[j-nsp] Junos CoS - how to set PLP bit depending on a Bandwi dth threshold ?

[Robert O'Hara]

Hi Mario..

When two streams are ingressing the router and are destined for the queue, Drop Profiles, along with Policers or Filters, can make the packets of one stream more eligible for discard than the other.

The PLP (packet loss priority) bit, which can be flexibly assigned using a firewall filter match statement may assign loss priority HIGH as an action for a packet that meets the match criteria (as noted in Guy's earlier email).   The PLP bit is not part of the IP Precedence or DSCP field.  The PLP bit is an internal router value that is associated with the individual packet and lives within the (notification*). The PLP bit never becomes part of the transmitted packet.

* The notification is the internal message that is the result of lookup in the packet forwarding engine (PFE).  So, do not confuse PLP with IP Precedence or DSCP.

So, if we want to use PLP to assign high loss to one type of traffic, we would perform the following:

For example:

[edit firewall]
M20># show
family inet {
    filter Set_PLP {
        term 1 {
            then {
		      loss-priority high;
                accept;
            }
        }
    }
} 


Next, the filter is assigned to the ingress logical interface whose traffic will have a higher discard eligibility. 

[edit interfaces so-0/2/0]
M20># show
no-keepalives;
encapsulation ppp;
sonet-options {
    fcs 32;
}
unit 0 {
    family inet {
        filter {
            input Set_PLP;
        }
        address 1.1.1.1/24;
    }
    family mpls;
} 

Next, the drop profiles are created and queue fullness/drop points are assigned:

[edit class-of-service drop-profiles]
M20># show
in-contract {
    fill-level 100 drop-probability 100;
}
discard-eligible {
    interpolate {
        fill-level [ 0 10 15 17 19 21 22 23 24 25 26 27 28 29 30 ];
        drop-probability [ 0 1 3 5 7 12 15 19 25 31 39 50 63 79 100 ];
    }
} 

Finally, the drop-profiles are assigned to the correct scheduler:

[edit class-of-service schedulers best-effort]
M20># show
best-effort {
    transmit-rate remainder exact;
    priority low;
    drop-profile-map loss-priority low protocol any drop-profile in-contract;
    drop-profile-map loss-priority high protocol any drop-profile discard-eligible;
} 

So - the PLP bit is not part of any published prioritaztion scheme and is relevant only within Junos.  

Thanks,

Bob O'Hara  

Systems Engineer
Juniper Networks - 'Every Bit IP'

...........................................
. Email:           rohara at juniper.net     .
. Web:             http://www.juniper.net .  
...........................................



-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net
[mailto:juniper-nsp-bounces at puck.nether.net]On Behalf Of
MPuras at solunet.com
Sent: Tuesday, August 05, 2003 9:51 AM
To: Guy.Davies at telindus.co.uk; mourad.berkane at lambdanet.fr;
juniper-nsp at puck.nether.net
Subject: RE: [j-nsp] Junos CoS - how to set PLP bit depending on a
Bandwi dth threshold ?


Depending on your interfaces, you "could" also set the PLP bit by
configuring the receive-bucket on the interface and setting the overflow
setting to "tag" although I would prefer using firewall policer. 

Just for clarification, does Juniper also uses the LSB in the precedence
field to tag a packet with a drop precedence?  I have heard that they use a
different bit (I think it was bit 2) and that it is propriatery.   Is it the
same bit when using IP Precendence or DSCP?  Could anyone clarify please?


Also on the example below, why would you want to discard the traffic if you
are setting the PLP and assigning it to a FC?   

Thanks for your help.


Thanks, 

Mario Puras 
SoluNet Technical Support
Mailto: mpuras at solunet.com
Direct: (321) 309-1410  
888.449.5766 (USA) / 888.SOLUNET (Canada) 



>-----Original Message-----
>From: Guy Davies [mailto:Guy.Davies at telindus.co.uk]
>Sent: Tuesday, August 05, 2003 8:51 AM
>To: 'Mourad BERKANE'; juniper-nsp at puck.nether.net
>Subject: RE: [j-nsp] Junos CoS - how to set PLP bit depending on a
>Bandwi dth threshold ?
>
>
>  
>-----BEGIN PGP SIGNED MESSAGE----- 
>Hash: SHA1 
>
>Hi Mourad, 
>  
>The simple answer is "yes". 
>  
>firewall { 
>    policer <blah> { 
>        if-exceeding { 
>            bandwidth-percent N; 
>            burst-size M; 
>        } 
>        then { 
>             loss-priority (high|low); 
>             forwarding-class <foobar>; 
>             discard; 
>       } 
>    } 
>} 
>  
>Regards, 
>  
>Guy 
>
>- -----Original Message----- 
>From: Mourad BERKANE [ mailto:mourad.berkane at lambdanet.fr
><mailto:mourad.berkane at lambdanet.fr> ] 
>Sent: Tuesday, August 05, 2003 1:24 PM 
>To: juniper-nsp at puck.nether.net 
>Subject: [j-nsp] Junos CoS - how to set PLP bit depending on a 
>Bandwidth
>threshold ? 
>
>
>
>
>Is it possible with current Junos version to associate the 
>class-of-service
>classification of the *internal* CoS PLP bit(used by RED drop 
>profile) with
>a bandwidth policer:
>
>IF BW > threshold       THEN    plp-set         ELSE    plp-clear 
>
>Hope it's possible :-) 
>
>Thanks in advance. 
>Mourad 
>
>
>-----BEGIN PGP SIGNATURE----- 
>Version: PGP 8.0 
>
>iQA/AwUBPy+oSI3dwu/Ss2PCEQIA/QCgzGZdEtpWyhkC1Gr1KRb/fnCja+IAn2GN 
>IvGoUWeB1s4VlBn+xdxPcibg 
>=EO6N 
>-----END PGP SIGNATURE----- 
>  
>
>  
>  
>
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