Solved

Cannot pull dhcp ip switchport problem?

Posted on 2010-11-17
13
469 Views
Last Modified: 2012-05-10
I have a 2960 connected with 1gb copper to our 4507 core. Recently, we've noticed we cannot pull ip addresses from some of the switch ports, via DHCP. Specifically ports 1-3

What would be the cause of this?  There are 161 total mac addresses in the cam table. Several of them are learned via the uplink to the core. I have over 8000 mac entires free, so I don't think my CAM table is full

We have an IP phone which can plug into the mentioned switchports, and pull an IP via DHCP no problem. PCs cannot pull an IP if plugged directly into the switchports. However, if plugged into the back of the avaya phone, they can pull an ip

These switchports were also trunk links, with a default vlan in the data network. I changed some to a regular access port, and the pcs still could not pull an IP
0
Comment
Question by:orus
  • 7
  • 6
13 Comments
 
LVL 1

Expert Comment

by:clawrimore
ID: 34159472
Ports 1-3 need to be assigned to a specific VLAN, one which either has a DHCP server on it or for which BOOTP helpers have been created.  Even though they are no longer trunk ports, you need to either assign them to a VLAN or they will default to Native VLAN (VLAN1).
0
 

Author Comment

by:orus
ID: 34159493
yes they are part of vlan 14 (data)
0
 
LVL 1

Expert Comment

by:clawrimore
ID: 34159505
Is the rest of the switch on VLAN14?  Are you able to post an Interface config?
0
 
LVL 1

Expert Comment

by:clawrimore
ID: 34159520
Is Spanning-Tree enabled?  When you plug a device into the port, how long before the LED turns green?
0
 

Author Comment

by:orus
ID: 34159531
here are ports 1-3. I'm having the issue on other ports as well. Ip-phone works, but pcs cant pull anything plugged directly in
interface GigabitEthernet1/0/1

 switchport access vlan 14

 srr-queue bandwidth share 10 10 60 20

 queue-set 2

 priority-queue out

 mls qos trust dscp

 auto qos voip trust

!

interface GigabitEthernet1/0/2

 switchport trunk native vlan 10

 switchport mode trunk

 srr-queue bandwidth share 10 10 60 20

 queue-set 2

 priority-queue out

 mls qos trust dscp

 auto qos voip trust

!

interface GigabitEthernet1/0/3

 description ***IT WAP***

 switchport mode trunk

 srr-queue bandwidth share 10 10 60 20

 queue-set 2

 priority-queue out

 mls qos trust dscp

 auto qos voip trust

!

Open in new window

0
 

Author Comment

by:orus
ID: 34159540
yep, STP is enabled. Also, other ports are fully functional. It is strange indeed
0
Zoho SalesIQ

Hassle-free live chat software re-imagined for business growth. 2 users, always free.

 
LVL 1

Accepted Solution

by:
clawrimore earned 500 total points
ID: 34159616
OK.  Where is the DHCP server in relation to switchport 1?  Is it on the same switch? Different VLAN?  Is there still a trunk port to carry VLAN14 to the router?  If there is still a trunkport, is it #3?  Is #3 plugged in to an accesspoint?
0
 

Author Comment

by:orus
ID: 34159680
DHCP server is on a different switch, going through gig1/0/48.  It is on a different VLAN, VLAN 1. yes there is a trunk port to carry VLAN14

#3 is an AP and it is working yes
0
 
LVL 1

Expert Comment

by:clawrimore
ID: 34159802
DHCP on VLAN 1.
Client on VLAN14.
They can PING each other if they use static IP addresses.
Is there anything else on VLAN14?
It really sounds like BOOTP helper is not configured for VLAN14.  Because DHCP requests are broadcast, it needs the router to forward DHCP requests from VLAN14 to VLAN1.
On the router, interface VLAN14, do you have a command that is similar to "ip helper-address <dhcp>"?  You need one...
0
 

Author Comment

by:orus
ID: 34159818
we have had it on there a while actually. This is from the core switch. Do we need the ip helper command on the access switch as well

interface Vlan14
 description ***IT Personnel VLAN***
 ip address 172.16.14.1 255.255.255.0
 ip helper-address 172.16.1.14
0
 
LVL 1

Expert Comment

by:clawrimore
ID: 34159878
This command looks good and should be issued on the router only.  And of course, the DHCP server has 172.16.1.1 as it's default gateway?  And the client and DHCP server can PING if using static?
0
 

Author Comment

by:orus
ID: 34159886
i will try static and report back
0
 
LVL 1

Expert Comment

by:clawrimore
ID: 34169273
Were you able to test ping to ensure connectivity between VLANs?
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Cisco C3750X Switch 19 96
Arista Switches 2 53
Trunk port configuration for Wireless VLANs 11 71
Network Infrastructure for Branch Office 16 87
The worst thing when starting a new job is when the previous Network Administrator left behind no documentation. How do you get into the devices? If you've been in this situation or just accidently mistyped your password, this article will hopefully…
I see many questions here on Experts Exchange regarding switch port configurations and trunks. This article is meant for beginners in the subject to help to get basic knowledge about Virtual Local Area Network (VLAN (http://en.wikipedia.org/wiki/Vir…
Delivering innovative fully-managed cloud services for mission-critical applications requires expertise in multiple areas plus vision and commitment. Meet a few of the people behind the quality services of Concerto.
A company’s greatest vulnerability is their email. CEO fraud, ransomware and spear phishing attacks are the no1 threat to a company’s security. Cybercrime is responsible for the largest loss of money to companies today with losses projected to r…

943 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

9 Experts available now in Live!

Get 1:1 Help Now