Re: multi-homing association

Hi Santi,

see my comments in-line.

Best regards
Michael

On May 5, 2006, at 2:57 PM, Santiago Muñoz (E2/EEM) wrote:

>  Hi,
> In the RFC2960 clause 10 it is suggested a upper layer to SCTP  
> layer interface (API), in fact clause 10.1 B) is about the  
> establishment of an association, and there it is said that a list  
> of possible destination IP addresses can be specified.
> Though the API method is just a suggestion and the list of  
> destination addresses may only consist of one, so to know several  
> destination IP addresses by the upper layer is just optional,  
> though I dare say desirable (at least two for the case you describe).
>
> If the SCTP upper layer knows several destination addresses, the  
> most optimal implementation of the API should be to specify them  
> all in the ASSOCIATE method to SCTP so it is in charge of trying  
> all specified addresses in the establishment, off loading of such  
> task to the upper layer.
That is why there are connectx() and sendx() calls in the socket API  
in addition to the
connnect() and send() calls.
>
> In case only one is indicated to SCTP, if it is down then the  
> association is never established.
>
> How the upper layer knows about the destination addresses, I think  
> it depends on the upper layer implementation, local manual  
> configuration, DNS resolution, any dynamic discovery procedure are  
> valid methods through which the SCTP can knows the destination IP  
> addresses.
There is one problem with the DNS. If you get multiple IP-addresses  
from DNS, you
do not know if they belong to one host.
>
> Best regards, Santi
> -----Original Message-----
> From: Michael Tuexen [mailto:[email protected]]
> Sent: viernes, 05 de mayo de 2006 14:25
> To: devayya
> Cc: [email protected]
> Subject: Re: [Sigtran] multi-homing association
>
> Hi,
>
> see my comments in-line.
>
> Best regards
> Michael
>
> On May 5, 2006, at 1:59 PM, devayya wrote:
>
>> Hi,
>>
>> I have question, Is it possible or mandatory for the upper layer to
>> know that the SCTP endpoints(source and destination) are multi-  
>> homed?
>> and also the list of destination ip address available with the SCTP
>> multi-homed destination?
> The interface between SCTP and its upper layer is not specified in  
> an RFC. However, there is an ID describing the socket API which is  
> implemented by some SCTP stacks like the one in *BSD, Linux  
> (LKSCTP), and Solaris.
>>
>> Consider if the SCTP layer is multi-homed(source and peer end) and  
>> the
>> upper layer knows only about a single address, through which the  
>> upper
>> layer asks the SCTP to initiate a association. Suppose during this
>> initiation if the peer end address through which initiation is
>> happening, is down. Is there any approach where the upper layer knows
>> the list of multihomed destination ip addresses, and it tries to
>> initate the through the other destination ip addresses?
> If the initiating endpoint knows more than one address of the peer,  
> it can use the
> connectx() or sendx() call to make use of this knowledge. It is up  
> to the implementation how to make use of it.
>> If not possible,  is it that the association between these to
>> endpoints will never come up untill the known destination ip address
>> comes up?
> If the endpoint knows only one address of the peer and that address  
> is not reachable, than the association can not be setup.
>
> However, in the SIGTRAN environment is is pretty common (at least  
> from my experience) that an endpoint knows all the addresses of the  
> peer in advance (by
> configuration) and can
> make use of it even during associations setup.
>>
>> Please clarify...
>>
>> Thanks and regards,
>> devayya
>>
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>
>
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