[zeromq-dev] ROUTER not routing?

Justin Karneges justin at affinix.com
Fri Feb 14 19:44:00 CET 2014


Having the local socket tell the remote peer about the mapping it has 
created seems very roundabout. How about just allowing the mapping in 
the local socket to be replaced anytime identity information is received 
from the remote peer?

I don't know how this works at the ZMTP level, but I assume that 
explicit identities are traded (if set on either side) at every 
connect/reconnect. I also assume that if the local socket receives 
identity information from a remote peer for which it already has a 
mapping, then it ignores the data. If these assumptions are true, then 
the solution is for the local socket to not ignore subsequent identity 
data and instead modify its mapping.

Am I wrong in my assumptions?

On 02/14/2014 12:50 AM, Laurent Alebarde wrote:
> The existing IDENTITY socket option is useless for your purpose because
> it is transmitted at the end of the handcheck in the metadata. When a
> ROUTER receives a new connection, it assigns to it a own forged identity
> (random for the first peer and then incremented for the next ones). It
> is a 5 bytes blob, the first one is always zero, the 4 others are mapped
> to a int.
>
> So, when the peer reconnects, it is seen as a new peer and the handcheck
> is reprocessed, whatever you do with the IDENTITY option. IMHO, I don't
> see any use case for this option.
>
> So, the only way I foresee is to have the ROUTER transmit to its peer
> the identity it has assigned to it. The best place I think is in the
> greeting's feeler: 31 bytes available not used (cf ZMTP). On the peer
> side, before it reconnects, it shall set a new identity option you shall
> add to libzmq, with the value previously retrieved.
>
> So, you should have one option used by the ROUTER, both to transmit the
> assign 5 bytes identity to the peer in the greeting's filler, and to get
> the one transmitted by the peer To have it work, use 6 bytes in the
> filler, one would be a validity flag, because it wouldn't be a good idea
> that the peer transmit an identity of its own, to avoid collisions. So
> first time it connects, the blob is {0, 0, 0, 0, 0, 0}. ROUTER will send
> say {1, 0, 5, 240, 72, 13}. Peer will have to send {2, 0, 5, 240, 72,
> 13}when it reconnects. It is better to differentiate how the blob has to
> be interpreted. 0: not valid, do nothing, 1: here is how I have
> identified you, 2: I reconnect, please use this to identify me. This
> would be necessary in the case of ROUTER-ROUTER, and ease greatly the
> use of this architecture.
>
> And you should have one option to be used by the peer to retrieve and
> resend the identity at the next connexion.
>
> Hope it helps,
>
>
> Laurent.
>
>
>
> Le 13/02/2014 23:51, Justin Karneges a écrit :
>> I'd like to move forward with fixing this. Can I get a confirmation that
>> I should proceed? Basically I want to make it so if a connection
>> reconnects, and an explicit identity is received from the peer, then it
>> should overwrite any previously set identity for that peer.
>>
>> Also I tried to log an item in the Jira but I'm not sure how. Maybe I
>> need special access rights? I created an account at least. Also, I see
>> issues in github too. Which is the right place to log things?
>>
>> Thanks.
>>
>> On 02/08/2014 11:53 AM, Justin Karneges wrote:
>>> Here's an even simpler example using REQ/ROUTER:
>>> https://gist.github.com/jkarneges/1fa64e9763561f53daef
>>>
>>> It doesn't demonstrate the routing problem but it does demonstrate the
>>> identity binding oddity. You can see the ROUTER side that the envelope
>>> id is always the first id it has ever seen, even if the id printed by
>>> the REQ side is different every time.
>>>
>>> On 02/07/2014 02:33 PM, Justin Karneges wrote:
>>>> Here's some small sample code to reproduce the issue:
>>>> https://gist.github.com/jkarneges/ab2b1abea1ee4cfc1332
>>>>
>>>> A (ztest1.py) creates REQ and ROUTER sockets. B (ztest2.py) creates REP
>>>> and ROUTER sockets. B binds and provides a random identity to its ROUTER
>>>> socket. A connects its sockets to B. A queries for B's id using the REQ
>>>> socket, and then attempts to send a message via the ROUTER socket right
>>>> after that. This is repeated every 2 seconds.
>>>>
>>>> A and B can be started in any order. A can be restarted and things will
>>>> still work. If B is restarted, then A's ROUTER socket will never work
>>>> again until A is restarted also.
>>>>
>>>> A uses ZMQ_ROUTER_MANDATORY to show that the failures are on A's side.
>>>>
>>>> On 02/07/2014 02:16 PM, Justin Karneges wrote:
>>>>> It is my understanding that being able to route requires the socket to
>>>>> have an identity mapping in its routing table for the peer.
>>>>>
>>>>> For peers that do not explicitly specify their own identity, then I
>>>>> believe you are correct that routing is not possible until at least one
>>>>> message has been received from the peer. It is at this point that the
>>>>> ROUTER socket will make up an identity for this peer and store it in its
>>>>> routing table.
>>>>>
>>>>> However, for peers that *do* explicitly specify their own identity (as I
>>>>> am doing), then this identity information is delivered immediately after
>>>>> the connection is established, allowing routing to the peer even if the
>>>>> peer has not sent a message yet.
>>>>>
>>>>> I should have been more clear in my original message. The B program is
>>>>> explicitly specifying a random UUID as the identity of its socket before
>>>>> binding.
>>>>>
>>>>> On 02/07/2014 02:06 PM, Panu Wetterstrand wrote:
>>>>>> I did not quite get the problem but could this be because (I think)
>>>>>> router is not able to route messages to socket from which it has not
>>>>>> reveived data first...
>>>>>>
>>>>>> 7.2.2014 22.51 kirjoitti "Justin Karneges" <justin at affinix.com
>>>>>> <mailto:justin at affinix.com>>:
>>>>>>
>>>>>>         Hi,
>>>>>>
>>>>>>         1) ROUTER in program A is set to connect to a bind socket in program B.
>>>>>>         2) Both programs are started, and the connection is established.
>>>>>>         3) A determines B's socket identity out-of-band, and is able to send
>>>>>>         messages to B.
>>>>>>         3) B is terminated and the connection is lost.
>>>>>>         4) B is started again, and the connection is re-established.
>>>>>>         5) A determines B's socket identity out-of-band, and is no longer able
>>>>>>         to send messages to B.
>>>>>>
>>>>>>         It seems this problem does not happen if B retains the same socket
>>>>>>         identity across reconnects. However, if it uses a random identity (to be
>>>>>>         discovered out-of-band by A), then routing will never work again after
>>>>>>         the first restart of B. The A program must be restarted in order to make
>>>>>>         things right again.
>>>>>>
>>>>>>         My guess is that each connect queue on a ROUTER socket is somehow bound
>>>>>>         for life against the first identity it sees. Is this intentional
>>>>>>         behavior?
>>>>>>
>>>>>>         Thanks,
>>>>>>         Justin
>>>>>>         _______________________________________________
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>>>>>>         http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>>>>>>
>>>>>>
>>>>>>
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