Assign two DHCP servers for two VLANS on SG300?

[tourtelot1]

I am running a simple closed AoIP network on two Cisco SG300 switches.  I have two VLANs.  One for the Dante AoIP stream (192.168.0.xxx) and one for various controllers, CCTV, remote (iPad) control, etc. (192.200.0.xxx)

I have the Front of House (FOH) switch set to serve DHCP to all the devices on VLAN1 (192.168.0.xxx), the Dante stream.  I think there is a way to set up a second DHCP server to serve those devices on VLAN2 (192.200.0.xxx).

I have tried some ideas I saw online, and on the Cisco Tech Talk videos.  I have not gotten this to work yet.  Could anyone quickly explain how I might get my FOH switch to serve two IP ranges with unique IP addresses?  Or point me to a link that explains this.  I am not a network newbie but I am just in the beginning stages of understanding.  

Thanks for any help.

Doug

[Georg Pauwen]

Hello,

the SG300 can function as DHCP server for up to 8 different pools. Have a look at page 333 of the attached admin guide:

https://www.cisco.com/c/dam/en/us/td/docs/switches/lan/csbms/sf30x_sg30x/administration_guide/Cisco_300Sx_v1_4_AG.pdf

[tourtelot1]

Thanks Georg. 

I am confused by one of the fields in the DHCP Server Pool configuration.  When it asks for Subnet IP Address, I am not sure what to put in the box.  I tried 192.200.0.254 and 192.200.0.1 and neither stuck.  Thoughts?

Doug

[tourtelot1]

And I have set my second pool to serve the range of 192.200.0.100 to 192.200.0.150 but how does it know to serve only VLAN2?

Doug

[Georg Pauwen]

Hello,

subnets end in 0, that is probably why it the input was not accepted. You need to subnet 192.200.0.0/24 into two /25 subnets in order to create two pools that each serve on Vlan. The SVI usually takes the first IP address:

Subnet 1

Network 192.200.0.0/25

SVI/Vlan IP:192.200.0.1/25

Host Range: 192.200.0.2 - 192.200.0.127

Subnet 2

Network 192.200.0.128/25

SVI/Vlan IP:192.200.0.129/25

Host Range: 192.200.0.130 - 192.200.0.254

The hosts connected to each Vlan will 'know' from which pool to pull an address because they come through the corresponding SVI.

[paul driver]

Hello

You dont require two dhcp servers, but two dhcp scopes on a dhcp server, I have nerver had any exposure to this switch model however runing a dhcp service is basically the same whatever platform it runs on, router, l3 switch or server.

Basic cisco equivelant example-
ip dhcp pool DHCP-Scopes
network 192.168.1.0 255.255.255.0
network 192.200.1.0 255.255.255.0 secondary
override default-router 192.200.0.254
default-router 192.168.1.254
dns-server x.x.x.x y.y.y.y  < - dns server(s) you wish your client to use
lease 0 8 < - lease time of dhcp allocation ( refresh 50% of lease duration,set shorter lease for wifi cleints)

ip dhcp excluded-address 192.168.1.1 192.168.1.10  <  - exclusion ranges you dont want dhcp to allocate
ip dhcp excluded-address 192.200.1.1 192.168.200.10

[tourtelot1]

Hi-

So I changed something that I thought would make this easier but still. no joy.

VLAN1 is 195.168.0.XXX

VLAN2 is 195.168.2.XXX

I want to set my SG300 switch to serve DHCP to both VLANs, VLAN1 to a range of 192.168.0.100 to 192.168.0.150.  VLAN2 to a range of 192.168.2.100 to 192.168.2.150

I set up a second network pool, and tried with a Subnet Mask of 255.255.255.0 on both pools.  It didn't work (and maybe, of course).  I then changed my Subnet Mask in both pools to 255.255.0.0.  It still didn't work.

Would someone please talk me through the specifics, on an SG300, about how to do this?  I use a browser interface.  I am pretty sure that this can be done if I fill the boxes in correctly and check the boxes appropriately.

Thanks for helping out someone who's brain is still addled by network stuff. 

