Icmp ping – Amer Networks E5Web GUI User Manual
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3.12. ICMP Ping
The combination of the ICMP echo request and echo reply messages are known as ping. They
provide a simple diagnostic tool to find out if a host is reachable. In the cOS Core CLI, the ping
command provides this feature.
In its simplest form, the CLI command to ping a remote IP address takes the form:
Device:/> ping
For example, to ping the IPv4 address 10.6.58.10:
Device:/> ping 10.6.58.10
Sending 1 4-byte ICMP ping to 10.6.58.10 from 192.168.3.20
using PBR rable "main"
ICMP Reply from 192.168.1.1
seq=0
time=<10 ms
TTL=128
Ping Results:
Sent: 1, Received:1, Avg RTT: 10.0 ms
Here, the RTT is the round trip time for the ICMP echo request and reply messages. The TTL value
is the Time To Live which is a hop counter. The initial TTL value is set by the sender and
decremented by each router passed. When it reaches zero, the packet is discarded preventing
packets from circulating forever.
This basic form of the ping command is also available in the cOS Core Web Interface by going to:
Status > Tools > Ping.
Choosing the Routing Table
By default, the outgoing source interface for ICMP ping is chosen by performing a lookup of the
destination IP address in the main routing table. This can be overridden with the -pbr option in
order to specify which routing table to use for the lookup. For example, if the routing table
my_routing_table is to be used, the command would be:
Device:/> ping 10.6.58.10 -pbr=my_routing_table -verbose
Note: The -pbr option cannot be used with the -srcif option
The -pbr option cannot be used with packet simulation using the -srcif option described
later. This is because the routing table lookup for the outgoing interface is not relevant
when simulating incoming packets.
IP Rules and Policies for Outgoing Ping Messages
When the ICMP ping message is outgoing from cOS Core, it does not require any IP rules or IP
policies to allow the traffic since cOS Core is always trusted. In the cOS Core event message logs,
an outgoing ping will generate a con_open and con_close log event using the
Stock_Allow_All_Rule. The source interface will always be the core interface (meaning cOS Core
itself ).
IP Rules and Policies for Incoming Ping Messages
Any ping messages that are incoming require an allowing IP rule or IP policy for cOS Core to
respond and these should have the associated Service object set to be the predefined service
Chapter 3: Fundamentals
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