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1500 questions
13
votes
2 answers
What is SNR Margin and Line Attenuation?
I'm currently using an adsl connection and last week an engineer from my ISP came and told me that my SNR margin and line attenuation is not good, and they need to replace the main telephone cable to provide cable tv. I tried researching on SNR…
Dilum Jayawardhana
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13
votes
1 answer
How does a packet get corrupted in a network?
I recently read about CRC, a checksum to detect package corruption and drop corrupted packages.
But how does a packet in an IP-based network get corrupted in the first place?
Tehmas
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13
votes
1 answer
RIB vs FIB differences?
Can someone explain the differences between a RIB and FIB a little further? I didn't see any similar questions on the site so I thought this would be a good addition. The RIB routes and the FIB forwards? Is that all there is to it?
stets
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13
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2 answers
Detecting different Ethernet frames
How can someone distinguish between different packets in the Ethernet protocol? It has no "length" field/area as higher-level protocols use to do so.
Because this protocol has handling in both the physical and the logical scopes, I assume that the…
Reflection
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13
votes
5 answers
What is the reason for T568A and T568B termination?
There are two types of pinouts for terminating twisted pair cable with a 8P8C (RJ45) connector:
But why must one not simply align the wires serially, e.g:
Green pair - Orange pair - Blue pair - Brown pair
Why do the current standards offer a…
Alexander Gonchiy
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13
votes
5 answers
Why does OSPF need Type2 LSAs?
Learning more about OSPF for CCNP studies. I'm looking at how OSPF builds its links, and have just covered Type1 LSAs. Looking at Type1 LSAs, I'm wondering why these are even necessary?
The book I'm reading implies that Type2 LSAs are used to…
A L
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13
votes
1 answer
Can a router send ARP requests to hosts?
I play with libpcap in C recently to create an arp sniffer program that captures arp requests on the air. I came up with a strange effect. I captured arp requests from my router. I don't know if this is a bug of my program, but I was curious (even…
user33076
13
votes
5 answers
What IPv6 prefixes should never be routed?
Seems clear to me that the Link Local, and Unique Local, addresses should at least be filtered.
Is there anything other than LLA/ULA that should be filtered?
For LLA, is it standard practice to blanket filter the full fe80::/10, or just filter the…
Craig Constantine
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13
votes
4 answers
MTU and Fragmentation
Consider the following: NAS with 10G interface connected to 10G interface on switch. Client computers connected to switch via gigabit Ethernet.
Will there be any gain in performance if MTU size is increased on NAS and switch port to which NAS is…
sardean
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13
votes
6 answers
Why do I need to specify a subnet mask on interface?
When assigning an IP address to an interface, why do I need to specify a subnet mask? I understand the purpose of subnet masks in a routing table for example (to specify a range of IP addresses as destination). But why is it necessary on an…
Gradient
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13
votes
4 answers
Why do I need a crossover cable to connect devices of the same type?
I know that a crossover cable should be used to directly connect devices of the same type and patch cable is used to connect devices of different types.
But I never understood why is it so exactly? Why does such design has been chosen? Does the…
syntagma
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13
votes
4 answers
Minimum ethernet frame is 64 bytes, Why the payload must be padded to at least 46 bytes
What is reason to pad payload to mininum 46bytes, to form a ethernet frame of 64 bytes.
Following says min would be 41 bytes.
https://stackoverflow.com/questions/14526139/what-is-the-minimum-packet-size-for-tcp-over-ipv4
I could not connect the…
Vasu
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13
votes
3 answers
Wifi TCP iperf throughput: 1 stream vs multiple streams?
In a WLAN iperf TCP throughput test, multiple parallel streams will give me higher throughput than 1 stream. I tried increasing the TCP window size, but I still cannot achieve the max throughput with just 1 stream. Is there something else in the TCP…
elin05
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13
votes
3 answers
Two-factor authentication for SSLVPN (cisco)?
Just got asked today about implementing two factor authentication for users of SSLVPN within our company (connecting via Cisco AnyConnect we don't support/use WebVPN). Currently we use LDAP for authentication.
I've identified a company that…
A L
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13
votes
3 answers
Tracking down an invalid source mac address
I have inherited support of a remote site which contains a Cisco 4500 and is connected to ~2 dozen cisco access switches - primarily 2960s with a couple of 3750s and 3560s. Not all access switches are directly connected to the 4500 - there is some…
User123456
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