GLBP - Router DHCP Server

Answered Question
Apr 26th, 2012

Hello all,

Here is the scenario and my question

VoIP deployment 100 phones, PC's, two ISR's and a switch. I would like to setup a DHCP server for the phones on the ISR and have a DHCP helper for the PC's.  I wanted to setup an environment where there is a level of redunancy for the DHCP pools on the ISR's. 

How does the DHCP server portion work on the router in the event of a failure?  Is it wise to setup identical or split up DHCP pools on both ISR's?

Routers.jpeg

I have this problem too.
0 votes
Correct Answer by csarto about 1 year 11 months ago

Probably as a best practice it's better to split the poon on two parts (as from this presentation

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6600/ps6641/prod_presentation0900aecd803116a7.pdf )

Anyway as stated here:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a00800f0804.shtml

"At the address assignment, the DHCP checks for conflicts with ping and gratuitous ARP."

So you can have two DHCP servers with the same pool.

  • 1
  • 2
  • 3
  • 4
  • 5
Average Rating: 5 (1 ratings)
csarto Thu, 04/26/2012 - 23:51

I suppose that both ISR are default gateaway for voice vlan and data vlan.

In this scenario you can set up both ISR with DHCP-Server service enabled for each vlan.

The pool can be the same, then after release an IP the DHCP server check if it's pingable, if not it lease the address to the client.

The first DHCP Server that respond to che client request is the DHCP server for that client.

h.grankvist Fri, 04/27/2012 - 01:03

csarto, are you sure that won't create a problem? You can't even do that on Windows servers.

The only way I know of to accomplish this is to have the same pool on the two routers but exclude half the range so each router has one half of the IP-range.

Correct Answer
csarto Fri, 04/27/2012 - 01:20

Probably as a best practice it's better to split the poon on two parts (as from this presentation

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6600/ps6641/prod_presentation0900aecd803116a7.pdf )

Anyway as stated here:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a00800f0804.shtml

"At the address assignment, the DHCP checks for conflicts with ping and gratuitous ARP."

So you can have two DHCP servers with the same pool.

jan.ifkovitz Fri, 04/27/2012 - 01:25

hi,

are you using HSRP ? then one of the routers is the active an one is the standby for the ip interfaces. so if you configure isr1 witch x.x.x.2 and isr2 with x.x.x.3 an the virtuel interface with x.x.x.1..... the ip helper will be the virtuell interface... the primary router will answer.

fruition3000 Mon, 04/30/2012 - 06:03

I wouldnt be using HSRP I would be using GLBP to take advantage of load balancing.  Have any of you tried the configuration I am proposing? 

Actions

Login or Register to take actions

This Discussion

Posted April 26, 2012 at 7:30 PM
Stats:
Replies:5 Avg. Rating:5
Views:829 Votes:0
Shares:0

Related Content

Discussions Leaderboard

Rank Username Points
1 15,007
2 8,150
3 7,725
4 7,083
5 6,742
Rank Username Points
165
82
69
65
55