Ipv6 QoS

If you already grasp QoS concepts for IPv4, IPv6 QoS is a piece of cake!

As with IPv4, IPv6 uses MQC (Modular QoS CLI)to configure Diffserv (Differentiated services) QoS.

IPv6 QoS is very similar to IPv4 QoS except for some details:

• NBAR, the first version, doesn’t support IPv6.
• cRTP (Compressed-RTP).
• No way to match directly RTP.
• CAR (Committed Access Rate) replaced by CB- Policing already in IPv4 and no need to keep supporting it in IPv6.
• PQ/CQ replaced by MQC (Modular QoS CLI).
• IPv6 supports only named ACL.
• Layer2 (802.1q) commands works only with CEF- Switched ports not with process- switched nor router originated traffic.

The following is the topology used to deploy IPv6 QoS, no IPv4 addressing scheme. The serial link between the two routers is the bottleneck of the network where QoS is needed.

Figure1: Topology

Classification & Marking

The first and the most crucial step in deploying QoS is classification of traffic.

In this step you need to:

• identify various applications and protocols running on your network.
• understand the application behavior with respect to the available network resources.
• identify the mission critical and non-critical application.
• Categorize the applications and protocols in different classes of service accordingly.

The classification is based on packet native classifiers like:

• source/destination IPv6 addresses, IP protocol and source/destination ports.
• precedence and dscp.
• source/destination MAC.
• TCP/IP header parameters (packet length…).
• IPv6 specific classifiers (not currently used).
• IPv6 (traffic class) used in the same way as IPv4 (ToS).

IPv4 can take advantage of NBAR, very useful to automatically recognize applications and provides statistics about bandwidth utilization. Without NBAR, you will need to manually determine which classifiers define the application you want QoS to handle. Unfortunately NBAR doesn’t support IPv6, NBAR2 does.

For IPv6 traffic, you can use other tools such “Netflow” or any traffic analyzer software for more granular inspection, then build IPv6 ACLs matching the relevant classifiers with the relevant values.

table1: Application classification and marking

ACL name	Permit/ Deny	Protocol	Source			Destination
			IP	mask	Src port	IP	Mask	Dst port
FTP	permit	tcp	2001:b:b:b::b	–	ftp (21)	any	–	–
	permit	tcp	2001:b:b:b::b	–	ftp-data (20)	any	–	–
UStream	permit	udp	any	–	–	any	–	1234

Table1 summarizes the applications used in the lab for demonstration purpose.

Table2: Application classification and marking

Application	Bandwidth allocated	Flow direction	traffic classifiers	Class	Markers
unicast streaming	700 kbps	From HostB to HostA	dest IPv6=2001:a:a:a::a	MatchUStream	dscp=ef
			protocol I =Pv6
			dest port 1234
FTP download	30 kbps	From HostB to HostA	src port 21 (control)	MatchFTP	dscp=af41
			protocol I =Pv6
			src port 20 (data)
scavenger appli video streaming	150 kbps	From HostB to Host A	src port …

Generally dscp “ef” is reserved for VoIP which requires the most stringent QoS, in this lab we use the dscp marking  just to check at the destination host (hostA) whether the classification works.

The end-to-end model used to test IPv6 QoS is depicted in Figure2.

Figure2: End-to-End QoS model

Congestion Management & avoidance

For the purpose of the lab, the unicast streaming application is given the highest priority and it is supposed to have stringent bandwidth, latency, delay and jitter requirements, LLQ (Low Latency Queuing) is the most appropriate queuing mechanism for such applications.

The FTP traffic is considered critical with a minimum of  30kbps of bandwidth guaranteed .

Any other traffic, default-class is considered “scavenger” and will have no privilege during congestion.

Each application is being allocated the needed bandwidth to perform correctly.

Table3: Classes and bandwidth allocation

Class	Bandwidth reserved	Queue	DSCP	Priority
MatchUStream	700 kbps	LLQ	af41	High
MatchFTP	30 kbps	CBWFQ	af21	Medium
class-default	no guarantee	WFQ	0	Low

policy-map QoS_Policy   class MatchUStream    set dscp ef    priority 700   class MatchFTP    set dscp af41    bandwidth 30   class class-default    fair-queue    set dscp default

Figure3 and 4 show a summary of general QoS mechanisms and queuing system types.

Figure3: Software and Hardware queuing systems

Figure4: QoS mechanisms

RouterB:

ipv6 access-list FTP permit tcp host 2001:B:B:B::B eq ftp any permit tcp host 2001:B:B:B::B eq ftp-data any ! ipv6 access-list UStream sequence 20 permit udp any any eq 1234 ! class-map match-all MatchFTP   match protocol ipv6   match access-group name FTP class-map match-all MatchUStream   match protocol ipv6   match access-group name UStream

Monitoring:

RouterB(config-pmap-c)#do show policy-map int s1/0 Serial1/0   Service-policy output: QoS_Policy     Class-map: MatchUStream (match-all)       23625 packets, 32602500 bytes       30 second offered rate 538000 bps, drop rate 0 bps       Match: protocol ipv6       Match: access-group name UStream       QoS Set         dscp ef           Packets marked 23624       Queueing         Strict Priority         Output Queue: Conversation 264         Bandwidth 700 (kbps) Burst 17500 (Bytes)         (pkts matched/bytes matched) 1455/2007900         (total drops/bytes drops) 1/1380     Class-map: MatchFTP (match-all)       5886 packets, 8192512 bytes       30 second offered rate 135000 bps, drop rate 0 bps       Match: protocol ipv6       Match: access-group name FTP       QoS Set         dscp af41           Packets marked 5929       Queueing         Output Queue: Conversation 265         Bandwidth 30 (kbps) Max Threshold 64 (packets)         (pkts matched/bytes matched) 3486/4784640         (depth/total drops/no-buffer drops) 0/0/0     Class-map: class-default (match-any)       105 packets, 8292 bytes       30 second offered rate 0 bps, drop rate 0 bps       Match: any       Queueing         Flow Based Fair Queueing         Maximum Number of Hashed Queues 256         (total queued/total drops/no-buffer drops) 0/0/0       QoS Set         dscp default           Packets marked 50 RouterB(config-pmap-c)#

RouterB(config-pmap-c)#do sh int s1/0 Serial1/0 is up, line protocol is up   Hardware is M4T   MTU 1500 bytes, BW 1024 Kbit, DLY 20000 usec,      reliability 255/255, txload 165/255, rxload 1/255   Encapsulation HDLC, crc 16, loopback not set   Keepalive set (10 sec)   Restart-Delay is 0 secs   Last input 00:00:07, output 00:00:00, output hang never   Last clearing of “show interface” counters 00:08:49   Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 21   Queueing strategy: weighted fair   Output queue: 0/1000/64/1 (size/max total/threshold/drops)      Conversations  0/3/256 (active/max active/max total)      Reserved Conversations 1/1 (allocated/max allocated)      Available Bandwidth 38 kilobits/sec   30 second input rate 4000 bits/sec, 8 packets/sec   30 second output rate 666000 bits/sec, 59 packets/sec      4066 packets input, 261676 bytes, 0 no buffer      Received 61 broadcasts, 0 runts, 0 giants, 0 throttles      0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort      32082 packets output, 44217146 bytes, 0 underruns      0 output errors, 0 collisions, 0 interface resets      0 output buffer failures, 0 output buffers swapped out      0 carrier transitions     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up RouterB(config-pmap-c)#

Shaping & Policing

Shaping and policing work exactly as in IPv4.

Policing:

• Applied inbound and outbound.
• Drops non conforming traffic.
• More efficient in term of memory utilization.
• Drops packets more often, therefore more TCP retransmission.

Shaping:

• Applied only outbound.
• Queues excess traffic.
• Less efficient because of additional queuing, but less dropping  (only when congestion occurs).
• Causes variable delay (jitter) and increases buffer utilization, therefore more delays.

Figure5 shows the mechanism of token bucket used in shaping and policing.

Figure5: shaping and policing

Here is how the FTP traffic diagram looks like before any shaping or policing:

Figure6: FTP before shaping and policing

The following figurex shows different behaviors based on three configurations of shaping and traffic:

Figure7: FTP with shaping and traffic

The first part of the graph corresponds to FTP traffic with just a configured guaranteed bandwidth of 30kbps.

policy-map QoS_Policy   class MatchFTP    bandwidth 30

In the second part of the graph, a high limit is set for FTP class using policing at 100kbps, you can note that this results in a frequent TCP global synchronization, a TCP protocol behavior when congestion occurs somewhere in the path to the destination, as long as the congestion exists the source continues to receive requests to decrease the sending rate back from zero and so on, hence the form of the graph (repeated short bursts from the bottom to the maximum).

policy-map QoS_Policy   class MatchFTP    bandwidth 30    police 100000

The third part of the graph represents the result of using shaping instead of policing, more optimal use of the bandwidth. Instead of dropping the TCP traffic and causing global synchronization, the exceed packets are queued for a certain amount of time and then sent, hence the higher used average bandwidth.

policy-map QoS_Policy   class MatchFTP    bandwidth 30    shape average 100000

RouterB#sh policy-map int s1/0 …     Class-map: MatchFTP (match-all)       32045 packets, 47038153 bytes       30 second offered rate 99000 bps, drop rate 0 bps       Match: protocol ipv6       Match: access-group name FTP       QoS Set         dscp af41           Packets marked 32074       Queueing         Output Queue: Conversation 265         Bandwidth 30 (kbps) Max Threshold 64 (packets)         (pkts matched/bytes matched) 17595/26364666         (depth/total drops/no-buffer drops) 0/0/0       Traffic Shaping            Target/Average   Byte   Sustain   Excess    Interval  Increment              Rate           Limit  bits/int  bits/int  (ms)      (bytes)            100000/100000    2000   8000      8000      80        1000         Adapt  Queue     Packets   Bytes     Packets   Bytes     Shaping         Active Depth                         Delayed   Delayed   Active         –      11        17134     25746208  17096     25689056  yes …

Conclusion

Make sure you understand first IPv4 QoS, especially the difference between shaping and policing and their impact on your own applications.