Scheduled 640-801 (July 31st) Q&A

I'm the type of person who needs a deadline to push me so I've scheduled the test for July 31st (2 weeks exactly). Considering the test didn't change from the time I took off until now I'm sure a strong 2-week locked door session should be enough. Back to business.

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tech-airman

markzab wrote:

Possible protocols found in the protocol field of an IP header:

ICMP 1
IGRP 9
EIGRP 88
OSPF 89

etc...

Thats from my notes...those numbers are the port numbers, correct?

markzab,

No, those are not port numbers. Those are numbers in the protocol field of the IP header.

Remember the encapsulation and decapsulation process. For example, from the Transport Layer to the Network Layer, ....

Transport Layer   [TCP Header |Source Port|Destination Port][Data]

     |
     |
     v
Network Layer [IP Header |Source IP address|Destination IP Address|Protocol][TCP Header |Source Port|Destination Port][Data]

Think of the protocol field like special stamps on the envelope or packaging like "Do not bend" or "Fragile." Just like your printed IT certificate that comes in the mail may be stamped "Do not bend" suggests that the contents maybe a paper certificate, the same goes with protocol numbers. During the decapsulation process, the numbers in the protocol field in the IP (Network Layer) header gives a clue of what (in this case, a TCP segment) is inside the IP Packet.

I hope this helps.

markzab

Ok, that was a bit more than I needed bro.

So in short, they aren't the port numbers of the protocol, but more like its identifier?

markzab

Damn, I'm starting to notice that this 2 month hold-over may have screwed me up a bit. When I first wrote the notes from the Lammle book they worked great because the book was still fresh in my mind. Now some of the stuff in my notes confuses me or doesn't seem full enough. Grrrr.

markzab

Ok, I think I asked this a while ago but it's bothering me again so I probably forgot the answer.

I have no problems subnetting. It's one of my strong points. But where the heck does 256 come from? Add up all the bits in an octet and you get 255, understandable. But in the little formula to figure out valid subnets you subtract the subnet mask from 256 to get the block size.

Why 256? Is it a number they just made up that works for the formula? It bothers me because sometimes I mix up the 255 with 256 for the total of an octet.

tech-airman

markzab wrote:

Ok, that was a bit more than I needed bro.

So in short, they aren't the port numbers of the protocol, but more like its identifier?

markzab,

Yes, that is correct.

tech-airman

markzab wrote:

Ok, I think I asked this a while ago but it's bothering me again so I probably forgot the answer.

I have no problems subnetting. It's one of my strong points. But where the heck does 256 come from? Add up all the bits in an octet and you get 255, understandable. But in the little formula to figure out valid subnets you subtract the subnet mask from 256 to get the block size.

Why 256? Is it a number they just made up that works for the formula? It bothers me because sometimes I mix up the 255 with 256 for the total of an octet.

markzab,

In general, a network address consists of two parts: 1) network part 2) host part. An IP address is 32 bits long. That 32 bit long binary "word" is broken up into 4 octets. Each octet contains 1 byte. 1 byte is 8 bits. So let's say we're dealing with the Class C Private IP range. So we know that the first three octets are the "network part" and the last octet is the "host part." Here's the important part:

1) In binary, a single octet VALUE ranges from .00000000 through .11111111 . In dotted decimal, that range is .0 ~ .255

2) However, in the decimal number system, .00000000 binary is the 1st host ID, .00000001 binary is the 2nd host ID, .00000010 binary is the 3rd host ID, and so on until .11111111 is the 256th host ID.

So in dotted decimal notation .255 represents the 256th host ID, therefore maybe that's where "256" is coming from?

markzab

tech-airman wrote:

markzab wrote:

Ok, I think I asked this a while ago but it's bothering me again so I probably forgot the answer.

I have no problems subnetting. It's one of my strong points. But where the heck does 256 come from? Add up all the bits in an octet and you get 255, understandable. But in the little formula to figure out valid subnets you subtract the subnet mask from 256 to get the block size.

