07-31-2014 07:15 AM - edited 03-07-2019 08:13 PM
Device: Cisco IOS Software, C3560 Software (C3560-IPBASEK9-M), Version 12.2(55)SE7, RELEASE SOFTWARE (fc1)
DHCP Pool:
ip dhcp pool ITS_Voice
network 10.xxx.4.xxx 255.255.255.0
default-router 10.xxx.xxx.xxx
dns-server 10.xxx.xxx.xxx 10.xxx.xxx.xxx 10.xxx.xxx.xxx
domain-name xxxx.com
option 150 ip 10.xxx.xxx.xxx
VLAN Interface:
interface Vlan2
ip address 10.xxx.4.xxx 255.255.255.0
ip helper-address <ISE-Node>
ip helper-address <ISE-Node>
no ip redirects
no ip proxy-arp
The question is why does the layer 3 interface not pass the DHCP broadcast to the helper address? Devices get ip assignements.
I did a "debug ip DHCP server packets". I do not see the broadcast sent to the helper addresses. I need to send those DHCP Packets to the Identity Services Engine for profiling.
I confirmed the problem by adding another switch and trunking it to the first one. Then I added a L3 interface on the second switch with the helper addresses and that works. Again using the DHCP debug I can see the broadcast being forwarded to the ISE nodes.However this is not a fix, more like a workaround wasting address space.
Anyone have any Ideas?
07-31-2014 11:26 AM
08-04-2014 05:11 AM
Since we are using ISE (Identity Services Engine) we do need that relay address so we can profile devices on those switches.
I have found the resolution. The problem is when a DHCP binding exists already for a device. If I have a new device access the switch for the first time the relay address works. If I remove that device and reconnected it with out removing the DHCP binding the relay address will not be used.
08-04-2014 05:48 AM
I found this on TCPIPGUIDE.com that supports my findings.
"One difference between BOOTP and DHCP is that certain communications from the client to the server are unicast. The most noticeable instance of this is when a client tries to renew its lease with a specific DHCP server. Since it sends this request unicast, it can go to a DHCP server on a different network using conventional IP routing, and the relay agent does not need to be involved."
05-03-2019 03:23 AM
Hi,
Could you please let me know the resolution for this issue, i am facing the same problem.
I have the DHCP pool configured locally on the Switch.
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