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DHCP broadcasts crossing router.... 1

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Kazhbu

MIS
Jul 23, 2001
28
US
Okay, I need Linux Guru. I need to be able to monitor DHCP similarly to the monitoring that is possible in Windows. We are having an issue with DHCP and I am trying to narrow down exactly where the trouble lies. Below is a description of the problem.

Here is what I am dealing with.

On a network I support, (all windows servers) I have come across an extremely strange issue. I upgraded some old Compaq DL380 G1s to Dell 2850s. The new servers were given the same name and IP Address of the old Compaqs they were replacing. The problem arose almost immediately. Some, but not all, PCs were saying “Limited or no connectivity” and showed that they were not getting an IP address from the DHCP server. (The new Dells are now the Domain Controller, DNS Server, and DHCP Server at each location). Upon checking the DHCP scope on the server I found that the server HAD issued an IP to that client. I then discovered that if I hit F5 to refresh the view that the lease expiration would increment one second ever second. By doing packet captures simultaneously on the server and client I discovered that it appears that the initial broadcast is crossing Vlans. All switches are Cisco, and what’s more, some of the locations are in desperate need of upgrading. They are running equipment and CatOS/IOS that is about 6 years old. Other locations have been upgraded approximately 2 months ago and are running the latest and greatest of equipment and IOS. Here is some of the testing I’ve done:
1) Upgraded the drivers on both the server and client (three different versions on each)
2) Installed a 3Com 3c905 B NIC and the trouble disappeared. (This NIC is 10/100)
3) Installed 4 different gigabit Nics and the trouble remained.
4) Set the port speed, duplex, and flow control manually on the switches and Nics. No joy.
5) Moved a few of the PCs that were having issues into vlan 1 with the server so that no Vlan routing was taking place. Trouble disappeared.
6) Moved the DHCP scope onto the Cisco 6509 and problem disappeared.

So now it looks like the issue only occurs when I use 10/100/1000 Nics, and they must cross Vlans to acquire an IP.
We have since also installed 7 IBM 3650 at other locations. They are having the same issues.
I have now installed Redhat 9.0 onto one of the IBM’s to take Windows out of the equation. Dell and Cisco are both at a loss and are looking for any reason to blow me off. I need to confirm exactly where the trouble lies so that I can push for higher escalation of the issue.

Any ideas?
 
Yes I have.

I've got Dell and Cisco going nuts. We all thought this was impossible. ;-)

Leave it to me.

What I'm trying to do now is take Windows out of the mix. If Linux works fine, I need to get Microsoft involved. If Linux has the same issue, then it's a Cisco problem. Personally I think it has to do with the extensions in GIG speeds. I think they are not being handled correctly by the switches.
 
If I understand your post correctly .... with the gigabit cards the workstations request an IP address, the address is assigned, but never gets back to the client? Please post a copy of your switch configuration.
 
It appears from the packet captures that what is happening is the original layer 2 broadcast reaches the server, which is on another vlan, and then the unicast broadcast from the ip helper command hits the server. The server sends an ack, then a nack, but the nack reaches the client first, and the whole process starts again. BTW, Cisco saw nothing wrong with the config, but here is the config anyway.

-=-=-=-=-=-=-=-=Cisco Catalyst 6509-=-=-=-=-=-=-=-
Younge-C6509-Rtr1#show run
Building configuration...

