MPLS QoS Testing Tools

When you're setting the mpls experiment bit on the PE router for traffic coming from CE router you must use imposition for QoS treatment. You cannot use topmost because the packet is IP packet. If you're on a P router you can set or match on the topmost label for the swap function. If you're on the PE router receiving traffic from the P router then you can also set and match on the topmost label.
Whether a customers sets the DSCP/TOS or you set an mpls exp bit inbound on a PE router you have to match on the mpls experiment bits as the packet leaves the PE router going to the P router because the packet is an mpls packet not an IP packet. If a packet is marked by a customer with a DSCP or TOS value, that value will be honored/mapped to an mpls experiment value. See the chart below for mappings honored:-

TOS	TOS Binary	DSCP	DSCP Binary	MPLS EXP	HEX	HEX Binary
0	000|000	0-7	000000 - 000111	0	00-1F	0000|0000 - 0001|1111
1	001|000	41501	001000 - 001111	1	20-3F	0010|0000 - 0011|1111
2	010|000	16-23	010000 - 010111	2	40-5F	0100|0000 - 0101|1111
3	011|000	24-31	011000 - 011111	3	60-7F	0110|0000 - 0111|1111
4	100|000	32-39	100000 - 100111	4	80-9F	1000|0000 - 1001|1111
5	101|000	40-47	101000 - 101111	5	A0-BF	1010|0000 - 1011|1111
6	110|000	48-55	110000 - 110111	6	C0-DF	1100|0000 - 1101|1111
7	111|000	56-63	111000 - 111111	7	E0-FF	1110|0000 - 1111|1111

You can verify your QOS policies by using the ip telnet tos in hex command. This works great, for example if you want to generate traffic with a TOS value of 6 or a DSCP value of 54 you would use the command ip telnet tos 11000000. Telnet from one CE router to the other CE router and the telnet traffic will be marked with TOS 6 or DSCP 54.

After you configure ip telnet tos xx on an edge device telnet to the far end of your network and run some commands in order to generate some telnet traffic. Next use the "show policy-map interface and look for packets matched to see if your policy is configured correctly.

You can also see the TOS or DSCP value set on IP traffic traversing the network use ip accounting precedence output or input on the PE or CE router. Then use the show interface precedence command.


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Qos Interview Questions?

1. What is QOS and why it is required?
2. What is layer2 qos and layer3 qos?
3. What is tail drop?
4. Describe methods of QOS?
5. What is hardware QOS and Software QOS?
6. Difference between a policer and a shaper?
7. What is token bucket algorithm?
8. Where to define the markings?
9. Does QOS increase the load of the equipment?
10. What is TOS and IP DSCP?
11. what are the different classes available?
12. How to calculate the decimal value of classess?
13. What is the difference between priority and bandwidth command?
14. What is low latecy queueing?
15. what is class based weighted fair queuing?
16. What is first in first out queue (FIFO)?
17. What is fair queue?
18. If I give teh ip precendence five to data traffic, what will happen?

Other Useful Questions
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Advantages of MPLS

A interview always start with the question called "Advantages of MPLS" and most of the time students don't know much about it and start fumbling with not good answers. I am giving few quick answers about MPLS advantages, if some is having other than that please share.

1. No propagation of routes in the core of service provider.
2. In legacy GRE customer is responsible for the management but in case of MPLS SP is responsible.
3. Customers can use the same ip address which is not possible in case of GRE.
4. MPLS saves cost as compared to ATM or frame relay network.
5. MPLS increase the response time.
6. Customers can have the QOS according to their requirements.
7. Fast reroute features by using traffic engineering.
8. MVPN support which saves lot of bandwidth.

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Different VPN Using QOS But SP Core Has One Class Of Service

In this test lab core consists of 3 routers which are running MPLS with 2 as provider edge routers and one as provider router. Two different VPNs are connected from PE1 and PE2 routers. Both different VPNs has different QOS requirement and to meet the service level aggrements different class of service profiles have been created on PE routers. But the core is running with four type of class of services. So what ever the packets are coming from customers are checked according to the profile created on edge router and are forwarding in the core according to the class of services defined. I have shown the one way communiaction, but in real network bi directional quality of service requires. So it could be enabled but not shown in the given test lab. The QOS policies are mapped according to the high level diagram shown in previous post.

I have used the type of services to mark the packets from the customer routers and same has been checked with the help of ip accounting precedence command on remote CE routers.

