Aaron's Worthless Words

• 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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• 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.

More Posts - Website

• 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.

More Posts - Website

Here are some more notes from my studies.  Of course, no one cares about them but me, but it’s my blog.  I’m sure someone will find it useful.  Please help to correct dumbass mistakes.

• Congestion
  • Speed mismatch – traffic leaves a lower-bandwidth interface than the one it came in on
  • Aggregation problem – lots of links with one egress of equal bandwidth
  • Confluence problem – a bunch of traffic needs to egress out of the same interface
• Queuing
  • Transmit queue (TxQ) – hardware queue; there’s only one you can’t touch
  • Software queue – where packets wait to be sent; there are many queue-types that you modified to police traffic
• FIFO
  • If I beat you to the router, I leave the router first.
  • Possible long delays, jitter, and starvation
• Priority queuing (PQ)
  • Four queues
    • High-priority
    • Medium-priority
    • Normal-priority
    • Low-priority
  • Scheduler starts from high and work to low
  • When the high queue is empty, it processes a packet from medium, then starts all over
  • Can you say starvation?
• Round robin queuing (RR)
  • One packet from this queue, one from the next, etc., then start over again
• Custom queuing (CQ)
  • Weighted round robin
  • Queues are given weights (bandwidth guarantees)
• Weighted Fair Queuing (WFQ)
  • Default queuing on slow links ( < E1 )
  • Divides traffic into flows
  • Equal bandwidth is given to each flow
  • Provides faster scheduling to low-volume flows
  • Provides more bandwidth to higher-priority flows
  • Flows identified by a hash
    • Source IP
    • Destination IP
    • Protocol number
    • ToS
    • Source port
    • Destination port
  • Each unique has is a new flow
  • No way to allocate bandwidth among the flows
  • By default, up to 256 queues are made, but that is changeable to a power of 2 between 16 and 4096
  • If the max number of flows is reached, queues are reused for other flows
  • If a queue is full, a packet may be dropped.
  • WFQ early dropping drops packets when the queue reaches the congestive discard threshold (CDT)
  • Advantages
    • Simple configuration
    • No starvation
    • Guarantee processing of all flows
    • Drops packets from big-hitter flows
    • Faster service no low-hitters (interactive) flows
    • Standard on (nearly) all IOS devices
  • Disadvantages
    • Classification and scheduling are not configurable
    • Only on slow links
    • No guarantee of bandwidth or delay
• Class-based Weighted Fair Queuing (CBWFQ)
  • User-defined queues for flexibility
  • Configured with class-maps via MQC
  • Weights are calculated based on values give in class-map
    • Bandwidth – guarantee this much bandwidth
    • Bandwidth percent – give me this much of the available bandwidth
    • Bandwidth remaining percent
  • Advantages
    • User-defined traffic classes
    • Each queue gets its own bandwidth
    • Scalability
  • Disadvantages
    • No delay guarantee (not good for real-time application like voice)
  • Configuring

    class-map TESTCM1
     match access-group 100
    !
    class-map TESTCM2
     match access-group 200
    !
    policy-map TESTPM
     class TESTCM1
      bandwidth 64
     class TESTCM2
      bandwidth 128

• Low-latency Queuing
  • Includes strict priority queue for delay-sensitive data
  • Strict priority queue is policed to avoid starvation of other queues
  • Configured the same way as normal CBWFQ, but with the priority keyword
  • This configuration makes TESTCM2 a priority queue

  class-map TESTCM1
   match access-group 100
  !
  class-map TESTCM2
   match access-group 200
  !
  policy-map TESTPM
   class TESTCM1
    bandwidth 64
   class TESTCM2
    priority bandwidth 128

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.

More Posts - Website

Here’s another set of notes from my ONT studies.  I’m sure someone will find it useful.  Please help to correct dumbass mistakes.

• Classification is done with traffic desriptors
  • Ingress interface
  • CoS value on ISL or 802.1P frames
  • Source/destination IP address
  • IP Precedence or DSCP value
  • MPLS EXP
  • Application type
• Layer 3 QoS
  • Type of Service (ToS) is 8-bit field.
  • First 3 bits of ToS are the IP precedence.
  • First 6 bits of ToS are the DSCP value.
  • Last 2 bits of ToS are explicit congestion notification (ECN).
• Layer 2 QoS
  • Ethernet
    • Class of Service (CoS)
    • On 802.1P frame
    • 3-bit priority (PRI) field
      • 000 – Routine – Best-effort
      • 001 – Priority – Medium priority
      • 010 – Immediate – High priority
      • 011 – Flash – Call signaling
      • 100 – Flash-Override – Video conferencing
      • 101 – Critical – Voice bearer
      • 110 – Internet – Reserved
      • 111 – Network – Reserved
  • Frame Relay
    • 1-bit discard eligible (DE) field
  • ATM
    • 1-bit cell loss priority (CLP) field
  • MPLS (layer 2 1/2)
    • 3-bit experimental (EXP) field
    • By default, the 3 most significant ToS bits (IP Precedence bits) are copied to EXP
• Per-hop Behavior (PHB)
  • “an externally observable fowarding behavior of a network node toward a group of IP packets that have the same DSCP value”
  • In other words, treat packets with the same DSCP value in the same manner – scheduling, queuing, policing, etc.
  • Behavior aggregate (BA) is a group of packets with the same DSCP value
• DSCP
  • DSCP is chopped up into 4 PHBs
    • Class selector PHB – (000) old IP precedence compatibility
    • Default PHB – (000) best effort
    • Assured forwarding (AF) PHB – (001, 010, 011, 100) guarantee bandwidth
      • Provides 4 queues for 4 classes of traffic (AF1-4)
      • Also specifies drop preference (ex., AF41, A13) where second number is preference (higher is more probable to be dropped)
      • Each queue must have (W)RED to avoid drops
      • No queue is any better than the other
      • Backward compatible with IP precedence
  • • Expedited forwarding (EF) PHB – (101) low delay
      • Minimum delay
      • Bandwidth guarantee
      • Policing
• Trust boundaries
  • Establish DSCP values as close to the source as possible
    • On the device (IP phone), access switch, or distribution switch
    • The core should never assign DSCP values
  • Only trust DSCP values from devices you trust
  • Examine and rewrite values from untrust sources
• Network-based Application Recognition (NBAR)
  • Protocol discovery – discovers what protocols you’re running on your network
  • Traffic statistics collection – keeps tracks of stats on each protocol
  • Traffic classification – NBAR protocols can be used in class-maps to define traffic to be services
  • Packet description language models (PDLMs) – table of what protocols NBAR recognizes
  • Limitations
    • Doesn’t work on EtherChannel interfaces
    • Only handles 24 URLs, hosts, or MIME types
    • Only analyzes first 400 bytes of the packets
    • Requires CEF
    • Doesn’t work on HTTPS, multicasts, or fragments
    • Ignored traffic destined for the router itself
  • NBAR commands
    • Router(config)# ip nbar pdlm pdlm-name : Update the PDLM table
    • Router(config)# ip nbar port-map protocol-name [tcp|udp] port-number : Adds an entry to the PDLM table
    • Router# show ip nbar port-map protocol-name : Shows what’s in the PDLM table
    • Router# show ip nbar protocol-discovery : Shows what’s been discovered
    • Router(config-cmap)# match protocol name : a class-map match for an NBAR-discovered protocol
  • Special protocol matching
    • Can match beyond the port number with deep packet inspection
    • Matches HTTP hostname, URL, or MIME type
    • Matches fast-track P2P
    • Matches RTP content

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.

More Posts - Website