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1500 questions
35
votes
3 answers
What is "oversubscription" in Networking?
I have a question about oversubscription in networking. I read a lot of documentation but I still don't understand what it means. I read the following on the Cisco website,
oversubscription of the ISL is typically on the order of 7:1 or
…
infra
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34
votes
8 answers
How can I stop an intruder plugging into an Ethernet wall socket getting access to the network?
Is MAC address filtering the most suitable option to prevent someone connecting their own device to the network by plugging into Ethernet wall sockets? What if they unplug a device and clone its MAC?
Qgenerator
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33
votes
5 answers
Better Enterprise Multihoming
I would like to get some opinions regarding ways in which I can improve a BGP dual-provider, dual-router design. Each provider supplies a /24 public subnet. I will refer to the routers, circuits, subnets, HSRP groups and providers as A and B,…
Dennis Olvany
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33
votes
1 answer
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 an agent. I have details as to where the MIB is…
sosytee
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32
votes
5 answers
Why do we still use Ethernet?
There's no doubt the vast majority of Ethernet frames are transporting IP packets. I know there are various other protocols that can be transported over Ethernet as well, but those can be transported over IP as well.
With modern Ethernet networks…
rfb
- 329
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32
votes
9 answers
Why use SSH and VPN in combination?
My employer requires me to first log on to a VPN, and only then I can SSH into the servers. But, given the security of SSH, is a VPN overkill?
What is the use of a VPN in terms of security if I am already using SSH?
JavaDeveloper
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31
votes
2 answers
Is multicast on the public internet possible? And if yes: How?
Is it possible to use multicast on the public internet? If yes: How? Are special IP addresses required and where do you get them from?
Matthias Merkel
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31
votes
8 answers
What are the downsides of OpenVPN?
I have been seeing so many people always wrestling with IPSec, and many other secure VPN technologies.
I, for one, have always simply used OpenVPN, with beautiful and simple and versatile results. I've used it on DD-WRT routers, big servers and…
user1056
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30
votes
8 answers
Why does DHCP use UDP and not TCP?
DHCP uses UDP as its transport protocol. DHCP messages that a client sends to a server are sent to well-known port 67 (UDP—Bootstrap Protocol and DHCP). DHCP Messages that a server sends to a client are sent to port 68, so can DHCP use TCP ?
guidev
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30
votes
5 answers
Are CoS and QoS ever interchangeable?
The terms CoS & QoS are often used interchangably, particularly in the SP space when providing "Class of Service profiles" etc as part of Product sets. I'm looking to re-affirm my understanding that CoS is just one way in which traffic can be…
MattE
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30
votes
4 answers
Exactly when is PMTUD performed? (Path MTU discovery)
In discussions that have spurred from other questions on this site, I've realised that I don't have a solid understanding of when Path MTU Discovery (PMTUD) is performed.
I know what it does -- discover the lowest MTU on a path from Client to…
Eddie
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30
votes
4 answers
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 mechanism so the switch doesn't mistakenly think…
Celeritas
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29
votes
7 answers
Why isn't UDP with reliability (implemented at Application layer) a substitute of TCP?
TCP provides reliability at transport layer while UDP does not. So, UDP is fast.
But, a protocol at application layer can implement reliable mechanism while using UDP.
In this sense, why isn't UDP with reliability (implemented on Application layer)…
mallea
- 519
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29
votes
2 answers
What is the meaning of the CRC counter on a cisco device?
If the CRC counter of an interface is high, normally it's a bad sign, but why?
If the count is high, what does this mean technically?
What can cause this counter to go up?
On which layer in the OSI model will this counter react?
Bulki
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29
votes
1 answer
Route servers and looking glasses - what are they?
I've heard the term "route server" and "looking glass" thrown around here. What are they, and why should I care?
John Jensen
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