Below is the config shown for the core routers with the policies defined for customers:- Config of PE2

Class Map and Policy Map Configured For VPN-2:-

class-map match-all FROM-CE2-2
match ip precedence 2
class-map match-all FROM-CE2-3
match ip precedence 3
class-map match-all FROM-CE2-1
match ip precedence 1

policy-map FROM-CE2
class FROM-CE2-1
set mpls experimental imposition 1
class FROM-CE2-2
set mpls experimental imposition 2
class FROM-CE2-3
set mpls experimental imposition 3

interface FastEthernet0/0
description connected to ce2
ip vrf forwarding TEST
ip address 172.16.1.1 255.255.255.252
ip accounting precedence input
duplex auto
speed auto
service-policy input FROM-CE2

Class Map Configured For VPN-3:-

class-map match-all CE3-2
match ip precedence 2
class-map match-all CE3-5
match ip precedence 5


policy-map FROM-CE3
class CE3-2
set mpls experimental 2
class CE3-5
set mpls experimental 5
class class-default
set mpls experimental 0

interface FastEthernet2/0
ip vrf forwarding CE3
ip address 2.2.2.14 255.255.255.252
duplex half
mpls label protocol ldp
mpls ip
service-policy input FROM-CE3


Class Map Configured Towards P:-

class-map match-all TO-P-2-3
match mpls experimental topmost 2 3
class-map match-all TO-P-1
match mpls experimental topmost 1
class-map match-all TO-P-5
match mpls experimental topmost 5
!
!
policy-map TO-PE1
class TO-P-1
bandwidth 1000
class TO-P-2-3
bandwidth 5000
class TO-P-5
bandwidth 5000
policy-map TO-P
class TO-P-1
bandwidth 1000
class TO-P-2-3
bandwidth 5000
class TO-P-5
bandwidth 2000
class class-default
!

Interface Config of P
interface FastEthernet0/0
ip address 2.2.2.2 255.255.255.252
duplex auto
speed auto
mpls label protocol ldp
mpls ip
service-policy output TO-PE1
!
interface FastEthernet0/1
ip address 1.1.1.2 255.255.255.252
duplex auto
speed auto
mpls label protocol ldp
mpls ip


Config of PE1

class-map match-all TO-CE-5
match qos-group 5
class-map match-all TO-CE-1
match qos-group 1
class-map match-all TO-CE-3
match qos-group 3
class-map match-all TO-CE-2
match qos-group 2
class-map match-all MPLS-COS-5
match mpls experimental topmost 5
class-map match-all MPLS-COS-1
match mpls experimental topmost 1
class-map match-any B-TELNET
match dscp ef
class-map match-all MPLS-COS-3
match mpls experimental topmost 3
class-map match-all MPLS-COS-2
match mpls experimental topmost 2
!
!
policy-map TO-CE1
class TO-CE-1
bandwidth 1000
class TO-CE-2
bandwidth 2000
class TO-CE-3
bandwidth 3000
policy-map TO-CE3
class TO-CE-2
bandwidth 2000
class TO-CE-5
bandwidth 1000
policy-map MPLS-COS
class MPLS-COS-1
set qos-group 1
class MPLS-COS-2
set qos-group 2
class MPLS-COS-3
set qos-group 3
class MPLS-COS-5
set qos-group 5
!


Interface of PE1

interface FastEthernet0/0
ip vrf forwarding TEST
ip address 172.168.2.1 255.255.255.252
ip accounting precedence output
load-interval 30
duplex auto
speed auto
service-policy output TO-CE1 (VPN-2)
!
interface FastEthernet0/1
ip address 2.2.2.1 255.255.255.252
load-interval 30
duplex auto
speed auto
mpls label protocol ldp
mpls ip
service-policy input MPLS-COS
!
interface FastEthernet2/0
ip vrf forwarding CE3
ip address 23.23.23.1 255.255.255.252
duplex auto
speed auto
service-policy output TO-CE3 (VPN-3)
!


Outputs of Policy Map On PE1 which is depicting the packet matches in customer profile as well as in the core profile.


