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https://github.com/servalproject/serval-dna.git
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4e0c9bfd02
when receiving a frame and determining if it is broadcast etc. (one major use case that has been fixed is broadcast nexthop, and unicast destination, e.g., for link-local broadcast).
425 lines
17 KiB
C
425 lines
17 KiB
C
/*
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Serval Distributed Numbering Architecture (DNA)
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Copyright (C) 2010 Paul Gardner-Stephen
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation; either version 2
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of the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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/*
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Serval Overlay Mesh Network.
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Basically we use UDP broadcast to send link-local, and then implement a BATMAN-like protocol over the top of that.
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Each overlay packet can contain one or more encapsulated packets each addressed using Serval DNA SIDs, with source,
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destination and next-hop addresses.
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The use of an overlay also lets us be a bit clever about using irregular transports, such as an ISM915 modem attached via ethernet
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(which we are planning to build in coming months), by paring off the IP and UDP headers that would otherwise dominate. Even on
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regular WiFi and ethernet we can aggregate packets in a way similar to IAX, but not just for voice frames.
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The use of long (relative to IPv4 or even IPv6) 256 bit Curve25519 addresses means that it is a really good idea to
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have neighbouring nodes exchange lists of peer aliases so that addresses can be summarised, possibly using less space than IPv4
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would have.
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One approach to handle address shortening is to have the periodic TTL=255 BATMAN-style hello packets include an epoch number.
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This epoch number can be used by immediate neighbours of the originator to reference the neighbours listed in that packet by
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their ordinal position in the packet instead of by their full address. This gets us address shortening to 1 byte in most cases
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in return for no new packets, but the periodic hello packets will now be larger. We might deal with this issue by having these
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hello packets reference the previous epoch for common neighbours. Unresolved neighbour addresses could be resolved by a simple
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DNA request, which should only need to occur ocassionally, and other link-local neighbours could sniff and cache the responses
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to avoid duplicated traffic. Indeed, during quiet times nodes could preemptively advertise address resolutions if they wished,
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or similarly advertise the full address of a few (possibly randomly selected) neighbours in each epoch.
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Byzantine Robustness is a goal, so we have to think about all sorts of malicious failure modes.
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One approach to help byzantine robustness is to have multiple signature shells for each hop for mesh topology packets.
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Thus forging a report of closeness requires forging a signature. As such frames are forwarded, the outermost signature
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shell is removed. This is really only needed for more paranoid uses.
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We want to have different traffic classes for voice/video calls versus regular traffic, e.g., MeshMS frames. Thus we need to have
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separate traffic queues for these items. Aside from allowing us to prioritise isochronous data, it also allows us to expire old
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isochronous frames that are in-queue once there is no longer any point delivering them (e.g after holding them more than 200ms).
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We can also be clever about round-robin fair-sharing or even prioritising among isochronous streams. Since we also know about the
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DNA isochronous protocols and the forward error correction and other redundancy measures we also get smart about dropping, say, 1 in 3
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frames from every call if we know that this can be safely done. That is, when traffic is low, we maximise redundancy, and when we
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start to hit the limit of traffic, we start to throw away some of the redundancy. This of course relies on us knowing when the
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network channel is getting too full.
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Smart-flooding of broadcast information is also a requirement. The long addresses help here, as we can make any address that begins
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with the first 192 bits all ones be broadcast, and use the remaining 64 bits as a "broadcast packet identifier" (BPI).
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Nodes can remember recently seen BPIs and not forward broadcast frames that have been seen recently. This should get us smart flooding
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of the majority of a mesh (with some node mobility issues being a factor). We could refine this later, but it will do for now, especially
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since for things like number resolution we are happy to send repeat requests.
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This file currently seems to exist solely to contain this introduction, which is fine with me. Functions land in here until their
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proper place becomes apparent.
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*/
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#include "serval.h"
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int overlayMode=0;
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overlay_txqueue overlay_tx[OQ_MAX];
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keyring_file *keyring=NULL;
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int overlayServerMode()
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{
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/* In overlay mode we need to listen to all of our sockets, and also to
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send periodic traffic. This means we need to */
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fprintf(stderr,"Running in overlay mode.\n");
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/* Get keyring available for use.
