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ONT Notes – AutoQoS

Aaron Conaway — Wed, 10 Feb 2010 23:02:04 +0000

AutoQoS benefits
- Automates QoS for most deployments
- Protects business-critical apps to maximize availability
- Simplifies QoS deployments
- Reduces configuration errors
- Cheaper, faster, and simpler deployments
- Follows DiffServ
- Allows complete control over QoS configs
- Allows modification of auto-generated configs
AutoQoS phases of evolution
- AutoQoS VOIP – Early version that configures the basics without discovery
- AutoQoS for Enterprise – Second version that only runs on routers and uses two-step process
  - Autodiscovery using NBAR
  - Generation of class maps
AutoQoS key elements
- Application classification
- Policy generation
- Configuration
- Monitoring and reporting
- Consistency
Interfaces that you can configure AutoQoS on
- Serial ifs with PPP and HDLC
- FR point-to-point subifs (NOT multipoint)
- ATM point-to-point subifs
- FR-to-ATM links
Prerequsites
- No Qos policy already configured on if
- CEF enabled on if
- Correct bandwidth configured on if
- IP address on low-speed if
Configuring AutoQoS Enterprise on a router (NOT a switch)
- auto qos discovery – begins discovery process
- auto qos – generates and applies MQC-based policies
Configuring AutoQoS VOIP
- auto qos voip [ trust | cisco-phone ]
Verifying AutoQoS on router
- show auto discovery qos – get autodiscovery results
- show auto qos – examine configuration generated
  - Number of classes
  - Classification options
  - Marking options
  - Queuing mechanisms
  - Other QoS mechanisms
  - If, subif, PVC where policy is applied
- show policy-map interface – look at if stats
Verify AutoQoS VOIP
- show auto qos
- show policy-map interface
- show mls qos maps – shows CoS to DSCP mappings
Possible issues with AutoQoS
- Too many traffic classes – manually consolidate some
- Configuration doesn’t change – rerun AutoQoS
- Configuration may not fit your situation – fine-tune it by hand
Fine-tuning AutoQoS
- Use QPM
- CLI
- copy policy into editor, change, reapply
AutoQoS can match on characteristics besides ACLs and NBAR
- match input interface
- match cos
- match ip precedence
- match ip dscp
- match ip rtp

Aaron Conaway

I like to lean my head to the left, hit it with the palm of my right hand, and document what knowledge falls out.

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ONT Notes – Pre-classify and End-to-end QoS

Aaron Conaway — Thu, 04 Feb 2010 03:13:53 +0000

VPNs (Didn’t ISCW cover this?)
- Provide
  - Confidentiality
  - Integrity
  - Authentication
- Types
  - Remote-access
    - Client-initiated
    - NAS-initiated
  - Site-to-site
    - LAN-to-LAN
    - Extranet
L3 Tunneling protocols
- GRE
- IPSec
Pre-classify allows traffic to be classified before being sent across a tunnel or crypto-ed.
- qos pre-classify
- Provides a view into the original IP headers
- To classify on pre-tunnel header, apply the policy to the tunnel interface WITHOUT pre-classify.
- To classify on post-tunnel header, apply the policy to the physical interface WITHOUT pre-classify.
- To classify on pre-tunnel header, apply the policy to the physical interface WITH pre-classify.
SLA – agreement with provider to guarantee QoS mechanisms across their network based on your markings.
- Assures availability, loss, throughput, delay, and jitter.
End-to-end QoS
- To be effective, each hop in the path must have QoS configured similarly.
- Necessary in three locations
  - Campus – within the customer network
  - The edges – customer facing the provider, provider facing customer
  - On the provider network
QoS tasks
- Campus access switches
  - Speed/duplex settings
  - Classification
  - Trust
  - Phone/access switch configs
  - Multiple queues on switch ports, including priority for VOIP
- Campus distribution
  - L3 policing and marking
  - Multiple queues on switch ports, including priority for VOIP
  - WRED
- WAN edge
  - SLA definitions
  - LLQ
  - LFI
  - WRED
  - Shaping
- Provider cloud
  - Capacity planning
  - PHB
  - LLQ
  - WRED
Enterprise campus QoS implementation
- Implement multiple queues to avoid congestion
- Assign VOIP and video to highest priority queue
- Esablish trust boundaries
- Use policing to rate-limit excess traffic
- Use hardware QoS when possible
Control Plane Policing (CoPP)
- Applies QoS policy to traffic destined for the router
  - Routing protocols
  - Management protocols
- Can be used to avoid DOS attacks
- Applied to control-plane in global config

Aaron Conaway

I like to lean my head to the left, hit it with the palm of my right hand, and document what knowledge falls out.

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ONT Notes – Congestion Avoidance, Policing, Shaping, and Link Efficiency

Aaron Conaway — Wed, 03 Feb 2010 03:09:47 +0000

Tail drop drawbacks
- TCP synchronization – Dropping TCP packets from different flows can cause them all to window down and back up again at the same time in cycles.
- TCP starvation – Non-TCP or aggressive flows can starve everyone else out when TCP throttles back.
- No differentiated drop – Tail drop doesn’t care who you are, so you get dropped if the queue is full.
RED – Random Early Detection
- Avoids tail drop by randomly dropping packets from the queue before it gets full
- Only dropped TCP flows slow down instead of everyone who has sent a packet since the queue filled
- Queues are smaller.
- Link utilization is more efficient
- Configured with
  - Minimum threshold – start dropping when the queue is this size
  - Maximum threshold – if the queue is this big, start tail dropping
  - Mark probability denominator (MPD) – 1/MPD is the ratio of packets to drop when between the thresholds
WRED – Weighted RED
- Based on IP precedence or DSCP values
- Less-important packets are dropped more aggressively than important packets
- Applied to an interface, VC or a class within a policy map
CBWRED – Class based WRED
- Configured with CBWFQ
Policing
- Limits subrate bandwidth (give you 100kbps on a T1)
- Limits traffic of certain applications
- Any traffic that exceeds police is dropped or re-classified; it’s a hard limit
- Inbound or outbound
Shaping
- Sets a limit but buffers any in excess
- Requires memory to store the buffer
- Buffers = delay and/or jitter
- Outbound only
- Can respond to network signals like BECNs and FECNs
Token and bucket
- The queue is a bucket; if a byte of data needs to be sent, it needs a token.
- If there are enough tokens, the traffic is considered conforming.
- If there aren’t enough tokens, the traffic is considered exceeding, which triggers the drop (policing), re-classify (policing), or buffer (shaping).
Frame relay traffic shaping (FRTS)
- Only controls frame relay traffic
- Applied on subif or DLCI
- Support fragmentation and interleaving
- Reacts to FECNs and BECNs
Compression
- Removed redundancy and patterns in data
- Less data = less latency
- Hardware compression or hardware-assisted compression does not involve the main CPU
- Software compression does
- Payload compression
- Header compression
Link fragmentation and interleaving
- Small data might be waiting for larger data pieces to finish sending
- Chunks data into smaller fragments so they don’t have to wait
- Interleaving shuffles flows in the Tx queue

Aaron Conaway

I like to lean my head to the left, hit it with the palm of my right hand, and document what knowledge falls out.

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