PE2#sh policy-map interface
FastEthernet0/0

Service-policy input: FROM-CE2

Class-map: FROM-CE2-1 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 1
QoS Set
mpls experimental imposition 1
Packets marked 0

Class-map: FROM-CE2-2 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 2
QoS Set
mpls experimental imposition 2
Packets marked 0

Class-map: FROM-CE2-3 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 3
QoS Set
mpls experimental imposition 3
Packets marked 0

Class-map: class-default (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
FastEthernet0/1

Service-policy output: TO-P

Class-map: TO-P-1 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 1
Queueing
Output Queue: Conversation 265
Bandwidth 1000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0

Class-map: TO-P-2-3 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 2 3
Queueing
Output Queue: Conversation 266
Bandwidth 5000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0

Class-map: TO-P-5 (match-all)
20 packets, 2440 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 5
Queueing
Output Queue: Conversation 267
Bandwidth 2000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 1/122
(depth/total drops/no-buffer drops) 0/0/0

Class-map: class-default (match-any)
971 packets, 81819 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
FastEthernet2/0

Service-policy input: FROM-CE3

Class-map: CE3-2 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 2
QoS Set
mpls experimental imposition 2
Packets marked 0

Class-map: CE3-5 (match-all)
5 packets, 570 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 5
QoS Set
mpls experimental imposition 5
Packets marked 5

Class-map: class-default (match-any)
5 packets, 570 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
QoS Set
mpls experimental imposition 0
Packets marked 5



Output of P router

P#sh policy-map interface
FastEthernet0/0

Service-policy output: TO-PE1

Class-map: TO-P-1 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 1
Queueing
Output Queue: Conversation 265
Bandwidth 1000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0

Class-map: TO-P-2-3 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 2 3
Queueing
Output Queue: Conversation 266
Bandwidth 5000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0

Class-map: TO-P-5 (match-all)
15 packets, 1830 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 5
Queueing
Output Queue: Conversation 267
Bandwidth 5000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 1/122
(depth/total drops/no-buffer drops) 0/0/0

Class-map: class-default (match-any)
662 packets, 56017 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any


Output of PE1 router


PE1#sh policy-map interface
FastEthernet0/0

Service-policy output: TO-CE1

Class-map: TO-CE-1 (match-all)
0 packets, 0 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: qos-group 1
Queueing
Output Queue: Conversation 265
Bandwidth 1000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0

Class-map: TO-CE-2 (match-all)
0 packets, 0 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: qos-group 2
Queueing
Output Queue: Conversation 266
Bandwidth 2000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0

Class-map: TO-CE-3 (match-all)
0 packets, 0 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: qos-group 3
Queueing
Output Queue: Conversation 267
Bandwidth 3000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0

Class-map: class-default (match-any)
112 packets, 11393 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: any
FastEthernet0/1

Service-policy input: MPLS-COS

Class-map: MPLS-COS-1 (match-all)
0 packets, 0 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 1
QoS Set
qos-group 1
Packets marked 0

Class-map: MPLS-COS-2 (match-all)
0 packets, 0 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 2
QoS Set
qos-group 2
Packets marked 0

Class-map: MPLS-COS-3 (match-all)
0 packets, 0 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 3
QoS Set
qos-group 3
Packets marked 0

Class-map: MPLS-COS-5 (match-all)
10 packets, 1220 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: mpls experimental topmost 5
QoS Set
qos-group 5
Packets marked 10

Class-map: class-default (match-any)
385 packets, 30566 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: any
FastEthernet2/0

Service-policy output: TO-CE3

Class-map: TO-CE-2 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: qos-group 2
Queueing
Output Queue: Conversation 265
Bandwidth 2000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0

Class-map: TO-CE-5 (match-all)
10 packets, 1140 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: qos-group 5
Queueing
Output Queue: Conversation 266
Bandwidth 1000 (kbps)Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0

Class-map: class-default (match-any)
113 packets, 11453 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any


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Quality Of Service Framework

High level QOS framework is depicted in the image. The traffic is shown one way for dual way the same policies need to be implemented on different interfaces.

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End To End CPE QOS Marking Delivery Without Enabling QOS In Backhaul

In this topology a small test is elaborated where in the customer is forwarding the ip packets with ip precedence of 3 and service provider which is offering the mplsvpn sevrvices is not using any qos in the cloud but still the precedence sent by the customer is delivered to the remote locations. If means the service provider cloud preserves the ip precedence bits during the forwarding of vpn traffic.

Test Setup

TEST Policy is created on CE2 with precence value of 3 which is set to all the outgoing traffic from fa0/0. The marking of packets can be checked by enabling ip accounting.



CE2#

policy-map TEST
class class-default
set ip precedence 3


interface FastEthernet0/0
ip address 172.16.1.2 255.255.255.252
ip accounting output-packets
ip accounting precedence input
duplex auto
speed auto
service-policy output TEST
!



