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Posts: 6
Registered: ‎05-12-2018

DHCP client doesn't show up in DHCP leases or DNS

I have a USG 3P running 4.4.22.5086045 and an old Lacie 2big NAS that is exhibiting some strange behavior. I have the Lacie set to use DHCP, and I've set it to a fixed IP in the controller. The USG correctly issues the IP to the Lacie, and the Lacie correctly uses the fixed IP. I can get to the Lacie using the IP, but not the host name. On the USG, neither the IP nor the MAC show up in "show dhcp leases" or /var/run/dhcpd.leases.

 

I tried setting the Lacie to a different static IP, then turning DHCP back on, and it correctly used the fixed IP again. I also set a different fixed IP in the controller, provisioned the USG, then rebooted the Lacie. It again grabbed the current fixed IP. So that shows that the USG is handing out the right IP, but why isn't it saving the DHCP lease or adding it to DNS? I'm not seeing anything relevant in /var/log/messages. Is there anywhere else I should be looking?

 

Thanks in advance for your help!

 

Ubiquiti Employee
Posts: 1,211
Registered: ‎02-28-2017
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Re: DHCP client doesn't show up in DHCP leases or DNS

The Lacie has to send its hostname in the DHCP request packet so the USG can store it in /etc/hosts, can you search there and see if the hostname is present?
Brandon Jaffe | UniFi Routing & Switching | Austin, TX
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Posts: 6
Registered: ‎05-12-2018

Re: DHCP client doesn't show up in DHCP leases or DNS

It is not in /etc/hosts either, but I think the more alarming issue is that there's no actual DHCP lease even though USG is handing out an IP.

 

Ubiquiti Employee
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Re: DHCP client doesn't show up in DHCP leases or DNS

"show dhcp lease" won't show static mappings like you've set for the Lacie.

What you can do is SSH to the USG and type:
sudo tcpdump -npi ethx port 67 or port 68 -vv

where "x" = the LAN interface (eth1 on the USG3, or eth0 on the USG pro 4).

Then while you're running the tcpdump, renew the lease on the Lacie and check the DHCP request packet (source: 0.0.0.0:68 destination 255.255.255.255:67) and see if the Hostname Option 12 is there with the Lacie's hostname. Below is an example of my tcpdump for reference:

USG-XG:~$ sudo tcpdump -npi eth1.30 port 67 or port 68 -vv
tcpdump: listening on eth1.30, link-type EN10MB (Ethernet), capture size 262144 bytes
10:11:12.554783 IP (tos 0x0, ttl 255, id 13259, offset 0, flags [none], proto UDP (17), length 328)
    0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] BOOTP/DHCP, Request from 3c:2e:ff:9a:xx:xx, length 300, xid 0x43524e31, Flags [none] (0x0000)
	  Client-Ethernet-Address 3c:2e:ff:9a:xx:xx
	  Vendor-rfc1048 Extensions
	    Magic Cookie 0x63825363
	    DHCP-Message Option 53, length 1: Request
	    Parameter-Request Option 55, length 7: 
	      Subnet-Mask, Classless-Static-Route, Default-Gateway, Domain-Name-Server
	      Domain-Name, Option 119, Option 252
	    MSZ Option 57, length 2: 1500
	    Client-ID Option 61, length 7: ether 3c:2e:ff:9a:xx:xx
	    Requested-IP Option 50, length 4: 192.168.30.58
	    Lease-Time Option 51, length 4: 7776000
	    Hostname Option 12, length 10: "brandonphone"
Brandon Jaffe | UniFi Routing & Switching | Austin, TX
New Member
Posts: 6
Registered: ‎05-12-2018

Re: DHCP client doesn't show up in DHCP leases or DNS

Alright, so it's not sending option 12 (which is odd because it has a setting to specify the hostname).

 

I'm still perplexed by the leases though. Shouldn't there still be a lease in /var/run/dhcpd.leases with no expiration? It's been a while since I've used DHCPD, so I might be mistaken. 

 

Do you have any idea when DHCP & DNS will be enhanced? There seem to be a lot of people screaming for improvements in this area. Looking at my old ASUS router, when you assign a permanent IP via DHCP, you can enter a hostname right there which must be feeding into DNS. That explains why this wasn't an issue on my old setup. 

