Qos on Aaron's Worthless Words

QoS? Really?

Sat, 20 Aug 2016 00:00:00 +0000

I wrote this post during Cisco Live and said “I’ll just give it a once-over tonight and publish it.” That was something like 6 weeks ago now. What a loser I am.

Yes, really. QoS has actually gotten some attention this year. After how many years of living in the dark and being feared by junior and senior engineers alike, we’re seeing some really cool technologies coming out for it.

QoS Notes - IPP and DSCP Values

Tue, 30 Jul 2013 00:00:00 +0000

This is a study note post, so please don’t take this as written. I’m not the authority on the subject, so please correct me if needed.

Back in the day, somebody decided that we all needed to have a Type of Service (ToS) field in the header of IP packets. Only God knows what this spawn of Satan wanted to do with it, but we’re stuck with it on the CCIE R&S exams.

Stubby Post - Time-based ACLs and Policy-maps

Wed, 28 Apr 2010 00:00:00 +0000

Certain divisions of the company tend to shoot themselves in the foot by kicking off large file transfers during business hours, so I had a thought that maybe we could use time-based ACLs to do some QoSing for those guys. I fired up GNS3 with a 3600 running 12.4(25b) with some virtual PCs on it’s Ethernet interfaces.

time-range BUSINESSHOURS
 periodic daily 8:00 to 17:00
!
ip access-list extended PINGS
 permit icmp any any time-range BUSINESSHOURS
!
class-map match-all PINGS
 match access-group name PINGS
!
policy-map PM-F0/0-OUT
 class PINGS

First, I set the router’s time to outside of the time range and sent some pings over.

NBAR and HTTP Data Conversations

Mon, 08 Mar 2010 00:00:00 +0000

I’m still working on the ONT test and doing labs, so I marked up a lab for me to work. I’m using the same setup as I did last time. The two routers are 3640s running 12.4(25b).

Part of the lab was to identify HTTP traffic coming into F0/0 and mark it as CS3. That’s pretty easy, right? Of course, the lab I made up was a little more complicated, but the point comes clear with a simpler example.

QoS Pre-classify and Class-map Order

Sat, 06 Mar 2010 00:00:00 +0000

I’m still studying for the ONT test, so I did some labs tonight. One of them was to demonstrate the qos pre-classify command for tunnel interfaces. When you have a packet sent over a GRE tunnel, the ToS field gets copied to the GRE packet, but there’s no way to see the original packet’s higher-level headers on the way out the interface. This can be a problem if your service policy needs to see protocol, port, IPs, etc. The fix for that is to enable qos pre-classify on the tunnel interface and cyrpto map; doing so will provide a copy of the original packet to the physical interface to classify the packet thoroughly.

ONT Notes - QoS On Wireless Networks

Thu, 11 Feb 2010 00:00:00 +0000

Wireless LANs (WLANs)
- Extensions to wired LANs
- Carrier sense multiple access collision avoidance (CSMA/CA) as media access method
- Uses distributed coordinated function (DCF) for collision avoidance
- DCF is based on RF carrier sense, inter-frame spacing (IFS), and random wait timers
Wifi QoS standards
- 802.11e
  - IEEE standard
  - 0-7 priority levels
- Wifi Multimedia (WMM)
  - Four access categories
    - Platinum (voice) - 6 or 7 802.11e
    - Gold (video) - 4 or 5 802.11e
    - Silver (BE) - 0 or 3 802.11e
    - Bronze (Background) - 1 or 2 802.11e
- WMM and 802.11e replace DCF with EDCF
Cisco Split-MAC
- Splits functions between Lightweight access points (LWAPs) and WLAN controllers (WLCs)
- LWAPs handle real-time functions
  - Beacon generation
  - Probe transmission and response
  - Power management
  - 802.11e/WMM scheduling and queuing
  - Packet buffering
  - Encryption/decryption
  - Control frame/message processing
- WLCs handle non-real-time functions
  - Association/disassociation/reassociation
  - 802.11e/WMM resource reservation
  - 802.1x EAP
  - Key management
  - Authentication
  - Fragmentation
  - Ethernet-WLAN bridging
End-to-end QoS
- Step 1: WLC copies DSCP from switch to outer DSCP and outer 802.1p and sends to LWAP over LWAPP tunnel
- Step 2: LWAP copies outer DSCP from WLC to 802.11e/WMM field and sent to client
- Step 3: LWAP copies 802.11e/WMM value from the client to outer DSCP and sends it to WLC
- Step 4: WLC copies outer DSCP from WLAP to 802.1p (CoS) fields and sends it to the switch
Web interface (do you even need to know this?)
- Controller>QoS Profiles
  - Per-User Bandwidth Contracts - set avg data rate, burst data rate, avg real-time rate, and burst real-time rate
  - Over the Air QoS
    - Maximum RF usage per AP (%)
    - Queue Depth - queue size before dropping packets
    - Wired QoS Protocol - 802.1p or None
- Controller>WLANs>Edit
  - For each WLAN ID, set the QoS value: plat, gold, silver, bronze
  - WMM Policy
    - Disabled - 802.11e/WMM QoS requests are ignored
    - Allowed - 802.11e/WMM QoS requests are sent
    - Required - 802.11e/WMM QoS requests are required

