13.1
ICMPv4 and ICMPv6 Messages
Internet Control Message Protocol (ICMP) provides feedback about issues related to the processing of IP packets under certain conditions
ICMPv4 is the messaging protocol for IPv4. ICMPv6 is the messaging protocol for IPv6 and includes additional functionality.
The ICMP messages common to both ICMPv4 and ICMPv6 include
Host reachability
Destination or Service Unreachable
Time exceeded
ICMP Echo Message can be used to test the reachability of a host on an IP network
An ICMP Destination Unreachable message can be used to notify the source that a destination or service is unreachable.
When the Time to Live (TTL) field in a packet is decremented to 0, an ICMPv4 Time Exceeded message will be sent to the source host.
ICMPv6 Messages
ICMPv6 has new features and improved functionality not found in ICMPv4, including four new protocols as part of the Neighbour Discovery Protocol (ND or NDP).
Messaging between an IPv6 router and an IPv6 device, including dynamic address allocation are
Router Solicitation (RS) message
Router Advertisement (RA) message
Messaging between IPv6 devices, including duplicate address detection and address resolution are
Neighbour Solicitation (NS) message
Neighbour Advertisement (NA) message
ICMPv6 Messages (Cont.)
RA messages are sent by IPv6-enabled routers every 200 seconds to provide addressing information to IPv6-enabled hosts.
RA message 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.
An IPv6-enabled router will also send out an RA message in response to an RS message.
ICMPv6 Messages (More)
A device assigned a global IPv6 unicast or link-local unicast address, 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 NS 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 to the sending device that the address is in use.