Why 256? Is it a number they just made up that works for the formula? It bothers me because sometimes I mix up the 255 with 256 for the total of an octet.

markzab,

In general, a network address consists of two parts: 1) network part 2) host part. An IP address is 32 bits long. That 32 bit long binary "word" is broken up into 4 octets. Each octet contains 1 byte. 1 byte is 8 bits. So let's say we're dealing with the Class C Private IP range. So we know that the first three octets are the "network part" and the last octet is the "host part." Here's the important part:

1) In binary, a single octet VALUE ranges from .00000000 through .11111111 . In dotted decimal, that range is .0 ~ .255

2) However, in the decimal number system, .00000000 binary is the 1st host ID, .00000001 binary is the 2nd host ID, .00000010 binary is the 3rd host ID, and so on until .11111111 is the 256th host ID.

So in dotted decimal notation .255 represents the 256th host ID, therefore maybe that's where "256" is coming from?

Ok, I can buy that.

If that's the answer then it's odd that they associate using 256 when figuring out a network block size when it's in regards to a host ID. Know what I mean?

markzab

Got another one for you guys. Should be pretty easy. In regards to VLANs the VLAN database is not stored in NVRAM, just RAM. What happens if for some reason your power goes down and the generator doesn't keep everything up. Do you lose all of the VLAN info you had on the switches? That'd be pretty crappy.

markzab

And another kind of off topic question.

My 2509 acts as a terminal server and is connected to all devices in my lab. Can someone tell me why I need a terminal server (2509) when I could just telnet into each device to configure it?

LOkrasa

markzab wrote:

Got another one for you guys. Should be pretty easy. In regards to VLANs the VLAN database is not stored in NVRAM, just RAM. What happens if for some reason your power goes down and the generator doesn't keep everything up. Do you lose all of the VLAN info you had on the switches? That'd be pretty crappy.

VLAN info is saved in nvram on Server and Transperant mode. It is only not saved on Client mode.

LOkrasa

markzab wrote:

And another kind of off topic question.

My 2509 acts as a terminal server and is connected to all devices in my lab. Can someone tell me why I need a terminal server (2509) when I could just telnet into each device to configure it?

Telnetting gets confusing if you go from one to another device. 2509 lets you make a p2p connection on all of your equipment regardless of its state... You can telnet to other devices but what if you are configuring it and the device is still not on your network, you would have to move the console cable. Telnetting only really works when its configured and accessible. Having a TAS will connect you to each console port so regardless of the state of the router/switch you have access to it. You just need to console into the TAS instead of moving the console port to all the the other devices if the connections b/w them are down. This is obviously priceless if you are in a real world enviroment and want to remotely do administration since all you have to do is connect to the 2509 to be able to access everything else. Hope that helps.

markzab

LOkrasa wrote:

markzab wrote:

And another kind of off topic question.

My 2509 acts as a terminal server and is connected to all devices in my lab. Can someone tell me why I need a terminal server (2509) when I could just telnet into each device to configure it?

Telnetting gets confusing if you go from one to another device. 2509 lets you make a p2p connection on all of your equipment regardless of its state... You can telnet to other devices but what if you are configuring it and the device is still not on your network, you would have to move the console cable. Telnetting only really works when its configured and accessible. Having a TAS will connect you to each console port so regardless of the state of the router/switch you have access to it. You just need to console into the TAS instead of moving the console port to all the the other devices if the connections b/w them are down. This is obviously priceless if you are in a real world enviroment and want to remotely do administration since all you have to do is connect to the 2509 to be able to access everything else. Hope that helps.

Ok, thats what I figured but in regards to a home lab with say 3 switches and 4 routers I guess the terminal server is kind of pointless once you've configured everything for the first time. I mean after you've done your first lab with all devices connected to eachother you could really just use telnet from that point on.

I understand the ease of the TAS though. Thank you.

markzab

LOkrasa wrote:

markzab wrote:

Got another one for you guys. Should be pretty easy. In regards to VLANs the VLAN database is not stored in NVRAM, just RAM. What happens if for some reason your power goes down and the generator doesn't keep everything up. Do you lose all of the VLAN info you had on the switches? That'd be pretty crappy.

VLAN info is saved in nvram on Server and Transperant mode. It is only not saved on Client mode.

