Thanks for the reply Peter. Correct. By "flat" network, I mean that each site only has a single LAN/VLAN. The ISR is NOT configured as a DHCP Relay Agent as this was not necessary whilst it ran IOS 12.2(24), but I am currently searching docs about configuring this as a possible fix as I suspect this to be the problem or solution. The problem manifested itself as follows -> After upgrading the ISR to IOS 15.1.(3) DHCP clients could no longer obtain IPs. Nodes with already assigned DHCP IPs continued to work fine unless these released or renewed the IPs in which case they would not be assigned an IP. If the admins try to manually assign a MAC OSX node for example, a free IP from the DHCP range a message is displayed stating that the IP is already in use when in reality it is free. Unfortunately I do not have the required detailed information to facilitate troubleshooting this issue as I only have access to the ISRs’ but not to the respective DHCP servers or other nodes at these sites. The little information I have regarding the DHCP problem is what has been transmitted to me by the respective local admins. I understand how this lack of information makes troubleshooting the problem rather ambiguous however I was simply hoping by creating this post that it would be spotted by someone who has experienced the same issue and be able to suggest a workaround e.g. switch off the DHCP service on the ISR. In the meantime as mentioned, I am searching info on configuring the DHCP relay option in the hope this will resolve the issue. Thanks again for your timely response. Paulo
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Recently I upgraded all my sites’ ISRs’ IOS versions from 12.4(24) to 15.1(3). The upgrade caused no problems for all except 2 sites where Windows DHCP servers stopped being able to assign IP addresses due to IPs having already been assigned when in reality this is not the case. The main common denominator with the 2 problem sites is that they both have a flat network whilst all the successfully upgraded sites have segmented networks. As the ISRs are not configured for DHCP and whilst I await further diagnostic details from the remote admins, for the time being I can only assume that DHCP traffic is handled differently in IOS 15.1 running on flat networks. Is anyone aware of any new DHCP related features introduced with IOS 15.1 that could be causing this issue? Has anyone experienced this same problem and found a workaround? Thanks in advance for any replies.
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