18
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 ...
- 6,018
14
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 ...
- 320
12
votes
Accepted
Measuring per-link latency/jitter/packet-loss
On Cisco devices, you can use Cisco IP SLA. You need to first configure and enable it, and then monitor the results.
Steps:
1. ip sla monitor operation-number
2. type echo protocol ipIcmpEcho {...
10
votes
Accepted
What is an acceptable spell of total packet loss for public Internet traffic?
The issue: Customers can experience total packet loss for 10s, 30s and more. This brings the TCP connection delivering the prices to a halt, thus rendering the website useless. All connectivity from ...
- 29.5k
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 ...
- 69.5k
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):
+-------...
- 13.9k
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 ...
- 62k
6
votes
Measuring per-link latency/jitter/packet-loss
On juniper hardware you can use the RPM service to get those measurements. The service can be configured to monitor specific interfaces which will help with the 'per-link' requirement.
- 158
6
votes
Accepted
Why do wireless signals interfere with themselves regularly?
Self-interference is an identity issue within mesh wireless networks, primarily with pre 802.11b wireless networks. The standards prior to 802.11n required only 3 non-overlapping channels of the 2....
- 387
6
votes
Accepted
overcome microbursts in cisco router or transmitting linux machine
So first of all show fabric utilization all shows fabric utilization, not CPU utilization. Fabric doesn't have CPU component per se, and you can go all up to 100% of fabric utilization without any ...
- 4,010
6
votes
MTR packet Loss at intermediate hop
However, when we run the same WinMTR tool to our gateway, we receive a 0% packet loss on the gateway, but as of last test a 9% packet loss on the router...
[snip]
... I'm not entirely sure how to ...
- 29.5k
6
votes
Accepted
What is Packet Loss Rate?
Both are possible. If no units are mentioned, I would assume it means
(# packets lost)/(# packet sent).
Often, this ratio will be given as a percentage.
When 'packet loss rate' is meant as a rate ...
- 4,591
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 ...
- 6,018
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 ...
- 26.7k
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
What is an acceptable spell of total packet loss for public Internet traffic?
Total Packet loss for 10-30 seconds is surely caused by other factors than lost packets somewhere on Internet. A lost tcp packet would normally generate a retransmit within ~10-100ms. Congested links ...
- 141
5
votes
What causes packet loss when using full bandwidth from ISP?
There are a number of possibilities here, not limited to, but including:
The CPE's CPU is maxing out. (CPE=Customer Premesis Device)
Check the specifications for the router you are using to make ...
- 151
5
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 ...
- 173
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 ...
- 62k
4
votes
Why do wireless signals interfere with themselves regularly?
If you receive a packet on frequency X, you can't also transmit the same info on that same frequency. So you need to wait. that's why if you use the newer 802.11 protocol's who use more then one ...
- 126
4
votes
Measuring per-link latency/jitter/packet-loss
Etherate enables you to measure throughput, latency and packet (frame) loss down at layer 2 directly over Ethernet (which sounds like what you are looking for). It doesn’t measure jitter at present ...
- 5,270
4
votes
Measuring per-link latency/jitter/packet-loss
Check out Y.1731 protocol (or IEEE 802.1ag, or OAM). It's fairly easy to implement in software (I'm guessing that's what you're aiming at), and it's supported by all the physical network elements.
...
- 41
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 ...
- 62k
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 (...
- 276
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 ...
- 92.7k
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
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 ...
- 29.5k
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 ...
- 92.7k
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 ...
- 11.6k
Only top scored, non community-wiki answers of a minimum length are eligible