Ron Trunk
  • Member for 8 years, 6 months
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What is the meaning / origin of the terms north-south and east-west traffic?
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76 votes

The terms are usually used in the context of data centers. Generally speaking, "east-west" traffic refers to traffic within a data center -- i.e. server to server traffic. "North-south" traffic is ...

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OSI Model and Networking Protocols Relationship
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47 votes

There are two important facts about the OSI model to remember: It is a conceptual model. That means it describes an idealized, abstract, theoretical group of networking functions. It does not ...

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How does a switch learn a switch table?
46 votes

Layer 2 switches (bridges) have a MAC address table that contains a MAC address and physical port number. Switches follow this simple algorithm for forwarding frames: When a frame is received, the ...

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Difference between control plane, data plane and management plane?
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45 votes

These terms are abstract logical concepts, much like the OSI model. Data plane refers to all the functions and processes that forward packets/frames from one interface to another. Control plane refers ...

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Speed of Light in Copper VS Fiber - Why is Fiber Better?
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43 votes

No, the numbers are right (Page 46). If I can reword your question, it's "Why should I use fiber if the propagation delay is worse than copper?" You are assuming that propagation delay is ...

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How can the latency value be so low from Singapore to USA (~2ms)?
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34 votes

As others have pointed out, Google DNS uses IP anycast, which allows multiple servers in multiple locations to effectively share an IP address. Google (like many others) has many servers around the ...

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What is "industrial ethernet"?
33 votes

Like many IT terms, it's primarily a marketing term. It usually refers to Ethernet switches that are designed for harsh environments (i.e. industrial). The switches may have higher temperature ...

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Is it safe to use any wifi channel in the 2.4GHz band?
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30 votes

The 2.4GHz band is one of many portions of radio spectrum, called the Industrial, Scientific and Medical (ISM) bands that are allocated for unlicensed use. As long as you operate within the power and ...

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Why does DHCP use UDP and not TCP?
25 votes

Since the source has no IP address (0.0.0.0) and the destination is everyone (255.255.255.255), it's hard to see how you would identify a particular session. But even if you could, what would be the ...

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VLANs over internet
24 votes

VLANs are a layer 2 construct, so they only exist on your local network and end at your router. The Internet has no concept of VLANs.

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Who has control over allocating MAC address to device manufacturers?
23 votes

UPDATED The IEEE assigns MAC address blocks to manufacturers. The IEEE assigns the leftmost (most significant) digits. The IEEE can assign blocks of different sizes depending on the manufacturer's ...

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Interpreting TTL in ping results
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23 votes

So needless to say, nobody on the planet knows how many nodes there are between here and there. I know how many nodes. There are exactly 16. The reason you get different responses is because ...

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How does the shortage of IPv4 public IPs influence existing firewalls?
20 votes

You're late to the game: IPv4 addresses are already exhausted, and have been for a number of years. All the major manufacturers have included IPv6 capability (in varying degrees) in their product ...

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vlan 0, 1, and 4095 are reserved: what are they reserved for?
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20 votes

The Wikipedia article you mention gives a succinct explanation: VLAN identifier (VID): a 12-bit field specifying the VLAN to which the frame belongs. The hexadecimal values of 0x000 and 0xFFF are ...

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Is 30 Mbit/s fibre faster than 30 Mbit/s copper?
19 votes

You might consider pointing out to your "network engineering professional" that the propagation delay in copper is LESS that that of fiber (in most cases). The difference between the two is ...

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What is "oversubscription" in Networking?
17 votes

Oversubscription generally refers to potentially requiring more resources from a device, link, or component than are actually available. Let me explain with an example: Consider a typical 2-layer ...

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IP addresses from public IP block in my LAN
17 votes

EDITED I'm assuming you're considering using an IP block that is not registered to you. Otherwise, skip to the last paragraph. Besides being a very poor practice, if you use public addresses on your ...

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Undo last command(s) in case of losing connection to a Cisco Router
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16 votes

You can configure the auto rollback feature to revert to a previous configuration in case you lose access. First, you need to configure configuration archive on the router. For example: archive path ...

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Cisco 3750X Power Cable
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16 votes

The cable pictured is a standard: IEC320-C15. The difference is in the temperature rating of the cable. These are rated to 120C, while the "ordinary" ones (IEC320-C13) are 70C. I believe the ...

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What is IP squat space
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15 votes

IPv4 address space is in short supply, so some people decide to use IP space ( allocated, but not advertised) that doesn't belong to them. The consequences are pretty well described in the article ...

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Why do we need MAC Address if we can uniquely identify each machine with an IP Address
15 votes

There is a historical reason for this, as @ronmaupin alludes to. In small networks, you don't need a layer 3 protocol. All the devices are directly addressable, so layer 2 addresses work fine. As ...

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How does BGP work over TCP?
14 votes

Routing protocols do not "achieve" L3 connectivity. They populate the routing (forwarding) table of the router with information learned from other routers. BGP is an "application" that runs over ...

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Cascading Switches. Will it affect performance?
13 votes

Is this okay? Hardly ideal. I assume since you are using cheap, obsolete switches, that you're on a very limited budget. You'll have to weigh the factors below. Does a cascade of switches affect ...

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Port mirroring just the Rx (or Tx) direction of a port?
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13 votes

On Cisco switches, you can configure whether you mirror rx, tx or both. For example: monitor session 1 source interface gi0/1 rx For receive only: monitor session 1 source interface gi0/1 tx For ...

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Why do FTP and SMTP not use IP?
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13 votes

TCP and UDP are layer 4 (transport) protocols. They always use IP as the layer 3 (network) protocol. The text you quote is just plain wrong. You may notice that the page you reference was marked ...

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How to know at what OSI Layer(s) does a firewall operate
13 votes

Since firewalls essentially filter data, the answer depends on what kind of filtering you do. If you filter based on IP address (for example), you can say that your firewall is filtering at layer 3. ...

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When a ping is lost, what happens?
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13 votes

IP protocol provides no guarantee that packets will arrive, arrive on time, or arrive in the proper order. The only thing IP can verify is that the packet header is intact (due to the header checksum)...

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What does no shutdown command do? Cisco
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12 votes

In the simplest sense, shutdown turns the interface off. no shutdown turns the interface on (enables it). You can configure an interface in either case. Using the shutdown command is one of the ...

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routing between vlans not working
12 votes

You don't have NAT enabled (you don't have ip nat outside on Vl 20). Without NAT, the ISP doesn't know how to route back to your 192.9.200.0 network. If you NAT to the VLan 20 address, the ISP ...

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Does a switch always get a MAC address from a PC?
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12 votes

A switch learns the source MAC from the sender. If the destination is not in the CAM table, the switch floods the frame out all ports. So if the receiver never responds, the switch will never learn ...

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