Questions tagged [switch]

For questions about network switches, the term commonly refers to a multi-port network bridge that processes and routes data at the data link layer (layer 2) of the OSI model.

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5
votes
3answers
9k views

The maximum length of CAT6 for intranet network?

Recently I purchased CAT6 cable with a length of 150 meter. I bought another CAT6 with a length of 148 meter. I joined both the cables using RJ45 cable coupler. I tested it using LAN TESTER, and ...
22
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3answers
55k views

How does a switch learn a switch table?

Say the switch table is empty. If computer A sends a frame destined to computer B, the switch will broadcast asking who has the mac address of B. What if C suddenly sends a frame to A? What is the ...
33
votes
1answer
65k views

Using SNMP to retrieve the ARP and mac-address tables from a switch

I would like to get ARP tables from a switch to a syslog-ng server that has been set up on Ubuntu Server 12.04 LTS. I have read about SNMP and I know the server will act as a manager and the switch as ...
15
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4answers
5k views

Why is the CAM table in a switch called CAM table and not MAC table even though it holds MAC addresses?

I know the CAM table in a switch holds MAC addresses and the ports that are associated with the respective MAC addresses. There are no such thing as CAM addresses from my knowledge, so why is it ...
40
votes
4answers
35k views

Bits per second vs. Packets per second

Lately I have been checking datasheets of several switch models from diferent vendors. For a given switch, vendors publish a couple of figures that I think are a measure of the capacity/performance of ...
22
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8answers
6k views

Why can't devices on different VLANs, but on the same subnet, communicate?

I have a question about switching. I have two devices connected to a switch with IP addresses 192.168.5.20 and 192.168.5.10. Both devices have the same prefix, /24. That means they are on the same ...
10
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3answers
34k views

How does a switch learn a MAC address not in its lookup table?

I have a relatively dumb question. Suppose the Switch just started, and it received a frame that contains a destination MAC address for a network device not in its MAC addresses table. What happens ...
12
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1answer
4k views

Mac / CAM entries from non-Cisco switches with Q-BRIDGE-MIB

How do I do community string Indexing for other switches like D link DES 3526 and Brocade Fastiron SX800? I am running a java program to poll a specific vlan on a Brocade sx 800 l3 switch. The ...
19
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2answers
23k views

Ethernet autonegotiation differences between (10M | 100M | 1G) Ethernet

I am studying for CCNA and on Wendell Odom's book is said that(regarding autonegotiation): When autonegotiation fails on one node, to choose (half/full-duplex) we must use the rule: If you have a 10/...
7
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3answers
4k views

Does a switch understand packets? If yes, what is the frame terminology for?

I was a little confused between packet and frame. The confusion was based on, if a switch is a layer 2 device, how does it reads a packet from a layer 3 device, and where is the 'frame' thing which is ...
12
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3answers
2k views

Is there such thing as a network bridge?

Is there such a thing as a network bridge or is it always meant as a switch implementing a bridging function? Whilst bridges are described as devices that create separate collision domains in network ...
14
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2answers
11k views

Why does “show interface” show “Last input never” when packets input is incrementing?

Why is it that when I perform a show interface command I see that Last input always shows never? FastEthernet1/31 is up, line protocol is up (connected) Hardware is C6k 100Mb 802.3, address is 000d....
9
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3answers
1k views

What is a “Layer 3 Switch”?

What is a "Layer 3 Switch"? I essentially understand the OSI model, well maybe I don't and maybe that is why I don't understand. Its just that I don't see how/when/if a "managed switch" becomes a "...
5
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2answers
3k views

How does a layer-2 switch work with UDP?

If UDP and/or TCP send packets via IP to an Internet Protocol Address, how can a layer-2 switch forward these? Is this possible or do you need a layer-3 switch?
1
vote
1answer
4k views

HSRP issue both device active stats

Here is the Diagram. Ip address: ISP: [VIP]- 10.107.25.5 [R1] - 10.107.25.6 [R2] - 10.107.25.7 Me: [VIP] - 10.107.25.10 [SW1] - 10.107.25.11 [SW2] - 10.107.25.12 Configuration on port: SW1 ...
9
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3answers
17k views

Assign an IP address based on switch port

Short: I want DHCP server to assign a preconfigured IP address based on a port (on a switch, ideally) a device is connected to. Long: My situation: I am building an automated indoor farm (for ...
5
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2answers
3k views

Does a switch MAC address table sync across all switches in the same VLAN?

