Switches / Hubs





A switch is a device that filters and forwards packets of data between LAN segments. Switches operate at the data link layer or the network layer of the Open Systems Interconnection (OSI) Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs. A hub is a connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports; when a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

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While trying to apply a QoS outbound rule to a Catalyst 9300:

Invalid queuing class-map!!! Queuing actions supported only with dscp/cos/qos-group/precedence/exp based classification!!!

The config we are using is below:

policy-map Shoretel-Input-Policy
class class-shoretel-media-input
  set dscp ef
class class-shoretel-signaling-input
  set dscp cs3
class class-default
  set dscp default
policy-map Shoretel-Output-Policy
class class-shoretel-media-output
  set dscp ef
  priority level 1 percent 5
class class-shoretel-signaling-output
  set dscp cs3
  bandwidth remaining percent 15 
 class class-default
  set dscp default
  bandwidth remaining percent 60

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On a Cisco 6509 w Sup 720 - is there a way to tell if the 10Gbps fiber transceivers are multimode or single?
Or find out other attributes? The commands I'm running keep showing me unhelpful info like:

#show interface TEn 5/4 transceiver module 5  
Transceiver monitoring is disabled for all interfaces.

ITU Channel not available (Wavelength not available),
Transceiver is internally calibrated.
If device is externally calibrated, only calibrated values are printed.
++ : high alarm, +  : high warning, -  : low warning, -- : low alarm.
NA or N/A: not applicable, Tx: transmit, Rx: receive.
mA: milliamperes, dBm: decibels (milliwatts).

                                         Optical   Optical
            Temperature  Voltage  Current   Tx Power  Rx Power
Port        (Celsius)    (Volts)  (mA)      (dBm)     (dBm)
----------  -----------  -------  --------  --------  --------
Te5/4         34.0        N/A       5.7 --   -2.9      -3.7
HP 2930 switches use VSF for stacking. Documentation describes "chain" and "ring" configurations.  Is it possible to use VSF in a "star" configuration?
I'm trying to get an HP 2920-48G Procurve switch setup with multiple VLANs that received DHCP from a Server 2012 R2 server on one of the VLANs. I'd also like one of the VLANs (VLAN 30) to be restricted from seeing any other traffic and only able to route outside.

I am having a difficult time getting DHCP to work on any VLAN other than VLAN 1 and that only works because it is on the same subnet.

The DHCP server IP address is
VLAN 1 is
VLAN 10 is
VLAN 20 is
VLAN 30 is
VLAN 40 is yet to be determined

Internet firewall is

Below is my config. I have recently updated the firmware on the switch to the latest stable release from HP. Any help would be greatly appreciated.

Startup configuration: 8

; J9728A Configuration Editor; Created on release #WB.16.08.0001
; Ver #14:

hostname "HP-2920-48-1"
module 1 type j9728a
trunk 48 trk1 lacp
ip route
ip routing
snmp-server community "public" unrestricted
   ip address dhcp-bootp
router rip
   redistribute connected
vlan 1
   name "DEFAULT_VLAN"
   no untagged 1-15,17-47
   untagged 16,Trk1
   ip address
vlan 10
   name "Business VLAN"
   untagged 1-15,17-47
   tagged Trk1
   ip address
   ip helper-address

I have a set of 3 HPE 2920-24G-PoE devices currently running with the stacking module connecting the 3 together.  I need to add a 4 switch to my network to accommodate new drops in the building and have a spare HPE 2920-48G-PoE device and a stacking module.  Can I just add the 48 port device to the stack of 3 - 24 port devices?

We have an HP 2530-24G-PoE+ (J9773A) where our port 11 keeps going on-line and then off-line. The device that we have connected to it is a wireless AP that uses POE. When I go into the logs of the switch all it says is that Port 11 is now on-line and then the next line is that it has gone offline. With no other information. What can I do to find out what's wrong with that port? I'm still very new to programming on a switch.
Hi guys, I have bought some mellanox gear pretty cheap off Ebay. I need to set some time aside to properly read through everything and learn what i am doing. But i am just trying to get it online to do some basic testing and even that seems to be a bit of a pita.

My setup is blade M1000e with 2x M4001T switches both showing as online. I then have 40Gb NICs in two R730 servers. Both these connections are showing as disconnected. (if they connect direct without the switch they work perfectly)

I purchased a 56Gb/s card for a blade server and installed that. I then installed OpenSM / mellanox software and i created the mellanox service. I then started the service and the first port came online. I assigned it a static Ip address but none of the other ports came online.