ONT Notes - AutoQoS

Wed, 10 Feb 2010 00:00:00 +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

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

Thu, 04 Feb 2010 00:00:00 +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

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

Wed, 03 Feb 2010 00:00:00 +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

ONT Notes - Queuing

Sun, 24 Jan 2010 00:00:00 +0000

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

ONT Notes – Classification, Marking, and NBAR

Fri, 22 Jan 2010 00:00:00 +0000

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

ONT Notes - Intro to QoS

Thu, 21 Jan 2010 00:00:00 +0000

I’ll try to keep it a little shorter this time.

Major issues for converged enterprise networks

Available bandwidth: competition among applications
- Fixes
  - Increase bandwidth: More power!
  - Properly queue based on classification and marking: QoS
  - Compress: cRTP, TCP header compression, etc.
Delay: Lead time to get a packet to the destination
- Types of delay
  - Processing delay: routing, switch delay
  - Queuing delay: how long a frame stays in an output queue
  - Serialization delay: how long to put the frame on the wire
  - Propagation delay: the time to cross the physical medium
Jitter (delay variation): Variation is the delay
- Different delays mean different arrival times
- De-jitter buffers save up packets to reduce jitter (like the old CD writers)
- Fixes
  - More bandwidth
  - Prioritize sensitive data and forward first
  - Remark (reclassify) packets based on sensitivity
  - Enable L2 payload compression: make sure compression delay isn’t worse than the jitter
  - Use header compression
Packet loss: Packets are lost in the network somewhere
- Fixes
  - More bandwidth
  - Increase buffers space: more room for the queue on the interface
  - Provide guaranteed bandwidth: Queuing and QoS
  - Congestion avoidance
    - Random Early Detection (RED) and weighted RED (WRED) drop packets before the queue is full
    - Selective dropping is better than FIFO or LIFO dropping

QoS History

Cheat Sheets from Packetlife.net

Wed, 28 May 2008 00:00:00 +0000

My friend Josh over at blindhog.net has found a collection of cheat sheet gems for the network dude(tte). There’s sheets on BGP, OSPF, Subnetting, QoS, connector types, and more. Check it out.

Cheat Sheets - Packetlife.net

Qos Priority

Tue, 08 Apr 2008 00:00:00 +0000

We just talked about tagging traffic and policing traffic, but we haven’t talked about prioritizing traffic. Tagging just sets a value in the header. Policing sets a “bandwidth ceiling” that can’t be crossed. Prioritization guarantees a certain amount of bandwidth for a flow/app/etc. no matter what’s going on.

Prioritization offers you a certain amount of bandwidth; it doesn’t carve it out and hand it over. If you’re using less than the priority value, you only get as much as you need and the rest of the reserved bandwidth goes into the pot for everyone to use. As priority traffic grows, though, you’re given as much as you need up to the configured value. When you go over that, your extra traffic just goes into the best-effort queue with everything else (Note: Don’t go over the limit with VOIP traffic. Echoes and artifacts suck). For example, if you give your VOIP traffic 70% of the bandwidth of an interface but are only using 40%, the other 30% can be used by the other apps on the line. If you’re using 80%, that 10% over is competing with everything else for bandwidth.

QoS Policing

Mon, 07 Apr 2008 00:00:00 +0000

We covered QoS tagging the other day, but that just marks packets. I think you’re old enough now that we should actually do some policing. Policing is where you restrict the amount of bandwidth that a flow or set of flows can use. For example, say you have a site that serves webpages to the rest of the network. HTTP is the primary function, but the SysAdmins also have to maintain the boxes via SSH, right? To make sure that their SSH sessions don’t squash the bandwidth that your HTTP servers need, you can police the SSH sessions by giving the a bandwidth ceiling that they can’t cross.

Qos Tagging

Sun, 06 Apr 2008 00:00:00 +0000

I’ve been trying to get some experience on Cisco VOIP, and, as you probably know, Quality of Service (QoS) is quite important in that realm. Since VOIP is very time-sensitive, you have to be sure your gear delivers the voice packets first. A packet in an HTTP transaction can wait another 200ms without any problems. A voice packet with another 200ms on it means static and digital artifact on the line. Not good. There are lots of things you can do in the world of QoS, but I’ll talk about tagging this time (I may get to some of the other topics later, though).