CatOS to IOS QoS compatibility?

[Solomon Sands]

All,

Are there any considerations to make for connecting newer IOS devices to older CatOS?

Summary:

6509 switch with CatOS 8.7, policer values shaping 20M cos 5. Router connected is 891 with IOS 12.x. Traffic is untagged and being sent at a rate of 20M going in to the 6509, it is then tagged with a VLAN and cos value to get accross the network. With the CatOS policer on, the traffic slows to 5M and the only way to get the traffic up to 20M is to either remove the policer or turn it up to 60M with max allowed burst and eburst. It's being mentioned that there may be an issue with IOS and CatOS as far as policing rate and the time rate that the policer evaluates traffic.

Hoping sombody here can provide some insight in to this.

[Joseph W. Doherty]

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Posting

Policers commonly restrict bandwidth below their nominal settings as short term bursts are subject to packet drops.  Increasing Bc (and Be) might help.  (If I understand your posting, you've already discovered increasing Bc/Be increases throughput, but I wouldn't expect you to also need to increase the nominal bandwidth, unless Bc and Be are very restricted in how large you can set them.)

[Solomon Sands]

Right, we have bumped up the burst initially but the traffic still never made it past 7M.  Is is possible to alter the Tc (Time interval) on either devices? Or perhaps a known fomulaic solution for converting speeds between devices?  I know that, for example, IOS measures in bps, CatOS in kbs, but with different Tc and thus Bc and Be rates, is there again any known or published knowledge / Best Pactices on the issue?

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

Tc should change with Bc/Be, I believe.

Concerning formula solutions, I think I recall some Cisco papers on setting CIR Bc and Be on Cisco's main website.