The documentation for this specific switch is eluding me. If anyone has some information on what i need to do for the config it would be appreciated!

I have ordered a serial cable to plug in to the device but from what i read, i was led to believe i wouldnt need one as i can use opensm to configure the switches and bring them online.
What is the best practice for restarting (After Hours or Before Hours) Juniper switches ? - Should those switches be restarted once per month - twice for the year - once a year etc ?

Juniper EX Series Ethernet Switches
We have an Allworx phone system, with HP and Aruba Procurve (PoE) switches connecting the phones and servers. We have a problem with intermittent one-way audio- I think I know the cause but I don't know how to solve it. Our phones are supposed to obtain IP addresses in the range from the Allworx server. I have found that a small number of phones randomly obtain IP addresses from our Windows DHCP server in the range The VoIP VLAN is set to 200 and the Windows distribution VLAN is set to the default (I believe it is numbered as 0 on the switches). Every time a phone has the one-way audio problem, it is in the Windows distribution range. Not every phone in the windows range has the problem, but every time a phone has a problem it is in that range. We don't want to expand the VoIP traffic into the Windows range. But I think the problem is the phones that get the wrong IP addresses. It is not limited to a set of phones, but there are usually about 5 or 6 that could be any of 45 phones at this site. All phones are statically set when they are issued to use VLAN 200, and the problem occurs regardless of phone or switch port. Users are not moving equipment around, so that is not the cause.

So the problem is that DHCP appears to be bleeding into VLAN 200. The PC's on the DEFAULT VLAN never get IP addresses in the network. Switches are up-to-date with firmware. We have this problem at other sites as well, but one site …
cannot resolve issue after  reading this question - viewing Win 2008 NPS Server and Cisco Switches.

Hi I have followed the 2 wordpress instructions to configure my router with "aaa" and have also followed screenshots for configuring a test windows 2008 standard test radius server but in the eventviewer it states:

"A radius message was received from the invalid radius client ip address x.x.x.x which is the ip address of my directly connected router  fasterethernet interface, which is attached to my only windows 2008 server.

steps carried out after following wordpress screenshots:

i have no vlans in place as router is set to defaults ie vlan 1
i have left cisco 2950 switch not configured with access or trunk port connecting to router as left as defaults
i can ping from windows 2008 server all the way to the switch & the router - successfully

i opened up putty directly on my windows 2008 server and selected 'COM' port to test login which allows me in but not successful to the radius server - as states on router:

"radius-4-radius_dead: radius server x.x.x.x: 1812, 1813 is not responding
"radius-4-radius_alive: radius server x.x.x.x: 1812,1813 is being marked as active

- i also added 1645 & 1646 on my router so both entries say same thing as above - on windowns 2008 it states in properties both 1812, 1813, 1645 & 1646 so i assumed i can use either or …
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We have a switch 3560 where two physical ports are configured and two ports are put into channel as the below.  On the channel, do we need to add the same configuration on the channel as the physical port? Thank you

interface GigabitEthernet0/20
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 10
 switchport mode trunk
 switchport nonegotiate
 channel-group 10 mode on
I'm looking at installing 14 switches in a data closet and I wanted to know exactly how many amps will that draw at startup, to ensure I have enough power circuits.
I've looked at the technical specs found below, but I'm trying to calculate exactly how many amps each switch will draw, so I know if I need 2 or 3 circuits?

I'm planning to have (7) 2960X -48-FPD-L in a stack, and each one on a APC.  Also was trying to figure out if I need a 20amp or 30amp circuit, I'm guess if I get a 30 amp circuit,
it gives me more options for the APC to use.

Any thoughts?
We are moving into 2 new buildings.  One is a church and the other is an admin building, corporate.  There will be fiber connecting both buildings.

Option 1
I'm debating whether it's better for the church to have it's own separate ISP connection, firewall, it's own switches and not be tied to the admin building in any way, or option 2.

Option 2
Or should I just have one ISP connection for both the admin and church buildings, and have switches that I manage on their own vlans for the church, but have one big network for both buildings?

Any idea's for best practice.  For management purposes, it's easier to just have one large network instead of creating two separate ones, with each having their own ISP connections.