Ok, I have read up about this 16K limit for the MAC address table, or better known as the CAM table, on certain switches. Lets say I have 14 different edge switches with that 16K limit, and I have ...
5
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2answers
274 views

Why FastEthernet STP Link Selected over EtherChannel?

What are the possible reasons why STP would choose to use a FastEthernet link over an EtherChannel? Below is a network diagram where this is happening.
4
votes
1answer
634 views

What is the point of a subnet mask on a local network?

I have a question regarding subnet masks and my understanding (or misunderstanding of them). So when a subnet mask is used, a bitwise AND is performed using the subnet mask and the IP address(es). ...
4
votes
3answers
476 views

Is there any reason to use a hub over a switch?

Given that hubs are essentially the same as switches, as far as I know, except they share bandwidth between all connected devices, while switches do not, resulting in faster connections. I am simply ...
3
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1answer
351 views

question about switches and frame and forwarding table

hey guys was wondering if someone can potentially explain this to me but lets say switch-A just learned a Ethernet address on port 4 (00:0f:4b:02:63:ae) based on the forwarding table now a station ...
2
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4answers
34k views

What is the difference between smart vs managed switch?

I want to buy a new switch to replace an old one which is unmanaged and I see that there are smart and managed switches.. what it the difference?
2
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1answer
118 views

Do unmanaged switches honour QoS priorities set by managed switches?

Details about the devices We have a 24 port NETGEAR managed POE switch that has QoS capabilities. We also have the following unmanaged switches, 24 port Cisco POE, 48 port Cisco, 48 port NETGEAR, ...
9
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3answers
5k views

Generate list of subnets on switch using SNMP?

Is anyone familiar with an approach to generate a list of subnets on a particular switch (let's pick a more popular one - Cisco) using SNMP? How about a list of VLANs? If so, can you point me to the ...
19
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5answers
17k views

Should portfast be used on a port potentially connecting to an unmanaged switch?

I understand the basics of how spanning tree works and why you would want to use portfast on user access ports. When dealing with a topology with a large number of dumb switches under desks and ...
10
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4answers
16k views

Two hosts of different subnets connected to switch

Two host of different subnets, let it be A - 10.1.2.1/24 and B - 10.1.3.1/24 be connect to the same switch S. Can they communicate? So as far I understand: A sends a packets with IP of B S receives ...
14
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3answers
40k views

How to Monitor Vlan Traffic?

We have migrated to a new ISP who provide us several services (Internet+VoIP+VoD) and have divided each service in one vlan 100,101,102 respectively. Now I'm looking for a solution to monitor each ...
11
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11answers
3k views

Locate a host on Network

What is the best method of locating a particular workstation on a VLAN ? I sometimes need to do this, if a workstation IP address, shows up on an ACL Deny torrent use High bandwidth usage (Top ...
11
votes
2answers
1k views

How did I break (half of) my network?

I'm looking for some post-event advice so this event doesn't happen again. We have a network core of two Cisco 4500x switches, configured for VSS redundancy. From those, we have iSCSI devices, our ...
10
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4answers
134k views

What can cause “FastEthernet is up, line protocol is down” on a Cisco Switch?

I wonder what can cause the first line output of the command show interfaces to be: FastEthernet is up, line protocol is down. In other words, Is the cable that is connected to the local interface, ...
9
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3answers
32k views

Spanning tree Default Priority Values

This question is a repost of the same question in The Cisco Learning Network; however, the answers are unique to Stack Exchange. I have always accepted that the defualt priority value of STP (802.1d) ...
8
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1answer
2k views

Something is filling my force10 ARP table

I have 2 force10 s25 switches that are used for a dark fiber link between two school buildings. One of my switches is filling its ARP table to the brim and then failing. This can happen as often as ...
7
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5answers
20k views

Copy running config in one line

I want to make a script to copy the running config of a switch 4506 in one line. So far, I see two option : copy run tftp: sw#copy run tftp://10.0.0.1/cfg.cfg Address or name of remote host [10....
5
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2answers
9k views

Why each and every single port on Layer 2 switches need to have it's own MAC address?

