ... for all of the struggling, poor cisco cert slaves this is manna from heaven... anyone who cannot afford their own in house lab should go immediately to this site... it is free, it utilizes real ios.bin's (although you have to scavenge them from not always reputable sources), it has a graphical topology and will packet capture in real time... it supports every protocol that the ios you've found supports... it is not a simulator, you are in fact running ios on your box...
tutorials are all over youtube, and on the internet... not only http://www.gns3.net/ , sites such as http://blindhog.net/ , et al... no more whining i can't afford the equipment, DYNAMIPS and GNS3 are here...
ok,ok... it is hardware intensive when the topology starts to get large and switch support is short, but it's ios and it doesn't cost several hundred dollars per router...
and why isn't CISCO embracing this technology, because it's a DIY threat...
anyway, the following is a great introduction to the GNS3 revolution...
use it, abuse it...
http://blog.ipexpert.com/2010/03/31/gns3-on-windows-7-the-ipexpert-way
a few months ago i stumbled upon http://www.gns3.net/ ... for all of the struggling, poor cisco cert slaves this is manna from heaven... anyone who cannot afford their own in house lab should go immediately to this site... it is free, it utilizes real ios.bin's (although you have to scavenge them from not always reputable sources), it has a graphical topology and will packet capture in real time... it supports every protocol that the ios you've found supports... it is not a simulator, you are in fact running ios on your box...
tutorials are all over youtube, and on the internet... not only http://www.gns3.net/ , sites such as http://blindhog.net/ , et al... no more whining i can't afford the equipment, DYNAMIPS and GNS3 are here...
ok,ok... it is hardware intensive when the topology starts to get large and switch support is short, but it's ios and it doesn't cost several hundred dollars per router...
and why isn't CISCO embracing this technology, because it's a DIY threat...
anyway, the following is a great introduction to the GNS3 revolution...
use it, abuse it...
http://blog.ipexpert.com/2010/03/31/gns3-on-windows-7-the-ipexpert-way
enter rfc's, odom and lammle...
i spent three months trying to get subnetting down, mostly from posts on the internet... it was difficult to be sure... most taught the binary method which is clunky... there had to be an easier way... i started digging into rfc's, this was very exciting... if you have a bout of insomnia on a given night, go to http://www.rfc-editor.org/ , after about ten minutes you'll sleep like the dead... however, private addressing http://www.rfc-editor.org/rfc/rfc1918.txt , CIDR http://www.rfc-editor.org/rfc/rfc4632.txt , and VLSM http://www.apps.ietf.org/rfc/rfc1817.html are must reads... the very reasons behind and the necessity of subnetting are explored in great detail in these pages...
i started bumping into wendell odom ( ccie 1624, one of the early guys)... his ccna book was expensive, a single volume back then, dry and difficult to get through... although incredibly useful, it didn't help me find the path of least resistance in mastering the art of subnetting... again, a must read...
in walks todd lammle who claims he can teach me how to subnet in my head... impossible... of course i bought his book, and when i got through his binary style of subnetting and then into what i call the minus 256 technique of subnetting, i had found the grail... another nice thing about todd's books is that they are a more pleasant reading experience... he makes some cheesy jokes along the way but he proves that networking doesn't have to be an awful learning experience...
fancy that... i once posted my interpretation of todd's method and it is still out there... here is the link... http://unixresources.net/linux/lf/58/archive/00/00/06/53/65383.html
that was 2004 and it's still there, damn...
also, here is a place that will hone your subnetting abilities:
http://www.subnettingquestions.com/
below is the text for those who do not know how to use the internet:
i started bumping into wendell odom ( ccie 1624, one of the early guys)... his ccna book was expensive, a single volume back then, dry and difficult to get through... although incredibly useful, it didn't help me find the path of least resistance in mastering the art of subnetting... again, a must read...
in walks todd lammle who claims he can teach me how to subnet in my head... impossible... of course i bought his book, and when i got through his binary style of subnetting and then into what i call the minus 256 technique of subnetting, i had found the grail... another nice thing about todd's books is that they are a more pleasant reading experience... he makes some cheesy jokes along the way but he proves that networking doesn't have to be an awful learning experience...
fancy that... i once posted my interpretation of todd's method and it is still out there... here is the link... http://unixresources.net/linux/lf/58/archive/00/00/06/53/65383.html
that was 2004 and it's still there, damn...
also, here is a place that will hone your subnetting abilities:
http://www.subnettingquestions.com/
below is the text for those who do not know how to use the internet:
subnetting technique
Author: arteq Posted: 2004-03-09 11:16:08 Length: 5,119 byte(s)
[Original] [Print] [Top]
subnetting
the minus 256 technique
this presupposes knowledge of binary and ip addressing conventions,
and is not recommended for the newcomer
jump for the rest
jump for the rest
Thursday, October 27, 2011
bi to the two minus 2, or how i learned to stop worrying and love hex...
two is bi... it always helps me learn when i can put ideas in a sexual context...
two to the fourth will get you sixteen, and sixteen will get you 20 so be careful there... wait, 16 will get you hex, that's legal... but back to bi...