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Required for MDP, and very soon as a complete replacement for the
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HLR for DNA lookups, even in non-overlay mode. */
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keyring=keyring_open_with_pins("");
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if (!keyring) {
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return WHY("Could not open serval keyring file.");
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}
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/* put initial identity in if we don't have any visible */
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keyring_seed(keyring);
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/* Set default congestion levels for queues */
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int i;
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for(i=0;i<OQ_MAX;i++) {
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overlay_tx[i].maxLength=100;
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overlay_tx[i].latencyTarget=5000; /* Keep packets in queue for 5 seconds by default */
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}
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/* But expire voice/video call packets much sooner, as they just aren't any use if late */
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overlay_tx[OQ_ISOCHRONOUS_VOICE].latencyTarget=500;
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overlay_tx[OQ_ISOCHRONOUS_VIDEO].latencyTarget=500;
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/* Get the set of socket file descriptors we need to monitor.
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Note that end-of-file will trigger select(), so we cannot run select() if we
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have any dummy interfaces running. So we do an ugly hack of just waiting no more than
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5ms between checks if we have a dummy interface running. This is a reasonable simulation
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of wifi latency anyway, so we'll live with it. Larger values will affect voice transport,
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and smaller values would affect CPU and energy use, and make the simulation less realistic. */
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struct pollfd fds[128];
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int fdcount;
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/* Create structures to use 1MB of RAM for testing */
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overlay_route_init(1);
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/* Get rhizome server started BEFORE populating fd list so that
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the server's listen socket is in the list for poll() */
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if (rhizome_datastore_path) rhizome_server_poll();
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while(1) {
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if (servalShutdown) servalShutdownCleanly();
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/* Work out how long we can wait before we need to tick */
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long long ms=overlay_time_until_next_tick();
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memabuseCheck();
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int filesPresent=0;
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fds[0].fd=sock; fds[0].events=POLLIN;
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fdcount=1;
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rhizome_server_get_fds(fds,&fdcount,128);
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rhizome_fetching_get_fds(fds,&fdcount,128);
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overlay_mdp_get_fds(fds,&fdcount,128);
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for(i=0;i<overlay_interface_count;i++)
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{
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/* Make socket non-blocking so that poll() behaves correctly.
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We then set non-blocking before actually reading from it */
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fcntl(overlay_interfaces[i].fd, F_SETFL,
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fcntl(overlay_interfaces[i].fd, F_GETFL, NULL)&(~O_NONBLOCK));
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if ((!overlay_interfaces[i].fileP)&&(fdcount<128))
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{
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if (debug&DEBUG_IO) {
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fprintf(stderr,"Interface %s is poll() slot #%d (fd %d)\n",
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overlay_interfaces[i].name,
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fdcount,
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overlay_interfaces[i].fd);
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}
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fds[fdcount].fd=overlay_interfaces[i].fd;
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fds[fdcount].events=POLLRDNORM;
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fds[fdcount].revents=0;
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fdcount++;
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}
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if (overlay_interfaces[i].fileP)
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{ filesPresent=1; if (ms>5) ms=5; }
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}
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/* Progressively update link scores to neighbours etc, and find out how long before
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we should next tick the route table.
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Basically the faster the CPU and the sparser the route table, the less often we
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will need to tick in order to keep each tick nice and fast. */
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int route_tick_interval=overlay_route_tick();
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if (ms>route_tick_interval) ms=route_tick_interval;
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if (debug&DEBUG_VERBOSE_IO)
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fprintf(stderr,"Waiting via poll() for up to %lldms\n",ms);
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int r=poll(fds,fdcount,ms);
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if (r<0) {
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/* select had a problem */
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if (debug&DEBUG_IO) perror("poll()");
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WHY("select() complained.");
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} else if (r>0) {
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/* We have data, so try to receive it */
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if (debug&DEBUG_IO) {
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fprintf(stderr,"poll() reports %d fds ready\n",r);
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int i;
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for(i=0;i<fdcount;i++) {
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if (fds[i].revents)
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{
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fprintf(stderr," #%d (fd %d): %d (",i,fds[i].fd,fds[i].revents);
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if ((fds[i].revents&POLL_IN)==POLL_IN) fprintf(stderr,"POLL_IN,");
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if ((fds[i].revents&POLLRDNORM)==POLLRDNORM) fprintf(stderr,"POLLRDNORM,");
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if ((fds[i].revents&POLL_OUT)==POLL_OUT) fprintf(stderr,"POLL_OUT,");
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if ((fds[i].revents&POLL_ERR)==POLL_ERR) fprintf(stderr,"POLL_ERR,");
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if ((fds[i].revents&POLL_HUP)==POLL_HUP) fprintf(stderr,"POLL_HUP,");
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if ((fds[i].revents&POLLNVAL)==POLLNVAL) fprintf(stderr,"POLL_NVAL,");
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fprintf(stderr,")\n");
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}
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}
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}
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overlay_rx_messages();
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if (rhizome_datastore_path) {
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rhizome_server_poll();
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rhizome_fetch_poll();
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overlay_mdp_poll();
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}
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} else {
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/* No data before tick occurred, so do nothing.
