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When DHCPRelay is configured on FTD and the DHCP client sends a DHCP Discovery message with the Broadcast flag set to 0 (Unicast) the DHCP Offer is not consumed properly by the FTD. The result is that the DHCP Offer is not sent by the DHCPRelay to the DHCP Client. FTD capture on DHCP Server-facing interface in case of a working scenario (DHCP Broadcast flag set to 1): FTD# show cap CAPO 1: 19:56:11.936017 192.0.2.1.67 > 203.0.113.1.67: udp 305 <-- DHCP Discover 2: 19:56:11.936551 203.0.113.1.67 > 192.0.2.1.67: udp 300 <-- DHCP Offer 3: 19:56:11.937207 192.0.2.1.67 > 203.0.113.1.67: udp 317 <-- DHCP Request 4: 19:56:11.937573 203.0.113.1.67 > 192.0.2.1.67: udp 300 <-- DHCP ACK The packet trace shows: FTD# show cap CAPO trace | i output-interface output-interface: INSIDE output-interface: INSIDE FTD capture on DHCP Server-facing interface in case of a non-working scenario (DHCP Broadcast flag set to 0 (Unicast)): FTD# show cap CAPO 1: 20:02:09.853486 192.0.2.1.67 > 203.0.113.1.67: udp 305 <-- DHCP Discover 2: 20:02:09.854036 203.0.113.1.67 > 192.0.2.1.67: udp 300 <-- DHCP Offer 3: 20:02:13.854737 192.0.2.1.67 > 203.0.113.1.67: udp 305 <-- DHCP Discover 4: 20:02:13.855271 203.0.113.1.67 > 192.0.2.1.67: udp 300 <-- DHCP Offer 5: 20:02:36.163748 192.0.2.1.67 > 203.0.113.1.67: udp 305 <-- DHCP Discover 6: 20:02:36.164191 203.0.113.1.67 > 192.0.2.1.67: udp 300 <-- DHCP Offer 7: 20:02:39.914610 192.0.2.1.67 > 203.0.113.1.67: udp 305 <-- DHCP Discover 8: 20:02:39.915129 203.0.113.1.67 > 192.0.2.1.67: udp 300 <-- DHCP Offer The trace shows: FTD5555# show cap CAPO trace | i output-interface output-interface: NP Identity Ifc output-interface: OUTSIDE output-interface: OUTSIDE output-interface: OUTSIDE In some cases after multiple DHCP Discovery messages the DHCP Client manages to get the DHCP Offer
DHCP Unicast flag is set
N/A
When DHCPRelay is configured on FTD and the DHCP client sends a DHCP Discovery message with the Broadcast flag set to 0 (Unicast) the DHCP Offer is not consumed properly by the FTD. The result is that the DHCP Offer is not sent by the DHCPRelay to the DHCP Client. It is also possible if a customer upgrades from a version that has this bug to a version that does not have this bug, they may need to remove ALL dhcp relay settings(interface and dhcp connecting servers), deploy, test, then add them back to resolve issue.