Doug

[amikat]

Hi,

The address ranges for DHCP pools can be configured as follows:

using CLI

ip dhcp pool network Pool1
 address low 192.168.0.100 high 192.168.0.150 255.255.255.0

ip dhcp pool network Pool2
 address low 192.168.2.100 high 192.168.2.150 255.255.255.0

using gui

IP Configuration > DHCP Server > Network Pools:

Add
Pool Name: Pool1
Subnet IP Address: 192.168.0.0
Mask (Network Mask): 255.255.255.0
Address Pool Start: 192.168.0.100
Address Pool End: 192.168.0.150
Apply

Add
Pool Name: Pool2
Subnet IP Address: 192.168.2.0
Mask: (Network Mask): 255.255.255.0
Address Pool Start: 192.168.2.100
Address Pool End: 192.168.2.150
Apply

Other parameters like lease, domain-name, default-router, dns-server are typically configured under the DHCP pools.

Best regards,

Antonin

[tourtelot1]

Thanks for your reply, Antonin.  I set the values to those you suggested and the first pool continues to serve DHCP in the 192.168.0.XXX range but there is no service from Pool #2, 192.168.2.XXX.  I do notice that the subnet IP addresses do not remain in the box after I apply the changes.  I rebooted the switch after the values were saved.

What else might I need to do the make this work?  FYI, I am running the switch as an L2 and not as an L3.  Could that be the problem?

Other than that, any other ideas.  This is a tweak that I'd like to get working but it is not a deal-breaker.  I am using a Linksys wireless access point as a DHCP server on VLAM2.  The Linksys was unplugged from the switch during the test.

Thanks for your help.

Best,

Doug

[amikat]

Hi,

Thanks for the information provided. Yes, to my knowledge this switch must operate in layer 3 mode to act as a DHCP server for various vlans.

Best regards,

Antonin

[tourtelot1]

Thanks SO much for your great help.  As you are probably aware, when I switch my SG300 from L2 to L3, the switch reboots to factory default with no configuration.  When I try and restore my working configuration, the error message says that the configuration will not work in L3.  Is there any way to get my configuration over to my, now, L3 switch without rebuilding the whole thing from scratch.

If not, I most certainly will keep the switch as an L2 switch and serve VLA2's configuration from the Linksys Wireless Access Point.

Best,

Doug

[amikat]

Hi,

I am sorry to hear that you have not backed up your configuration before changing the switch system mode. When changing the mode the startup configuration file kept in the flash memory is deleted and the system is rebooted, ie. both your running and startup configurations are lost. Under normal circumstances there are also backup configuration and mirror configuration files kept in flash that to my knowledge are not automatically deleted after you start L3. Can you please try the following procedure (I understand that you manage your box via GUI only):

Administration > File Management > Download/Backup Configuration/Log 

choose via HTTP/HTTPS  as Transfer Method

choose Backup as Save Action

choose Backup Configuration file as Source File Type

choose Plaintext as Sensitive Data

Apply

after Copy Finished repeat this procedure for the Mirror Configuration file.

Then please check the files copied to your PC whether they contain the requested information (text files). If yes then you can copy back to your switch as Startup or Running Configuration after changing to L2 back again.

Best regards,

Antonin

[tourtelot1]

Hello-

Thanks again.

Sorry I was a bit unclear.

I do have backup .txt files for the L2 configurations on all my switches.  What I noticed was that after I changed my switch to L3, the .txt backup configuration for the switch (L2) would not translate and load up on the switch that was now set to L3.

It was super easy to factory default the switch and load the .txt backup file and all is what it was, of course my switch converting back to L2.  So all is good and I can continue to use the Linksys WAP for serving DHCP to the VLAN #2 on the L2 switch.  Easy peasy.

I was hoping that, somehow, I could get all my switch setting from the L2 switch to restore to the L3 switch but I can see how that might not be possible.  It's not worth the struggle to install all my current settings from scratch along with learning the idiosyncrasies of the L3 configurations right now although I might get bold and try it in the future knowing that I can easily reboot the switch to factory default and load up the running config .txt file and be back at square one.  I was not aware of the "mirror" function and I will look into that although it seems that restoring from the running-config .txt file works to bring me back to a fully functioning switch.

Thanks for all your help.

Best,

Doug 

All part of my networking education.  Still lots t

[tourtelot1]

I just reread you idea for using the "mirror" config to translate the LA config to L3.  I will give that a try and report back.

Doug

[amikat · Accepted solution]

Hi,

I am glad to hear you have your backup configuration available. The mirror configuration however cannot help you to migrate to L3, this one is just automatically kept copy of the last known stable configuration (ie. L2 again in your case).

I am not aware of any GUI method as how to simply transform the L2 config to L3 one. But in my view the SG300 switch configuration is not very complicated and can easily be built manually (ie. L3 from the known L2 data).

I am sorry I cannot provide better advice.

Best regards,

Antonin