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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.

closed as off-topic by Ron Maupin Jun 7 '18 at 17:27

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "NE is a site for to ask and provide answers about professionally managed networks in a business environment. Your question falls outside the areas our community decided are on topic. Please visit the help center for more details. If you disagree with this closure, please ask on Network Engineering Meta." – Ron Maupin
If this question can be reworded to fit the rules in the help center, please edit the question.

  • Experimental hardware (like rPI) and consumer-grade devices are off topic here. If this is not the case, please describe your hardware setup, including your DHCP server. – Ron Trunk Jun 7 '18 at 16:06
  • My question is really about the network standards and I believe the answer should be independent of hardware. However, I'm working on getting the DHCP server configuration information. – Rick Jun 7 '18 at 16:36
  • There is no "standard." You will probably get opinions either way, which also makes this off-topic. – Ron Trunk Jun 7 '18 at 16:51
  • Unfortunately, questions about host/server configurations and protocols above OSI layer-4 are off-topic here. You could try to ask this question on Server Fault for a business network, or on Super User for a personal network. – Ron Maupin Jun 7 '18 at 17:27
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Using the DHCP server as gateway is just guessing. It might work or it might not (most likely only in very small networks).

A serious DHCP server setup includes a default gateway when possible.

Since there seems to be a DHCP relay the DHCP server itself is located in another subnet and cannot work.

should the device use the DHCP server ip address as the default gateway?

If the DHCP server is located within the client's /24 subnet chances are 99.6% it is not the correct default gateway. So, no, it shouldn't.

  • Indeed there is a DHCP relay. I suppose I misworded my question, and meant the ip address of the DHCP relay. – Rick Jun 7 '18 at 17:09
  • Makes no difference. There's a 1:253 chance it's correct. – Zac67 Jun 7 '18 at 17:10

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