Netdemo and ARP protocol

Ian Caddy ianc at
Fri Sep 13 02:18:18 UTC 2002

Hi Mario,

I am not quite sure what processor, or Ethernet chip you are using so it 
is hard to give detailed information but I have a couple of pointers for 

1. Your physical address that you are using is a multi-cast address and 
shouldn't be used for your normal Ethernet address.  The 6 byte physical 
address should NOT set the lowest bit of the first byte, i.e. your first 
byte is 0x31.  The 1 indicates a multicast address.  This will cause all 
sorts of problems.  I recommend that you set this byte to 0.  Also, if 
you want to talk to real pieces of equipment you will have to get a 
proper Ethernet address at some stage.

2.  Are you writing your own Ethernet driver or just trying to get one 
of the existing drivers running?


Ian Caddy

Mario Vieira wrote:

> Hi, I am a newbie with RTEMS and I need help.
> I am porting RTEMS to a board from quicklogic. I'm testing the network 
> with the netdemos-4.5.0/netdemo and I find out (printing the mbuffer) 
> that the initial ARP packet that is sent is incorrect.
> Below I send the capture packet that is exactly like the mbuffer:
> Frame 1 (60 on wire, 60 captured)
>     Packet Length: 60 bytes
>     Capture Length: 60 bytes
> Ethernet II
>     Destination: ff:ff:ff:ff:ff:ff (ff:ff:ff:ff:ff:ff)
>     Source: 31:32:33:34:35:36 (31:32:33:34:35:36)
>     Type: ARP (0x0806)
>     Trailer: 0000C1888F010000000004D200090328...
> Address Resolution Protocol (opcode 0x0604)
>     Hardware type:  (0x0000)                                 <- HERE short
>     Protocol type: Unknown (0x0001)
>     Hardware size: 8
>     Protocol size: 0
>     Opcode: Unknown (0x0604)
>     Sender hardware address: 0001313233343536
>     Target hardware address: C1888F0100000000  
> The "HERE short" isn't supposed to be there. From there the codes are 
> correct but moved 2 bytes.
> I look at the procedure to send out ARP Requests but I could see what 
> is wrong.
> Please help me.
> Thanks in advance,
> Mário Vieira


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