A switch doesn't alter the frame, and source/destination mac addresses remain how sending host specified them,so let me say it again Layer 2 Switching never changes the frames means no changes in MAC ...
4
votes
1answer
173 views

Strange flooding during installing new switch in network

This is very strange issue i am noticing. In our datacenter we have every switch in rack has cisco vPC configured in short whole datacenter running vPC so there is no loop for spanning-tree anywhere ...
10
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4answers
16k views

Setting up DHCP server on the router or on the switch?

We're using the Cisco 1921/K9 with a SG300 L3 switch. Does one set up DHCP server on the router or on the SG300? If both is capable, what is the reason to choose one over the other? Note: I have 4 ...
10
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2answers
815 views

Transaction based CLI on Ethernet Switches

I am familiar with CLI on managed Ethernet switches. However, recently I came across a term 'transaction based CLI' on switches. I am not exactly sure what is that and purpose of having it in switches....
6
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1answer
644 views

Router benefits in 2018 compared to a L3 Switch

What are the benefits nowadays to use a Router instead of a L3 Switch ?
4
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2answers
2k views

Gateway of Last Resort on Cisco Switch Stack

When I run show ip route on my Cisco 3850 switch stack, i get the following output PO-SW-SVR-SS-02(config)#do show ip route Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP ...
4
votes
3answers
15k views

Meaning of the ip default-gateway L2 switch

What is meaning of the ip default-gateway command on a Cisco L2 switch? I read something about it on the Internet, but there was written that it allows you to Telnet to the switch. I am little bit ...
2
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2answers
813 views

Is there a way to detect how many switches are between a host and the router?

As switches don't decrease the IP TTL header field, I can't detect how many steps are between a host and the router by using tracert. Are there any ways to detect the number of switches between a host ...
2
votes
1answer
324 views

spanning-tree port type edge trunk on port-channel vs physical interface

If i configure spanning-tree port type edge trunk on physical interface instead of port-channel does that work? Or i have to do spanning-tree port type edge trunk on port-channel ? Example: ...
9
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2answers
3k views

3750G Switch Buffer Monitoring

We have put some 3750Gs in a stack for our DC access switches. We are concerned that these won't be able to handler higher data loads as traffic increases due to their limited buffers. What statistic/...
7
votes
3answers
11k views

HP 2920 - Can stack without stacking module?

Is it possible to stack HP 2920 switches via ethernet connections (without add-in stacking modules)? I've consulted several of the docs on HPs site but can't find a definitive answer. I have older ...
6
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2answers
1k views

How to monitor SPAN port for a routed port on 3560G

Is configuring the SPAN port same for a routed port vs a switch port? I have a routed port on my layer-3 3560G for which I need to configure SPAN and capture packets ingress and egress for ...
6
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4answers
3k views

Advantage of layer 3 switch over Router

What is the advantage of Layer 3 switch over the Router ??
6
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2answers
8k views

How to synchronize MD5 digest between VTP Server and Client?

Follow up to this Q&A. According to one of the answers it should be possible to solve a MD5 digest mismatch by synchronizing username, password and domain between VTP Client and Server and ...
5
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1answer
559 views

Switch FIB and router FIB

Forwarding Information Base (FIB) also called Forwarding Table or Mac Table according to wikipedia. I first explain my understanding of the FIB in both Switch and Router. Does not hesitate to correct ...
5
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5answers
287 views

What blocks a computer from another network in the same switch from answering an ARP request?

Let's suppose I have 3 computers A, B and C connected to the same switch with only the native VLAN active. A and B belong to the same network, let's say that their IP addresses are 192.168.1.1/24 for ...
5
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2answers
402 views

Where should I start when it comes to organizing my switches? [closed]

I inherited a bit of a mess. And I'm not all that experienced with cabling, so I was hoping to get some advice on where to start when it comes to organizing things. In the image, patch panels are ...