Subject: Re: ospf-scalability-04.txt

From: "Choudhury, Gagan L, ALABS" <[email-masked]>
Date: Wed, 21 May 2003 09:02:03 -0500

Vivek,
   Thanks for your comments on Recommendation 1. Here are the responses 
to the two points you make.  With regards,

        Gagan

Point 1: Recommendation 1 basically says to give higher
priority to hellos/acks over other OSPF packets both during 
transmitting them and during receiving them.  It does not say 
anything about whether priority is to be given to one neighbor
over others during processing.  It also does not say whether
"high priority" class and "low" priority class has to
be per neighbor or globally. So your suggestion of
"just process all hellos/acks with higher priority" is
included.

Point 2: Ack is generated based on received LSU.  However,
we do not recommend all received LSUs to be treated at higher 
priority since in that case almost all received OSPF packets
will be at a higher priority and the basic purpose of
prioritization of Hellos/Acks over others will be defeated.  We 
recommend that once an Ack has been generated it should go to its
intended destination at a higher priority (even though the
received LSU that caused this Ack is not given higher
priority).  We simulated this scheme and as you will see
from Table 2 in Appendix B.2 just prioritizing Hellos and
Acks (and not the received LSU that caused the Ack) can
significantly improve scalability and stability.  

-----Original Message-----
From: Vivek Dubey [mailto:[email-masked]]
Sent: Wednesday, May 21, 2003 1:29 AM
To: [email-masked]
Subject: Re: ospf-scalability-04.txt

Gagan,

2. Recommendations

(1) ......"While receiving a packet from a neighbor
and while transmitting a packet to a neighbor,
try to process a "high priority" packet ahead
of a "low priority" packet"

Few questions
-------------
Mainly from implementors view ............

The point to treat packets with higher/lower
priority based on receiving from particular
NBR is not very clear.

1)
OSPF might be having multiple interfaces (each
interface in turn having multiple NBRs).

IP will pass all OSPF packets ...where they
can be treated with high/low priority based
on above classification. So while processing
these high priority packets (hellos/acks), is it
required to choose them as per NBR ....... if so
which NBR will be given higher priority.

It would be better if we just process all
hellos/acks with higher priority (won't
it save much overhead).

2)
Ospf acks (delayed ones also) are sent
in response to LSU packets. So to give priority
to a "ack to be transmitted to a NBR", received LSU
should be processed fast.
Not very clear to me...... is there some conflict here ???

thanks,
vivek