[c-nsp] control-plane packet transmit priority on PFC + lan card platforms

[Andriy Bilous]

Control-plane traffic is governed by pak_priority inside the router
http://www.cisco.com/en/US/tech/tk543/tk544/technologies_tech_note09186a0080094612.shtml

This document is pretty old and doesn't reflect newer platforms, though
basics remain the same I believe.

Some little bit is also here:
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/WANQoS.html#wp96436

There are also recommendations how to treat CS6/CoS 6 traffic.

On Thu, Mar 18, 2010 at 3:23 PM, Anton Kapela <tkapela at gmail.com> wrote:

> List,
>
> I've been trying to determine if c6500 pfc2/3 and msfc2/3 support
> something like transmission priority for control-plane generated
> protocols (layer2 and 3 control protocols, that is -- lldp, ospf,
> isis, bgp, rsvp, stp, cdp, etc). I've read over this:
>
> "Egress LAN Port Scheduling.."
>
> http://www.cisco.com/en/US/docs/routers/7600/ios/12.2SXF/configuration/guide/qos.html#wp1698086
>
> ...and can observe that, at least for switchports set to 'mode trunk,'
> packets from the msfc2 or 3 are emitted with CoS 6 and 7 set, on
> packets that are clearly OSPF and PIM hellos. My assumption is that I
> can simply map CoS to queues (prio or regular) and assign a drop
> threshold like I normally do, but is this a safe assumption? 2nd
> question: is there already some "unconditional priority" queue hidden
> from MLS or the MQC configuration which is uses to transmit
> control-plane sourced messages?
>
> My recollection was that on sonet and various other lower-speed serial
> lines, things like PPP LCP packets were unconditionally transmitted
> head-of-line by whatever control plane was handling the port, ie.
> rsp4, 2800, 7200, etc.
>
> Best,
>
> -Tk
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