Current configuration : 26844 bytes
!
upgrade fpd auto
version 12.2
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
service counters max age 5
!
hostname Younge-C6509-Rtr1
!
boot system flash bootdisk:s72033-ipservicesk9-mz.122-18.SXF8.bin
no logging console
!
no aaa new-model
ip subnet-zero
!
!
!
no ip domain-lookup
ip domain-name private.stclair.k12.il.us
ip name-server 10.1.1.11
ip name-server 10.1.1.12
ipv6 mfib hardware-switching replication-mode ingress
mls ip multicast flow-stat-timer 9
no mls flow ip
no mls flow ipv6
no mls acl tcam share-global
mls cef error action freeze
!
!
!
!
!
!
!
!
redundancy
mode sso
main-cpu
auto-sync running-config
spanning-tree mode pvst
diagnostic cns publish cisco.cns.device.diag_results
diagnostic cns subscribe cisco.cns.device.diag_commands
!
vlan internal allocation policy ascending
vlan access-log ratelimit 2000
!
!
!
!
interface GigabitEthernet1/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet1/2
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet1/3
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet1/4
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet1/5
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet1/6
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet1/7
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet1/8
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet2/1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet2/2
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet2/3
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet2/4
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet2/5
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet2/6
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet2/7
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet2/8
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface GigabitEthernet3/1
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/2
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/3
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/4
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/5
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/6
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/7
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/8
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/9
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/10
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/11
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/12
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/13
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/14
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/15
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/16
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/17
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/18
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/19
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/20
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/21
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/22
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/23
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/24
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/25
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 5
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/26
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 5
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/27
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
speed 100
duplex full
spanning-tree portfast
!
interface GigabitEthernet3/28
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 50
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/29
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 5
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/30
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 5
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/31
description Cisco 3640
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
speed 100
duplex full
spanning-tree portfast
!
interface GigabitEthernet3/32
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
speed 100
duplex full
spanning-tree portfast
!
interface GigabitEthernet3/33
description IBM 3650 Nic1
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
speed 1000
duplex full
flowcontrol receive on
flowcontrol send on
spanning-tree portfast
!
interface GigabitEthernet3/34
switchport
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
speed 100
duplex full
spanning-tree portfast
!
interface GigabitEthernet3/35
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/36
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
spanning-tree portfast
!
interface GigabitEthernet3/37
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 10
switchport mode trunk
switchport voice vlan 3
no ip address
 
It appears the configuration got cropped off. Have you tried putting a laptop or workstation on the same vlan as the servers with the gig card?
 
You are right, it did get cropped.

I did put my laptop on the network and it had the same issue.

I haven't put my laptop on the same Vlan, but I moved some of the clients that have been a consistent problem to Vlan 1, where the server is located, and created a small DHCP scope on that Vlan. The clients worked perfectly. Move them back where they have to be routed across Vlans and the trouble returns. A real head scratcher, isn't it? ;-)
 
Well if they work fine on the same subnet as the servers, then your issue is clearly a switching issue. In the switch look at the arp table and ensure the switch has the proper mac address to ip address mapping.
 
Well, the switches have all been restarted, and since the PCs can't get an IP, there is no mapping of MAC to IP.

This morning I have new information though. I placed a Windows 2000 server on the network and moved DHPC to that box. Everything works perfectly. So there seems to be 3 things that must be in place for the issue to arise.

1) The DHCP server must be using a 10/100/1000 NIC
2) The server must be running Windows Server 2003
3) The DHCP broadcast must be routed across Vlans

If I remove any one of those three items, the problem disappears.

Does this give anyone an idea of what the heck is going on?

Thanks!!!
 
research the ip helper command for cisco ios it should be in your switch config to allow devices on different vlans to obtain an ip address.
 
The IP helper command exists and is configured correctly.
 
I'm having This Very same problem, With better much the same setup. Any new infomation on this
 
I don't have much further information for you. Unfortunately I was instructed to back burner this item so I created a new vlan and pointed it to a 3640 for DHCP. Then I moved the affected machines into that Vlan. Here is what I can tell you.

1) The original DHCP broadcast is reaching the DHCP server. The server responds and immediately the DHCP Unicast from the IP Helper statement hits the server and gets a nack. The nack reaches the PC BEFORE the original ack so it all starts again.

2) At this point it seems that three things must be in place for the issue to arise.
1) The server must be running Windows 2003
2) The DHCP broadcast must cross Vlans
3) The server must be using a 10/100/1000 NIC

I have taken each of these items out of the mix one at a time and it resolves the issue. Personally I am convinced that it is a problem with Intel chipsets. I collected the manufacturer information on approximately 200 NICs and they were all Intel chipsets. I haven't looked for new drivers in about 6 months, so I would look there first.

Good luck. If there is anything I can do to help, feel free to ask.
 
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