 

 

Ubiquiti Employee
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Registered: ‎02-28-2017
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Re: DHCP client doesn't show up in DHCP leases or DNS

I'm checking with ubnt-cmb on the leases file, I feel like the static mappings should be in there as well.

As far as with DNS and domain overrides, those will make their way into the controller, they're on the roadmap. I don't have an ETA for them though.
Brandon Jaffe | UniFi Routing & Switching | Austin, TX
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Registered: ‎03-09-2018
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Re: DHCP client doesn't show up in DHCP leases or DNS

Hi!

 

I'm having the same problem. But in my case Option 12 is sent by the client but not registered.

/etc/hosts is empty.

 

nslookup does not work as described in this thread:

https://community.ubnt.com/t5/UniFi-Routing-Switching/No-DNS-resolution-for-one-windows-host/m-p/239...

 

admin@gateway:~$ sudo tcpdump -npi eth3 port 67 or port 68 -vv
tcpdump: listening on eth3, link-type EN10MB (Ethernet), capture size 262144 bytes
10:19:57.968002 IP (tos 0x0, ttl 128, id 20187, offset 0, flags [none], proto UDP (17), length 328)
    10.0.0.250.68 > 10.0.0.253.67: [udp sum ok] BOOTP/DHCP, Request from f4:6d:04:xxxxxx, length 300, xid 0x3abff1b6, Flags [none] (0x0000)
          Client-IP 10.0.0.250
          Client-Ethernet-Address f4:6d:04:xxxxxxx
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message Option 53, length 1: Request
            Client-ID Option 61, length 7: ether f4:6d:04:xxxxxxx
            Hostname Option 12, length 5: "SPOCK"
            FQDN Option 81, length 8: "SPOCK"
            Vendor-Class Option 60, length 8: "MSFT 5.0"
            Parameter-Request Option 55, length 14:
              Subnet-Mask, Default-Gateway, Domain-Name-Server, Domain-Name
              Router-Discovery, Static-Route, Vendor-Option, Netbios-Name-Server
              Netbios-Node, Netbios-Scope, Option 119, Classless-Static-Route
              Classless-Static-Route-Microsoft, Option 252
10:19:57.975366 IP (tos 0xc0, ttl 64, id 16595, offset 0, flags [none], proto UDP (17), length 357)
    10.0.0.253.67 > 10.0.0.250.68: [udp sum ok] BOOTP/DHCP, Reply, length 329, xid 0x3abff1b6, Flags [none] (0x0000)
          Client-IP 10.0.0.250
          Your-IP 10.0.0.250
          Server-IP 10.0.0.253
          Client-Ethernet-Address f4:6d:04:xxxxxxx
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message Option 53, length 1: ACK
            Server-ID Option 54, length 4: 10.0.0.253
            Lease-Time Option 51, length 4: 86400
            RN Option 58, length 4: 42294
            RB Option 59, length 4: 74694
            Subnet-Mask Option 1, length 4: 255.0.0.0
            BR Option 28, length 4: 10.255.255.255
            FQDN Option 81, length 21: [SO] 255/255 "unifi.benner.local"
            Domain-Name-Server Option 6, length 4: 10.0.0.253
            Default-Gateway Option 3, length 4: 10.0.0.253
            Domain-Name Option 15, length 12: "benner.local"
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New Member
Posts: 30
Registered: ‎03-09-2018
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Re: DHCP client doesn't show up in DHCP leases or DNS

[ Edited ]

Found out, that i had checked "use dnsmasq as dhcp server". After unchecking and ipconfig /renew on my windows client, everything works as expected -> client is in /etc/hosts and is "nslookable"

 

 

 

 

 

EDIT:

 

cat /var/run/dnsmasq-dhcp.leases

 

1529675103 f4:6d:04:xxxxxx 10.0.0.250 unifi 01:f4:6d:xxxxxxx

 

so the clienthostname "SPOCK" is registered as "unifi". I think that is because the unifi controller runs on that machine.

How can i change this?

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