Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

SG200-26P DHCP or DNS problem

Hi forum

I'm having some bother with a SG200-26P.

Its new, and I think the only setting changed was its IP address.

I'm thinking all the other settings might be default/s.

All our workstations and servers have connected via the switch as expected.  One of those servers provides DHCP service.

We also have a bunch of Cisco phones that worked fine with the old switch, BUT  ...

When I plug the phones into the SG200-26P they start to boot up.

After the message "Initializing Network", they all get stuck on "Checking DNS".

It seems all the phones cannot get any IP address or DNS settings from the DHCP server, so failure is assured.

Pleases and thankyous for any tips or clues to get this working as desired.

I'm hoping its just a PBKAC.

Everyone's tags (3)
2 ACCEPTED SOLUTIONS

Accepted Solutions
New Member

Re: SG200-26P DHCP or DNS problem

I'm having quite the same problem with an SG200-26, but the effect is wider.

Several Cisco 7911G phones work smoothly on our network, before connecting the SG200-26.

After connecting the cisco switch (15-30 seconds), they goes into "registration" status and get stuck there. Despite the fact that they already were registered and working, they become unreachable, even by PING.

Note that the phones are NOT connected to the Cisco Switch, nonetheless they are affected by its presence.

Disconnecting the Cisco Switch also restores the normal situation of the 7911Gs (after 20-30 seconds).

To complicate my understanding, PC are NOT affected by the Cisco SG200-26 presence.

As for Brian Roper, the only set I modified on the switch are name/address/passwords. No VLANs.

You can guess that such a device is quite devastating for our services, instead I bought it to solve problems.

Any other suggestion?

New Member

SG200-26P DHCP or DNS problem

Ok, I did some tests.

There is someting broken with CDP/LLDP (smart port detection) in ip phone, I think.

I used sg200-26 + 7911G (SIP 9.3.1-SR2).

Default configuration: cannot ping

Manually change smart port to IP phone: pingable, everything works

I tried to downgrade to 8.5.4-S: everything works ok without playing with smartports

13 REPLIES
Bronze

SG200-26P DHCP or DNS problem

Dear Brian,

Thank you for reaching Small Business Support Community.

It's been several days since you first posted your inquiry with no answer from our community members so far.  The SG200 is not pre-configured with DHCP server functions or DNS resolution, therefore the switch should not be the problem in my opinion.  I suggest you to first make sure yours in not a routing issue where the DHCP server is not reachable by a regular host and if that's ok then check on the admin guide, chapter 5, starting on page 111 for Voice and media configuration settings;

http://www.cisco.com/en/US/docs/switches/lan/csbss/sg200/administration_guide/78-19562.pdf

If yours are Cisco IP Phones I would also recommend you to inquire about the problem on the Voice and Conferencing Small Business Support Community;

https://supportforums.cisco.com/community/netpro/small-business/voiceandconferencing

If it is not a Cisco IP Phone I would then suggest you to contact the manufacturer for support.  Please do not hesitate to reach me back if there is anything I may assist you with in the meantime.

Kind regards,

Jeffrey Rodriguez S. .:|:.:|:.
Cisco Customer Support Engineer

*Please rate the Post so other will know when an answer has been found.

Jeffrey Rodriguez S. .:|:.:|:. Cisco Customer Support Engineer *Please rate the Post so other will know when an answer has been found.
New Member

Re: SG200-26P DHCP or DNS problem

Hi Brian,

Whenever you have isues with DHCP on a device you want to ensure with a PC that DHCP connectivity works. If the phones are operating in a different VLAN I would plug a PC into a port with said Voice VLAN untagged and see if you are able to get an IP address.  If you are not, then there is some issue with the DHCP server. 

If you have a single DHCP Server operating in multiple VLANs then you will need to look into some form of DHCP relay, otherwise DHCP will not work on the VLANs the DHCP server doesn't have network connectivity to.

If you can verify that the DHCP server is functioning in the same VLAN via a PC then the next step would be packet captures.

Setup port mirroring on one of the ports you are going to plug a phone into.  Ensure the destination port where the PC is connected has wireshark running.  Then plug the phone in and see if you are receiving DHCP Packets (you can filter with bootp in wireshark).

If you are seeing a DHCP Offer from the DHCP Server after the DHCP Discover but no DHCP request coming from the Phone then there is some problem with the phone.  A factory default may be a good idea or you should contact the manufacturer.

Let me know if you have any questions!

-Trent Good

*Please rate useful posts!*

-Trent Good ** Please rate useful posts! **
New Member

Re: SG200-26P DHCP or DNS problem

I'm having quite the same problem with an SG200-26, but the effect is wider.

