CBWFQ + WRED enquiry

[bigeric]

Dear Sir,

I have a question on CBWFQ + WRED

for example

policy-map test

class ftp-traffic

bandwidth 2000

random-detect

class other

fair-queue

My requirement is to give minimum bandwidth to all ftp traffic on my wan link and also reduce packet loss by using congestion avoidance technique.

In this case, the bandwidth command guarantees bandwidth for all ftp traffic. As all ftp trafifc has no IP precedence, how can WRED prevent drop of ftp traffic by dropping other non-ftp traffic?

thanks

Eric

[vkapoor5]

In your case, you are using Class based RED. Enable it even in "other" class also. By default, in your case WRED assumes all packets with precedence "0". And your FTP traffic class gets reserved bandwidth of 2000, so if it crosses or nearing to this limit only WRED drops packets in this class. But, in "Other" class, packets can drop at any time during congestion.

[bigeric]

As I know, WRED is used to drop packet before the queue is full in order to avoid tail drop. am I correct ?

I understand that in "other" class, as I didn't apply any congestion avoidance technique, it will use tail drop , right?

But in ftp class, I have applied WRED. I assume the WRED will drop packet before threshold to avoid tail drop. However, as all ftp traffic in that class are with same IP precedence, how will WRED drop packet ?

Will WRED drop ftp traffic in the queue randomly ?

[ozgur.guler]

you should use random-detect

under your "class other" or "class-default" if you want to protect your ftp traffic.

class class-default

fair-queue

random-detect