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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GLBP Configuration

I have configured GLBP on R3,R4,R5 shown in the topology above.
I would like to know why,in the output below, the Standby Router is showing the R5 instead of R4 , they have the default priority. I wonder if the Highest Mac address factors in the election if Standby Router.
another thing that I want to understand is the keyword "Preempt" in the configuration routers that are not AVG.
I know that Priority will determine which router will be the AVG now and which router will take over as AVG if the current AVG is down, but the keyword "Preempt" is still not clear to me when it should factor in

R3#sh run | sec glbp
 glbp 1 ip
 glbp 1 priority 150
 glbp 1 preempt

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R4#sh run | sec glbp
 glbp 1 ip
 glbp 1 preempt

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R5#sh run | sec glbp
 glbp 1 ip

R3#sh glbp brief    
Interface   Grp  Fwd Pri State    Address         Active router   Standby router
Gi0/0       1    -   150 Active   local 
Gi0/0       1    1   -   Active   0007.b400.0101  local           -
Gi0/0       1    2   -   Listen   0007.b400.0102    -
Gi0/0       1    3   -   Listen   0007.b400.0103    -

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*** another issue that I cannot figure out  the cause is the Traceroute from Hosts. if it goes through R3( the AVG) , it will make it to R2, but when Traceroute goes through R4 or R5 it displays the Exclamation Mark with H letter, as shown below:


Type escape sequence to abort.
Tracing the route to

  1 12 msec 12 msec 12 msec
  2 !H  !H  !H
Host#clear arp              

Type escape sequence to abort.
Tracing the route to

  1 1016 msec 12 msec 8 msec
  2 44 msec 20 msec 24 msec
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Hello All.

I like to see if I can get this worked out.

first question is can an SFP connector pass VLAN information? If the answer is no, then disregard the rest of this question and I then have my answer, if the and is yes  please read on.

So I have a edgerouter eth0 is config for ISP, eth1 -8 are all briged .
I have config a DHCP for eth1 and I connected a cable from eth1 to port 1 on the EdgeSwitch 24 ports PEO 250w.
All works correctly, not problem whatsoever.

A week later I created a VLAN2 to separate my wireless traffic, this is my config

on Router created a VLAN2, with its DCHP IP
On the EdgeSwitch I config the ports like this
switch port config
So far everything works correctly, I get an IP for my LAN 192.168.5.x and an IP for my Wireless 10.10.5.x

Now , remember I have a cable connected from port eth01 to port 1 on the switch.

My problem is when I disconnect the cable from the eth01 to the switch port 1 I can only get lan traffic, the wireless traffic dies
I have one switch that is giving me a problem, randomly, once or twice a week, the trunk ports just shuts down.  I noticed all the ports have lights on them, except the trunk port.
I have restarted the switch and the port still doesn't come up.  If I unplug the cable and plug it into another port, then plug it back into the trunk port, then it comes back up.

I reviewed the config and as far as I can see, it's all the same except one switch is using the: spanning-tree portfast default  command.
I wonder if I should even be using that command, as I noticed some switches have the command and some do not.  
Besides that, the config is the same, so I wonder what is causing port 28 on switch .38 to shut down.  So port 28 on switch .38 is connect on port 50 switch .39.

I have attached the configs, if anyone has an idea's, I'm all open to hear them.
Can't access GUI on Cisco 2960S. Any ideas?

This is what I get when I try to use the GUI.
VoIPSwitch#sh flash

Directory of flash:/

    2  -rwx    10893632   Jan 1 1970 00:01:22 +00:00  c2960s-universalk9-mz.122-55.SE2.bin
    3  -rwx         676   Mar 1 1993 00:42:04 +00:00  vlan.dat
    4  drwx         512   Mar 1 1993 00:03:02 +00:00  online_diag
    5  -rwx        3096   Mar 1 1993 00:18:29 +00:00  multiple-fs
    6  -rwx        1915   Mar 1 1993 00:18:29 +00:00  private-config.text
    8  -rwx        7582   Mar 1 1993 00:18:29 +00:00  config.text

System image file is "flash:/c2960s-universalk9-mz.122-55.SE2.bin"

cisco WS-C2960S-48LPS-L

Switch Ports Model              SW Version            SW Image
------ ----- -----              ----------            ----------
*    1 52    WS-C2960S-48LPS-L  12.2(55)SE2           C2960S-UNIVERSALK9-M

Configuration register is 0xF

Here is the running config
VoIPSwitch#sh run
Building configuration...

Current configuration : 7582 bytes
version 12.2
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
hostname VoIPSwitch
enable secret 5 $1$7zA0
enable password 7 0000GqN8z/tU
username admin password 7 104359121112104359121112104359121112104359121112

no aaa new-model
switch 1 provision ws-c2960s-48lps-l
no ip …
On a cisco Nexus 3172 Chassis - if I enable flow control in and then out on an existing up/up port, will there be
an interruption in traffic flowing over the port? Generally these ports are part of an Etherchannel group. TY
Microsoft Windows 2008 R2 Server NPS

I recently set up a Microsoft Windows 2008 R2 Server running an AD, DNS, Certificate Authority, and NPS.  The goal is to authenticate wireless and wired clients via EAP/TLS and PEAP-MSCHAPv2.

