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Re: snmpconf PM MIB Policy vs. QOS Policy



Hi all,

Steve Waldbusser wrote:

sw> From time to time I see policies described simply as packet treatment
sw> specs like:
sw> 
sw>   if (srcIP == a.b.c.d)
sw>   then set DSCP to EF
sw> 
sw> I don't expect that implementations will execute scripts on a per-packet
sw> basis to determine treatment of the packet as this would be somewhat
sw> slow (understatement of the year!) The policy above would really be a
sw> directive to the diffserv system (for example) telling it how to treat
sw> packets - in other words it would all exist in the policyAction.

I agree.  It would be configured in the diffserv MIB.  This kind
of statement is most definitely something that diffserv supports.

sw> But the
sw> other problem is it doesn't say which interfaces should treat packets
sw> this way.

If there are no further delimiters (e.g., if roleMatch("accounting")),
then I can only guess that you want this on all diffserv-enabled
interfaces.  It will be up to the filter to choose the
appropriate set of interfaces to do this to.

sw> From the perspective of "what exactly do I do to configure my network",
sw> I always look at packet-treatment-specs as incompletely specified -
sw> policy fragments if you will. Since PM MIB policies are in the "what
sw> exactly will happen to my network" category we need to be more specific.
sw> 
sw> To complete the example, this would really be:
sw> 
sw> policyFilter: your choice, something like "roleMatch("access")" or
sw> "roleMatch("trunk") or "getvar("ifType") == 6" (i.e. isEthernet)
sw> policyAction: add a diffserv path that treats packets with srcIP=a.b.c.d
sw> a certain way

I agree.  Applying this sort of packet treatment requires the
delimitation in the filter.

sw> I suppose if I took the example at face value I would assume it meant
sw> apply this treatment everywhere to all inbound and outbound interfaces
sw> on all routers, switches, servers and desktops. If you really wanted to
sw> do that, it would look like:
sw> 
sw> policyFilter: "return 1" // i.e. match everything (all interfaces
sw> anyway)
sw> policyAction: add a diffserv path that treats packets with srcIP=a.b.c.d
sw> a certain way
sw> 
sw> But I don't think you ever want to do that.

That would be foolish, I believe.  This is a typical sort
of multi-field classification that you'd want to do in an
access router to get a particular set of traffic placed into the
right diffserv aggregate.

sw> This is a confusing area because what we end up with is
sw> "policy-in-a-policy" or "QOS-Policy-in-a-Config-Policy". But it's
sw> necessary.

Cheers,

--
David Partain                  David.Partain@ericsson.com
Ericsson Radio Systems AB      Tel:    +46 13 28 41 44
Research and Innovation        Fax:    +46 13 28 75 67
P.O. Box 1248                  http://linlab.ericsson.se/~epkpart
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