DHCP server do not reply to DHCP discover from OpenWrt

Installing and Using OpenWrt Network and Wireless Configuration
1

Hello,

Since few weeks ago noticed could not connect as a client using a router as did many times before.

After hours troubleshooting what I could have done wrong seems the issue is a server side, with other AP's works fine.

In resume, DHCP server do not reply at all to the DHCP Discover sent from openwrt, seems it simply ignore it.

using "udhcpc" I tried to send it without MAC, etc and same behavior.

Bellow you can see the wireshark from a laptop (OK - offer received) and from openwrt (NOK - no reply at all).

From laptop working fine

Bootstrap Protocol (Discover)
    Message type: Boot Request (1)
    Hardware type: Ethernet (0x01)
    Hardware address length: 6
    Hops: 0
    Transaction ID: 0xd7ae0e37
    Seconds elapsed: 0
    Bootp flags: 0x0000 (Unicast)
    Client IP address: 0.0.0.0
    Your (client) IP address: 0.0.0.0
    Next server IP address: 0.0.0.0
    Relay agent IP address: 0.0.0.0
    Client MAC address: aa:aa:aa:aa:aa:aa
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (53) DHCP Message Type (Discover)
        Length: 1
        DHCP: Discover (1)
    Option: (12) Host Name
        Length: 9
        Host Name: Room
    Option: (55) Parameter Request List
        Length: 16
        Parameter Request List Item: (1) Subnet Mask
        Parameter Request List Item: (28) Broadcast Address
        Parameter Request List Item: (2) Time Offset
        Parameter Request List Item: (3) Router
        Parameter Request List Item: (15) Domain Name
        Parameter Request List Item: (6) Domain Name Server
        Parameter Request List Item: (119) Domain Search
        Parameter Request List Item: (12) Host Name
        Parameter Request List Item: (44) NetBIOS over TCP/IP Name Server
        Parameter Request List Item: (47) NetBIOS over TCP/IP Scope
        Parameter Request List Item: (26) Interface MTU
        Parameter Request List Item: (121) Classless Static Route
        Parameter Request List Item: (42) Network Time Protocol Servers
        Parameter Request List Item: (249) Private/Classless Static Route (Microsoft)
        Parameter Request List Item: (33) Static Route
        Parameter Request List Item: (252) Private/Proxy autodiscovery
    Option: (255) End
        Option End: 255
    Padding: 000000000000000000000000000000000000000000000000...

OpenWRT NOT working

Bootstrap Protocol (Discover)
    Message type: Boot Request (1)
    Hardware type: Ethernet (0x01)
    Hardware address length: 6
    Hops: 0
    Transaction ID: 0x0c931ebe
    Seconds elapsed: 0
    Bootp flags: 0x0000 (Unicast)
    Client IP address: 0.0.0.0
    Your (client) IP address: 0.0.0.0
    Next server IP address: 0.0.0.0
    Relay agent IP address: 0.0.0.0
    Client MAC address: Tp-LinkT_
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (53) DHCP Message Type (Discover)
        Length: 1
        DHCP: Discover (1)
    Option: (57) Maximum DHCP Message Size
        Length: 2
        Maximum DHCP Message Size: 576
    Option: (55) Parameter Request List
        Length: 8
        Parameter Request List Item: (1) Subnet Mask
        Parameter Request List Item: (3) Router
        Parameter Request List Item: (6) Domain Name Server
        Parameter Request List Item: (12) Host Name
        Parameter Request List Item: (15) Domain Name
        Parameter Request List Item: (28) Broadcast Address
        Parameter Request List Item: (42) Network Time Protocol Servers
        Parameter Request List Item: (121) Classless Static Route
    Option: (60) Vendor class identifier
        Length: 12
        Vendor class identifier: udhcp 1.30.1
    Option: (12) Host Name
        Length: 6
        Host Name: Room
    Option: (255) End
        Option End: 255
    Padding: 0000000000000000000000000000000000000000

Any tip?

2

I remember I had experienced this problem several years ago and it turns out to be the DHCP server of my ISP do not like the DHCP request sent by the openwrt DHCP client. When I switched the client to another one, it works.

3

Hi rtau,

I suspect the same but struggling to understand what server don't expect or expect in order to tune it.

Have you managed fix it?

4

I remember I've installed another DHCP client on OpenWRT and things work.

I've since changed to another ISP thus do not have that setup now.

5

Is there a mac address or some name?

6

Hi trendy

Forgot to say, I removed the mac address from this post, but doesn't seem to be the issue as I tried with hidden mac and same behavior.

Will try the suggestion from rtau and revert

7

Perhaps you remember the client?
I have tried the ones available in the repository seems not working.

8

I think it was "dhcpcd"

9

Thank you.

I almost build same content from the working one with the command

udhcpc -i wlan0 -o -O 1 -O 28 -O 2 -O 3 -O 15 -O 6 -O 119 -O 12 -O 44 -O 47 -O 26 -O 121 -O 42 -O 249 -O 33 -O 252 -V Windows -C -x hostname:Room

Just with issue to remove the vendor, I can edit but not void to send it.

Option: (60) Vendor class identifier
Length: 12
Vendor class identifier: udhcp 1.28.4

And this one

Option: (57) Maximum DHCP Message Size
    Length: 2
    Maximum DHCP Message Size: 576
10

For reference.

Seems the issue is in a specific AP and not clear the reason why in some cases reply back and others no.

Anyway a solution could be the one reffered by @rtau or use the options available in udhcpc as explained.

11

This topic was automatically closed 10 days after the last reply. New replies are no longer allowed.