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20 votes
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What does TCP DUP ACK mean?

There can be several things going on - the most common would be the use of TCP Fast Retransmission which is a mechanism by which a receiver can indicate that it has seen a gap in the received sequence ...
rnxrx's user avatar
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18 votes
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TCP and Go-Back-N

To add to the previous answer: A "Cumulative ACK" implies that all the bytes sent by the sender (so far) have been received correctly by the receiver. In order words, when the sender receives an ACK ...
thomassawyer's user avatar
8 votes
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Packet Collison Avoidance

A wireless network is only a single, shared medium with a limited total bandwidth. The more clients compete for bandwidth the smaller each slice gets. Additionally, the simple presence of clients ...
Zac67's user avatar
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7 votes
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What happens in SACK when there are multiple gaps in the received packets?

The Selective ACK Option can specify more than one "block" of received traffic. Here is what the option looks like on the wire (taken from RFC 2018, Section 3): +-------...
Eddie's user avatar
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7 votes

Packet Collison Avoidance

Because everyone is competing for airtime. It's the same reason traffic slows down on a highway as more cars travel on it. BTW 802.11 uses CDMA/CA That's collision avoidance, not collision detection ...
Ron Trunk's user avatar
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6 votes
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How does a router behave when some of the fragments of a packet is lost?

There's no mechanism to request a fragment be resent. The entire packet cannot be reassembled, so the entire packet will have to be resent. This is why Fragmentation Is Bad(tm). Routers typically do ...
Ricky's user avatar
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6 votes
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How ethernet links can have a delay and loss

All links introduce latency. It's a trivial amount when passing traffic over a 2M Ethernet patch cable but it's substantial on a trans-Pacific circuit. Some links also have packet loss. It might ...
rnxrx's user avatar
  • 6,124
6 votes

Packet Collison Avoidance

If a wireless network has collision detection and avoidance, how comes the network slows down if more clients connect to it? To begin with I wanted to note that 802.11 makes use of collision ...
YLearn's user avatar
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5 votes

What is Packet Loss Rate?

On its own packet loss per second is a relatively meaningless metric. 2 packets lost per second could be devastating to a flow of 2 packets per second, but to something sending 100pps, like a 10ms ...
Acyclic Tau's user avatar
5 votes

Cisco ASA 5585X Internal-Data0/1 interface errors

From Cisco tech note: The ASA interface error counter "overrun" tracks the number of times that a packet was received on the network interface, but there was no available space in the interface ...
Ron Trunk's user avatar
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4 votes
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What happens when an intermediate hop router encounters a packet whose MTU size is more than what it can handle?

If the MTU of the outgoing interface is smaller than the packet, the router will fragment the packet unless the DF flag is set. In that case the router will drop the packet and send an ICMP packet too ...
Ron Trunk's user avatar
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4 votes

What could cause network to duplicate packets? STP during convergence?

I have understood that real networks have routing changes, leading to out-of-order delivered IP packets. Out of order packets are usually caused by multiple links of different latency, rather than ...
Ron Trunk's user avatar
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4 votes

Will packet loss get bigger if the hop count gets bigger?

No, its not that simple. Because packet loss is related to link quality and utilization, not hop count. Another mechanism is the TTL (max. hop count) set in packets. If your target is to far away (...
Winnie Tigger's user avatar
3 votes
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How to find packet loss in Wireshark network dump file?

Yes, you can use wireshark (and/or tcpdump) for this. I would run wireshark on both source and destination hosts, with a capture filter for the traffic you are interested in, and then check if the ...
JFL's user avatar
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3 votes
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MTU 1500 gigabit connections translated to 9000 jumbo packets over 10 gigabit connection

Switching a frame through a different speed port can't change the frame size. The sender uses what it is configured to and what it chooses at that moment. The frame stays that way until it is ...
Zac67's user avatar
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3 votes
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How sliding window protocols handle duplicate packets caused by extreme network delays?

I'm also of the view this is phenomenally unlikely and poses no real problem in any network I know about. So the answer to "commonly-used methods" against it is that there aren't any. ...
jonathanjo's user avatar
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3 votes
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TCP and internal packet retransmission

Only the two endpoints, the TCP peers, even know that TCP is used. Routers route packets at layer-3, but TCP send segments at layer-4. The TCP segments are encapsulated inside the IP packets, and the ...
Ron Maupin's user avatar
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3 votes
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Limiting NIC speed leads to better video quality

The likely cause of this is small buffers in the switch combined with poor design of the video streaming application. Most likely the video streaming application doesn't send a paced stream of ...
Peter Green's user avatar
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3 votes
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What could cause network to duplicate packets? STP during convergence?

Real networks also have frequent packet loss. If a network suffers frequent packet loss it is either badly designed or its load has outgrown its capacity. Packet loss does appear in almost any ...
Zac67's user avatar
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3 votes
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Will packet loss get bigger if the hop count gets bigger?

Packet loss is primarily due to congestion in the path. If more packets are trying to use a link than the link can support, some packets will need to be dropped. While it may happen that the more ...
Ron Maupin's user avatar
  • 99.9k
3 votes

Packet Collison Avoidance

Straight from Wikipedia: Collision Avoidance: if another node was heard, we wait for a period of time (usually random) for the node to stop transmitting before listening again for a free ...
jonathanjo's user avatar
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3 votes
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Bonding and switching between 2 different Links/WANs/Interfaces

I don't want to use "both" interfaces/links/Wans at the same time, instead I want to use one of them and in case it fails Bonding will switch to the other source. That is not bonding, where you ...
Ron Maupin's user avatar
  • 99.9k
3 votes

pathping command 100% packet loss

You already know the answer: I know for security reason some router don't respond to ICMP packet. Please do not post images of text. copy and paste the text using the preformatted { } option.
Ron Trunk's user avatar
  • 67.7k
3 votes

Why does TCP sender drop rate 50% on lost-packets?

TCP adapts the receive window size when it detects congestion, ie. when packet loss occurs. There are several congestion algorithms, starting with the original Tahoe. An overview: https://en.wikipedia....
Zac67's user avatar
  • 85.6k
2 votes

Upload speed issues with two ISPs on the same tower

First thing I would suggest, assuming this ISP manages the AP installed at your location, is get them out there to align the AP properly. At 15 degree offset you will be pointed off the water tower ...
John K.'s user avatar
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2 votes
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can the loss of 4 packets in 1000 cause performance issues

0.4% packet loss is quite high on an internal network. Packet loss will definitely affect performance, but the effects are also dependent on RTT. The Mathis Equation describes the maximum TCP ...
Ron Trunk's user avatar
  • 67.7k
2 votes

can the loss of 4 packets in 1000 cause performance issues

(Assuming TCP over public WAN) Yes - your equipment is taking a performance hit when packets get dropped because data packets are being resent in response to the ones that got dropped. However: A 0....
Ted Quanstrom's user avatar
2 votes

CRC errors and ICMP packets loss correlation

It depends on the type of the noise. If it is an ideal random noise, then yes, you will get much higher packet loss with bigger packets. It suggests a layer1 problem. In this case, setting a smaller ...
peterh's user avatar
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