Archive for the ‘qos’ tag
Stubby Post – Time-based ACLs and Policy-maps
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.
R1#sh clock
00:01:13.107 UTC Wed Apr 28 2010
R1#sh access-lists
Extended IP access list PINGS
10 permit icmp any any time-range BUSINESSHOURS (inactive)
R1#sh policy-map int f0/0
FastEthernet0/0
Service-policy output: PM-F0/0-OUT
Class-map: PINGS (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps
Match: access-group name PINGS
Class-map: class-default (match-any)
11 packets, 1140 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
Alright, that’s expected. Now let’s set the clock to within the time range and repeat.
R1#sh clock
13:00:12.887 UTC Wed Apr 28 2010
R1#sh access-lists
Extended IP access list PINGS
10 permit icmp any any time-range BUSINESSHOURS (active) (10 matches)
R1#sh policy-map int f0/0
FastEthernet0/0
Service-policy output: PM-F0/0-OUT
Class-map: PINGS (match-all)
10 packets, 980 bytes
5 minute offered rate 0 bps
Match: access-group name PINGS
Class-map: class-default (match-any)
20 packets, 1970 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
How about that? Time-based ACLs seems to work with policy-maps. I didn’t know that.
NBAR and HTTP Data Conversations
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.
class-map match-all HTTP match protocol http ! policy-map PM-F0/0-IN class HTTP set dscp cs3 ! interface FastEthernet0/0 service-policy input PM-F0/0-IN
I fired off a small script on TestHost1 to repeatedly do NMap scans on TCP/80 of TestHost2 to generate some traffic.
root@bt:~#while ( true ) do nmap -sT -p 80 -v -n 172.16.2.101; done
I let that run for a while and checked out the service policy on F0/0; there were absolutely no matches on that class.
R1#sh policy-map int f0/0 input class HTTP
FastEthernet0/0
Service-policy input: PM-F0/0-IN
Class-map: HTTP (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: protocol http
QoS Set
dscp cs3
Packets marked 0
I thought that was strange, so I kept the script running and captured the traffic coming out of S1/0. Looking at the packets in Wireshark showed that none of the HTTP packets were showing up as being marked as CS3; they’re all set to the default DSCP value.
No matter how many NMap scans cycled through, the class never incremented a bit. I let it run for two full minutes and generated a few hundred HTTP packets, but there was still nothing.
On a whim, I enabled NBAR protocol discovery on F0/0 to see if that would shed any light on my mess. Guess what I found. That’s right; there were no HTTP matches to NBAR, either. That makes sense since the class-map I defined uses the NBAR protocol. Alright, so it seems that it’s NBAR that doesn’t see the packets as HTTP, but why?
Looking through the packet captures again, I noticed that there was no real data in the streams. I saw the 3-way TCP handshake (a.k.a., my signature wrestling move) and then a RST,ACK. I only told NMap to check if the port was open, so I changed the while loop a bit and enabled version detection with the “-sV” flag. This time when I can the script, NMap was actually getting the HTTP banner. It was much traffic, but it was an actual HTTP conversation, so I checked NBAR again. Success! The same for the class, too.
For craps and smiles, I created a class-map that matched SIP, added it to the same policy-map, and set NMap after TCP/5060 without version detection. Without having a real SIP conversation, the class counters incremented as long as I was sending packets. That would seem unexpected until you realize that NBAR has some advanced knowledge of HTTP; you can actually match on URLs, hostnames, and MIME-types. I guess that means it also know when a real HTTP conversation is taking place.
To finish out the testing, I added an ACL to the router that matched any-any-eq-80. I made the class-map into a match-any and added the ACL. Since the ACL just matches the destination port and doesn’t care what the content is, every packet sent matched the class as expected. I remember reading several places and seeing a couple videos that said that you can use NBAR matching and ACLs interchangeably. That may not really be true when it comes to HTTP.
Send any Cisco learning credits questions my way.
QoS Pre-classify and Class-map Order
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.
Here’s the lab. I was testing from TestHost1 to TestHost2 and configuring R1 to do the pre-classification. Both R1 and R2 are 3640s running IOS 12.4(25b) and have a GRE tunnel between them.
I created a policy map that simply acknowledges the existence of ICMP packets; the router doesn’t do anything except match them in a class-map and smile at them on the way through. Here’s the snippet.
class-map ICMP match protocol icmp ! policy-map PM-S1/0-OUT class ICMP ! interface S1/0 service-policy output PM-S1/0-OUT ! interface tunnel 0 qos pre-classify
Not much going on there. We match ICMP using NBAR’s built-in protocols and do absolutely nothing. I did a few pings and noticed that there were no matches to the ICMP class and that all the packets were classified as class-default . I thought that the pre-classify wasn’t working, so I cursed for a while after making no progress at all. I had no idea what was wrong.
R1#sh policy-map int s1/0
Serial1/0
Service-policy output: PM-S1/0-OUT
Class-map: ICMP (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps
Match: protocol icmp
0 packets, 0 bytes
5 minute rate 0 bps
Class-map: class-default (match-any)
467 packets, 39832 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
I need to stop here so people don’t get confused. The configuration that you see is correct; the problem was actually with the NBAR protocols in the class-map. As Jeremy Stretch notes at the bottom of this article, there’s some issue with matching NBAR protocols. I later used an extended ACL to match ICMP which worked. The same is true for the SSH stuff later. Back to the show.