2 to the seventh is a significant number... it is the beginning of the class b range of addresses and two to the eighth will get you 256... so what is this 255 horseshit? 0 = 0 and 255 = 1... what happened to 256... it took me a while but 0 to 255 is 256 numbers total... now 2 to the 8th makes sense...
hex is not bi and it's sixteen based so why does f = 15? because it includes the zero... 0 to 9 are decimal numbers that are included in hex... so what is 10 in hex? with hex you need to know your abc's...
0 = off, and 1 = 255 which in turn equals on... 0 and one are bi, but 1 is always turned on... better off hooking up with the one, more action there...
there are 8 bits in an octet and 32 bits in an ip address... 8 is two to the third, 32 is 2 to the fifth.. how many octets in an ip address?
the numbers started to turn me on...
two to the fourth will get you sixteen, and sixteen will get you 20 so be careful there... wait, 16 will get you hex, that's legal... but back to bi...
2 to the seventh is a significant number... it is the beginning of the class b range of addresses and two to the eighth will get you 256... so what is this 255 horseshit? 0 = 0 and 255 = 1... what happened to 256... it took me a while but 0 to 255 is 256 numbers total... now 2 to the 8th makes sense...
hex is not bi and it's sixteen based so why does f = 15? because it includes the zero... 0 to 9 are decimal numbers that are included in hex... so what is 10 in hex? with hex you need to know your abc's...
0 = off, and 1 = 255 which in turn equals on... 0 and one are bi, but 1 is always turned on... better off hooking up with the one, more action there...
there are 8 bits in an octet and 32 bits in an ip address... 8 is two to the third, 32 is 2 to the fifth.. how many octets in an ip address?
the numbers started to turn me on...
a layered approach...
application - a written or spoken request...
presentation - how am i looking today...
session - quality time with your shrink
transport - a car, a train, etc...
network - a netlike combination of veins, filaments, etc...
datalink - the missing link; often...
physical - a song by olivia newton john
i needed to get layered...
it took a while to understand the osi model, to truly understand it and how it becomes essential to troubleshooting networks... i began to like theory; the biter got bitten...
encapsulation:
how i get my request prettied up for the shrink and into the car to a bunch of veins in search of the missing link dancing to an olivia newton john song?
presentation - how am i looking today...
session - quality time with your shrink
transport - a car, a train, etc...
network - a netlike combination of veins, filaments, etc...
datalink - the missing link; often...
physical - a song by olivia newton john
i needed to get layered...
it took a while to understand the osi model, to truly understand it and how it becomes essential to troubleshooting networks... i began to like theory; the biter got bitten...
encapsulation:
how i get my request prettied up for the shrink and into the car to a bunch of veins in search of the missing link dancing to an olivia newton john song?
the beginning...
a few years ago i began a journey, a cisco certification journey... i worked in a nortel shop, nortel layer 3 core, nortel layer 2 switches at the edge, nortel up the ass... i knew then that to apply myself to learning this technology would not suit me well in the end... i think a nortel certification was not even available... it seemed a waste of brain cells and for my advanced age, i had killed enough of them along the way, i could afford to lose no more...
we had a t1 connection to the internet back then and the thought was to upgrade to a routed connection to our isp via a cisco 3614... when the opportunity was presented to our group, nobody bit... i was doing mostly day to day desktop support for this organization, had only a locally specific notion of IP, gaps everywhere in my network knowledge, and of course, i became the biter...
with help from knowledgeable staff at our isp i managed to get the 3614 up and into production... i was suddenly the cisco guy, and i knew nothing...
we had a t1 connection to the internet back then and the thought was to upgrade to a routed connection to our isp via a cisco 3614... when the opportunity was presented to our group, nobody bit... i was doing mostly day to day desktop support for this organization, had only a locally specific notion of IP, gaps everywhere in my network knowledge, and of course, i became the biter...
with help from knowledgeable staff at our isp i managed to get the 3614 up and into production... i was suddenly the cisco guy, and i knew nothing...
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