Cisco Switching/Routing :: QoS / Queue Drops On 3750 Switches?

Apr 30, 2013

We currently have a  site with a very simple topology that uses a 3750X switch stack for a  collapsed core. Everyday, the users have a conference call and  experience poor voice quality.Its not bad when users call from several  conference phones, but when everyone calls in on individual phones,  there is choppy and almost inaudible voice quality experienced. The  voice traffic flow would be as follows: Phone <-> 3750 switch  <-> Voice GW We  have packet captures showing that RTP packet loss is occuring from the  phone to the voice gateway, but none from the voice gateway to the  phones. We also have drops in the output queues that match drops on the  asics. I can reset the counters and they will be clear until the call,  and then they increment significantly during the call. The voice gateway  and phones are non-Cisco. The switch stack has 6 switches. We are trusting the DSCP settings on the  phones. All the queue drops from the phones are usually in queues 0-3,  but all drops on the voice gateway is in queue 0. Below are the QoS  settings; they are mostly default and we have not changed any queuing,  thresholds, or buffers. Should we specify larger buffers and threshold  for a designated queue and send EF traffic to that queue?
MySwitch#sh mls qos
QoS is enabled
QoS ip packet dscp rewrite is disabled
 Typical Port
trust state: trust dscp


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Cisco Switching/Routing :: Output Queue Drops On 3750 Core Stack And 3560 Edge Switches

Jan 10, 2013

I've been fighting what seems to be an increased number of outqueue drops on our core stack and edge switches for the last 3 or 4 weeks.(The core consists of a stack of 5 3750s in 32-gig stack mode. The wkgrp switches are 3560s. all are at 12.2.52) The  wkgrp switches are directly connected to users. We use Nortel IP phones with the phone inline with the user PC. auto-neg to 100/full. [code] However I have tried turning off QOS on a couple of workgroup switches (no mls qos, but left individual port configurations the same) but am still seeing drops.Since I have disabled qos on the switches in question (no mls qos)  (not the core tho) I am presuming these commands have no affect on the switch operation and therefore cannot be related to the problem. With QOS turned off one would presume that it is general congestion - especially at the user edge where busy PC issues might contribute. So I wanted to see if I could see any instances of packets in the output queues building up.
 I wrote some scripts and macros that essentially did a snapshot of 'show int' every 20 seconds or so, and looked for instances of 'Queue: x/' where x was greater than zero.What I found after several days of watching the core stack, and a few of the workgroup switches that are most often displaying the behavior, was that I NEVER saw ANY packets in output queues. I often saw packets in Input queues for VLAN1, once in a great while I would see packets on input queues for fa or Gi interfaces, but NEVER on output queues. [ code] Additionally, when I look (via snmp) at interface utilization on interfaces showing queue drops (both core and wkgroup), they are occurring at ridiculously low utilization levels (as low as 4 to 8%). I've tried to look for microbursts between the core and a wkgroup switch where the core interface was experiencing drops, but haven't seen any (using observer suite). [code] While the queue-drop counts aren't critically high at this point, they are happening more frequently than in the past and I would like to understand what is going on... In most cases, no error counters are incrementing for these interfaces. Is there some mechanism besides congestion that could cause output queue drops?

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Cisco Switching/Routing :: 3560 And 3750 - Any Way To Check For MLS QoS Input Queue Drops?

Feb 10, 2012

I feel that 3560 and 3750 perform differently with the following two commands:
srr-queue bandwidth shape 5 0 0 0
srr-queue bandwidth limit 50
 On 3750, the bandwidth for queue 1 is limited to 100mbps x 50% / 5 = 10mbps
On 3560, the bandwidth for queue 1 is limited to the smaller value of BW / shape weight and BW x limit%.
Does it sound about right?  is there a way to check for mls qos input queue drops? The show mls qos interface xxx stat only shows the output queue drops. Maybe for some reason the input queue never drops?

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Cisco Switching/Routing :: Adding Vlan To Trunk Drops HP Switches 3750 Behind

Nov 13, 2012

I have a 3750 as a core and have a series of HP Procurve switches that are daisy chained using one port.  I have two vlans on the port now (6 &9) and everything works fine, all switches communicate and end devices on the switches are also talking.  There is a requirement to add a device towards the end of the chain which requires it to connect using Vlan1.  Once I add Vlan1 to the port onthe 3750 I lose connectivity to all the HP switches.

