skb->priority on arp packets

skb->priority on arp packets

[Marc Donner]

hi @all,

is it possible to set the skb->priority on arp packets generated by the 
kernel?
I want to to set the 802.1p priority on arp and ip packets on an interface. On 
ip packets, this can be done by the iptables CLASSIFY target and the 
skb->priority mapping from the vlan implementation.

any ideas?

thx
Marc

RE: skb->priority on arp packets

[Waskiewicz Jr, Peter P]

> is it possible to set the skb->priority on arp packets 
> generated by the kernel?
> I want to to set the 802.1p priority on arp and ip packets on 
> an interface. On ip packets, this can be done by the iptables 
> CLASSIFY target and the 
> skb->priority mapping from the vlan implementation.
> 
> any ideas?

Currently unclassified ip packets have skb->priority set in ipsockglue,
by translating the IP TOS field into a Linux priority.  This is not the
same priority as 802.1p, rather, it's a Linux-based OS priority
classification for dequeuing priority in schedulers such as sch_prio.
802.1p lives in the VLAN tag, which is separate from skb->priority.  I'd
suggest reading http://lartc.org/howto/lartc.qdisc.classless.html to see
what exactly skb->priority is used for in sch_prio and pfifo_fast, and
how the ip layer determines a packet's priority.  The skb->priority
field is also used in other ways in other qdiscs I'm not completely
familiar with, but it's not directly related to priority of the packet.
I'd need to look closer at those qdiscs to be specific.

That being said, the only way I can think of manipulating skb->priority
on arp packets (and actually setting it) is modifying a qdisc to set
skb->priority if it matches a filter created using the tc command.

Cheers,
-PJ Waskiewicz

Re: skb->priority on arp packets

[Ben Greear]

Waskiewicz Jr, Peter P wrote:
>> is it possible to set the skb->priority on arp packets 
>> generated by the kernel?
>> I want to to set the 802.1p priority on arp and ip packets on 
>> an interface. On ip packets, this can be done by the iptables 
>> CLASSIFY target and the 
>> skb->priority mapping from the vlan implementation.
>>
>> any ideas?
> 
> Currently unclassified ip packets have skb->priority set in ipsockglue,
> by translating the IP TOS field into a Linux priority.  This is not the
> same priority as 802.1p, rather, it's a Linux-based OS priority
> classification for dequeuing priority in schedulers such as sch_prio.
> 802.1p lives in the VLAN tag, which is separate from skb->priority.  I'd
> suggest reading http://lartc.org/howto/lartc.qdisc.classless.html to see
> what exactly skb->priority is used for in sch_prio and pfifo_fast, and
> how the ip layer determines a packet's priority.  The skb->priority
> field is also used in other ways in other qdiscs I'm not completely
> familiar with, but it's not directly related to priority of the packet.
> I'd need to look closer at those qdiscs to be specific.
> 
> That being said, the only way I can think of manipulating skb->priority
> on arp packets (and actually setting it) is modifying a qdisc to set
> skb->priority if it matches a filter created using the tc command.

If you do manage to get the skb->priority set, then you can use vconfig
to set up mapping between skb->priority and the VLAN priority field.

Thanks,
Ben

> 
> Cheers,
> -PJ Waskiewicz
> -
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-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com