QoS with 6800/4500/3850

[Arjun Dabol]

Hi Experts,

seek some help here with respect to QOS on some advance platforms such as 4500/6500/6800 -

1. I understand that these platform have significant difference compare to MLS that runs on 3750s. these platform just do not support MLS anymore. and lot of things are enabled by default.

Can you just help me understand some high level, regarding QOS on these platforms like what has changed ?

2. More specifically - when any marked packet comes at ingress of these platform - will they trust by default ? or we need to do anything ?

for ex:   cisco phone-----3850-----4500----6500

In above example : do I need to trust marking on ingress of 3850 done by cisco phone  or its by default trusted?

also How ingress interface of 4500/6500 will treat packets marked by cisco phone ?

Thanks

Abhishek

[InayathUlla Sharieff]

Abhishek.

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/qos/configuration_guide/b_qos_3se_3850_cg/b_qos_3se_3850_cg_chapter_0100.html#reference_E759D1E32E5B4F62B8933FD8967967B2

Check this out.

[Mark Malone]

Just to add on a 3850 you can set auto qos as per InayathUllas link above and depending what you put in access port it will generate a different map type but it will also trust DSCP values by default , we ran through this with TAC, we only cared about it being honoured and not re-written on some 3850 interconnects we had , so we ran this command to confirm what TAC said and then we use a span to capture traffic on egress and ingress to confirm packets entering and leaving didn't get altered or changed in markings , we did use the actual auto qos on a couple of access switches on another site and that worked fine too

first is voice /second is video

#show platform qos dscp-cos counters gigabitEthernet 1/0/2 | i DSCP46
Ingress DSCP46 211234066     0
Egress DSCP46 798025994     0
#show platform qos dscp-cos counters gigabitEthernet 1/0/2 | i DSCP34
Ingress DSCP34 89330715      0
Egress DSCP34 174876983     0

That's ios-xe 45s and 65s on ios work differently depending on what sup you have in place , some are auto qos some are mls and some are set differently

as example here is sup720-3b , this tells you below as per doc below

The CoS value is carried only by Inter-Switch Link (ISL) and dot1q frames. Untagged frames do not carry CoS values. Untagged frames do carry ToS values which are derived from IP precedence or differentiated services code point (DSCP) from the IP packet header. In order to trust the ToS value, you need to configure the port to trust IP precedence or DSCP. DSCP is backward compatible to IP precedence. For example, if you have configured a switch port as Layer 3 port, it does not carry dot1q or ISL frames. In this case, you need to configure this port to trust DSCP or IP precedence.

#sh queueing int g3/9 detailed
Interface GigabitEthernet3/9 queueing strategy:  Weighted Round-Robin

  QoS is disabled globally
Trust boundary disabled

  Trust state: trust DSCP
  Extend trust state: not trusted [COS = 0]
  Default COS is 0
    Queueing Mode In Tx direction: mode-cos
    Transmit queues [type = 1p2q2t]:

[SIDNEYOBRIEN8830]

I don't have auto QOS but if I look at the interface I see below

interface GigabitEthernet1/2/2
description Avaya Phone Connections via Avaya ethernet switch
switchport
switchport mode trunk
platform qos statistics-export
platform qos vlan-based
platform qos trust cos

Does this mean that QOS is enabled on this interface?

[Joseph W. Doherty]

I recall (?) on the 4500 and/or 6500/6800 some form of QoS is always active. Of course, if device, by default is resetting all packet's CoS/ToS to zero, all traffic get treated alike, i.e. effectively QoS appears to be inactive, but that's because just one egress queue is being used.

[Joseph W. Doherty]

#1 The reason those chassis devices' QoS are so different from the 3750, they support various supervisors and line cards, both of which can have very or rather different QoS architectures. (Very different, 3750<>4500<>6500/6800 - rather different 4500 sup X <> 4500 sup Y or 6500/6800 sup X and/or line card A <> 6500/6800 sup Y and/or line card B)

Helping you understand what's changed, is difficult, because again, even on the same platform, how QoS works can vary much based on what's installed in the chassis.

Unfortunately, safest course is to read QoS documentation for specific platform's hardware and/or IOS.

#2 I believe most of those older platforms, will, by default, not trust an ingress packet's ToS unless somehow configured to do so. However, that might not be the case on latest IOS versions and/or follow-on devices. For example, recently dealt with similar question for a 4500-X, which appears, by default, to trust ingress packets unless auto-QoS is configured, than trust depends on CDP seeing device as a VoIP phone, if it does, it trusts, otherwise it doesn't. (Think that's what I found.)