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1500 questions
11
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1 answer

Non-Cisco SFP's defaulting to an err-disable state in 2960s and 2960 PoE Switch

I recently came across an issue while setting up a stack to replace an older M switch setup. I stacked 3 switches - 2 Cisco 2960's and 1 C2960 PoE using SFP cables to their backplane. My plan was to use the SFP modules on the front end of the…
HAL
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11
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1 answer

SNMP v2: What is the difference between SNMP v2c and SNMP v2u

I usually hear about SNMP v2c. But recently I came across v2u when configuring an SNMP agent. What are the differences between the SNMP v2 flavors v2c and v2u? And which is the more recent version among these two?
thilina R
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11
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5 answers

VLANs over internet

How does VLANs work over the internet and span across multiple geographical locations? VLAN headers are removed when frames move to another switch or a router? How does it happen?
Rumesh Madhusanka
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11
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2 answers

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. Is it similar to database transactions where…
modest
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11
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2 answers

Why is RIP not scalable?

Most of the references say "RIP is not scalable" hence can be used only in smaller networks. But none say "WHY?" What is that in RIP that actually preventing it from scaling to larger networks? And HOW OSPF overcomes the disadvantage of RIP?
gulam
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11
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1 answer

Is there a way to capture only gratuitous ARP's using tcpdump?

I'm trying to set up tcpdump to filter only gratuitous ARP's. I know that I need to search for packets with a host set to ff:ff:ff:ff:ff:ff. And I found the arp.opcode parameter, but I can't seem to get it to work. For example, this: tcpdump -i wm0…
Jason Mitchell
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11
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2 answers

Why does Cisco ios save and display access list entries out of order?

Consider the following access-list: access-list 25 remark city1 access-list 25 permit 10.1.120.0 0.0.0.255 access-list 25 remark city2 access-list 25 permit 10.2.120.0 0.0.0.255 access-list 25 remark city3 access-list 25 permit 10.3.120.0…
User123456
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11
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3 answers

Quagga routing and security

I have a quagga router with two transit neighbors and announcing my own IP space. I recently joined a public peering exchange (IXP) and so I'm part of their local network (/24), together with all other participants. So far everything works fine. Now…
Alessandro
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11
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1 answer

Is a FIN only segment legal?

It would be convenient to mark TCP segments with just the FIN flag set, as an intrusion (without tracking the reply). I have always assumed that a FIN without an ACK, while rude and rare, is legal, based on connection termination. But then I read…
fundagain
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11
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2 answers

Cisco ASA double NAT with DNS translation

I'm trying to set up double Auto NAT with DNS translation on Cisco ASA 9.0(3), and I'm having a few challenges with the DNS portion. I got double NAT working correctly, such that I have a server in production and in the lab with the same IP…
Mike Pennington
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11
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3 answers

Why is DNS an application layer protocol?

The main role of DNS is to translate Domain Names to their corresponding IP adresses, so why is necessary to be an application layer protocol? I think that DNS is an application layer protocol because if for example i want to create a TCP connection…
D.Rotnemer
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11
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2 answers

dhcpv6 - stateful VS stateless, what is difference between it?

Can someone explain me, what is difference between DHCPv6 Stateful and Stateless? I was looking on the net and, surprisingly, I found only the remains of information but some general comparison or description of the differences between them did not…
Paul
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11
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2 answers

Why does FTP passive mode use a range of ephemeral ports as opposed to a single well known port?

In FTP passive mode, I read that the server sends a random port number to the client where it can establish a data channel. Then client establishes a data channel from its random port number to this port number sent by the server. My question is why…
Zephyr
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11
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2 answers

Why don't iperf, scamper and path MTU discovery packet captures agree on the path's MTU?

Let's do some path MTU discovery between two Debian hosts separated by a Debian router that runs Shorewall-generated iptables rules. Each of the two hosts uses a single Ethernet link while the router uses tagged VLANs over two aggregated Ethernet…
Jean-Marc Liotier
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11
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1 answer

Why does 10Gbps ethernet claim PAM16 encoding then use a squared DSQ128 constellation?

I've been looking into the way that 10 Gbps Ethernet encodes its data and I'm a little confused by the nomenclature. I have gathered, e.g. from here http://www.ikn.no/download/Whitepaper-10G-Ethernet-10-08.pdf, that Pulse Amplitude Modulation is…
CharlieB
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