Experimental Physics and
Industrial Control System

Heinz Junkes via Tech-talk <tech-talk at aps.anl.gov> · Sat, 23 Apr 2022 20:17:21 +0200

Unfortunately, I don't understand it.

If one would stick to the intended protocol, then wouldn't it work to simply route the packet content with the server address in it into the subnet?

Why is the server IP address not entered in the announcement server but '\xff\xff\xff\xff'?

def __init__(self, tcpport, key=0,
                 tcpaddr='\xff\xff\xff\xff',
                 udpaddrs=[('<broadcast>',5049)],
                 period=15.0):
        if sys.version_info[0] < 3:
            self.msg = _Ann.pack(0x5243, 0, tcpaddr, tcpport, 0, key)
        else:
            self.msg = _Ann.pack(0x5243, 0, tcpaddr.encode('latin-1'), tcpport, 0, key)

And is that why castudp.c contains this workaround?

static void haveCandidate(caster_t *self,
                          casterAnnounce *buf,
                          osiSockAddr* peer)
{
    if(ntohs(buf->pid) != RECAST_MAGIC)
        return; /* not a recast announcement */

    if(ntohs(buf->version)!=0)
        return; /* reserved for later expansion */

    self->nameserv.ia.sin_family = AF_INET;
    if(ntohl(buf->serverIP)==0xffffffff) {
        /* direct from the source */
        self->nameserv.ia.sin_addr = peer->ia.sin_addr;
    } else {
        /* proxied */
        self->nameserv.ia.sin_addr.s_addr = buf->serverIP;
    }
    self->nameserv.ia.sin_port = buf->serverPort;

    /* ignore TOU16(buf,0xA) */

    self->servkey = ntohl(buf->serverKey);

    self->haveserv = 1;
} 

Surely this would not have to be the case if the announcer were to enter his address?

Can you bring light into my darkness?

Danke, Heinz

> On 22. Apr 2022, at 21:41, Michael Davidsaver <mdavidsaver at gmail.com> wrote:
> 
> On 4/22/22 11:51, Heinz Junkes via Tech-talk wrote:
>> Hi,
>> we need to route the announcements from our central Channelfinder server to a subnet so that the
>> recasters on the IOCs in the subnet can send their PV information to the server.
>> Unfortunately, the announcement package does not contain the IP of the server but FF:FF:FF:FF.
> 
> How are you planning to "route"?
> 
> Playing games with routing rules, or mangling via. something like iptables/netfilter won't change
> the IP source address, which is what SERV ADDR == 0xffffffff means (as with CA or PVA).
> 
> If you are thinking to create an active repeater (application level proxy), then this app. will
> need to copy the original IP source address into SERV ADDR field.
> 
> https://github.com/ChannelFinder/recsync#udp-protocol
> 
> 
>> root@priscilla:~# socat -ls -u -v -x UDP4-RECVFROM:5049,broadcast,fork,bind=141.14.143.255 UDP4-SENDTO:10.0.1.255:5049,broadcast
>>> 2022/04/22 17:22:18.879313  length=16 from=0 to=15
>> 52 43 00 00 ff ff ff ff 84 81 00 00 61 bf c1 23  RC..........a..#
>> Gruss Heinz
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System