I program it. Here's the code:

status_t
ether_add_vlan( const char *parentif, const char *vlanname, uint16_t vlan_id)
{
    struct vlanreq vlan_data;
	struct ifreq ifr;
	status_t ret;
	
	if ( _eth_fd < 0 ) {
        if ( ( _eth_fd = socket( AF_INET, SOCK_DGRAM, 0 ) ) < 0 ) {
            return ( errno );
        }
    }
    
   	if (!parentif || !vlanname || (strlen(parentif) > IFNAMSIZ) || (strlen(vlanname) >IFNAMSIZ))
   		return(TN_SYS_ERROR_INVALID_ARG);   	
   		
    memset(&ifr,0,sizeof(struct ifreq));
    strcpy(ifr.ifr_name, vlanname);
	ret=ioctl(_eth_fd, SIOCIFCREATE, &ifr);
	if (ret!=SUCCESS) {
		if (errno!=EEXIST)
			return(errno);
		else
			return(SUCCESS);	
	}
	
    memset( &vlan_data, 0, sizeof( struct vlanreq ) );
    strcpy(ifr.ifr_name,vlanname);
    ifr.ifr_ifru.ifru_addr.sa_family=AF_INET;        
    ifr.ifr_ifru.ifru_data=(object_t)&vlan_data;
    
    ret=ioctl_socket(_eth_fd, SIOCGETVLAN, &ifr);
	if (ret!=SUCCESS)
		return(errno);
		         	
    vlan_data.vlr_tag = vlan_id;
	ret=ioctl_socket( _eth_fd, SIOCSETVLAN, &ifr );
	if (ret!=SUCCESS)
		return(errno);
		
	memset( &vlan_data, 0, sizeof( struct vlanreq ) );
	ifr.ifr_ifru.ifru_data=(object_t)&vlan_data;
	ret=ioctl_socket(_eth_fd, SIOCGETVLAN, &ifr);
	if (ret!=SUCCESS)
		return(errno);
		
	strcpy(vlan_data.vlr_parent,parentif);
	vlan_data.vlr_tag = vlan_id;
	
    return(ioctl_socket( _eth_fd, SIOCSETVLAN, &ifr ));
}

status_t
ether_del_vlan( const char *vlanname)
{
    struct vlanreq vlan_data;
	struct ifreq ifr;
	status_t ret;
	
	if ( _eth_fd < 0 ) {
        if ( ( _eth_fd = socket( AF_INET, SOCK_DGRAM, 0 ) ) < 0 ) {
            return ( errno );
        }
    }
    
   	if (!vlanname || (strlen(vlanname) > IFNAMSIZ))
   		return(TN_SYS_ERROR_INVALID_ARG);
   		
    memset(&ifr,0,sizeof(struct ifreq));
    memset( &vlan_data, 0, sizeof( struct vlanreq ) );
    strcpy(ifr.ifr_name,vlanname);
    ifr.ifr_ifru.ifru_addr.sa_family=AF_INET;    
    ifr.ifr_ifru.ifru_data=(object_t)&vlan_data;
    
    ret=ioctl_socket( _eth_fd, SIOCGETVLAN, &ifr );
    if (ret!=SUCCESS)
    	return(errno);
    	
    printf("vlan_parent=%s,vlanid=%d\n",vlan_data.vlr_parent,vlan_data.vlr_tag);
    memset( &vlan_data, 0, sizeof( struct vlanreq ) );
    ifr.ifr_ifru.ifru_data=(object_t)&vlan_data;
    vlan_data.vlr_parent[0]='\0';	
    vlan_data.vlr_tag = 0;

    ret=ioctl_socket( _eth_fd, SIOCSETVLAN, &ifr );
    if (ret!=SUCCESS)
    	return(ret);    
    ifr.ifr_ifru.ifru_data=NULL;
    
    return(ioctl(_eth_fd, SIOCIFDESTROY, &ifr));	
}

After the code runs, the out put of ifconfig contains (I create multiple):

# ifconfig
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 33192
        inet 127.0.0.1 netmask 0xff000000
en0: flags=8043<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
        address: 00:1f:aa:ff:ff:d0
        inet 10.7.0.40 netmask 0xffffff00 broadcast 10.7.0.255
en1: flags=8043<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
        address: 00:1f:aa:ff:ff:d1
        inet 10.7.0.41 netmask 0xffffff00 broadcast 10.7.0.255
en2: flags=8002<BROADCAST,MULTICAST> mtu 1500
        address: 00:1f:aa:ff:ff:d2
en3: flags=802<BROADCAST,SIMPLEX> mtu 1500
        address: 00:1f:aa:ff:ff:d3
en4: flags=802<BROADCAST,SIMPLEX> mtu 1500
        address: 00:1f:aa:ff:ff:d4
en5: flags=802<BROADCAST,SIMPLEX> mtu 1500
        address: 00:1f:aa:ff:ff:d5
en6: flags=802<BROADCAST,SIMPLEX> mtu 1500
        address: 00:1f:aa:ff:ff:d6
en7: flags=802<BROADCAST,SIMPLEX> mtu 1500
        address: 00:1f:aa:ff:ff:d7
en8: flags=802<BROADCAST,SIMPLEX> mtu 1500
        address: 00:1f:aa:ff:ff:d8
en9: flags=802<BROADCAST,SIMPLEX> mtu 1500
        address: 00:1f:aa:ff:ff:d9
en10: flags=802<BROADCAST,SIMPLEX> mtu 1500
        address: 00:1f:aa:ff:ff:da
en11: flags=802<BROADCAST,SIMPLEX>...

We did a change to one of our drivers (for a broadcom chip 5691) and that seemed to make a difference. Its working now.

Thanks,
Santosh
> On Wed, Aug 20, 2008 at 11:23:55PM -0400, Santosh Kumar wrote:
> > Hi Sean,
> > 
> > I tried doing a ifconfig up and then set vlan. Same result. Actually without
>  IFF_UP we cant even send packets out of the interface.
> 
> I did a quick test here and it worked.  Does 'ping -n ...'
> behave any differently?
> 
> -seanb
> 
> 
> lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 33192
>         inet 127.0.0.1 netmask 0xff000000
>         inet6 ::1 prefixlen 128
>         inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
> wm0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         capabilities rx=7<IP4CSUM,TCP4CSUM,UDP4CSUM>
>         capabilities tx=3f<IP4CSUM,TCP4CSUM,UDP4CSUM,TCP6CSUM,UDP6CSUM,TSO4>
>         enabled=0
>         address: 00:0e:0c:34:36:88
>         media: Ethernet autoselect (100baseTX)
>         status: active
> vlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         vlan: 1234 parent: wm0
>         address: 00:0e:0c:34:36:88
>         inet 11.0.0.2 netmask 0xff000000 broadcast 11.255.255.255
>         inet6 fe80::20e:cff:fe34:3688%vlan0 prefixlen 64 scopeid 0x3
> seanb2:/home/seanb >ping -c1 11.1
> PING 11.1 (11.0.0.1): 56 data bytes
> 64 bytes from 11.0.0.1: icmp_seq=0 ttl=255 time=0 ms
> 
> ----11.1 PING Statistics----
> 1 packets transmitted, 1 packets received, 0% packet loss
> round-trip min/avg/max = 0/0/0 ms   variance = 0 ms^2