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Cisco Switching/Routing :: Packet Drops On Queue On 6509 Even Though QOS Is Disabled

Mar 9, 2013

I can see drops on the 6509 Queue for interface gi1/6 , qos is disabled globaly with qos disabled all packets are in one Queue using best effort my question is if I can see drops using the sh queueing int Gi1/6 command  why I am not seeing any drops when I run the Sh int (interface number )  command. [code]

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Cisco Switching/Routing :: Input Queue Drops On Vlan 6500

Sep 8, 2012

I can  see drops on one of our busy L3 vlan in the input queue and are going up very frequently.System image file is "sup-bootflash:s72033-psv-mz.122-18.SXD3.binHardware  =  6509

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Cisco Switching/Routing :: Large Number Of Queue Output Drops On 6509E

Apr 3, 2013

we have two 6509E, as our core switches. Recently I noticed that on some connections I have a high output queue drop rate.
These 4 x 2 interfaces (gigabit) are connected to our blade encolure, consisting of 4 x WS-CBS3120X-S. The utilization of the links is really quite low, when I see the increase of the drops. (~=60Mbps). All the links are fiber (SFP) and the distance between the core switches and the enclosure is about 15-20m.
I am not aware of any service degradation on the part of the servers. No CRCs, collisions etc, on the interfaces, apart from the drops.
The line card is a WS-X6748-SFP, but other interfaces don't seem to be experiencing any problems.

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Cisco Switching/Routing :: Catalyst 4507r / Queue Usage - QOS - Total Output Drops?

Jan 14, 2013

We're having kind of a problem with our Catalyst 4507r switches. If we do a "show interface" command we're getting a lot of "Total output drops" on some of our interfaces. It seems to be most of the time on the same vlan.I was wondering if it has got something to do with QOS or queue selection As we don't have any QOS markings configured, is it possible that all traffic is using only one of the four tx queue's? 

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Cisco Switching/Routing :: 2921 / Catalyst 3560 - Router Interface Input Queue Drops?

Nov 6, 2011

i have an 2921 connected to an Catalyst 3560. My router interface shows quite a lot of input queue drops. Load is not too much max 5/255.

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Cisco Switching/Routing :: 3750 - How To Decide On Which Queue / Threshold To Use

Mar 8, 2012

I am working on a QoS design which I hope to test at some point, but at this stage its from the books.My question is how to decide which queue and threshold to use for video traffic, then lower priority traffic.I understand the shaping and sharing commands, its the queuing and threshold bit I'm not clear on.The plan is to use the priority-queue for EF marked voice, this will be policed on ingress to provide an upper limit to EF traffic levels, then my second priority traffic will be video. Which queue will get serviced first once the priority queue is empty, and how do I decide which threshold to allocate my video traffic to? The document ion is not at all clear, I want to prioritse my traffic in the following order:

1 voice, use the priority queue
2 video, this to get serviced ahead of data, after voice.
3 interactive data
4 Bulk data
5 Best effort
So Q1 settings are ignored due to priority queue. Q2 gets 70%, Q3 25% etc.Is it as simple as putting video into Q2 T1, then interactive data into Q2 T2, will Q2T1 get a higher priority over Q2 T2 once the PQ is serviced?

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Cisco Switching/Routing :: Understanding Mls Qos Queue Set Output With 3750

Apr 16, 2012

I've been  working on breaking down and understanding the default auto qos  configuration on a Cisco 3750 in the hopes of putting together a QoS  strategy that will fit our environment.  I'm having some difficulty  understanding how the "mls qos queue-set output" syntax works.
From another post, at [URL], the author offers the following example and explanation;
mls qos queue-set output <1/2> threshold 2 400 400 100 400thresshold 1: 400%
thresshold 2: 400%
thresshold 3: 100% (implicit, not configurable)
reserved: 100%
max: 400%
However, I'm having trouble understanding what is meant.  Here, it looks like it's saying, for example;
mls qos queue-set output 1 threshold 2 400 400 100 400
How  come there is syntax stating "threshold 2" when in the succeeding part  the 400 refers to thresshold 1 and threshold 2 again?  The syntax 400 400 is, apparently, already referring to thresshold 1 and 2, no?

