Subject: Re: [alto] ALTO extension for representing SDN policies

From: Wendy Roome <[email-masked]>
Date: Tue, 14 Apr 2015 17:10:27 -0400

Guohai,

I agree with Richard¹s earlier comment that the consensus of the WG was
that an endpoint is in one PID.  Here are my reasons for supporting that.

I believe that clients do not care about PIDs. PIDS are irrelevent.
Clients really care about endpoints. We introduce PIDs because an
endpoint-to-endpoint cost matrix is too large (for today¹s computers,
anyway!).  So we partition the 2^32 (or 2^128) addresses into a few
hundred, or maybe a few thousand, equivalence classes, called PIDs, and
have a cost matrix from PID-PID rather than endpoint-endpoint. So when a
client wants to cost from EP1 to EP2, the client maps each EP to a PID,
and gets to costs between those PIDs.

But that makes it essential that an endpoint is in only one PID. If it's
in several PIDs, then that endpoint has several different costs. Which one
should the client use?

It is like the old observation that a person with one watch always knows
the time of day. But a person with two watches is never sure. :-)

So whenever someone suggests an extension that would allow an endpoint to
be in multiple PIDs, my immediate question is, What would a client do with
that information? Why would a client care?

Incidentally, what if the server offered multiple Network Maps, with
different endpoint partitions, and different cost maps?  That certainly is
supported by RFC 7285, and (in a sense) allows an endpoint to be in more
than one PID. However, it then raises the question of how the client
decides which Network Map to use.

	- Wendy Roome

On 04/14/2015, 15:00, "[email-masked]" <[email-masked]>
wrote:

>Message: 1
>Date: Tue, 14 Apr 2015 04:50:02 +0800 (GMT+08:00)
>From: ??? <[email-masked]>
>To: "Y. Richard Yang" <[email-masked]>
>Subject: Re: [alto] ALTO extension for representing SDN policies
>Message-ID: <[email-masked]>
>
>Dear Richard,
>
>The longest prefix matching mechanism in ALTO maps each IP address into a
>single PID, this is the non-overlapping property of an ALTO network map.
>But in the end-to-end
>policies such as GBP, EPGs may be overlapped, some endpoints may belong
>to multiple EPGs, the longest prefix matching mechanism should be changed
>to adapt for that.
>I think that one prefix or IP address can be mapped into a PID list that
>contains one or multiple PIDs. We can still use the longest prefix
>matching, but the result is a PID list,
>not a single PID.

---

From: "Y. Richard Yang" <[email-masked]>
Date: Wed, 15 Apr 2015 01:36:29 -0400

Wendy, Guohai,

Please see below.

> in several PIDs, then that endpoint has several different costs. Which one

Not to say that I am convinced about an approach, but here is one,
motivated by TCAM: introducing priority to distinguish multiple matches (in
two dimensions), by assigning priority values to different entries. How
stupid is this idea?

Richard

> On 04/14/2015, 15:00, "[email-masked] <javascript:;>" <
> [email-masked] <javascript:;>>
> wrote:
>
> >Message: 1
> >From: ??? <[email-masked] <javascript:;>>
> >To: "Y. Richard Yang" <[email-masked] <javascript:;>>
> >Message-ID: <[email-masked]
> <javascript:;>>
> >
> >Dear Richard,
> >
> _______________________________________________
> alto mailing list
> [email-masked] <javascript:;>
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>

-- 
Richard

---

From: ChenGuohai <[email-masked]>
Date: Wed, 15 Apr 2015 11:48:52 +0000

Huaming, Richard, Wendy,
I do support that one EP should be mapped into a single PID.
EPGs may be overlapped and policies are attached to EPGs. There are two introduced by EPG polocy. 
The first one is that there are some constraints in divide EPs to PID. For example there are fifteen hops between Group A(under 100.20.30.00/24) and Group B(under 100.20.50.00/24) and there is one policy says that EPs from 100.20.30.100 to 100.20.30.120 should not accept https request from Group B but could accept ones from Group C(under 100.20.90.0/24). So Group A should be divided to three PIDs.
The second is that one policy may be attached to multiple PIDs because EPs in one EPG are divided into several PIDs.

BR
Guohai
>>matching, but the result is a PID list,
Date: Wed, 15 Apr 2015 01:36:29 -0400
From: [email-masked]
To: [email-masked]
CC: [email-masked]
Subject: Re: [alto] ALTO extension for representing SDN policies

Wendy, Guohai,
Please see below.

should the client use?
Not to say that I am convinced about an approach, but here is one, motivated by TCAM: introducing priority to distinguish multiple matches (in two dimensions), by assigning priority values to different entries. How stupid is this idea?
Richard

        - Wendy Roome

alto mailing list

[email-masked]

-- 
Richard

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