When I connect my custom embedded device to my network the DHCP responses do not include the router option (3). In this case should the device use the DHCP server ip address as the default gateway? My computer that is connected to the same network is indeed using that address, but I don't know if falling back to the DHCP relay's IP address is acceptable for most/all networks. Is there a standard that specifies that this is the correct behavior?
Here's wireshark's interpretation of the ACK in case that's helpful:
Bootstrap Protocol (ACK) Message type: Boot Reply (2) Hardware type: Ethernet (0x01) Hardware address length: 6 Hops: 0 Transaction ID: 0xe7b50663 Seconds elapsed: 0 Bootp flags: 0x0000 (Unicast) Client IP address: 0.0.0.0 Your (client) IP address: 172.18.164.91 Next server IP address: 172.18.160.207 Relay agent IP address: 172.18.164.250 Client MAC address: Microchi_87:c4:b1 (d8:80:39:87:c4:b1) Client hardware address padding: 00000000000000000000 Server host name not given Boot file name: BOOT\X64\WDSNBP.COM Magic cookie: DHCP Option: (53) DHCP Message Type (ACK) Length: 1 DHCP: ACK (5) Option: (58) Renewal Time Value Length: 4 Renewal Time Value: (43200s) 12 hours Option: (59) Rebinding Time Value Length: 4 Rebinding Time Value: (75600s) 21 hours Option: (51) IP Address Lease Time Length: 4 IP Address Lease Time: (86400s) 1 day Option: (54) DHCP Server Identifier Length: 4 DHCP Server Identifier: 172.18.160.202 Option: (1) Subnet Mask Length: 4 Subnet Mask: 255.255.255.0 Option: (255) End Option End: 255 Padding: 000000000000000000000000000000000000000000000000...
My device is connecting to a Cisco Meraki MX90 acting as the relay agent to a Windows 2012 R2 server running the DHCP.