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1500 questions
41
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5 answers

Why was the MTU size for ethernet frames calculated as 1500 bytes?

Why was ethernet MTU calculated as 1500 bytes? What specific calculation was done to arrive at 1500 byte ethernet MTUs, and what factors were considered for that calculation?
Padmaraj
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2 answers

TCPDump - Filter by MAC Address

I would like to display all traffic for or from a specific MAC address. For that I tried sudo tcpdump host aa:bb:cc:11:22:33 It does not work and returns me an error tcpdump: pktap_filter_packet: pcap_add_if_info(en0, 1) failed: pcap_add_if_info:…
phenetas
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40
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OSI Model and Networking Protocols Relationship

When most networking students first learn about the OSI model, they spend a great deal of time trying to figure out which layer of the model a particular protocol fits into. We get a lot of questions about OSI layers on this forum, and they are…
Ron Trunk
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4 answers

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 the switch: One value is always measured in…
Daniel Yuste Aroca
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40
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4 answers

How to check for a valid public IP address?

Consider a list of IP addresses as provided by the X-Forwarded-For HTTP header: 10.0.0.142 , 192.168.0.10 , 212.43.234.12 , 54.23.66.43 I would like to know which is the first publicly-accessible address in that list. I can look over them easily…
dotancohen
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39
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8 answers

How would a router with /32 WAN subnet mask communicate with the rest of the Internet?

I'm studying networking and one of the most basic things I've been told countless times is that computers can't communicate outside of their own subnet. On the other hand, by looking at some ADSL setups, I've seen that in case where a fixed IP…
AndrejaKo
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38
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3 answers

Why does the IPv6 header not include a checksum?

It is stated in Wikipedia that an IPv6 header does not include a checksum. What are the reasons that were behind this decision?
Paulo Tomé
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38
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11 answers

How do you prevent rogue wireless access points on a network?

Depending on what type of traffic is going over the network, it's often not feasible that an employee brings a wireless router and sets it up into your network. This is because often, they are not or poorly secured and present a backdoor into the…
Lucas Kauffman
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37
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2 answers

What is the actual size of an Ethernet MTU

I think I might be getting confused with terminology surrounding MTU. This definition from Wendell Odom's CCNA book on MTU: The IEEE 802.3 specification limits the data portion of the 802.3 frame to a minimum of 46 and a maximum of 1500 bytes. The…
Josh
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37
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3 answers

Does a traceroute/tracert show every hop, or does it skip/hide some details of the path?

I am currently in college for a bachelor's degree in Network Engineering, and one of my Professors explained in class that a traceroute that shows, for example, 15 hops is actually abstracting the path, and in reality many more nodes are involved.…
WilHall
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37
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5 answers

Why does ipv6 specify 128 bit address, when there are only 48 bits in MAC addresses?

So, I'm reading for a networking exam, and I'm just wondering if I have missed something basic. Is there a need for more ip addresses than MAC addresses, and how would a node with one network adapter be assigned many ip addresses in that case?
Lorentz Vedeler
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36
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5 answers

What is the proper term for ipaddress/hostname:port

What is the proper term for (example) hostname.tld:433 (hostname:portnumber)? It is not just hostname, and it is not really a URL either :) same goes for 10.0.0.1:3306 etc.
FelixHJ
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36
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3 answers

Why do network taps have four ports?

I've been looking at a hardware network tap like this one to replace a pseudo-permanent SPAN that's been running on a Catalyst switch. All the taps I find have four interfaces: A, B, and two output ports (one for each direction). Ideally I would…
Jeremy Stretch
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5 answers

Why are Ethernet Standards written in the form of 10/100/1000? Why not just 1000?

I always have seen Ethernet Standards written in the form "low value/middle value/max value", and always wondered why. Won't a router just reproduce a lower speeds anything below its maximum if it's configured as such, therefore making "/"…
user3121651
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3 answers

Why are IPv4 addresses 32-bit?

Many moons ago, when I was just a wee bairn commencing my career, I had a job interview for a low-level developer role. Having at that time just learned how CIDR was implemented, I was keen to show off my knowledge. Sadly, that tactic didn't work…
eggyal
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