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Cisco Switching/Routing :: 3750 Priority Queue Out Transmit Discards

Dec 13, 2011

After opening up Solarwinds NPM, I noticed that a few of my interfaces had lots of discards (who knows how long it's been sets the counters were reset)
interface GigabitEthernet1/0/25description Etherchannel to MamaCassswitchport trunk encapsulation dot1qswitchport mode trunkswitchport nonegotiatepriority-queue outchannel-group 4 mode on
interface GigabitEthernet2/0/25description Etherchannel to MamaCassswitchport trunk encapsulation dot1qswitchport mode trunkswitchport nonegotiatepriority-queue outchannel-group 4 mode on
interface Port-channel4switchport trunk encapsulation dot1qswitchport mode trunkswitchport nonegotiate,It looks as if priority-queue was configured outbound on these interfaces, could this be the cause of the transmit discards which are now up to 79,835, I just reset the counters on the interfaces a little while ago.
I'm not the best in the world when it comes to QoS, we do have some VoIP phones, but they are only a specific network, and do not travel outside, since there are used mainly for VoIP training. I do know both interfaces are running the default of FIFO.

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Cisco Switching/Routing :: 3750 - SRR-Queue Bandwidth Rate Limit?

Feb 25, 2013

If I have an interface configured as follows (on a Cisco 3750 Switch)
Interface gi 1/0/24
Bandwidth 100000
And then added the following command
srr-queue bandwidth limit 40
Would the result be 40% of the physical 1Gbps interface or 40% of the 100Mbps Bandwidth set under the interface bandwidth command.

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Cisco Switching/Routing :: 3750 QoS Output Dscp-map Queue Numbering Mis-match?

Feb 16, 2012

When configuring QoS on 3750s/3560s, we're mapping packets to particular interface output queues with commands such as: [code] The command to see what's actually being enqueued, dropped, etc. is: [code]
Note that these queues are numbered 0 - 3, and not 1 - 4.  We've been assuming that the first queue number in the "mls qos" (i.e., 1) command maps to the first queue (i.e., 0) in the "show mls qos" command.

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Cisco Switching/Routing :: 3750 Interface Total Output Drops Incorrect

May 15, 2011

I am seeing Interface output drops that appera to be incorrect.  When I do "Show Interface gi1/0/20", I will get interface output drops of "4294961382".  But, when I do the same command again it shows "0" drops.  Is this a reporting error? I am ruinning c3750-ipservicesk9-mz.122-58.SE.bin on a 3750 stack with 2 switches in the stack. [code]

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Cisco Switching/Routing :: Catalyst 3750 Switch Interface Output Drops

Mar 13, 2013

One of my Catalyst 3750 switch have many out drops, I execute "sh mls qos int g2/0/3 statist" command, there are many output drops in queue3 threshold3. [code]

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Cisco Switching/Routing :: Cat 3750 Drops First Frame / Packet With Port Security

Mar 5, 2013

our C3750 like the one described here [URL]
We have the port on the switch set like this:
switchport port-security maximum 25
switchport port-security
switchport port-security aging time 2
switchport port-security violation restrict
switchport port-security aging type inactivity
In case a device connected to the port is inactive for more than 2 minues ( aging time ) the first frame/packet the device generates arrives to the port on the switch, but the switch does not forward it to the appropriate port ( discards it or whatever ).
So far I tested on
1 30    WS-C3750E-24PD     15.0(2)SE2            C3750E-IPBASEK9-M       
2 30    WS-C3750E-24PD     15.0(2)SE2            C3750E-IPBASEK9-M       
3 52    WS-C3750G-48PS     15.0(2)SE2            C3750-IPBASEK9-M

When we remove port security from the port, it works perfectly fine, as expected.
It seems this is not HW or IOS version related. It seems it is not a stack synchronization issue, it does not matter if a device is connected to the first or other stack member. I tested on C3560 too, here there are no problems, so seems it is 3750 related.

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Cisco Switching/Routing :: 3750 Stackable Switches Etherchannel To Core Switches

Nov 18, 2011

If I have two stackable switches one switch uplinks to one 6509 core switch and the other connection uplinks to another 6509 core switch, and also the other stackable switch does not connect to the core switches. Because I am using hsrp and also we are not using vss then one uplink to the core is not in used only ones is so then how does creating an etherchannel between does two uplinks to both core switches benefit me in anyway such as more bandwith and using both uplinks at the same time or I'm I wrong?

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Cisco Switching/Routing :: 3750 Stackable Switches And 6509 Core Switches

Nov 14, 2011

If I have two stackable switches were only one stackable switch has two uplinks one uplink goes to one core 6509 switch and the other uplink goes to the other 6509 core switch can a Layer 3 etherchannel be used if each uplink go to a different core switch, by the way hsrp is running between both switches and also can you give an example how data will be routed from the stackable switch through the ethernetchannel to one of the core switch accross the WAN to another core switch?

