Subject: Re: draft-nair-sip-dhcp-00.txt

From: Bernie Volz <[email-masked]>
Date: Mon, 7 Feb 2000 13:44:49 -0500

Gautam:

I guess I still don't understand what the advantage of singling out
this backup server is? Is it somehow special? Is it somehow less
equal than the others?

If you wanted to communicate some "preference", why not use a format
whereby you have a preference value after each IP address in the
suboption 3 list. That way, you can give your backup server less
preference. The client logic might thus be arrange the addresses in
order of preference, for those of equal preference, pick one at
random. If that doesn't respond, pick another one of the same
preference or if none left, start with next lower preference and
so on until the list is exhausted (in which case, restart at the
beginning or ???).

- Bernie

---
Date: Mon, 07 Feb 2000 13:10:51 -0500
From: Gautam Nair <[email-masked]>

Bernie Volz wrote:

> Is the intent of the suboption 3 (IP address sub-option) that a client
> randomly picks one address and if that server doesn't respond, it goes
> to the backup server (suboption 4)? Why not have it try all of the
> servers in suboption 3 (round-robin fashion, starting with a randomly
> picked one).

You're right. The selection is to  be done in round-robin fashion starting
with a randomly picked one.

> That way, you might even be able to drop suboption 4 and
> simplify configuration a bit?
> Or, is suboption 4 intended for use in all cases (even when or if
> suboption 1 (DNS SRV) or suboption 2 (DNS 'A') are specified and used
> but that server fails to respond or the DNS server isn't responding)?

Sub-option 4 is intended for use as a last resort option in all cases
(sub-options 1, 2 and 3) if the SIP server fails to respond. Sub-option 4 is
used after all the SIP servers specified in the sub-options 1,2 and 3 have
been tried and have failed.

> In
> that case, are the clients not allowed to use suboption 3 anyway?
>

They are allowed to use sub-option 3. Only after an unsuccessful sub-option
3 attempt, does the client try sub-option 4. Sub-option 4 is required in
addition to sub-option 3 because there's no easy way to specify the *backup
only* server in the random round-robin selection scheme.
In case of failure of only the DNS server, sub-option 3 will be used.

> - Bernie Volz
>   Process Software

Thank you for your comments and suggestions,

Gautam Nair.
Columbia University.