Any recommendations, and why for each case.
We are moving into a new building, and we will have all newer Cisco switches, 2960X and 3850's for the cores.
I'm planning to have different vlans for the servers, PCs, VoIP phones, but I was thinking, since all of the different equipment need to communicate with the servers,
I will need to allow and route all the different vlans to access the servers vlan.  If that's the case, is then better to just create one flat network, everyone in one vlan, a /22 instead?
I guess I need to find some good articles on line to dig deeper into vlans, but on the surface, besides having a smaller broadcast domain, it just adds more complexity.

Any thoughts?
I have a Cisco ASA 5512x which I use as my router with Cisco switches and AP's.  I have configured one of the interfaces for our Guest Wi-Fi which it was working.  However I recently got new AP's and switches from Ubiquity  and now that Guest Wi-Fi does not work.  I want to know if it is just a configuration issue or is there just a flat out incompatibility between the 2 vendors?


As the title states we need to implement dt-lacp for our vsphere servers, iscsi will be in use to our msa2040 san as well so jumbo frames all around.

So far this is all straight forward.

The kicker here is we also want to implement a switch pair to function as the routing for our core. we run a dual homed network with ipv4 and ipv6 routing. dt-lacp does not work with v6 so how would the links to the route pair support high availability? STP seems to be the only way? is there a more novel approach i'm missing?
Hi One switch 3560 is connected to 4500 through two interfaces, which are bound as port-channel and as layer 2. Under the 3560, there are some PC and ip phone. so we use auto qos at each interface of 3560. Now we also need to configure auto qos voice trust on the port-channel. but 3560 port-channel does not support auto qos. How can we resolve the issue? Thank you
I have one DellS4148T switch and MXL force10 fabric switch . I need to configure both switch and also i need to enable lagging. For connectivity of both switches we are using 100GBE QSFP28 to QSFP28 passive copper. Please help me
Hai Guys

We have one Dell switch S4148T and its have four 100GBE and two  40 GBe  SFP+ port.  Same like we have one dell chassis M100E.  It have two dell force10 MXL 10/40 GBE balde switch. we connect the cable from S4148T to force10 MXL blade switch and do the initial configuration. But still swicth ports are down ( both 100GBe and 40 GBe) . Any one can help me to resolve this issue. Can you share the configuration with me
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Hi, we have an ubuiquti EdgeRouter, with a few vlans, now we created a separate vlan for testing our cameras today, and i edited the WAN_IN policy, but its not hitting my cameras.
What do i need to change on the ubuquiti to allow traffic to the camera on this vlan?
Brocade FWS648G Vs 7.4.00 is there any on line documentation available or user groups for this switch?   Or can you recommend a current source that would work as well?
We currently have two sites that are connected with an E-Lan that is provided by Spectrum. All switches are2960s so there are no L3 switches. We need to stream live video between the 2 sites; each site has an encoder and decoder for sending video. The encoders/decoders are in their own vlan (50) but there are other vlans for data. I have no experience with QoS and I'm very confused about how to implement it. I know I will use CoS but not sure how to go  about it. I'm including a diagram to help visualize it. Thanks for the help.

I have a cisco 3750G POE 24 switch, and it's not booting.  I have uploaded a new IOS via TFTP, did a reload, and now I'm at the switch: prompt
I have included a picture, I have tried a few things, but nothing I'm trying worked.  Any suggestions how I can get the switch to boot correctly?

I have an HP E5406zl switch with several vlans that was set up by a vendor. The switch seamlessly routes traffic for all vlans... meaning there appears to be no security between vlans.
All subnets can reach each other.

Is it possible for the switch to route selectively? Can I create an access list that prohibits certain vlans from communicating? (or is this just wrong?)

I can use a firewall to protect a vlan, but I'd like to do it with the switch itself if that even possible.

Thank you!
Hey guys,

I’ve two PowerConnect 6224 switches which are linked to a Dell SAN (for redundancy) and one of the switches are then plugged into the local LAN.  I’m changing the local LAN switch but when I connect the Power Connect SAN switch to the new one, it doesn’t work - I can’t access any of the servers on the SAN - it’s a big odd, as there’s no config on the previous LAN Switch- what am I missing?


Switches / Hubs





A switch is a device that filters and forwards packets of data between LAN segments. Switches operate at the data link layer or the network layer of the Open Systems Interconnection (OSI) Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs. A hub is a connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports; when a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.