Ya know what. I read my note wrong. It stated that "VTP clients only keep the VTP database in RAM and that's not saved to NVRAM." I interpreted the word clients not as client mode, but more generally, meaning all the switches. Oops.

tech-airman

markzab wrote:

And another kind of off topic question.

My 2509 acts as a terminal server and is connected to all devices in my lab. Can someone tell me why I need a terminal server (2509) when I could just telnet into each device to configure it?

markzab,

For starters, this topic is above and beyond the scope of the CCNA exam. However, since you asked I will try to answer the question.

Terminal servers are used for what is known as "out of band" network management. That is, the network traffic created by the commands you type does not add to the network traffic load on the "production network." This ability becomes very important when you're trying to troubleshoot connectivity problems associated with that networking device. If that networking device is the cause of networking connectivity problems, you may also have problems being able to telnet into that device at all.

Another benefit of using a terminal server versus a single PC with console cable is if you're trying to troubleshoot two or more networking devices at the same time, for example a possible dynamic routing update issue. A terminal server will be holding separate buffers of information for each connection from the terminal server to the networking device. That way, you can have a single continous source of output information, such as debug outputs. That way, you can compare continous debug outputs from say RouterA, RouterB, and RouterC. However, without a terminal server to be holding continuous output information from multiple sources, you may miss out on some critical debug or show output while you unplug the console cable from one router to plug it into another router. As previously mentioned, due to issues with the networking device, it may not even be possible to telnet to the problem networking device so how would you use telnet to configure it to fix the problem?

I hope this helps.

markzab

tech-airman wrote:

markzab wrote:

And another kind of off topic question.

My 2509 acts as a terminal server and is connected to all devices in my lab. Can someone tell me why I need a terminal server (2509) when I could just telnet into each device to configure it?

markzab,

For starters, this topic is above and beyond the scope of the CCNA exam. However, since you asked I will try to answer the question.

Terminal servers are used for what is known as "out of band" network management. That is, the network traffic created by the commands you type does not add to the network traffic load on the "production network." This ability becomes very important when you're trying to troubleshoot connectivity problems associated with that networking device. If that networking device is the cause of networking connectivity problems, you may also have problems being able to telnet into that device at all.

Another benefit of using a terminal server versus a single PC with console cable is if you're trying to troubleshoot two or more networking devices at the same time, for example a possible dynamic routing update issue. A terminal server will be holding separate buffers of information for each connection from the terminal server to the networking device. That way, you can have a single continous source of output information, such as debug outputs. That way, you can compare continous debug outputs from say RouterA, RouterB, and RouterC. However, without a terminal server to be holding continuous output information from multiple sources, you may miss out on some critical debug or show output while you unplug the console cable from one router to plug it into another router. As previously mentioned, due to issues with the networking device, it may not even be possible to telnet to the problem networking device so how would you use telnet to configure it to fix the problem?

I hope this helps.

That part was completely overlooked by me. Good stuff. Thanks.

I know it's above the scope but considering I own a TAS I was just wondering why in a non-critical home lab environment I would need one. The debug windows I guess would be the best reason in my case.

markzab

It's ALIVE!!!

And the way I just finished cabling it up if you can't see my beautiful notepad design in the above image

...

Wow, I'm just gonna love seeing my electric bill these coming months.

In regards to my layout, do you guys think that will do for most labs and topics covered in the CCNA? I'm trying to think of a technology that I won't be able to play with there but I can't come up with one. Heck, the 4th machine down is my 2524 frame switch which I decided not to even power up and throw in because, well...because I don't have anymore serial cables to hook it up to be honest.

So what do you think? Am I good to go? Start lab'in it up?

markzab

Started with a few labs from Lammle's book tonight. Played around with static routes getting all machines talking, and also with some default routes. Then removed the static routes and went dynamic with RIP. All machines talking.

Nothing beats seeing the !!!!! after pinging from LAB_C to LAB_A.

markzab

Something interesting I just noticed while playing around. I've got my setup above going...

(LAB_A)

(LAB_B)

(LAB_C)

I don't have the octo cable for the TAS so I've been switching the console cable around to configure the devices. One I got them talking I started just telneting into the next devide to work on it. And then I wanted to see how much I could telnet around. What I mean is I telnetted from C to A, then from A to B, then from B back to C, and then just to see if I could double up, from C again to A.

