[Anima] GRASP DULL, IPv6 LL scope and multicast and BSD sockets API
Michael Richardson <mcr+ietf@sandelman.ca> Tue, 06 April 2021 16:49 UTC
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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>, anima@ietf.org
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Date: Tue, 06 Apr 2021 12:49:49 -0400
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Subject: [Anima] GRASP DULL, IPv6 LL scope and multicast and BSD sockets API
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Brian, I think that I am making a mistake in how I am binding my IPv6 multicast sockets on which I expect to hear GRASP DULL messages. 1) I create a socket with an unspecified address, and the GRASP_PORT (7017): let rsin6 = SocketAddrV6::new(Ipv6Addr::UNSPECIFIED, grasp::GRASP_PORT as u16, 0, ifindex); let recv_try = UdpSocket::bind(rsin6).await; Note that I had originally expected that I should bind it to the IPv6-LL of the interface, but that meant that the socket does not match the multicast destinations. I mark SO_REUSEPORT, and SO_REUSEADDR on this socket. 2) I join the multicast address for that socket: let grasp_mcast = "FF02:0:0:0:0:0:0:13".parse::<Ipv6Addr>().unwrap(); recv.join_multicast_v6(&grasp_mcast, ifindex).unwrap(); Note that "ifindex" is the scope of the interface that I want to bind. 3) If that works, then, in order to send, I create a new socket, which I do not bind to multicast, but I do bind it to the interface: let ssin6 = SocketAddrV6::new(Ipv6Addr::UNSPECIFIED, 0 as u16, 0, ifindex); let send = UdpSocket::bind(ssin6).await.unwrap(); maybe I could use the above socket, but I think it is easier to have two sockets as it simplies threads. I have been binding a multicast listening socket for each "physical" interface. In testing with more than one interface I realized two things: a) I hear myself on the same interface. That is, M_FLOODs about address fe80::1234, are heard on the multicast socket bound to fe80::1234. Okay, I think, just filter those out since they come from "me" b) Oops, I hear myself on the other interfaces. So, M_FLOODs about fe80::1234 on ifindex 2 are heard on ifindex 3, (call it "fe80::abcd"). They aren't "me", so I actually have to talk my list of interfaces and filter out all the "me". I realized that the originating sockaddr provided in recvfrom() also has an sin6_scope which is filled in, so the multicasts which loop back internally can be filtered out by listening on for things which are on the ifindex I wanted to listen to. But, I still have to filter for the list of "me", because it could be that fe80::1234 and fe80::abcd are actually two ports in the same L2 domain. I actually ran into the last bit when looking at the IPsec policies that were being created. My IKEv2 daemon gets cross when you ask it to initiate to a peer which it is convinced it also self. I may have made some mistakes setting the IP TTL of my packets. I think they are set to 1. (The GRASP TTL was incorrectly set to that as well, which I fixed already.) I have been creating a GraspDaemon thread per interface. Since this is really just a Rust Async co-routine (a "green thread"), and not an actual system thread, I feel that the simplicity of just having the simplest of loops running outweighs the potential scaling issue of having hundreds of these running. The co-routine mechanism means that this all just leads down to an event loop and a call to select(2)/poll(2)/epoll(2), etc. all handled by tokio and the compiler and not me. But now, I'm thinking that I should have just done a single Grasp(DULL) daemon receive thread, listening on all interfaces. I can't really remember why I didn't do that. Maybe because I thought I would need a multicast socket per physical interface. On the transmit side, I have multiple loops sending, but that is easily merged into a single loop, and it would have the advantage that I could more easily stagger DULL announcements across different interfaces. I'm not actually sure how often M_FLOODs are supposed to be sent. I scanned through ACP (section 6.4) and through GRASP-15, and I didn't see anything. That is: loop { sleep(60s +- rand(10)); send-M_FLOOD-on-next-interface; } rather than: loop { sleep(60s); for if in interfaces { send-M_FLOOD-on(if) } } -- Michael Richardson <mcr+IETF@sandelman.ca> . o O ( IPv6 IøT consulting ) Sandelman Software Works Inc, Ottawa and Worldwide
- [Anima] GRASP DULL, IPv6 LL scope and multicast a… Michael Richardson
- Re: [Anima] GRASP DULL, IPv6 LL scope and multica… Brian E Carpenter
- Re: [Anima] GRASP DULL, IPv6 LL scope and multica… Michael Richardson