Re: [lwip-users] broken DHCP/ARP interaction

[Sergio R. Caprile]

Hi,
Quick&dirty workaround: disable ARP checking by defining
DHCP_DOES_ARP_CHECK to 0

Analysis:
I'm no expert in DHCP nor ARP, but I don't see anything similar to what
you are experiencing.
I've setup three scenarios:
1- different IP (static) prior to DHCP
2- same IP (static) prior to DHCP
3- 0.0.0.0
In scenarios 1 and 3, everything works "as expected"
In scenario 2, I see a "gratuitous ARP", but the address is accepted
anyway. Here is my capture:

No.     Time           Source                Destination          
Protocol Length Info
      1 0.000000000    192.168.1.42          255.255.255.255      
DHCP     350    DHCP Discover - Transaction ID 0xabcd0001

      2 0.001705000    192.168.1.1           192.168.1.42         
DHCP     342    DHCP Offer    - Transaction ID 0xabcd0001

      3 0.002564000    192.168.1.42          255.255.255.255      
DHCP     350    DHCP Request  - Transaction ID 0xabcd0002

      4 0.040420000    192.168.1.1           192.168.1.42         
DHCP     342    DHCP ACK      - Transaction ID 0xabcd0002

      5 0.040841000    3com_03:04:05         Broadcast            
ARP      60     Gratuitous ARP for 192.168.1.42 (Request)

Frame 5: 60 bytes on wire (480 bits), 60 bytes captured (480 bits) on
interface 0
Ethernet II, Src: 3com_03:04:05 (00:01:02:03:04:05), Dst: Broadcast
(ff:ff:ff:ff:ff:ff)
Address Resolution Protocol (request/gratuitous ARP)
    Hardware type: Ethernet (1)
    Protocol type: IP (0x0800)
    Hardware size: 6
    Protocol size: 4
    Opcode: request (1)
    [Is gratuitous: True]
    Sender MAC address: 3com_03:04:05 (00:01:02:03:04:05)
    Sender IP address: 192.168.1.42 (192.168.1.42)
    Target MAC address: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Target IP address: 192.168.1.42 (192.168.1.42)

      6 0.499760000    3com_03:04:05         Broadcast            
ARP      60     Gratuitous ARP for 192.168.1.42 (Request)


I suggest you check your options and step the code to see where this
rejection takes place

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