Currently, the wireless clients are authenticating with both PEAP/MSCHAPv2 and EAP/TLS as expected.

The wireless network is a Cisco 2504WLAN controller running 8.2.112 firmware.

However, none of my wired clients will authenticate with either EAP Type.  I do know they are contacting the NPS server because each time I initiate a connection I receive the following events.

4672, 4624 and 4634




The NPS event log does not have any entries in the system for when my wired clients attempt to authenticate.

I have tested with two different switches’.  One is a Cisco 3560CX running IOS 15.2 and the other is a NetGear GS110TP.

I did read in another forum that it could be the MTU setting on the NPS server and it suggested setting the MTU size in NPS to 1344 which I did.  This did not seem to make any change.  I’m not sure what to look at from here any help would be greatly appreciated.

I double and tripled checked the shared secret’s which at this point I have simply set to “password” for testing purposes.  Later obviously this will change.

Cisco switch configuration:

| => ssh Cisco@

c3560cx#sh run bri
Building configuration...

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Dear Experts, I'm testing the SPAN feature in Switch Cisco 3750. This is the diagram:

This is configuration on Core SW:

monitor session 1 source vlan 55 both
monitor session 1 destination interface g1/0/13

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It seems like working but the whole vlan 18 was hang, so I could NOT access the PC which was installed wireshark. How can I fix it? Can we just mirror traffic from some IP addresses, not all VLAN?

Many thanks as always!
I have a Mikrotik CCR 1009-8G 1S-1S+ and 5 Cisco Switches WS-C2960-24TC-L that were provided by the customer for our use in this network. I have a question on how to setup the VLANS so no Tenant in the building can access any other Tenants network. There is a mix of Static IP tenants and DHCP Tenants. I have the Mikrotik Setup with all the needed VLANS for each DHCP Tenant. I have also assigned each port for VLAN access to only one Tenant. My issue is how to secure the VLANS.

I know this is a vague description of what I have to work with so I have attached a PDF of the network. If any other information is needed please message me and I will attempt to comply.

Thanks in advance for any and all help.

I'm working with a customer who has a camera system and it's configured for remote viewing. Unfortunately, this is causing the customer (a retail store) to fail their PCI compliance scan due to open ports.

My suggestion was to purchase a second static IP from their WAN vendor (Verizon FiOS) and use 2 routers: one for their POS system (an existing SonicWall) and a new router for their WiFi and camera access. So the system would look like this:

Verizon FiOS ONT Box
HP 1810-8g Switch
SonicWall Netgear

The problem is that when I connect the SonicWall through the HP switch, the WAN port won't connect. When I set a laptop to the same static IP and plug in it to the same switch port on the HP, it connects fine and is able to pass data. As soon as I connect the SonicWall directly to the FiOS ONT, it works fine.

Here are a few more specifics:

SonicWall MTU: 1492
HP MTU: Default (1500?)
HP Switch: No VLANs set; LLDP disabled; jumbo frames off; port mirroring off; flow control off; green features off; loop protection off; advanced security off; no trunks configured; management port set to Port 8 on an unused subnet

Any help would be great. Thanks.
My office have many cisco switch and  routers. What is best centralized tool/ software to monitor\ control the cisco router and switch?
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In my environment, I have many IOS devices and 2 Nexus 5XXX switches. A former engineer configured radius for the IOS switches and the policy works without any challenges.

I followed the following article (https://www.802101.com/cisco-nexus-aaa-authentication-radius/)  for configuring RADIUS on the Nexus and the config appears to be correct. The challenge is that when I log in with my AD account, I am given a total of 17 commands instead of the full listing for priv-15.

I checked the event logs and see the Nexus are using the correct network policy.

I have tried the following values for the Cisco-AV-Pair without any success:

shell:roles=*”network-admin vdc-admin”
shell:roles=”network-admin vdc-admin”
priv-lvl=15, shell:roles=*"network-admin vdc-admin

Please see attached screenshot of the Network policy.

I have 2 Windows Server 2016 Std servers with the NPS role installed and configured.

Here is the running config for RADIUS - I have changed the IPs for privacy and changed the radius password for here:

Nexus5k01# sh ru radius all

!Command: show running-config radius all
!Time: Tue Jun  5 14:28:46 2018

version 6.0(2)N2(1)
radius-server key 7 "radius*password"
radius-server test username test password test idle-time 0 
radius-server timeout 5
radius-server retransmit 1
radius-server deadtime 0

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Does anyone have a good example for implementing QOS on a Nexus 9000 switch ?
I bought used cisco 3750 switches and after a reset I cannot get them into express setup mode
We currently have two Nexus 93180YC-EX and two Nexus N2K-C2248TP-E-1GE in our environment. From all the articles that I've read so far, the Nexus 9K will only support topology 1, but doesn't support topology 2 (see attachments), is that correct? Any input will be greatly appreciated.
Dear Experts, I'm testing this network diagram with EVE-NG

Without the NAT translation and access-list, all 3 VLAN PCs can ping to, SLA also work OK to switch from default route to backup route.

