Ethernet Switches & Routers

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New Contributor
Posts: 2
Registered: ‎03-08-2010

Trust DSCP

Does anyone have the whereabouts of technical documentation of the hows and whys of the brocade trust dscp QOS setup ?    Such as how traffic is alocated in buffers.  I know the config and setup of Cisco QOS, but I  am at a loso s as to how the  Brocade default behavior is as far as traffic engineering with QOS works.

Super Contributor
Posts: 1,087
Registered: ‎12-13-2009

Re: Trust DSCP

Hi Jim,

     For what platform and prodcut?  Fastiron or NetIron?

Thanks

Michael.

New Contributor
Posts: 2
Registered: ‎03-08-2010

Re: Trust DSCP

We are using FCX's for layer 2 and 3 along with FLS and FWS switches in the closets.   

Super Contributor
Posts: 1,087
Registered: ‎12-13-2009

Re: Trust DSCP

Hi jmaples,

All taken from the Fastiron

Configuration Guide Chapter 20 - tere is a lot of good information in that schaper for you.

Dynamic Buffer Allocation for an IronStack

The IronStack architecture by default allocates fixed buffers on a per-priority-queue per packetprocessor basis. In instances of heavy traffic bursts to aggregation links, such as in stacking configurations or mixed speed environments, momentary oversubscription of buffers and descriptors may occur. This can lead to dropped packets during egress queuing.

Brocade FastIron stackable devices provide the capability to allocate additional egress buffering and descriptors to handle momentary bursty traffic periods, especially when other priority queues may not be in use, or may not be experiencing heavy levels of traffic. This allows users to allocate

and fine tune the depth of priority buffer queues for each packet processor. The CLI commands for this feature are qd-descriptor and qd-buffer. A descriptor points to one or more packet buffers.

Starting with release 07.1.00, the FCX is configured by default to have a fixed and shared pool of buffers and descriptors on a per-packet processor basis. The shared pool is apportioned among the 1G, 10G, 16G, and stacking ports. This is in addition to the fixed pool of buffers and descriptors. The shared pool is useful in scenarios of heavy traffic bursts to aggregation links. When qd commands (qd-descriptor and qd-buffer) for the port are configured, the shared pool is disabled and the user-defined buffer and descriptor thresholds are applied. The system will fall back to the default behavior when the qd commands are un-configured.

The 48-port Brocade stackable switch has 2 packet processors. The 24-port Brocade stackable switch has a single packet processor. In an IronStack, each stack unit has the possibility of two packet processors, but the second processor for a 24-port stack unit cannot be configured. The number of actual available packet processors depends on the type and number of switches in the stack.

For example, for an 8-unit stack of 48 ports, the packet processor numbering scheme is as follows:.

Stack unit 1 - packet processors 0 and 1

Stack unit 2 - packet processors 2 and 3

Stack unit 3 - packet processors 4 and 5

Stack unit 4 - packet processors 6 and 7

Stack unit 5 - packet processors 8 and 9

Stack unit 6 - packet processors 10 and 11

Stack unit 7 - packet processors 12 and 13

Stack unit 8 - packet processors 14 and 15

In this configuration, if stack unit 3 and stack unit 7 are 24-port devices, the odd-numbered packet

processors 5 and 13 cannot be configured, and do not exist, although they are reserved.

Configuration Steps

The buffer and descriptor allocation process occurs in four sequential steps using the qd-descriptor

command.

FastIron648S Switch# qd-descriptor

Syntax: qd-descriptor <stack-unit> <x> <y>

NOTE

For FastIron CX devices, when you reset buffer values for the 10 Gpbs ports, the buffer values for the rear-panel 10 Gbps/16 Gbps ports are also reset.

1. Configure the allowable port descriptors by entering a command similar to the following:

FastIron648S Switch#qd-descriptor 1 2 -

Syntax: qd-descriptor <DeviceNum> <PortTypeVal> <NumDescriptors>

"DeviceNum: 1-x

"PortTypeVal : 1 for 1Gbps, 2 for 10Gbps

"NumDescriptors : Number of descriptors to allocate (minimum 1, maximum 4095

2. Configure the port descriptors for the queue by entering a command similar to the following:

FastIron648S Switch#qd-descriptor 1 2 76 2

Syntax: qd-descriptor <DeviceNum> <PortTypeVal> <NumDescriptors>

<PriorityQueue>

"DeviceNum: 1-x

"PortTypeVal : 1 for 1Gbps, 2 for 10Gbps

"NumDescriptors : Number of descriptors to allocate (minimum 1, maximum 4095)

"PriorityQueue: Designates a specific queue (0 to 7)

3.Configure the allowable packet buffers by entering a command similar to the

following:

FastIron648S Switch#qd-buffer 1 2 76

Syntax: qd-buffer <DeviceNum> <PortTypeVal> <NumBuffers>

"DeviceNum: 1-x

"PortTypeVal : 1 for 1Gbps, 2 for 10Gbps

"NumDescriptors : Number of descriptors to allocate (minimum 1, maximum 4095)

3. Configure the allowable packet buffers for the queue by entering a command similar to the following:

FastIron648S Switch#qd-buffer 1 2 76 2

Syntax: qd-buffer <DeviceNum> <PortTypeVal> <NumBuffers> <PriorityQueue>

"DeviceNum: 0-x

"PortTypeVal: 1 for 1 Gbps or 2 for 10 Gbps

"NumBuffers: Number of buffers to allocate (minimum 1, maximum 4095)

"PriorityQueue: Designates a specific queue (0 to 7).

Processing of classified traffic

The Tust level in effect on an interface determines the type of QoS information the device uses for

performing QoS. The Brocade device establishes the trust level based on the configuration of

various features and whether the traffic is switched or routed. The trust level can be one of the

following:

Ingress port default priority

Static MAC address

Layer 2 Class of Service (CoS) value – This is the 802.1p priority value in the Ethernet frame. It

can be a value from 0 through 7. The 802.1p priority is also called the Class of Service.

Layer 3 Differentiated Services Code Point (DSCP) – This is the value in the six most significant

bits of the IP packet header 8-bit DSCP field. It can be a value from 0 through 63. These values

are described in RFCs 2472 and 2475. The DSCP value is sometimes called the DiffServ value.

The device automatically maps the DSCP value of a packet to a hardware forwarding queue.

ACL keyword – An ACL can also prioritize traffic and mark it before sending it along to the next

hop.

Given the variety of different criteria, there are many possibilities for traffic classification within a

stream of network traffic. For this reason, the priority of packets must be resolved based on which

criteria takes precedence.

.

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