19
votes
Accepted
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 ...
- 6,104
17
votes
Accepted
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 ...
- 350
8
votes
Accepted
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 ...
- 82.7k
7
votes
Accepted
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):
+-------...
- 15k
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 ...
- 67.1k
6
votes
Accepted
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 ...
- 6,104
6
votes
Accepted
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 ...
- 31.8k
6
votes
Accepted
tcpdump not capturing all TCP packets when capturing whole packets
Found the solution to my own question with the help and hint from @Guy Harris.
The kernel was dropping packets due to that the buffer tcpdump uses got overfull when capturing whole TCP packets.
From ...
- 183
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 ...
- 27.2k
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 ...
- 282
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 ...
- 67.1k
4
votes
Accepted
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 ...
- 67.1k
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 ...
- 67.1k
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 (...
- 286
3
votes
Accepted
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 ...
- 98.8k
3
votes
Dropping packets routed between VLANs
If the problem only happens between VLANs, you need to look at the router which is used to route between the VLANs. It may be overloaded on its CPU or buffers, but that is the common point between ...
- 98.8k
3
votes
Accepted
Should using full bandwidth cause packet loss and latency (domestic cable service)?
Packets get dropped by interfaces when their queues are full but the packets keep coming in. This is likely to happen when a device has packets arriving on a faster link than the one they are leaving ...
- 71
3
votes
Accepted
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 ...
- 13.2k
3
votes
Accepted
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.
...
- 16.2k
3
votes
Accepted
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 ...
- 82.7k
3
votes
Accepted
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 ...
- 19.5k
3
votes
Accepted
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 ...
- 82.7k
3
votes
Accepted
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 ...
- 98.8k
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 ...
- 16.2k
3
votes
Accepted
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 ...
- 98.8k
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.
- 67.1k
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....
- 82.7k
2
votes
Accepted
Outer routing switch - collisions and packet loss
The Netgear DS524 is a hub, not a switch. Collisions are part of life with hubs. Switches separate collision domains per port, while hubs do not.
Hubs are layer-1 devices that constitute a single ...
- 98.8k
Only top scored, non community-wiki answers of a minimum length are eligible