[ECOS] ARP static entry

Michael Grimard michaelg@maxt.com
Wed Mar 29 20:06:00 GMT 2006

Merci Birahim.

It still doesn't work with gateway set For the gateway
parameter, I now pass the destination MAC address, since in the code,
Sebastien does a memcpy on ETHER_ADDR_LEN, which is 6 (48 bits).


But it still doesn't work. In arpresolve(), the sdl_alen field of
sockaddr_dl structure is 0, so I'm tracing to see why.

In the device, I will use the IFF_NOARP flag to disable the ARP. I guess it
would still be able to resolve the addresses that are set statically in the
table by the code, but not send request and reply to request.

I'm thinking to buy TCP/IP Illustrated, Volume 2: The Implementation, from
AW, any comments on this book? Does it explain well how the stack works


-----Original Message-----
From: ecos-discuss-owner@ecos.sourceware.org
[mailto:ecos-discuss-owner@ecos.sourceware.org] On Behalf Of Birahim Larou
Sent: March 28, 2006 4:12 AM
To: Michael Grimard
Cc: ecos-discuss@sourceware.org
Subject: RE: [ECOS] ARP static entry

1/ The argument gateway passed to the function may not be correct
char gateway[] = {01, 10,10,10}; // to be confirm or {10,10,10,01};
Also before to call ioct() declares the routes static: 
rt->rt_flags|=RTF_STATIC; // static route: added by user. This avoid the 
route to be removed on timeout
 Make a break  point for debug in function ip_output() and follows your 
packet until arp_request(); 
Why you want to disable this roote after interface set up?

2/UDP is connectionless but it needs a route to send data. So if it does 
not know its route, IP layer uses ARP to found the route. "UDP and TCP" 
can have the same route. UDP  add entry to the tab.

3/ More than two network  interface can share the same MAC adress but they 
must have different IP adress. When IP packets arrived,  data are passed 
to the interface that match with IP address of the dest addr of the  IP 
packet. Of course the best way, since you use freebsd, is to  use  eth0 
for redboot and eth1 for your appli with different address MAC. You should 
configure the cdl file to enable eth1 if it's not done.

4/ About lwip, for me it's ok,  you have just to modifie the ethernet 
logical driver for lwip (eth_drv) to bypass arp: 

hope this can help you!

PS: en utilisant lwip tu peux economiser jusqu'à 150Mo surtout que t'ulise 
pas TCP qui represente la moitié de lwip. Si on parle pas un peu le 
français, on risque de se faire taper par chirac :)

Fall Birahim
Elsys Design for SCM Microsystems

Thanks Birahim.

What I'm trying to do is modify the stack so that all configuration will 
static (no DNS and no ARP). Everything (Host name, IP Address and MAC
Address) will be known in advance and read from a configuration file to
configure the stack. My network is a closed network and it needs to be up
and running really fast after a reset, so there is no time (and need) to 
DNS and ARP protocols. Also, I only need to use UDP packet.

The first step I thaught to do is to add a static entry to the ARP and the
next step would have been to disable it.

I used the code posted by Sebastien to add a route in ARP table, ioctl()
returns 0 (no error), show_network_tables() show me a new route for (but the gateway is so the route is probably not
good. The first time I send a packet to, I see the ARP request
and reply packets on the wire... That confirms that the route/entry is not

I removed the code to add the entry to ARP table and call
show_network_tables() after the first packet is sent and the ARP protocol
has done is job, but I don't see the new entry (I have four entries, two 
eth0 ( and and two for lo0).

I have two questions: 

1- does UDP packet add entry to the table? UDP is connectionless, maybe 
route is saved elsewhere or differently.

2- The target machine is running eCos with Redboot. Both have an IP 
but only are using the same MAC. The route should be to Redboot (that will
pass it to eCos)? That is what I see with Ethereal, Ethernet destination 
Redboot and IP destination is eCos.

