Dell Networking S6000 Uživatelský manuál stáhnout pdf (Strana 714)

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But when queue 1 gets congested on switch B, PFC frames for tagged packets will not be generated as

PFC is not enabled on dot1p priority 5.

Support for marking dot1p value in L3 Input Qos Policy

In case the incoming packet is untagged and the packet which goes out to the peer is tagged, then the

dot1p should be marked appropriately using L3 Input Qos Policy. This is required because in the peer

switch PFC will be generated based on the dot1p value. Currently if the ingress is untagged and egress is

tagged, then dot1p priority 0(default) will be added as part of the tag header and from the next hop PFC

will be based on that dot1p priority. Support is added to mark the dot1p value in the L3 Input Qos Policy

in this feature. Hence it is possible to mark both DSCP and Dot1p simultaneously in the L3 Input Qos

Policy. You are expected to mark the Dot1p priority when the ingress packets are untagged but go out to

the peer as tagged

NOTE: L2 qos-policy behavior will be retained and would not be changed, that is we would not

allow to set both DSCP and Dot1p in the L2 Input Qos Policy.

Example case:

Consider that two switches A and B are connected back to back via a tagged interface. Consider the case

where untagged packets arrive on switch A, if you want to generate PFC for priority 2 for DSCP range

0-7, then you must need to match the interested traffic using the class map. You should create an L3

Input Qos Policy and mark vlan dot1p as 2. You have to associate both the L3 class map and L3 Input Qos

Policy to queue 1 using the policy map.

In switch B, global dot1p honoring should be enabled, this will queue the packets on queue 1 as the dot1p

will be 2 and PFC should be enabled for priority 2. The policy map applied on switch A need not be

enabled in switch B. When queue 1 in switch B gets congested, PFC will be generated for priority 2 which

will be honored in switch A.

You will not get the below CLI errors after adding this support:

Dell(conf)#qos-policy-input qos-input

Dell(conf-qos-policy-in)#set mac-dot1p 5

% Error: Dot1p marking is not allowed on L3 Input Qos Policy.

Dell(conf-qos-policy-in)#

You will also be able to mark both DSCP and Dot1p in the L3 Input Qos Policy:

Dell(conf)#qos-policy-input qos-input

Dell(conf-qos-policy-in)#set mac-dot1p 2

Dell(conf-qos-policy-in)#set ip-dscp 5

Dell Dell(conf-qos-policy-in)#

Weighted Random Early Detection

Weighted random early detection (WRED) is supported on the S6000 platform.

The WRED congestion avoidance mechanism drops packets to prevent buffering resources from being

consumed.

Traffic is a mixture of various kinds of packets. The rate at which some types of packets arrive might be

greater than others. In this case, the space on the buffer and traffic manager (BTM) (ingress or egress) can

be consumed by only one or a few types of traffic, leaving no space for other types. You can apply a

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Quality of Service (QoS)

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