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Well, for now let's just check anyway. */
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if (debug&DEBUG_IO) fprintf(stderr,"poll() timeout.\n");
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overlay_rx_messages();
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if (rhizome_datastore_path) {
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rhizome_server_poll();
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rhizome_fetch_poll();
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overlay_mdp_poll();
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}
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}
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/* Check if we need to trigger any ticks on any interfaces */
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overlay_check_ticks();
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}
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return 0;
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}
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int overlay_frame_process(int interface,overlay_frame *f)
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{
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if (!f) return WHY("f==NULL");
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long long now=overlay_gettime_ms();
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if (f->source_address_status==OA_RESOLVED&&overlay_address_is_local(f->source))
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return WHY("Dropping frame claiming to come from myself.");
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if (debug&DEBUG_OVERLAYFRAMES) fprintf(stderr,">>> Received frame (type=%02x)\n",f->type);
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/* First order of business is whether the nexthop address has been resolved.
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If not, we need to think about asking for it to be resolved.
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The trouble is that we do not want to trigger a Hanson Event (a storm of
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please explains/resolution requests). Yet, we do not want to delay
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communications unnecessarily.
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The simple solution for now is to queue the address for resolution request
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in our next tick. If we see another resolution request for the same
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address in the mean time, then we can cancel our request */
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switch (f->nexthop_address_status)
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{
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case OA_UNINITIALISED:
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/* Um? Right. */
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return WHY("frame passed with ununitialised nexthop address");
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break;
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case OA_RESOLVED:
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/* Great, we have the address, so we can get on with things */
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break;
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case OA_PLEASEEXPLAIN:
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return WHY("Address cannot be resolved -- aborting packet processing.");
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/* XXX Should send a please explain to get this address resolved. */
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break;
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case OA_UNSUPPORTED:
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default:
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/* If we don't support the address format, we should probably tell
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the sender. Again, we queue this up, and cancel it if someone else
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tells them in the meantime to avoid an Opposition Event (like a Hanson
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Event, but repeatedly berating any node that holds a different policy
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to itself. */
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WHY("Packet with unsupported address format");
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overlay_interface_repeat_abbreviation_policy[interface]=1;
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return -1;
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break;
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}
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/* Okay, nexthop is valid, so let's see if it is us */
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int forMe=0,i;
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int ultimatelyForMe=0;
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int broadcast=0;
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int nhbroadcast=overlay_address_is_broadcast(f->nexthop);
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int duplicateBroadcast=0;
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printf("destination is %s\n",overlay_render_sid(f->destination));
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printf("nexthop is %s\n",overlay_render_sid(f->nexthop));
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if (nhbroadcast) {
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if (overlay_broadcast_drop_check(f->nexthop)) duplicateBroadcast=1;
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forMe=1; }
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if (overlay_address_is_local(f->nexthop)) forMe=1;
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if (forMe) {
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/* It's for us, so resolve the addresses */
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if (overlay_frame_resolve_addresses(interface,f))
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return WHY("Failed to resolve destination and sender addresses in frame");
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broadcast=overlay_address_is_broadcast(f->destination);
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if (debug&DEBUG_OVERLAYFRAMES) {
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fprintf(stderr,"Destination for this frame is (resolve code=%d): ",f->destination_address_status);
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if (f->destination_address_status==OA_RESOLVED) for(i=0;i<SID_SIZE;i++) fprintf(stderr,"%02x",f->destination[i]); else fprintf(stderr,"???");
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fprintf(stderr,"\n");
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fprintf(stderr,"Source for this frame is (resolve code=%d): ",f->source_address_status);
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if (f->source_address_status==OA_RESOLVED) for(i=0;i<SID_SIZE;i++) fprintf(stderr,"%02x",f->source[i]); else fprintf(stderr,"???");
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fprintf(stderr,"\n");
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}
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if (f->source_address_status!=OA_RESOLVED) {
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if (debug&DEBUG_OVERLAYFRAMES) WHY("Source address could not be resolved, so dropping frame.");
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return -1;
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}
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if (overlay_address_is_local(f->source))
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{
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if (debug&DEBUG_OVERLAYROUTING)
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WHY("Dropping frame claiming to come from myself.");
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return -1;
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}
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if (f->destination_address_status==OA_RESOLVED) {
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if (overlay_address_is_broadcast(f->destination))
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{ ultimatelyForMe=1; broadcast=1; }
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if (overlay_address_is_local(f->destination)) ultimatelyForMe=1;
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} else {