Here’s what I wound up with after cursing a lot and making random configuration changes to get the blasted thing to work. Notice the order of the classes.
class-map match-any TUNNEL match protocol gre ! policy-map PM-S1/0-OUT class TUNNEL class ICMP
I know that order is going to be important, but these are matching two totally different things, so it shouldn’t matter, right? I checked out the policy-map again and saw that every packet was matching the TUNNEL class-map, and none were matching the ICMP class-map.
R1#sh policy-map int s1/0
Serial1/0
Service-policy output: PM-S1/0-OUT
Class-map: TUNNEL (match-any)
441 packets, 49392 bytes
5 minute offered rate 2000 bps
Match: protocol gre
441 packets, 49392 bytes
5 minute rate 2000 bps
Class-map: ICMP (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps
Match: access-group name ICMP
0 packets, 0 bytes
5 minute rate 0 bps
Class-map: class-default (match-any)
467 packets, 39832 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
I finally went downstairs, talked it over with my wife who is my rubber duck, and finally figured it wouldn’t hurt to change the order of the classes. Once I put ICMP before TUNNEL, it started matching. I thought that was odd, so I left ICMP and added an SSH class and put it after the TUNNEL class. I saw the ICMP match and the tunnel match, but I didn’t see a single match on SSH even though I was SSHed through (not to) the router.
R1#sh policy-map int s1/0
Serial1/0
Service-policy output: PM-S1/0-OUT
Class-map: ICMP (match-any)
252 packets, 28224 bytes
5 minute offered rate 0 bps
Match: access-group name ICMP
252 packets, 28224 bytes
5 minute rate 0 bps
Class-map: TUNNEL (match-any)
5 packets, 440 bytes
5 minute offered rate 0 bps
Match: protocol gre
5 packets, 440 bytes
5 minute rate 0 bps
Class-map: SSH (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps
Match: access-group name SSH
0 packets, 0 bytes
5 minute rate 0 bps
Class-map: class-default (match-any)
547 packets, 46588 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
When I moved SSH above TUNNEL, it started incrementing as it should. The best that I can tell is that both the original packet and the GRE packet are being evaluated when pre-classification is enabled. Since all the packets in the lab are going over a GRE tunnel, GRE will always be matched if you assess before everything else.
For the record, I did this lab twice – once with the GRE tunnel encrypted and once without encryption. The results of the pre-classification were the same in both attempts; GRE matches every time.
Send any ROUTE class vouchers questions my way.
ONT Notes – QoS On Wireless Networks
- 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
- Four access categories
- WMM and 802.11e replace DCF with EDCF
- 802.11e
- 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
- Controller>QoS Profiles
ONT Notes – AutoQoS
- 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
- VPNs (Didn’t ISCW cover this?)
- Provide
- Confidentiality
- Integrity
- Authentication
- Types
- Remote-access
- Client-initiated
- NAS-initiated
- Site-to-site
- LAN-to-LAN
- Extranet
- Remote-access
- Provide
- 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
- Campus access switches
- 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
- Applies QoS policy to traffic destined for the router
ONT Notes – Congestion Avoidance, Policing, Shaping, and Link Efficiency
- 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
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?
- Four queues
- 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
ONT Notes – Classification, Marking, and NBAR
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
- Ethernet
- 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
- Expedited forwarding (EF) PHB – (101) low delay
- DSCP is chopped up into 4 PHBs
- 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
- Establish DSCP values as close to the source as possible
- 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
ONT Notes – Intro to QoS
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.
- Fixes
- 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
- Types of delay
- 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
- Fixes
QoS History
- Priority queuing: gives certain data the right-of-way for transmission
- Weighted Fair Queuing (WFQ): prevents small packets from waiting too long for big packets
- RTP priority queuing: Gives voice packets the right-of-way
- CAC: Makes sure we don’t fill up the queue or pipe with voice traffic
Implementing QoS
- Step 1: Identify traffic types and requirements
- Network audit
- Business audit
- Define bandwidth requirements for each class found
- Step 2: Classify the traffic
- Common classes
- VOIP
- Mission-critical
- Signal traffic: for VOIP
- Transactional application: SAP, ERP
- Best-effort: Everything else
- Scavenger: Crap you don’t care about like P2P and your boss’s email
- Common classes
- Step 3: Define policies for each class
- Tasks for each class
- Set max bandwidth
- Set min bandwidth
- Assign relative priorities
- Apply congestion avoidance, congestion management, etc.
- Tasks for each class
QoS Models
- Best-effort: no QoS
- Scalable
- Easy
- No service guarantee: doesn’t care what you’re trying to do
- No service differentiation: all traffic is equal
- Integrated Service (IntServ)
- Hard-QoS
- Uses RSVP to guarantee bandwidth through the entire path
- Requires
- Admission control
- Classification
- Polices the traffic (ceiling)
- Queuing
- Scheduling
- Advantages
- End-to-end resource admission control
- Per-request policy admission control
- Signaling of dynamic ports
- Disadvantages
- Continuous signaling
- Not scalable
- Differentiated Services (DiffServ)
- Soft-QoS
- Configured on each hop
- Traffic is classified
- Enforces different treatment on different classes
- Defined based on business requirements
- Benefits
- Scalable
- Supports lots of service levels
- Drawbacks
- No absolute guarantee of service
- Complex configuration throughout network
QoS Implementation Methods
- CLI
- Old school
- Not used any more
- Modules QoS CLI (MQC)
- Step 1: class-map
- Step 2: policy-map
- Step 3: service-policy
- AutoQoS
- Automatically generates classes and policies based on traffic it sees
- Super-simple
- Requires CEF, NBAR, and correct bandwidth statements
- SDM QoS Wizard
- Next, next, next
- Can be used to implement, monitor, or troubleshoot QoS