QoS Marking problem on layer 2 port-Router 878?

[blackhat2020]

Hi every one.we have a 878 router and we want to mark traffics when entering on its lan interface.its lan interface is a layer 2 interface and we have created vlan interface and assosiated lan interface to that vlan.on vlan interface itself there is no service-policy command so we have to put serive-policy command on interace fast 0 itself which is layer 2 port.when we assign service-policy to fast 0 it doesnt work and it does not mark any traffic also class default counters doesnt increase to indicate any traffic is passing even it is not getting marked. ios version is advipservices.124.9T. so please guide me how to mark traffic on this port. ii dont know why service-policy command is supported on layer 2 interface when it doesnt work at all.how should i activate this ? thanks in advance

[Peter Paluch · Accepted solution]

Hi,

Can you explain the need for Layer2 QoS marking in your network? Using Layer2 QoS marking on routers is usually pointless because of two primary reasons:

• The QoS marking abilities on Layer2 are considerably limited. For example, with Ethernet, there are only 8 QoS classes available, and in addition, the 802.1Q encapsulation must be used (the CoS bits are present in the 802.1Q tag). With plain Ethernet frame format, no QoS marking is available at all.
• The QoS marking on Layer2 is not preserved when a packet is routed from one interface of a router to another, because in such case, a new frame is created by the router and the original IP packet is put into it. The new frame does not inherit the QoS marking of the old frame (in many cases, it even cannot - think of routing an IP packet from an Ethernet LAN through a PPP dialup connection). Thus, even if you set a Layer2 QoS marking, it will not extend beyond the boundaries of a single LAN.

Best regards,

Peter

[Nagendra Kumar Nainar]

Hi,

Per my knowledge, Qos is not supported in vlan or L2 interfaces of 878.

Regards,

Nagendra

[blackhat2020]

thanks for reply. actually i dont wnat to use CoS bit marking,i want to use dscp marking but my problem is that this version of ios doesnt support service-policy on vlan interface,actually in 6500 switches we can use service-policy on vlan interfaces when we use command mls qos vlan base on layer 2 port itself.

But sofar i think service-policy command on interface fast in 870 router just let you mark based on CoS not DSCP. thank u guys.