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if (debug&DEBUG_OVERLAYFRAMES) WHY("Destination address could not be resolved, so dropping frame.");
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return -1;
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}
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}
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if (debug&DEBUG_OVERLAYFRAMES) {
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fprintf(stderr,"This frame does%s have me listed as next hop.\n",forMe?"":" not");
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fprintf(stderr,"This frame is%s for me.\n",ultimatelyForMe?"":" not");
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fprintf(stderr,"This frame is%s%s broadcast.\n",
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broadcast?"":" not",duplicateBroadcast?" a duplicate":"");
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}
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if (duplicateBroadcast) {
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WHY("Packet is duplicate broadcast");
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return 0;
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}
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/* Not for us? Then just ignore it */
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if (!forMe) {
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return 0;
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}
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/* Is this a frame we have to forward on? */
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if (((!ultimatelyForMe)||broadcast)&&(f->ttl>1))
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{
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/* Yes, it is. */
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int len=0;
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if (broadcast&&(!duplicateBroadcast)&&
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((f->type==OF_TYPE_SELFANNOUNCE)
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||(f->type==OF_TYPE_RHIZOME_ADVERT)
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))
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{
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// Don't forward broadcast self-announcement packets as that is O(n^2) with
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// traffic. We have other means to propagating the mesh topology information.
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// Similarly, rhizome advertisement traffic is always link local, so don't
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// forward that either.
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if (debug&DEBUG_BROADCASTS)
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if (duplicateBroadcast)
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fprintf(stderr,"Dropping broadcast frame (BPI seen before)\n");
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} else {
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if (debug&DEBUG_OVERLAYFRAMES) fprintf(stderr,"\nForwarding frame.\n");
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int dontForward=0;
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if (!broadcast) {
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if (overlay_get_nexthop(f->destination,f->nexthop,&len,
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&f->nexthop_interface))
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WHY("Could not find next hop for host - dropping frame");
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dontForward=1;
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}
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f->ttl--;
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printf("considering forwarding frame to %s (forme=%d, broadcast=%d)\n",
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overlay_render_sid(f->destination),ultimatelyForMe,broadcast);
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if (overlay_address_is_broadcast(f->destination))
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if (overlay_broadcast_drop_check(f->destination))
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{
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dontForward=1;
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return WHY("Not forwarding or reading duplicate broadcast");
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}
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if (!dontForward) {
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/* Queue frame for dispatch.
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Don't forget to put packet in the correct queue based on type.
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(e.g., mesh management, voice, video, ordinary or opportunistic).
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But the really important bit is to clone the frame, since the
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structure we are looking at here must be left as is and returned
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to the caller to do as they please */
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overlay_frame *qf=op_dup(f);
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if (!qf) WHY("Could not clone frame for queuing");
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else {
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/* XXX we should preserve the queue priority of the frame */
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int qn=OQ_ORDINARY;
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WHY("queuing frame for forwarding");
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if (overlay_payload_enqueue(qn,qf)) {
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WHY("failed to enqueue forwarded payload");
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op_free(qf);
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}
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}
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}
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/* If the frame was a broadcast frame, then we need to hang around
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so that we can process it, since we are one of the recipients.
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Otherwise, return triumphant. */
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if (!broadcast) return 0;
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}
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}
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switch(f->type)
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{
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case OF_TYPE_SELFANNOUNCE:
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overlay_route_saw_selfannounce(interface,f,now);
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break;
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case OF_TYPE_SELFANNOUNCE_ACK:
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overlay_route_saw_selfannounce_ack(interface,f,now);
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break;
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case OF_TYPE_NODEANNOUNCE:
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overlay_route_saw_advertisements(interface,f,now);
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break;
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case OF_TYPE_RHIZOME_ADVERT:
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overlay_rhizome_saw_advertisements(interface,f,now);
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break;
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case OF_TYPE_DATA:
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WHY("saw mdp containing frame");
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overlay_saw_mdp_containing_frame(interface,f,now);
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break;
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default:
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fprintf(stderr,"Unsupported f->type=0x%x\n",f->type);
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return WHY("Support for that f->type not yet implemented");
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break;
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}
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return 0;
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}
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