Witch packets take precedence MPLS or IP?

Unanswered Question
May 25th, 2007

I have an interface that passes IP and MPLS traffic. When the router as to route the packets witch one as precedence?

I think its MPLS because it only as to look for the tag, but I haven?t found Cisco documentation for that.


David Costa

I have this problem too.
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frenzeus Fri, 05/25/2007 - 09:30

When u say which takes precedence, i think it would depend on what your outgoing qos policy is on the interface, if there is any & also whether the interface hardware queue (tx_ring) is congested, as only then will ur qos policy kick in. If you have no qos policy attached to the outgoing interface, then it depends on whether ip or mpls packet gets into the hardware tx queue first.


d-costa Fri, 05/25/2007 - 10:13

I don?t have any qos policy applied to the interface.

When you say is the first that gets into the hardware queue it?s because of the interface queue being a FIFO?

My doubt is before getting to the hardware queue what happens?

As I want to implement a MPLS solution for a client and still use IP for my traffic. I don?t want my traffic being neglected.


David Costa

frenzeus Fri, 05/25/2007 - 10:48

depends on what interface is used, but the default on lower speed links (x kbps

RaoulDukeGC Fri, 05/25/2007 - 11:29

Can you expound upon the configuration of the SP network? When you say IP, is that Internet bound traffic and MPLS is internal data?

jiangu Fri, 05/25/2007 - 21:59

If there is a LFIB entry for the destination prefix, CEF will label switch the packet. But the reason is not because it only has to look for tag, from router's point of view, there is no difference between looking for 20-bit tag or looking for a 32-bit IP, TCAM techonolgy can achieve line-rate lookup in both cases.

swaroop.potdar Sat, 05/26/2007 - 01:46

As a rule the router will always see the mpls label first, if its not there it will route it as per the layer 3 header info.

As far as you question to apply QOS policy for MPLS and IP goes for mix traffic going on a interface, you can match EXP and IP PREC/DSCP in the same class map, in the same service policy and apply it on the interface.

This way it will give the desired behaviour for MPLS as well as IP traffic both at the same time.




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