newbie question: option 82

[christian kueppers]

Hi all,

I`ll try to setup the sg300-10p with multiple vlans and networks. Buti i want to use only one dhcp server. How does theinsert look like to configure it on an2012r2 server?

[Tom Watts]

Hi Christian, as a layer 2 switch option 82 shouldn't be needed on the switch as it doesn't route anything. Your success would depend on your routing device.

In layer 3, the option 82 should be configured. But in this, the default gateway advertised by the DHCP should by configured for the SVI of the layer 3 vlan otherwise routing would be incorrect.

-Tom
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[christian kueppers]

Hi tom,

That's what i assumed. I switched to L3 .But how does Option look like so that i can configure the Microsoft DHCP Server for this Option? Which value dies it have? Mac address?

[Tom Watts]

Hi Christian, I'm not sure I understand the inquiry. Like other DHCP options, it inserts a field in to a packet.

In this query, option 82 will insert a 0x52 for the giaddr.

  ::= 0x52

For information for the MS server this may be helpful

http://blogs.technet.com/b/teamdhcp/archive/2012/10/01/option-82-support-in-dhcp-server-for-the-ip-source-guard-scenario.aspx

-Tom
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[christian kueppers]

Hi Tom,
I know this article, thanks. But within the article there is screenshot for configuring the Option with a long hex-value. I thought that the sg300 is setting this value, so that it can be queried by the Dhcp Server. And i thought that it has to be different by using more than one network.
But maybe i'm wrong.

Christian

[Tom Watts]

Hi Christian, the sx300 does set this value and I do believe it uses only hex format since other options are also hex format. The DHCP server still has an equal responsibility for routing. The fundamental of networking will dictate the DHCP server will still need IP connectivity or VLAN awareness to be able to pass traffic on the medium to a respected subnet, especially as layer 3 interfaces will discard broadcast packets.

I am not much of a server person but I do believe when creating your multiple IP pools they need to be bound to some sort of virtual interface otherwise the forwarding table wouldn't know where to allocate the address space.

-Tom
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[christian kueppers]

Hi tom,
I will search a little bit more... From the screenshot in the article and the article itself i didn't thought on multiple addresses for the dhcp server. I thought on different hex values given by SG300 which can be used by the dhcp server. My question was if these values are known and documented.

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[christian kueppers]

So whati neee is the information how remote id, agent id, relay agent innformatin looks like. This i have to configure on the dhcp server


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[Tom Watts]

Hi Christian, the only way to see this information is from a packet capture (Wireshark)

-Tom
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[christian kueppers]

Hi Tom,
thanks. That's what I've feared. On the catalyst switches I've read that I can query this by CLI. But i found no command for it in the sg300 cli reference. Is there any hidden one?
Last question before hard wireshark work ... :-)
Christian


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[Tom Watts]

Sadly no, this switch does not have any advance debug feature. That is something I've request many times on my wish list as IOS products have excellent debug features

The SX300/500 debug console is for engineering purpose only and has no practical usage for end user

-Tom
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[FoysaliSPBroadbandMetroWiFi]

Hi, Download CLI Command Reference at cisco.com and PuTTY download from internet setting up IP address and config from your console.

thank you