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New Member

IPv4 DHCP stopped working after IPv6 is enabled


This is really embarrasing ... we decided to deploy IPv6 internally, since our internal devices (cat6ks and c3750s) all support dual stack, I enabled IPv6 on all VLANs in cat6k (s222-adventerprisek9_wan-mz.122-18.SXF17a.bin) and OSPFv3 along with existing OSPFv2, all worked well. Today when I came to office, everybody was screaming because they all lost IPv4 connectivity, hosts can not get IPv4 DHCP address anymore. I had to remove all IPv6 configuration to recover. At this point, I can not say whether the the problem is on host side or on router side, did anybody have the same problem while deploying IPv6?



Everyone's tags (4)

IPv4 DHCP stopped working after IPv6 is enabled

Sounds odd.  They should be completely independent, I can't see why enabling IPv6 should break DHCP?

It might be worth explaining a bit more about the topology and where DHCP is being handled - maybe post some configurations?

I have this deployed in my test (home...) network and it all works well - I have DHCP for IPv4 & IPv6 being handled by two Windows servers (M & O bits set and A bit not set so no autoconfiguration).  I am using OSPF for IPv4 and OSPFv3 for IPv6.  My ISP doesn't provide IPv6 connectivity so I am going by a Tunnel Broker for external IPv6 connectivity.


Cisco Employee

IPv4 DHCP stopped working after IPv6 is enabled

Do you happen to have the exact configuration changes you made?  They should be independent.  What do you use for a DHCP server? 

When you said hosts could not get DHCP addresses, could they ping the DHCP server address?  Sounds like routing to the DHCP server got broken, and nobody noticed until the leases expired.

New Member

IPv4 DHCP stopped working after IPv6 is enabled

Only changes I made was configured IPv6 address on interface VLANs, and enabled ospfv3 passive interface on them.

I don't have seperate IPv6 DHCP server, IPv4 DHCP server is on Domain Controller in a different network. Yes, I can ping DHCP/DC IP address from the switch. This is unlikely due to DHCP, because when  I removed IPv6 address from interface VLAN, hosts in that VLAN were able to get IPv4 addresses fine.

I will try to find the root cause during next maintenance window and update my findings.