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.
Here are also all supported markings after you have classified your traffic :
- IP Precendence (set ip precedence <<value>>)
- DSCP (set ip dscp <<value>>)
- QoS group (set ip precedence <<value>>)
- MPLS experimental bits (set mpls experimental <<value>>)
- Frame Relay DE bit (set fr-de)
- ATM CLP bit (set atm-clp)
Here are all tools that we can use to classify the traffic under a class-map:
- ACL
- Existing markings ( CoS,IP Precedence,DSCP)
- QoS group
- Protocol (using NBAR)
- Traffic matching another class-map
- Mac-address (source or destination)
- Range of UDP ports
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)
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