Just as a reminder , CoS marking (Layer 2) doesn’t “survive” to Layer 3 as the route processor will remark it.
It is why the most of the time a Cos to DSCP rewriting policy must be applied on the input direction of the interface.
Before enabling AutoQoS , take in mind the following pre-requisites :
- CEF must be enabled as AutoQoS relies on NBAR which is dependant of CEF.
- No Policy QoS can be attached to the interface
- The correct bandwidth statement must be set up on the interface
- An IP address must be configured on an interface if its speed is less than 768 Kbps
- The interface can’t be in a shutdown mode
You can the ask why IP Address is an mandatory element ?
It is simply because if your speed links is less than 768 Kbps , then AutoQoS will enable Multilink PPP (MLP)
By default , a class-map will use the match-all criteria so it will tell that you must match all your conditions in your class-map before to classify the traffic .
If you want classify directly when at least one condition is met then use the criteria match-any.
Unclassified traffic will go in the default class.
Shaping can be applied only in the outbound direction and doesn’t discard the traffic exceeding the rate limit automatically. Shaping will bufferize the queue until the bandwidth become available or in last action will drop exceeding packets.
Compared to Policing , shaping preserves the bandwidth and is recommended on lower bandwidth links.
Qos Shaping is also considered as an Traffic Conditioner
Policing can be used in either the inbound or outbound direction and it discards packets which are exceeding a configured rate limit.
Pay attention to the fact that policing is dropping packets , it can result in retransmissions (TCP acknowledge), so it is better to use policing on higher bandwidth links !!!
Qos Policing is also considered as an Traffic Conditioner
Endpoints which are using multicast discovery will use the multicast adress 224.0.1.41 for GRQ
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