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Cisco WAN :: 3750X-24T Output Queue Drops

Mar 22, 2013

I have a 3750X-24T in our production environment that is showing very high number of OQD's in the 'show int sum' output for 4 of the Gigabit interfaces; the interfaces are each in a seperate port channel and there are no OQD's for the relevant port channel and there are no output drops showing in the output for the 'sh int' command for each interface.
The following are the OQD's for the relenvant interfaces
Gi1/1/1:     0
Gi1/1/2:     0
Gi1/1/3:     0
Gi1/1/4:     0
Gi2/1/1:     4252879251
Gi2/1/2:     4251090833
Gi2/1/3:     4251754140
Gi2/1/4:     4294942102
Po1:          0
Po2:          0
Po3:          0
P04:          0
Gi1/1/1 and Gi2/1/2 assigned to Po1, and so on.
IOS version: C3750E-IPBASEK9-M 12.2(58)SE2

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Cisco Switching/Routing :: InterVlan Routing With 3750 And 2960 Switches?

Nov 21, 2012

I am using a 3750 as a default gateway for multiple Vlans on a few 2960 switches. The trunk lines are configured and working and I have assigned ip addresses to each of the Vlan interfaces on the 3750. My issue is that I can only ping the ip address on the Vlan interface of the 3750 if I have a working computer plugged directly into the Vlan on the 3750. I only have 3 vlans on the 3750 that have hosts directly connected (vlans 2, 10 and 40) the other vlans ( 20 and 70) don't have any clients plugged into them on the 3750 but the hosts reside on 2 different 2960s that connect via trunk ports. How do I keep the vlan interface on the 3750 switch pingable when I don't have hosts directly connected in that vlan on the 3750? (yes, I have enabled ip routing on the 3750)

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Cisco Switching/Routing :: Policy Based Routing With 3750 Switches

Oct 17, 2011

I have a simple design with 3750. I configured a route-map which define a next hop. I defined this route-map on a policy on a vlan interface.When I test some ping and a debug ip policy and it seems that my policy never match.Is there any mechanism that prevent the switch from using PBR? I think of CEF .

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Cisco Switching/Routing :: Policy Based Routing And 3750 Switches?

Sep 5, 2012

I have a simple design with 3750.I configured a route-map which define a next hop.I defined this route-map on a policy on a vlan interface.When I test some ping and a debug ip policy and it seems that my policy never match.Is there any mechanism that prevent the switch from using PBR?

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Cisco WAN :: Input Queue Drops On 6500 VLan Interface?

Dec 6, 2011

Vlan interface would be dropping packets on the input queue? Refer to the drops/flushes below.  This is from a 6500 with a Sup720, there are a number of vlans on it. This 6500 and it's HSRP partner are exhibiting the same symptoms on all the vlans I bothered to check.  This particular vlan is quite lightly used, there are only about fifteen user PC's (each with 100 Mb interfaces) on it.
There is a bit of information on input queue drops on Cisco, but this is focused on physical interfaces where I can understand some packets being dropped.  I would think that Vlan interfaces would have different issues.I note the "no buffer" errors as well, that also concerns me, especially as that counter is quite close to the "flushes".
Vlan123 is up, line protocol is up  Hardware is EtherSVI, address is 00d0.04fd.6000 (bia 00d0.04fd.6000)  Description: Vlan123  Internet address is  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec, reliability 255/255, txload 1/255, rxload 1/255  Encapsulation ARPA, loopback not set  Keepalive not supported  ARP type: ARPA, ARP Timeout 04:00:00 
[Code] .......

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Cisco Switching/Routing :: Portchannel Between 3750 Switches

Feb 20, 2013

Switch A connects to Swich B and C using port channel. I am going to bring down one link on each.
switch A is server farm , switch B and C are core 01 and 02 . and all are 3750 switches.
1. what will be the impact on the network in terms of spanning tree recalculation
2. what duration are we talking about until the spanning tree convergence happens?
3.I plan to shut down the link from CLI to bring down the links

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Cisco Switching/Routing :: L3 Routing On 3750 Switches?

Jan 21, 2013

I have a small campus network using 3750 stackable switches  and a 3725 router (see diagram below). Currently the 3725 router is handling inter-vlan routing for the campus and it looks like it's not able to handle the amount of traffic we're pushing. The router CPU sometimes hits above 90% due traffic load. What I would like to accomplish is move L3 process over to the 3750 MDF stack and the IDF1 stack. I am thinking creating SVI's on both MDF stack and IDF1 stack, run HSRP between the two stacks and may be do load balance traffic between the two stack as well.

