You are working with a new MPLS network that is using the default EXP classifier and default schedules. A
small amount of traffic is being placed in the assured forwarding class. No other traffic is passing through the
network at this time.
In this scenario, what happens to the traffic that is being placed in the assured forwarding class?
A.
The traffic is reclassified to the best effort forwarding class and is forwarded.
B.
The traffic remains in the assured forwarding class and is forwarded.
C.
The traffic is reclassified to the network control forwarding class and is forwarded.
D.
The traffic remains in the assured forwarding class and is dropped.
Explanation:
https://www.juniper.net/documentation/en_US/junos15.1/topics/concept/forwarding-classesdefault-cos-config-guide.html
B correct
Situation – You don’t have congestion.
The default behavior in MX-Series routers with Modular Port Concentrators (MPC) is to copy the 3 most significant bits from the DSCP field into the exp bits of the MPLS label.
A packet that reaches the destination PE will be classified by that classifier, which will send the packets to the Assured-Forwarding or Expedited-Forwarding classes (depending on the markings). Below is the classifier setting:
user@Router> show class-of-service classifier type exp
Classifier: exp-default, Code point type: exp, Index: 10
Code point Forwarding class Loss priority
000 best-effort low
001 best-effort high
010 expedited-forwarding low
011 expedited-forwarding high
100 assured-forwarding low
101 assured-forwarding high
110 network-control low
111 network-control high
https://kb.juniper.net/InfoCenter/index?page=content&id=KB31032
1
0
The default behavior in MX-Series routers with Modular Port Concentrators (MPC) is to copy the 3 most significant bits from the DSCP field into the exp bits of the MPLS label.
From DSCP code points, the 3 most significant bits (001) covers assured-forwarding as shown below.
DSCP and DSCP IPv6 Code Point
000000 – best effort
001010 – assured-forwarding with a low plp
001100 – assured-forwarding with a high plp
001110 – assured-forwarding with a high plp
101110 – expedited-forwarding with a low plp
110000 – network-control with a low plp
111000 – network -control with a low plp
all other code points – best-efforts with a low plp
0
0