For LwIp, I will definitely take a look at it, but I will wait that the
patches to the latest version will be accepted.


-----Original Message-----
From: Birahim Larou Fall [mailto:BLFall@scmmicro.fr] 
Sent: March 27, 2006 3:17 AM
To: Michael Grimard
Cc: ecos-discuss@sourceware.org
Subject: Re: [ECOS] ARP static entry

The code posted by Sebastien just add a route in ARP table but does not 
disable/bypass the ARP protocole.  What does the function ioct returns?
use  show_network_tables(); to print all routes:

typedef int  pfunc( const char *fmt, ... ) 
externC void show_network_tables(pfunc *pfct);// 

show_network_tables(diag_printf);// show all routes.
Why you don't use use LWIP stack? you can easily remove the ARP protocole.
Give more informations about your project.
PS: je parle français mais l'anglais permet d'en faire profiter un max de 

Fall Birahim
Elsys Design for SCM Microsystems

"Michael Grimard" <michaelg@maxt.com> 
Sent by: ecos-discuss-owner@ecos.sourceware.org
25/03/2006 04:28


[ECOS] ARP static entry

  I need to enter some entries in the ARP table to bypass the ARP protocol
with the FreeBSD stack.

I started by using the code that came with this previous post:
http://sourceware.org/ml/ecos-discuss/2005-09/msg00023.html but I can’t 
it work.

Say that I want to link the IP Address to Ethernet Address
00:07:E9:E3:07:A7, what will the parameters be to the call of AddMAC

Any help/suggestion will be greatly appreciated. I’m new to eCos and
networking stuff, so I’m a little lost here


P.S.: Je parle français, alors si Sébastien Couret est encore sur la 
tu peux me faire un reply en français.

int AddMAC(const char* dest,const char* gateway,const int index)
 struct sockaddr_dl gway;             // Adresse passerelle
 struct sockaddr_in dst;              // Réseau/hote cible
 char ds[IPSTRING];
 struct ecos_rtentry *rt=NULL;        // Entrée dans la table de routage
 int s=0;                             // Descripteur de socket
 u_char cp[MACSTRING];                // Adresse MAC sous forme chaine
 memset(&gway,0,sizeof(struct sockaddr_dl));
 gway.sdl_family=AF_LINK; // AF_UNSPEC ?
 gway.sdl_len=sizeof(struct sockaddr_dl);
 memset(&dst,0,sizeof(struct sockaddr_in));
 dst.sin_len=sizeof(struct sockaddr_in);
 rt=(struct ecos_rtentry*)malloc(sizeof(struct ecos_rtentry));
 if (!rt)
  diag_printf("Erreur d'allocation d'une route :'%s'",strerror(errno));
 memset(rt,0,sizeof(struct ecos_rtentry));
 rt->rt_flags|=RTF_HOST; // Host entry
 memcpy(&(rt->rt_gateway), &gway, sizeof(struct sockaddr));
 memcpy(&(rt->rt_dst), &dst, sizeof(struct sockaddr_in));
 rt->rt_flags|=RTF_UP; // Route utilisable
// rt->rt_flags|=RTF_WAS_CLONED;
 rt->rt_metric=1;              // Reseau local
 diag_printf("Ajout d'une adresse MAC  pour '%s' :'%s' sur interface
 if (s<0)
  diag_printf("Socket error :'%s'",strerror(errno));
 if (ioctl(s,SIOCADDRT,rt)<0)
  diag_printf("Ioctl error :'%s'",strerror(errno));
  switch (errno)
   case EINVAL:diag_printf("Invalid Command or agument");
   case ENOTTY:diag_printf("Not a device");
   case EBADF:diag_printf("Bad File descriptor");
   case EEXIST:diag_printf("Already existing");
   default:diag_printf("Unknown error %d:'%s'",errno,strerror(errno));
  return (-1);
 diag_printf("ARP entry added");


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