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snmpconf PM MIB Policy vs. QOS Policy




>From time to time I see policies described simply as packet treatment
specs like:

  if (srcIP == a.b.c.d)
  then set DSCP to EF

I don't expect that implementations will execute scripts on a per-packet
basis to determine treatment of the packet as this would be somewhat
slow (understatement of the year!) The policy above would really be a
directive to the diffserv system (for example) telling it how to treat
packets - in other words it would all exist in the policyAction. But the
other problem is it doesn't say which interfaces should treat packets
this way.

>From the perspective of "what exactly do I do to configure my network",
I always look at packet-treatment-specs as incompletely specified -
policy fragments if you will. Since PM MIB policies are in the "what
exactly will happen to my network" category we need to be more specific.

To complete the example, this would really be:

policyFilter: your choice, something like "roleMatch("access")" or
"roleMatch("trunk") or "getvar("ifType") == 6" (i.e. isEthernet)
policyAction: add a diffserv path that treats packets with srcIP=a.b.c.d
a certain way

I suppose if I took the example at face value I would assume it meant
apply this treatment everywhere to all inbound and outbound interfaces
on all routers, switches, servers and desktops. If you really wanted to
do that, it would look like:

policyFilter: "return 1" // i.e. match everything (all interfaces
anyway)
policyAction: add a diffserv path that treats packets with srcIP=a.b.c.d
a certain way

But I don't think you ever want to do that.


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


Steve