[cisco-bba] How to reset DSCP/TOS on LNS?

Tony td_miles at yahoo.com
Mon Sep 6 01:27:19 EDT 2010

Hi Andy,

>From my reading of it that is correct. Bits 0-5 are used for TOS and bits 6-7 are used for Explicit Congestion Notification (ECN) or are UNUSED.

Some reading material:

The router is correctly setting the TOS bits to all zero as the TOS bits are only the first 6 and don't include the last two in this 8-bit header field. If your billing system is looking at all 8 bits as a TOS value then it could be suggested that it might not be an entirely correct implementation (or very old ?).

I've spent a few minutes googling and I can't find any way to explicitly changes the two ECN bits in IOS QoS. Doesn't mean it's not possible, just that nothing jumped out at me.


--- On Mon, 6/9/10, Andy Saykao <andy.saykao at staff.netspace.net.au> wrote:

> Sorry to re-open this again but is
> there a way to reset the entire TOS
> byte. Our Billing System uses the TOS value (bits 3-6) of
> the TOS byte
> for billing purposes to classify different traffic types
> (yes I know TOS
> value is outdated and we should move to DSCP but that's
> another story).
> If we reset the DSCP value (bits 0-5) or IP Precedence
> field, this
> doesn't really solve our problem of resetting the TOS value
> to zero.
> Take for example where a customer sets TOS Byte to 3.
> TOS Byte = 0000 0011
> The policy-map applied on the virtual-template will reset
> the DSCP
> fields to 0.
> policy-map QOS-POLICY-RESET-0
>  class CLASS-IP-ANY
>   set ip dscp 0
> The TOS value will now be xxx0 001x because the policy-map
> only resets
> bits 0-5 (a 1 remains in bit 6). We are left with a TOS
> value of 1. 
> We can probably get the Billing System to ignore any TOS
> value of 1 it
> sees but I was just wondering if there was a way to reset
> the entire TOS
> byte or TOS value to zero on the LNS???
> Thanks.
> Andy


More information about the cisco-bba mailing list