Then I exit'd out of A and I was at the C prompt again. I thought that if I typed exit there it would take me out of the router and to router C's "hit return to get started" screen but it took me back into the telnet session on B. So I guess I kind of looped my sessions overlapping eachother.

Thought that was interesting. I guess a question I could have out of this would be how many times could I loop telnet sessions above eachother? Is there a limit other than the amount of VTY lines I've got? I guess these loops are ok to have.

markzab

Um...ok...

LAB_C(config)#router igrp 10
^
% Invalid input detected at '^' marker.

LAB_C(config)#router ?
bgp Border Gateway Protocol (BGP)
eigrp Enhanced Interior Gateway Routing Protocol (EIGRP)
isis ISO IS-IS
iso-igrp IGRP for OSI networks
mobile Mobile routes
odr On Demand stub Routes
ospf Open Shortest Path First (OSPF)
rip Routing Information Protocol (RIP)

Um, where is IGRP???

markzab

And on my 2612...

LAB_A#conf t
Enter configuration commands, one per line. End with CNTL/Z.
LAB_A(config)#router ?
bgp Border Gateway Protocol (BGP)
eigrp Enhanced Interior Gateway Routing Protocol (EIGRP)
isis ISO IS-IS
iso-igrp IGRP for OSI networks
mobile Mobile routes
odr On Demand stub Routes
ospf Open Shortest Path First (OSPF)
rip Routing Information Protocol (RIP)

What the heck is going on???

Netstudent

Aw man that sucks. You need to upgrade.

markzab

Well IGRP isn't very hard for me so I think I can get by without it. Pretty easy to configure.

I just dont understand why my IOS would have RIP, EIGRP, OSPF, etc...but not IGRP.

Cucumber

I think IGRP has been discontinued

markzab

Cucumber wrote:

I think IGRP has been discontinued

I don't think that's the case even if true. Even if it was discontinued I don't think my IOS images are so new that they wouldnt have it on them.

Netstudent

here is a link to a snap shot of the CCIE ROUTING TCP/IP book. If hyou look on the second paragraph it tells you that IGRP has been discontinued as of IOS release 12.2(13)T.

http://books.google.com/books?id=JjdF2yWqJAwC&pg=PA251&lpg=PA251&dq=cisco+discontinuing+igrp&source=web&ots=Cc_Ekebwsd&sig=8Pwr1nidYTndCpLz0IPZsePF_s0

Cucumber

hmm I remember reading IGRP has been gone for a while but I really cant remember since what IOS version

edit: ah I didnt read the previous post

markzab

Damn Lammle book.

So it obviously wont be on the test?

Cucumber

that is correct, it wont be on the test
rather study rip, eigrp and ospf

markzab

Amazing how much more you learn with hands on lab work. There were a few things I wasn't sure about prior to re-reading my EIGRP section and actually configuring an EIGRP network on my router. I can't stress enough the importance of hands on. Over the past few days I was kind of down because for some reason I was worried that the information wasn't clicking all together like it did for me 6 years ago when I was rocking cisco certs left and right.

Some of you may know what I mean. It's like you've just read through all the material, even a few times, and you see it all layed out in your head...but it just wont come together into one big picture that all makes sense, together. Well after starting on my labs yesterday I started to notice it all slowly coming together. You know, that little field of images in your head that all of a sudden connects and you're like..."oh, I get it".

It might sound stupid but we're all tech geeks here so you'd be able to get this more than anyone else I could ever tell. It's almost like I'm starting to recognise what's on that screen...

You get my point.

Like, tonights clicks had to deal with summarization and discontiguous networks. To be honest I never really understood what discontiguous networks were but I guess in my own words they are simply 2 networks with different classful boundaries (class b and class c for example) being brought together into one network by the use of EIGRP (which supports discontigous networks) by the use of the no auto-summary command. And then that opened up the next door in regards to summarization because without the no auto summary command EIGRP wouldnt be able to support VLSM, since it would automatically bring the mask boundary back to its default classful mark.

Ok, did that make sense to anyone else except for me?

r_durant

Yes it did MZ...I'm right with you in this section

I'm on your tail...