Re: SCTP Multihoming Heartbeat ACK Behavior

[Daniel Borkmann <dborkman@redhat.com>]

On 07/01/2014 01:20 PM, Neil Horman wrote:
> On Tue, Jul 01, 2014 at 03:48:32PM +0800, Winston V. Tizon wrote:
...
>> (***) -> Based on SCTP RFC4960, expected behavior is secondary IP address
>>           should be used as path in sending the HB_ACK.
>>
> Actually, its quite the opposite, this confirms that the sctp protocol is
> functioning normally.  RFC 4960 says this about HB_ACK's:
>
> 3.3.6.  Heartbeat Acknowledgement (HEARTBEAT ACK) (5)
>
>     An endpoint should send this chunk to its peer endpoint as a response
>     to a HEARTBEAT chunk (see Section 8.3).  A HEARTBEAT ACK is always
>     sent to the source IP address of the IP datagram containing the
>     HEARTBEAT chunk to which this ack is responding.
>
> The only thing that a peer has to do regarding a HB frame is sent an HB_ACK to
> the source ip address of the corresponding HB frame (in this case172.168.39.4),
> which we do my recording the inbound transport that the HB frame arrived on.

I agree with you, Neil, the RFC only mentions that we need to "sent to the
source IP address", which was what I've quoted earlier on as well, so above
statement to use "secondary IP address should be used as path in sending
the HB_ACK" is not a MUST.