[cisco-voip] suggested/best practices for DHCP settings on routers

[Lelio Fulgenzi]

I also noticed that for IOS v15T, it has the following pre-requisites. However, I can't find a "service dhcp" statement in my config, but I know it's offering up DHCP addresses. Also, I can't issue the "show ip sockets details" command or the "show sockets detail" command. 

weird! 



http://www.cisco.com/en/US/docs/ios-xml/ios/ipaddr_dhcp/configuration/15-1mt/Configuring_the_Cisco_IOS_DHCP_Server.html#GUID-9F0ED96D-17EA-4307-A14C-0C23A335B5D4 




Before you configure the Cisco IOS DHCP server, you should understand the concepts documented in the DHCP Overview module. 




The Cisco IOS DHCP server and relay agent are enabled by default. You can verify if they have been disabled by checking your configuration file. If they have been disabled, the no service dhcp command will appear in the configuration file. Use the service dhcp command to reenable the functionality if necessary. 





Port 67 (the server port) is closed in the Cisco IOS DHCP/BOOTP default configuration. There are two logical parts to the service dhcp command: service enabled and service running. The DHCP service is enabled by default, but port 67 is not opened until the DHCP service is running. If the service is running, the show ip sockets details or show sockets detail command displays port 67 as open. 




The Cisco IOS DHCP relay agent will be enabled on an interface only when the ip helper-address is configured. This command enables the DHCP broadcast to be forwarded to the configured DHCP server. 


--- 
Lelio Fulgenzi, B.A. 
Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1 
(519) 824-4120 x56354 (519) 767-1060 FAX (JNHN) 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
Cooking with unix is easy. You just sed it and forget it. 
- LFJ (with apologies to Mr. Popeil) 


----- Original Message -----
From: "Robert Kulagowski" <rkulagow at gmail.com> 
To: "cisco-voip (cisco-voip at puck.nether.net)" <cisco-voip at puck.nether.net> 
Sent: Tuesday, May 10, 2011 11:23:59 AM 
Subject: Re: [cisco-voip] suggested/best practices for DHCP settings on routers 

On Mon, May 9, 2011 at 3:16 PM, Ryan Ratliff <rratliff at cisco.com> wrote: 
> An address conflict occurs when two hosts use the same IP address. During 
> address assignment, DHCP checks for conflicts using ping and gratuitous 
> Address Resolution Protocol (ARP). If a conflict is detected, the address is 
> removed from the pool. The address will not be assigned until the 
> administrator resolves the conflict. 
> 
> Yes it does. 
> -Ryan 

We ended up adding: 

no ip dhcp conflict logging 

to our router configuration so that we wouldn't end up with _all_ 
addresses unassignable. 
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