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Cisco Switching/Routing :: 3750 - Running 7 To 9 Switches In One Stack

Aug 6, 2012

Looking for feedback from other organizations that have large 3750 stacks.  I've got one stack of (8) 3750's composed of (6) 3750G's and (2) plain 3750's.  This particular stack is usually unresponsive to SNMP queries and often fails to write config when we make changes.  After a couple tries it will finally go.  Part of my probably here is likely the plain 3750's that always boot faster and come up as the master.  I should manually set the master to one of the G's.  What I'm wondering is who else has 7-9 3750's stacked and are they performing well for SNMP, telnet, etc?  I've got another newer stack of 7 3750E's that I need to add one more switch to.  Need to decide if I want extended downtime to break the stack up or just add the 3750X to make member 8 and hope it performs well.  I have 50+ 3750 stacks working great on our campus.

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Cisco Switching/Routing :: Connecting 3750 And 3650 Switches Together

Sep 16, 2012

I have a small network using a 24 port 3750 switch.  I need to add five computers in another room and only have one Cat 6 cable running there and no room left on the 3750.  I got a 3650 to put in the new room with the new computers.  The problem is, whenever I plug the new switch into the 3750, it shuts down the port and gives me an err-disable.  I can do a shut/no shut and re-enable the port.  I searched the web and read about trunking and clusters.  I'm not sure which, if either, is appropriate.  I see various documentation that shows you can put one switch behind the other.  But nothing tells me the configuration which will allow it.

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Cisco Switching/Routing :: 3750 Stackable Switches Uplink

Nov 14, 2011

If I have two stackable switches one that connects to the 6509 core switch and the other switch does not, do I have to uplink the switch to the other switch so that switch has route to the core switch or because the switches are daisy chain there is not need to cable one switch to to the other switch connected to core switch?

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Cisco Switching/Routing :: DHCP Limitation On 3750 Switches?

Jul 16, 2012

I want to clear following things regarding Cisco 3750 switch.

1. Can I configure Multiple DHCP pool on C3750?

2. Performance effect due to same?

3. Can I resrve IP addrese from DHCP pool for specific MAC address.

4. Can I Exempt IP address from DHCP pool ?

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Cisco Switching/Routing :: 3750 Stack Switches IOS Upgrade?

Nov 13, 2012

I am trying to do ios upgrade on 5 stacked 3750 switches. All the switches have different model number, so i am wondering which image file i should download. As far as i understand all the stacked switches should have the same IOS, i may be wrong. The switches have the following model numbers and SW images;
Switch   Ports  Model              SW Version              SW Image
------   -----  -----              ----------              ----------
     1   28     WS-C3750G-24PS     12.2(35)SE5             C3750-IPSERVICESK9-M
*    2   28     WS-C3750G-24PS     12.2(35)SE5             C3750-IPSERVICESK9-M
     3   52     WS-C3750G-48PS     12.2(35)SE5             C3750-IPSERVICESK9-M
     4   30     WS-C3750E-24PD     12.2(35)SE5             C3750E-UNIVERSAL-M
     5   30     WS-C3750E-24PD     12.2(35)SE5             C3750E-UNIVERSAL-M
which image file i should use as they all have different model numbers and Cisco provides different image files for each model.

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Cisco Switching/Routing :: SFP-10G-ER Is Not Supported On Catalyst 3750-X And On Other Switches

Sep 23, 2010

SFP-10G-ER are not supported on Catalyst 3750-X and on other switches ....
%PHY-4-SFP_NOT_SUPPORTED: The SFP in Gi1/1/1 is not supported
Why ?When will ER be supported ?

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Cisco Switching/Routing :: Two 3750 L3 Switches Connected Via Trunk

Jan 29, 2012

I have client who has two distant offices with 3750 L3 as core (do all vlan routing for local office) and multiple L2 access switches with multiple VLAN’s connected to it. First 3750 is hub also connected to internet, second 3750 is spoke and acting as a router on stick. We have eigrp configured on both side ISP provided client 100Mbps link as a trunk with two vlan; vlan10 for voice and vlan20 for data. We assigned two small subnets to these vlans and Hub addresses are and respectively. How to force voice over VLAN10 and data via vlan20, but still do some load balancing? How to setup default route on second (router on stick) switch?

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