Several Cisco 7911G phones work smoothly on our network, before connecting the SG200-26.

After connecting the cisco switch (15-30 seconds), they goes into "registration" status and get stuck there. Despite the fact that they already were registered and working, they become unreachable, even by PING.

Note that the phones are NOT connected to the Cisco Switch, nonetheless they are affected by its presence.

Disconnecting the Cisco Switch also restores the normal situation of the 7911Gs (after 20-30 seconds).

To complicate my understanding, PC are NOT affected by the Cisco SG200-26 presence.

As for Brian Roper, the only set I modified on the switch are name/address/passwords. No VLANs.

You can guess that such a device is quite devastating for our services, instead I bought it to solve problems.

Any other suggestion?

Green

Re: SG200-26P DHCP or DNS problem

Hi, I think folks are getting too far ahead here.

Is your network completely flat or is there a voice vlan?

Is the switch on the newest firmware? Some of the oldest firmware DID NOT support CDP...

Spanning tree... is port fast enabled or is the switch detecting the link state to put the phone forwarding as it should with port fast?

-Tom
Please mark answered for helpful posts

-Tom Please mark answered for helpful posts http://blogs.cisco.com/smallbusiness/
New Member

Re: SG200-26P DHCP or DNS problem

Hello Tom, thanks for your attention.

1) Our netword is flat. No voice VLAN. Are you suggesting to deactivate the "Voice VLAN enabled" set on the switch? It is supposed to word only if triggered and nothing trigs it.

2) The switch is a brand new one: firmware version 1.2.9.44

3) Spannig Tree: enabled

GM

New Member

Re: SG200-26P DHCP or DNS problem

It seems I've been able to get these phones working with the SG200-26 by changing/copying the VLAN interface settings for ALL the phone ports.

  Interface VLAN mode = Access

  Administrative PVID = 1

Now the phones can receive their DHCP and DNS settings correctly, and permit registration with sip server.

Thanks for your help, tips, and clues.

BTW, I'm thinking this "smartport" stuff might be sub-optimal, if I'm having more success making the settings manually.

(Using firmwares 1.2.9.44)

New Member

SG200-26P DHCP or DNS problem

Hi, I have the same problem...

I have SG200-26 (without PoE) and I suspected PoE injector... So I bought AC adapter, disable DHCP on phone and set manual IP address. I tried to disable SPT, Green Ethernet, MDIX, Auto negotiation... but the problem persists.

I can see the phone via CDP from switch, nothing strange in  the log:

21474835922013-Apr-27 09:00:33Warning%STP-W-PORTSTATUS: gi1: STP status Forwarding     
21474835932013-Apr-27 09:00:29Informational%LINK-I-Up:  gi1, aggregated (1)     
21474835942013-Apr-27 09:00:26Warning%LINK-W-Down:  gi1, aggregated (1)     
New Member

SG200-26P DHCP or DNS problem

I cannot say I found the real origin of the problem.

I found out that if I connected the SG-200 to 2 (two!) 3Com Switches, the problem came out.

So, I reorganized the branches, and put out of order the older 3Com, and connected the SG-200 to another 3Com but newer (10 years ago?) and the disturb never occurred again.
The strange thing is that all the 3Coms had the same settings.

New Member

SG200-26P DHCP or DNS problem

Hi,

I manually set Smart Port to IP phone and set Full Duplex on the Phone and it seems working.

I will try to check it today in the lab.

New Member

SG200-26P DHCP or DNS problem

Ok, I did some tests.

There is someting broken with CDP/LLDP (smart port detection) in ip phone, I think.

I used sg200-26 + 7911G (SIP 9.3.1-SR2).

Default configuration: cannot ping

Manually change smart port to IP phone: pingable, everything works

I tried to downgrade to 8.5.4-S: everything works ok without playing with smartports

New Member

Re: SG200-26P DHCP or DNS problem

Yes, the only way I can get my Cisco IP phones to join network successfully when connected via SG200-26P is to TURN OFF CDP.

Then it seems all working as intended.

Too many weeks of wasted time to find this answer.

New Member

Re: SG200-26P DHCP or DNS problem

Thanks.

During my tests I had deactivated various services (voiceVLAN, STP) but I don't remember if CDP was among them, probably yes.

New Member

Re: SG200-26P DHCP or DNS problem

We have verified the procedure at the customer two days ago.

1) change smartport to IP Phone

2) downgrade phones firmware to 8.5

3) revert configuration

4836
Views
10
Helpful
13
Replies
CreatePlease login to create content