With the NAT and access-list, PCs from VLAN11 and 12 could not ping although I allowed icmp on R1's interface. The PC on VLAN13 (not it NAT and access-list still could ping to How can I fix it with NAT and access-list?

I attached the configuration files.
TFTP connections, I just opened my tftp software, as I needed to save a switch config and I'm seeing tons of these entries in my tftp server.
Does anyone know what these are?  I haven't configured any switch to automatically backup configs or anything.
I have a cisco 3750G switch that for some strange reason, all of a sudden my trunk port, that is the link to the other switch just stopped working.
I have restarted the switch, works fine for a few hours and then shut off again.  I don't get any errors in the logs, just dies, any idea how to troubleshoot?
My customer has 1 pair of Cisco N5K configured with VPC.

I going to deploy 1 DellEMC Unity 300 storage to their infra. The Unity 300 will serve as their NFS server.
The proposed interface configuration is LACP on Unity 300.
which mean from SPA, I will have 1 connection to their first N5K switch and another connection to their second N5K.

I just want to know is this doable? from what I understand, VPC is 2 separated switch unlike stacked.

Dear Wizards, is it possible for a DHCP pool was deleted automatically? How can I check the log for that? Is it possible to check the historic commands on switch when the ssh connection was turned off? Many thanks.
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I have a HP 2530 24G switch that I'm trying to get into ICMP V3 mode.  Trying the command: <ip igmp lookup-mode ip> it tells me it's invalid.  I don't see any igmp commands that allow me to switch versions despite having version YA.16.05.0008 of firmware and the manual showing that I can configure this.  Any ideas?
configuring vlans on HP 5406zl
I'd appreciate some advice on configuring a data and voice vlan on a HP 5406zl, the current config is attached.
currently the whole switch is configured on the default vlan, however I want to add a voice vlan for a up coming voip phone system replacing the old analogue pabx.
the goal is to connect the pc's through the phones, phones on Vlan30 and Data on Vlan1.
I have added the vlan30 , however in need of some advice on the tagging and untagging of ports and the routing to enable the vlans to communicate with each other.
this switch also acts as the core switch and has IP routing enabled, it has 6 poe modules (ports A1- F24)
A1 to F22require both vlans , F23/F24 will be used to connect to switches on another floor and need to pass both vlans through. F17 is the link to the FW
appreciate some guidance on this as HP is not mother tongue, when switching.
Good afternoon All

I am looking for community help to get me started on a Dell PowerConnect X4012 (2switch stack) configuration for 3 Dell XC servers with Nutanix on them.  I also have a TOR switch stack of 2 x Dell 3024 switches.  I have found in the past best practice documents for configuring Dell kit for VMware but I can't find anything conclusive for the above.

What vlans am I going to require for Nutanix AHV HCI?  

Any help gratefully received.

I have 3 WS-C3550-48-SMI and they are connected to each other via 1000BaseCX Gigastack. But they are only half-duplex. My users are experiencing slow response. Could it be because of those trunks with half-duplex?

sh int status
Port      Name                      Status           Vlan       Duplex      Speed      Type
Gi0/1     Switch A & C       connected    trunk      a-half        a-1000      1000BaseCX Gigastack
I am trying to provide access to a camera on a remote network for a user by configuring VLAN on various L3 HP switches. The network I am working in has numerous VLANs and the path from the device to the camera crosses at least 4 L3 switches. I have been unable to get the connection to work and at this point need troubleshooting tips and a better understanding of how this should work.

At this point I would like to focus on a suggested methodology to troubleshoot connectivity on a VLAN. I have been told ping will not work because this is a L2 VLAN not intended to be routed from everything and that is why ping will not work, I think this is nonsense but please let me know if there is a way to track the VLAN path to see where the disconnect might be. Also, there has to be a L3 component as the source and destination networks are different and the route to the destination is specified on an L3 route table.

The following is the basic configuration:

Device :
Attaches to Switch 1 in VLAN 13 using an untagged (access) port. The PVID (native) VLAN on the configured port is 13.
There is no VLAN 13 interface configured on Switch 1. Using NDP and routing tables, I know that Switch 1 connects to Switch 2 using Tagged (Trunk) ports that include VLAN 13.
Switch 2 does not have an interface configured for VLAN 13.
I am unable to ping the camera from Switch 1 or Switch 2. There are no ARP entries for VLAN 13 in Switch 1. There are VLAN 13 entries in the ARP table on Switch …
We have ( 2 )   Cisco SG-300 switches and we have created Vlan ( Vlan ID - 5 ) without trunk port. Both switches are on different location. We connect them both on Vlan port.  

And now devices which are connected on that switches can communicate individually. but That switches are unable to communicate.

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.