DHCP Snooping

I was scratching my head for an issue which i encountered in one of my customer place where it did not make logic while troubleshooting.

Then i posted my question on a online forum and got an answer in a minute which totally embarrassed me :) I was happy that i was able to communicate the question clearly that the guy answered in a swift.

Okay enough story, This was my question.

Hi Techs,

The subject may sound hyping the issue, but i am really baffled. Apologize for the essay!

1. Core switch - EX4200 Stack

2. Access Switch - EX3200 48 pts

Core switch has a IP helper pointing to a windows DHCP server. Access switch is nothing but a dumb switch with just VLAN configured for desktop and IP phone's. Everything is working normally - meaning, if i plug in a new IP Phone or PC or daisy chain IPPhone and PC, every device can get IP from appropriate VLAN's.

Last week, we tried connecting a PC to one of the free ports and it got an IP address from DHCP server and life was good. When i wanted to change the IP address in the same subnet to a different IP statically, I lost connection to default gateway and even the LAN segment from that PC. Tried 2 different PC's - same result.

1. In PC, When i assigned static IP which was originally assigned by DHCP, it is working

2. When i assign static IP with different unused ip in the same segment, no reachability to even peers connected to same switch

3. When i 'reserve' the unused new IP in DHCP server with the PC Mac address, I receive the unused IP from DHCP server and everything is working good. 

Any insight is much appreciated.

Regards

Balaji M

Answer in probably 2-3minutes time

@mellowd

Certs: 350-001, CCNP, CCIP, JNCIA-EX

Are you sure DHCP snooping isn't configured?

I checked and Yes, DHCP snooping was enabled for that particular data VLAN. Lesson learnt. For more info on Juniper DHCP snooping, below given is the article.

http://www.juniper.net/techpubs/en_US/junos10.4/topics/concept/port-security-dhcp-snooping.html 

Regards

Balaji M 

How to make it work in tabs: GNS3 0.8.2 with SecureCRT 6.5 in Windows 7 64bit

I searched hours to get this working with routers separated by tabs and at last found the solution in the below post

http://forum.gns3.net/topic2490.html?sid=2fd553ad6c4d7c4b9e7a11ccfd49a113

1. Install SecureCRT, assume directory is C:\Program Files\VanDyke Software\SecureCRT

2. Add SecureCRT directory to OS PATH

Right click "My Computer", choose "Properties", click tab "Advanced", click button "Enviroment Variables", choose "PATH" in upper frame, click upper "Edit" button, add ";C:\Program Files\VanDyke Software\SecureCRT" in column "Variable value", click "OK" and "OK" and "OK" to exit.

Now restart your computer, implement following actions if you do not want to restart at this time.

Click Windows "Start", folder "All Programs", subfolder "Accessories" chose "Command Prompt". Type "PATH %PATH%;C:\Program Files\VanDyke Software\SecureCRT". Now you can type "PATH" to check SecureCRT directory is added to OS PATH. Type "exit" to quit.

3. Configure SecureCRT as console of GNS3

Open GNS3, click "Perferences..." under "Edit". Click tab "Terminal Settings" under "General", type "securecrt.exe /T /N "%d" /telnet %h %p" in "Terminal Command" column. Unselect "Launch this command using the system default shell". Click "OK".

Works perfectly!!!

Edited 3 days later: Dynamips crashing quite often. Like once every hour. Have installed XP in VM, will try and post the outcome.