FIFO stands for First In First Out .
So you can easily understand the meaning of this queuing mechanism : The first packet in the queue is the fisrt packet which will be sent out of the queue.
FIFO is also the default mechanism for software queue for higher speed interfaces ( > 2048 Mbps)
Queuing issometimes reerredto as congestion management as it identifies how trafic from multiple streams is sent out of an interface which is currentlyexperiencing congestion.
In other words, the queuing is the fact that a device( router or switch) will attempt to bufferize the extra traffic until the bandwidth will be available again
Here are the default values for the mapping until you decide to change it
First let’s see the CoS-to-DSCP mapping
- CoS 0 => DSCP 0
- CoS 1 => DSCP 8
- CoS 2 => DSCP 16
- CoS 3 => DSCP 24
- CoS 4 => DSCP 32
- CoS 5 => DSCP 40
- CoS 6 => DSCP 48
- CoS 7 => DSCP 56
After let see the reverse side with the DSCP-to-CoS mapping
- DSCP 0 => CoS 0
- DSCP 8,10 => CoS 1
- DSCP 16,18 => CoS 2
- DSCP 24,26 => CoS 3
- DSCP 32,34 => CoS 4
- DSCP 40,46 => CoS 5
- DSCP 48 => CoS 6
- DSCP 56 => CoS 7
Here are the default CoS assignement for the queue unless you modify the standard
- CoS value 0,1 => Queue 1
- CoS value 2,3 => Queue 2
- CoS value 4,5 => Queue 3
- CoS value 6,7 => Queue 4
To avoid to lose , all the QoS settings when your traffic is encapsulated into a VPN Tunnel , you can use the command qos pre-classify which will copy automatically bits for a packet’s ToS Byte into ToS byte from the tunnel header. With this you can preserve your QoS settings end-to-end even if you are crossing a VPN Tunnel.
NBAR stands for Network Based Application Recognition and can look beyond L3 and L4 information , all the way up to L7 .
Don’t forget also that NBAR relies on CEF enabled.
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