ICMPv6 and ICMPv4

Host Reachability

- An ICMP Echo Message can be used to test the reachability of a host on an IP network. - The local host sends an ICMP Echo Request to a host. If the host is available, the destination host responds with an Echo Reply.

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 an NS 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. In the figure, R1 sends a NS message to 2001:db8:acad:1::10 asking for its MAC address.

What does pinging loop back address test on a host?

A response from 127.0.0.1 for IPv4, or ::1 for IPv6, indicates that IP is properly installed on the host.

Destination or Service Unreachable Codes

Destination Unreachable codes for ICMPv4 are as follows: 0 - Net unreachable 1 - Host unreachable 2 - Protocol unreachable 3 - Port unreachable -------------- Destination Unreachable codes for ICMPv6 are as follows: 0 - No route to destination 1 - Communication with the destination is administratively prohibited (e.g., firewall) 2 - Beyond scope of the source address 3 - Address unreachable 4 - Port unreachable ----------------- ICMPv6 has similar but slightly different codes for Destination Unreachable messages.

Time Exceeded

ICMPv4: -An ICMPv4 Time Exceeded message is used by a router to indicate that a packet cannot be forwarded because the Time to Live (TTL) field of the packet was decremented to 0. -If a router receives a packet and decrements the TTL field in the IPv4 packet to zero, it discards the packet and sends a Time Exceeded message to the source host. ------------------- ICMPv6: -ICMPv6 also sends a Time Exceeded message if the router cannot forward an IPv6 packet because the packet has expired. Instead of the IPv4 TTL field, ICMPv6 uses the IPv6 Hop Limit field to determine if the packet has expired. ---------------- Time Exceeded messages are used by the traceroute tool.

ipconfig

The ping command is used to verify connectivity to a device,the commands ipconfig /flushdns will cause the adapter to flush the DNS cache, while ipconfig /**displaydns** will result in the display of the DNS information in the cache.

Ping Router Errors:

When the ping command is issued on a router, the most common indicators are as follows: ! - indicates receipt of an ICMP echo reply message . - indicates a time expired while waiting for an ICMP echo reply message U - an ICMP message of unreachability was received

RS Message

-An IPv6-enabled router will also send out an RA message in response to an RS message. -In the figure, PC1 sends a RS message to determine how to receive its IPv6 address information dynamically.

ICMPv6 Messages

-ICMPv6 includes four new protocols as part of the Neighbor Discovery Protocol (ND or NDP). Messaging between an IPv6 router and an IPv6 device, including dynamic address allocation are as follows: -Router Solicitation (RS) message -Router Advertisement (RA) message Messaging between IPv6 devices, including duplicate address detection and address resolution are as follows: -Neighbor Solicitation (NS) message -Neighbor Advertisement (NA) message ----------- ICMPv6 ND also includes the redirect message, which has a similar function to the redirect message used in ICMPv4.

RA Message

-Router Advertisement Message -RA messages are sent by IPv6-enabled routers every 200 seconds to provide addressing information to IPv6-enabled hosts. -The 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.

Traceroute (tracert)

-Traceroute (tracert) is a utility that generates a list of hops that were successfully reached along the path. -If the data reaches the destination, then the trace lists the interface of every router in the path between the hosts. -If the data fails at some hop along the way, the address of the last router that responded to the trace can provide an indication of where the problem or security restrictions are found. Round Trip Time (RTT): -The round-trip time is the time a packet takes to reach the remote host and for the response from the host to return. -An asterisk (*) is used to indicate a lost or unreplied packet. -This information can be used to locate a problematic router in the path or may indicate that the router is configured not to reply. If the display shows high response times or data losses from a particular hop, this is an indication that the resources of the router or its connections may be stressed. IPv4 TTL and IPv6 Hop Limit: -Traceroute makes use of a function of the TTL field in IPv4 and the Hop Limit field in IPv6 in the Layer 3 headers, along with the ICMP Time Exceeded message. The first sequence of messages sent from traceroute will have a TTL field value of 1. This causes the TTL to time out the IPv4 packet at the first router. This router then responds with an ICMPv4 Time Exceeded message. Traceroute now has the address of the first hop. Traceroute then progressively increments the TTL field (2, 3, 4...) for each sequence of messages. This provides the trace with the address of each hop as the packets time out further down the path. The TTL field continues to be increased until the destination is reached, or it is incremented to a predefined maximum After the final destination is reached, the host responds with either an ICMP Port Unreachable message or an ICMP Echo Reply message instead of the ICMP Time Exceeded message.

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 NS message with its own IPv6 address as the targeted IPv6 address, as shown in the figure. If another device on the network has this address, it will respond with an NA message. This NA message will notify the sending device that the address is in use. If a corresponding NA message is not returned within a certain amount of time, the unicast address is unique and acceptable for use. DAD is not required, but RFC 4861 recommends that DAD is performed on unicast addresses.

What are common ICMP messages to both ICMPv4 and ICMPv6

1. Host reachability 2. Destination or Service Unreachable 3. Time exceeded