SG300 DHCP Server Secondary DNS Allocation

[Paul Robinson]

I'm not sure this is possible but is the DHCP server able to allocate a secondary DNS server.

There only seems to be the option to put a single DNS entry in.

I current have DHCP setup to allocate a internet based DNS (Google's DNS on 8.8.8.8) so my workstations can access the internet, however I would like it to allocate a secondary dns so my workstations are aware able to connect to my internal servers via hostnames.

Is it possible on the SG300-20 to do this

Thanks

Paul

[Brandon Svec]

Paul, check release notes for latest software that was released about a week ago. I think I saw a feature enhancement about more dhcp options available.

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[Paul Robinson]

Brandon,

I upgraded my firmware and boot code to the latest release Sx300 Firmware Version 1.3.5.58

However when I try to access the Release Notes & Open Source Documentation Link I just get a 403 Forbidden on the url from ciscos website.

The new firmware does indeed have dhcp options but not got a clue how to configure what I want without any docs.

So bit stuck for now

Thanks

Paul

[Brandon Svec]

I saw another post where someone had trouble seeing the release notes.  This link works for me:

http://www.cisco.com/en/US/products/ps10898/prod_release_notes_list.html

As far as multiple DNS entries they normally are entered with comma between them.  Did you try like 4.2.2.2, 8.8.8.8 ?

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[Brandon Svec]

page 881 shows how to enter DNS entries.  I tested and verified it works by using comma between entries.

http://www.cisco.com/en/US/docs/switches/lan/csbms/sf30x_sg30x/administration_guide/CLI_300_1_3.pdf

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[Paul Robinson]

HI,

I tried through but the Web GUI and CLI and dont seem to be able to add the second address in

prcswitch01#config

prcswitch01(config)#ip dhcp pool network Workstations

prcswitch01(config-dhcp)#dns-server 8.8.8.8, 10.0.15.200

% bad parameter value

prcswitch01(config-dhcp)#dns-server 8.8.8.8,10.0.15.200

% bad parameter value

Thanks

Paul

[Brandon Svec · Accepted solution]

Weird, I am trying to remember what I did now.  Here is my show command proving that it worked:

switch706852(config-dhcp)#do sh ip dhcp pool network test

       Name                Address range            Mask         Lease   

------------------- --------------------------- ------------- -----------

       test            10.10.10.1-10.10.10.6    255.255.255.2  1d:0h:0m  

                                                48                       

Statistics:

All-range   Available   Free   Pre-allocated   Allocated   Expired    Declined 

----------- ----------- ------ --------------- ----------- ---------- ----------

     6           6        6           0             0          0          0     

DNS server: 4.2.2.2;8.8.8.8

Ah ha, history buffer shows no comma, but space!

switch706852(config-dhcp)#dns-server 4.2.2.2 8.8.8.8

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[Paul Robinson]

Thanks Brandon, that worked when I configure it through the CLI.

The GUI however only allows one entry.

Now trying to get my head around configuring my dns server correctly, not something ive done before.

I have it all working on internal hosts but can acess internet when I have the Primary set to my internal DNS.

Looking on the net looks like I need to setup a forwarder on my internel DNS to allow it to forward any external requests to the internet. 

Have configured my DHCP to give the primary DNS as my internal DNS server 10.0.15.200 and secondary to googles DNS server 8.8.8.8.  Once ive configured the forwarder on my internal server my hosts should be able to access both internal/external hosts.  Should my internal server be down it should fall back on the secondary DNS 8.8.8.8 which will give my machines access to external hosts.

I think thats how its meant to work.

Anyhow thats another issue for me to sort out and beyond the scope of this forum. 

Thanks again for all your help

Paul

[Brandon Svec]

Interesting about the GUI, but good it can be done via CLI.  You are on the right track about the internal DNS.  I have a similar setup at my office.  The main difference is I serve DHCP from my Meraki MX60.

Good luck.

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