ITNv7 lesson 13 - ICMP
Neighbor Advertisement (NA) message
Address resolution is used when a device on the LAN knows the IPv6 unicast address of a destination but does not know its Ethernet MAC address. To determine the MAC address for the destination, the device will send this message to the solicited node address. The message will include the known (targeted) IPv6 address. The device that has the targeted IPv6 address will respond with an NA message containing its Ethernet MAC address.
Loopback address
An IP address that indicates your own computer and is used to test TCP/IP configuration on the computer. 127.0.0.1 ::1
Router Solicitation (RS) message
An IPv6-enabled router will also send out an RA message in response to an RS message in order to provide IPv6 address information dynamically.
ICMPv6 Code 1
Communication with destination prohibited
time exceeded
ICMPv6 message sent when the IPv6 hop limit field of a packet is decremented to zero and the packet cannot be forwarded
ICMP
Internet Control Message Protocol. Used for diagnostics such as ping and tracert. It is common to block ICMP at firewalls and routers. If ping fails, but other connectivity to a server succeeds, it indicates that ICMP is blocked.
ICMPv6 Code 0
No route to destination
ICMP Code 3
Port Unreachable
IMCP Code 2
Protocol unreachable
Router Advertisement (RA) message
Sent by IPv6-enabled routers every 200 seconds to provide addressing information to IPv6-enabled hosts. Can include addressing information for the host such as the prefix, prefix length, DNS address, and domain name. A host using Stateless Address Autoconfiguration (SLAAC) will set its default gateway to the link-local address of the router that sent the RA.
What does a successful ping to the default gateway indicate?
The host and the router interface serving as the default gateway are both operational on the local network.
Hop Limit
The number of times that an IPv6 packet can be forwarded by routers on the network; similar to the TTL field in IPv4 packets. Once the Hop Limit field reaches a value of zero, it can no longer be forwarded and the receiving router will drop the packet.
ICMPv6
The version of ICMP used with IPv6 networks. Includes address resolution and address autoconfiguration.
Neighbor Solicitation (NS) Message
When a device is assigned a global IPv6 unicast or link-local unicast address, it may perform duplicate address detection (DAD) to ensure that the IPv6 address is unique. To check the uniqueness of an address, the device will send an this message with its own IPv6 address as the targeted IPv6 address. If another device on the network has this address, it will respond with an NA message notifying the sending device that the address is in use. If a NA message is not returned within a certain amount of time, the unicast address is unique and acceptable for use.
ICMPv6 Code 3
address unreachable
U
an ICMP message of unreachability was received
ICMPv6 Code 2
beyond scope of the source address
tracert command
displays every router hop along the path from a source host to a destination host on an IP network. Information about a router hop can include such information as the IP address of the router hop and the round-trip delay of that router hop.
ICMP Code 1
host unreachable
. (period)
indicates a time expired while waiting for an ICMP echo reply message
!
indicates receipt of an ICMP echo reply message
Destination net unreachable message
message received from the default gateway when the destination host is unreachable.
Four ICMP messages that are not used in ICMPv4 but are used in ICMPv6.
neighbor solicitations neighbor advertisements router solicitations router advertisements
ICMP code 0
network unreachable
ICMPv6 Code 4
port unreachable
ICMP messages
provide feedback about issues that are related to the processing of IP packets.
the IP address of the outbound interface
source IP address does a router use by default when the traceroute command is issued
Ping command
used to test the TCP/IP stack on a network host
