[lustre-discuss] LNET ports and connections

Degremont, Aurelien degremoa at amazon.com
Tue Feb 18 05:18:51 PST 2020

Thanks for your reply.
I think I have a good enough understanding of LNET itself. My question was more about how LNET is being used by Lustre itself.

LNET will established connections only if asked for by upper layers. 
When I was talking about client and server, I was talking about how Lustre was using it.

As far as I understood, Lustre server only contact clients when they need to send LDLM callbacks.
They do so through the socket already opened by the client (reverse import).
What happened if the socket is closed is what I'm not sure. I though the server is rather waiting for the client to reconnect and if not, is more or less evicting it.
Could it be possible that the server in this case opens the connection itself without waiting for the client to reconnect?


Le 18/02/2020 05:42, « NeilBrown » <neilb at suse.com> a écrit :

    LNet is a peer-to-peer protocol, it has no concept of client and server.
    If one host needs to send a message to another but doesn't already have
    a connection, it creates a new connection.
    I don't yet know enough specifics of the lustre protocol to be certain
    of the circumstances when a lustre server will need to initiate a message
    to a client, but I imagine that recalling a lock might be one.
    I think you should assume that any LNet node might receive a connection
    from any other LNet node (for which they share an LNet network), and
    that the connection could come from any port between 512 and 1023
    On Mon, Feb 17 2020, Degremont, Aurelien wrote:
    > Hi all,
    > From what I've understood so far, LNET listens on port 988 by default and peers connect to it using 1021-1023 TCP ports as source ports.
    > At Lustre level, servers listen on 988 and clients connect to them using the same source ports 1021-1023.
    > So only accepting connections to port 988 on server side sounded pretty safe to me. However, I've seen connections from 1021-1023 to 988, from server hosts to client hosts sometimes.
    > I can't understand what mechanism could trigger these connections. Did I miss something?
    > Thanks
    > Aurélien
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    > lustre-discuss at lists.lustre.org
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