"Rough cuts" of "CCIE Routing and Switching Exam Certification Guide, 4th Edition"

I was studying the 3rd Edition of "CCIE Routing and Switching Exam Certification Guide". Now comes the "Rough Cuts" of the 4th Edition!

Rough cuts?! I thought at the first glance the 4th Edition was already available. In fact, it is not! The explanation on the same page of this book says:

What is a Rough Cut?

The Rough Cuts service from Safari Books Online gives you exclusive access to an evolving manuscript that you can read online or download as a PDF and print. A Rough Cuts book is not fully edited or completely formatted, but you'll get access to new versions as they are created.

To dig further by clicking "Buy from Safari Books Online", I found this book is estimated to be published on November 06, 2009.

Interesting! Let's wait for it until the coming November!

IP Helper Address: what about "Source Address" of the diverted broadcast packets?

I crafted an sample "IP Helper Address" lab, and I found the "Source Address" of the diverted broadcast packets should be the unicast address of the interface which enabled "IP Helper Address".

The demonstration output capture is this:

1. When no "Helper" is enabled, all DHCP broadcasts (DISCOVERY) are just ignored.
2. Enabling "Helper". Note about the IP address (2.1.1.10) of this LAN interface and the configured diversion destination address (1.1.1.1)
3. From this time on, the debug output shows the DHCP broadcast's source address is changed from "0.0.0.0" to "2.1.1.10", and destination address is changed from "255.255.255.255" to "1.1.1.1". The packet is forwarded to DHCP server (R1).
   
4. Then, DHCP server's response (OFFER) packet is sourced from "1.1.1.1" to destination "2.1.1.10", as expected.
5. The "Helper" relays it to the client and changes the source address of the packet from "1.1.1.1" to its own address: "2.1.1.10", also the destination is changed from "2.1.1.10" to "255.255.255.255", as if the response were generated from itself.

R0#show ip int brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            unassigned      YES unset  up                    up      
FastEthernet0/0.200        2.1.1.10        YES manual up                    up      
FastEthernet0/1            unassigned      YES unset  administratively down down    
Serial1/0                  1.1.1.10        YES manual up                    up      
Serial1/1                  unassigned      YES manual administratively down down    
Serial1/2                  unassigned      YES unset  administratively down down    
Serial1/3                  unassigned      YES unset  administratively down down    
R0#
*Mar  1 00:42:43.599: IP: s=0.0.0.0 (FastEthernet0/0.200), d=255.255.255.255, len 604, rcvd 2
*Mar  1 00:42:47.111: IP: s=0.0.0.0 (FastEthernet0/0.200), d=255.255.255.255, len 604, rcvd 2
*Mar  1 00:42:51.159: IP: s=0.0.0.0 (FastEthernet0/0.200), d=255.255.255.255, len 604, rcvd 2
R0#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R0(config)#int f0/0.200
R0(config-subif)#ip helper-address 1.1.1.1
R0(config-subif)#end
R0#
*Mar  1 00:43:07.607: %SYS-5-CONFIG_I: Configured from console by console
*Mar  1 00:43:09.239: IP: s=0.0.0.0 (FastEthernet0/0.200), d=255.255.255.255, len 604, rcvd 2
*Mar  1 00:43:09.255: IP: tableid=0, s=2.1.1.10 (local), d=1.1.1.1 (Serial1/0), routed via FIB
*Mar  1 00:43:09.259: IP: s=2.1.1.10 (local), d=1.1.1.1 (Serial1/0), len 604, sending
*Mar  1 00:43:09.439: IP: tableid=0, s=1.1.1.1 (Serial1/0), d=2.1.1.10 (FastEthernet0/0.200), routed via RIB
*Mar  1 00:43:09.443: IP: s=1.1.1.1 (Serial1/0), d=2.1.1.10, len 328, rcvd 4
*Mar  1 00:43:09.459: IP: s=2.1.1.10 (local), d=255.255.255.255 (FastEthernet0/0.200), len 328, sending broad/multicast
*Mar  1 00:43:09.567: IP: s=0.0.0.0 (FastEthernet0/0.200), d=255.255.255.255, len 604, rcvd 2
*Mar  1 00:43:09.583: IP: tableid=0, s=2.1.1.10 (local), d=1.1.1.1 (Serial1/0), routed via FIB
*Mar  1 00:43:09.587: IP: s=2.1.1.10 (local), d=1.1.1.1 (Serial1/0), len 604, sending
*Mar  1 00:43:09.619: IP: tableid=0, s=1.1.1.1 (Serial1/0), d=2.1.1.10 (FastEthernet0/0.200), routed via RIB
*Mar  1 00:43:09.623: IP: s=1.1.1.1 (Serial1/0), d=2.1.1.10, len 328, rcvd 4
*Mar  1 00:43:09.635: IP: s=2.1.1.10 (local), d=255.255.255.255 (FastEthernet0/0.200), len 328, sending broad/multicast
R0#
R0#

I now have a conclusion: the "ip helper address" must have been WRONGLY described in this book: Wendell Odom, Rus Healy, Naren Mehta."CCIE Routing and Switching Exam Certification Guide, 3rd Edition", Page 128 and also Page 134!

VTP Password can be shown!

I did not notice that we can use "show" commands to display the VTP (VLAN Trunking Protocol) password!

I was reminded by my student these days. We can see this document "Configuring VTP Global Parameters" for a sample.

Switch#show vtp password
VTP Password:WATER
Switch#

I should have known this in CCNA courses. How careless I am!

VTP Explained in Animation, on Cisco.com

I came across this Flash animation explaining VLAN Trunking Protocol (VTP), right on Cisco.com.

It is very clear and fully explaining many details about VTP. I believe it would help you to understand VTP even further!

http://www.cisco.com/warp/public/473/vtp_flash/

Enjoy it!