CE2#ping 10.1.1.2 repeat 2

Type escape sequence to abort.
Sending 2, 100-byte ICMP Echos to 10.1.1.2, timeout is 2 seconds:
!!
Success rate is 100 percent (2/2), round-trip min/avg/max = 1040/1110/1180 ms
CE2#
CE2#
CE2#sh interfaces fastEthernet 0/0 precedence
FastEthernet0/0
Input
Precedence 3: 2 packets, 228 bytes


2 packets sent from CE2 with ip precedence 3. Now the packets reached to the PE2 where in Fa0/1 is the receiving interface which is setting the class of service 3 with label 19. Label 19 is used for vpnv4 route.


PE2#
*Nov 7 00:45:09.999: MPLS: Fa0/1: recvd: CoS=3, TTL=253, Label(s)=19
*Nov 7 00:45:10.867: MPLS: Fa0/1: recvd: CoS=3, TTL=253, Label(s)=19



From PE2 the packet reached to P router whith COS 3 and because of PHP the transport label removed and packet forwarded with label 18 to PE1 with exit interface Fa0/0.

P#
*Nov 7 00:45:06.359: MPLS: Fa0/1: recvd: CoS=3, TTL=254, Label(s)=16/18
*Nov 7 00:45:06.363: MPLS: Fa0/0: xmit: CoS=3, TTL=253, Label(s)=18
*Nov 7 00:45:07.487: MPLS: Fa0/1: recvd: CoS=3, TTL=254, Label(s)=16/18
*Nov 7 00:45:07.491: MPLS: Fa0/0: xmit: CoS=3, TTL=253, Label(s)=18



PE1 received the packet with COS 3 and forward the packet towards fa0/0 interface which is the vrf interface and attached with customer.
PE1#
*Nov 7 00:43:38.591: MPLS: Fa0/1: recvd: CoS=3, TTL=253, Label(s)=18
*Nov 7 00:43:38.595: MPLS: Fa0/0: xmit: (no label)
*Nov 7 00:43:39.779: MPLS: Fa0/1: recvd: CoS=3, TTL=253, Label(s)=18
*Nov 7 00:43:39.783: MPLS: Fa0/0: xmit: (no label)



CE1 received the packets with the ip precedence 3.

CE1#sh interfaces fastEthernet 0/0 precedence
FastEthernet0/0
Input
Precedence 3: 2 packets, 228 bytes
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QOS amenity of network

QOS is the basic amenity of network. With its implementation various attacks could be halted. Below is the varios steps which are required to implement QOS in network.Steps of implementing QOS
Step 1:- Classification
Tools used for classification
Access Control List (ACL)
COS
Differentiated Services Code Point
Input-interface
Media Access Control (MAC) address
Packet length
Precedence
Protocol
VLAN

Step 2:- Queuing

Marking
Policing
Drop


Steps 3:- Congestion Management
Queue-limit
Random-dete
Bandwidth
Fair-queue
Priority
Shape
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Sell Bandwidth Not Speed

Selling bandwidth to customers is quite easy but to maintain the speed is such a lobotomize work. Customers always mull to get the same speed whatever they subscribed for bandwidth. But its really hectic job to render the same what was commited to customer. Sales guys always sell the bandsith with respective to the speed. Lets take one example when the bandwidth of 10 Mbps was sold to customer then it doesnot mean customer would get 10 Mbps per/second but customers always demand the same. In fact if we do the calculations as per the given formula we would be able to get to know how much commited burst can be given to customer per interval.

BC=TC*CIR

BC=Commited Burst
TC=Commited Time Interval
CIR=Commited Information Rate

CIR means total number of bits that will be flown in a second or you can say the shaped rate.
TC=Commited time interval per burst.BC=Commited burst whcih can be sent in particular interval.
BC=Commited burst whcih can be sent in particular interval.

In Cisco IOS a second is divided into 8 time intervals of 125ms each(125*8=1000ms or 1 sec). If you want to provide 64000 bits or 64Kbps to a customer then you need to calculate the burst for that because that will be the maximum value which will occue in one time interval of 125ms. So CIR=64000 Tc=125ms Now calculate Bc which will be equals to (125/1000*64000) = 8000 bits. The result is lucid, it means in a sinle interval customer cannot pump more than 8000 bits per interval when he owns spped of 64Kbps. This is what we need to make clear to customer before selling the bandwidth.


regards
shivlu jain
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Use Of Scavenger Class In QOS

While implementing QOS the default class is implemented with best effort traffic. Best effort class uses DSCP marking 46. We have one more class which is below to default class, the class is recognized by scavenger class. It provides the less than best effort service. The class is used to distinguish lobotomize traffic. MArking use for class is CS1 or DSCP 8. The major advantage of class comes out when network is flooded with DOS attack & all type of traffic is being added to the class with 1% of bandwdith or what ever you want.


regards
shivlu jain
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CAR and Policing

CAR is proprietry to cisco where as policing supports RFC 2697. Rate-Limit is used for the implementation of CAR where as police command is used for policing. CAR works on single tocken bucket where as Policing works seperate token buckets for burst. CAr supports two coloring which is confirm and exceed action where as policing supports three coloring which is confirm,exceed and violate action. One major advantage of using policing is that you can remark the packets where as CAR doesnot support the same feature.

