Subject: [Dime] Some questions regarding RFC 3539

From: Yan Chen <[email-masked]>
Date: Tue, 11 Jun 2013 08:20:16 +0800

Hi, all

I am studying RFC 3539. While I have some difficulties to understand
"Appendix A - Detailed Watchdog Algorithm". Please provide some help.

1) Does AAA client or AAA Server (direct connection scenario) need to
follow the algorithm?
In section 3.4 we have: "The watchdog is used in order to enable a AAA
client or agent to determine when to resend on another connection." Does it
mean the algorithm is only required in AAA client? Without following the
algorithm AAA server would utilize the newly connected link earlier than
AAA client, which would cause some AAA server initiated procedures, such as
RAR, result in failure.

2) If the algorithm is required in AAA server, how to avoid the infinite
loop when both AAA client and AAA server enter "REOPEN" phase?
If the "connection up" event indicates to AAA client and AAA server, both
of them would send DWR to verify the link and enter "REOPEN" phase. While
in this phase only DWA is allowed to be a signal to trigger the state
machine going forward. It seems to me that both sides would discard the DWR
sent by their peer and run into an infinite loop.

3) If the DWR was out of the scope of Non-DWA, how to avoid the
inconsistent states between 2 AAA peers?
The total link verification time by the algorithm would be 2 x Tw + 3 x
(time of DWA - time of DWR). If one side sets its Tw much longer than the
other, it would run into the similar consequence of my question 1) - one
side would utilize the newly connected link earlier than the other.

4) Is RFC 3539 so strictly binding to RFC 3588?
RFC 3588 has many statements referring to RFC 3539, especially in its
transport description. I am quite confused about the coordination between
the state machine logic in the Section 5.6 of RFC 3588 and that in the
Appendix A of RFC 3539. I am wondering the strong binding is necessary to
the application of AAA or very diameter application.

Thanks...

BRs
Chen Yan