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∗ An application is very slow.
TCP Slow ACK
The time a connection has
taken to acknowledge data
exceeds the average
acknowledgment time of the
connection plus the Slow
ACK Time threshold.
Slow ACK Time – 250
milliseconds
∗ The acknowledgment packets are
being transmitted via a slower path.
∗ The network load is very high.
∗ The receiver or router is
overloaded.
TCP Port Scan
A local or remote station is
scanning the network for
opening TCP ports.
Port Scanning is an intrusion
indicator.
UDP Invalid Checksum
The checksum of a UDP
header and/or data is in
error. The checksum value
is calculated by the sender
and written to the packet,
and then recalculated from
the received packet by the
receiver. It indicates an
error if the two values are
different.
There is a faulty device on the
network.
Severity: Information
Event Description Threshold Possible causes and solutions
TCP Reset
Connection
An established TCP connection has
been reset by one end of the
connection, this results in an
abnormal termination of the TCP
connection.
∗ A server drops the connection because of
improperly configured resources or router
problems.
∗ A user aborts the Web connection due to
slow response from a server.
∗ Many older Web browsers use Reset
Connection to shut down their HTTP
connections; however, newer browsers are
better at complying with the TCP
disconnection procedures. Due to the fact
that many older browsers are still in use,
TCP Reset Connection events are very
common in many of today's LANs.
TCP
Window
Frozen
The TCP window size has been
stuck for three or more consecutive
packets and has dropped below a
percentage of the maximum
observed window for this
conversation.
Window Frozen –
50%
Check the source station for insufficient
network application.
TCP Low
Window
The TCP window size has dropped
below a percentage of the maximum
observed window for this
conversation.
Low Window –
10%
Check the source station for insufficient
network application.
Diagnoses
Network Analyzer
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Diagnosis references - network layer
Colasoft Capsa offers expert diagnosis for the following network layer events.
Severity: Notice
Event Description Possible causes and solutions
IP Time-To-Live
Too Low
An IP packet with a time-to-live field
set to 0 or 1 indicates that the packet
is about to expire.
∗ There is a routing table error somewhere in the
network.
∗ The packet is looping.
∗ The originating IP host transmitted the packet with a
low TTL to begin with.
∗ Try to locate the source of the original packet.
IP Fragment
Missing
An IP packet has been fragmented
and one of the fragments is missing.
This will usually result in a
retransmission.
∗ A fragment has been dropped by a switch or router.
∗ The traffic on the LAN is heavy.
IP Zero Broadcast
Address
An IP packet is being sent with the old
IP broadcast address of 0.0.0.0.
∗ This is an obsolete form of TCP/IP broadcast
address.
∗ Check the source endpoint for applications that may
be sending this packet.
Severity: Warning
Event Description Possible causes and solutions
ICMP Destination
Unreachable
A station receives an ICMP destination
unreachable message.
The destination network does not exist.
ICMP Host Unreachable A station receives an ICMP host
unreachable message.
The destination host does not exist.
ICMP Net Unreachable A station receives an ICMP network
unreachable message.
The destination network does not exist.
ICMP Parameter
Problem
A station sends an ICMP message
indicating a parameter problem.
ICMP Port Unreachable A station receives an ICMP port
unreachable message.
The destination port is not active on the station
that sent the message.
ICMP Redirect for Host A station receives an ICMP redirect
message with the Code value set to 1
(redirect datagrams for the host).
A router may have sent the message to inform
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