How to configure rate limit
rate-limit input 1536000 288000 576000 conform-action transmit exceed-action drop
rate-limit output 1536000 288000 576000 conform-action transmit exceed-action drop

How to configure policingpolicy-map MPLSVPN
class MPLS police 16000 2000 2000 conform-action transmit exceed-action drop

interface fastethernet 0/0 service-policy output MPLSVPN

Cisco recommends using the following formulas when calculating the normal and extended burst parameters in case of car.
normal burst (in bytes) = configured rate (in bits per second) * (1 byte)/(8 bits) * 1.5 seconds extended burst = 2 * normal burst


regards
shivlu jain
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Class Based Weighted Fair Queue

In my previous post of QOS I tried to describe the basic qos models. Dennis Hartman is already doing a great job on qos and the way he is explaining a fair enough to understand the basic concept of CBWFQ.
In this post, I only want to add the few common and unforgetable points which should be learn by heart for each and every technology guy.

Facts Of CBWFQ
1. 64 number of clases can be configured and by default per class allocates 64 packets in queue.
2. Trafic shaping and Policing is not supported by CBWFQ.
3. If wred is using under policy map then it cannot be added under interface.
(WRED is weighted random early detection)
4. CBWFQ is not supported on sub interfaces.
5. Default class uses the fair queue mechanism. If any other mechanism is implemented it is overriden.


regards
shivlu jain
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Basic Of QOS

Without implementing QOS in network it sounds like you are living without soul. The another problem is that network is open to accept more attacks. So with the addition to security QOS is also required in the network. QOS is very effective tool for service provider as well as for enterprise network. In this I am trying to give the brief of QOS model.

Types of QOS Models:-
a) Best Effort
b) DiffServ Model
c) Integrated Service

Prior to DSCP model we were having IP Precedence Value which was in IP header (TOS). It is having 3 bits, it means no more than of 8 combinations. But there after the TOS header was replaced by DS field header. The DS field header consist of 6 bits for DSCP and 2 bits for ECN(Explicit Congestion & Notification).

Best Effort Means no QOS will be used for packets. Packets will be forwarded with the least priority by default. Thats why it is called that on internet the traffic is sent as BE or best effort. Now the question comes how service provider or enterprise can use BE class in the network. It canbe implemented by with the help of MQC. In this we can classify and mark the itraffic which we are looking for & rest of traffic could be put in the BE class.

DiffServ Model consist of Class Selector, Assured Forwarding & Expediated Forwarding. Class selector (CS) is used for the backward compatibility with IP Precedence. Why it is required because the new ip header is using DSCP fields but there are many old ip header exists in the network and they are still on IP Precedence. For this reason Class Selector is used. But now the question comes how 6 bits equal to 3 bits of IP Precendence.

DSCP Class Selector Equivalent Precedence Values
CS0(Default) (000000) 0
CS1 (001000) 1
CS2 (010000) 2
CS3 (011000) 3
CS4 (100000) 4
CS5 (101000) 5
CS6 (110000) 6
CS7 (111000) 7

It is explicity showing that 3,4 & 5 bits are changing and 0,1, & 2 bits are the same. So we can the decimal value of DSCP is given below with respect to IP Precedence

0-7 (000000) 0
8-15 (001000) 1
16-23 (010000) 2
24-31 (011000) 3
32-39 (100000) 4
40-47 (101000) 5
48-55 (110000) 6
56-63 (111000) 7

If the next your router is receiving the values between 32 – 39 and you want to mark the ip precedence value on that packet then use 4 for the same.

DiffServ model is having two more important things besides class selector. One is assured forwarding and another is Expediated Forwarding. As per assured forwarding no more than 4 classes will be used and with in a class three types of drop probabiity is introduced. Lower the number least the drop probability. In expediated forwarding which is also known as EF and having only a one vale i.e 46. The EF class is used for low latency traffic like voip etc & always provide the quaranteed bandwidth. The traffic which falls in EF class will always get priority.

Integrated Model is used for signalling to reserve the bandwidth on per flow basics. RSVP & Admission Control is used in InterServ Model.


regards
shivlu jain
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