ICMP

Ping the default gateway

-A successful ping to the default gateway indicates that the host and the router interface serving as the default gateway are both operational on the local network. -If either the default gateway or another host responds, then the local host can successfully communicate over the local network. If the default gateway does not respond but another host does, this could indicate a problem with the router interface serving as the default gateway. -One possibility is that the wrong default gateway address has been configured on the host. -Another possibility is that the router interface may be fully operational but have security applied to it that prevents it from processing or responding to ping requests.

RS msg

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

what are the Unreachable host messages?

ICMPv4 -some of the Destination Unreachable codes for ICMPv4 are as follows: 0 - Net unreachable 1 - Host unreachable 2 - Protocol unreachable 3 - Port unreachable ICMPv6 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

how TCP/IP (Transmission Control Protocol/Internet Protocol) uses ICMP?

-Although IP is only a best-effort protocol, the TCP/IP suite does provide for error messages and informational messages when communicating with another IP device -These messages are sent using the services of ICMP -The purpose of these messages is to provide feedback about issues related to the processing of IP packets under certain conditions -ICMP messages are not required and are often not allowed within a network for security reasons

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.

RA msg

-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

-Traceroute (tracert) is a utility that generates a list of hops that were successfully reached along the path -This list can provide important verification and troubleshooting information -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

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.

ICMPv6

-most of the features and error control messages are the same as v4, but v6 adds some new features that ICMPv4 does not have. -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

What is Time Exceed message

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 -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. Time Exceeded messages are used by the traceroute tool

Ping the loopback

Ping can be used to test the internal configuration of IPv4 or IPv6 on the local host. - To perform this test, ping the local loopback address of : * 127.0.0.1 for IPv4 * ::1 for IPv6 -This response comes from the network layer -This simply tests IP down through the network layer of IP. -An error message indicates that TCP/IP is not operational on the host.

Why are ICMPv6 are used

-The types of ICMP messages, and the reasons why they are sent, are extensive -But common messages include: * Host reachability * Destination or Service Unreachable * Time exceeded

Round Trip Time (RTT)

-the time it takes for a small packet to travel from client to server and then back to the client -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.

Ping

a DOS(disk operating system) command that tests connectivity and isolates hardware problems and any mismatched configurations -also, an IPv4 and IPv6 testing utility that uses ICMP echo request and echo reply messages to test connectivity between hosts. -Ping has a timeout value for the reply. -If a reply is not received within the timeout, ping provides a message indicating that a response was not received. -This may indicate that there is a problem, but could also indicate that security features blocking ping messages have been enabled on the network. - also, It is common for the first ping to timeout if address resolution (ARP or ND) needs to be performed before sending the ICMP Echo Request. -After all the requests are sent, the ping utility provides a summary that includes the success rate and average round-trip time to the destination -Type of connectivity tests performed with ping include the following: Pinging the local loopback Pinging the default gateway Pinging the remote host

Pining a remote host

-Ping can also be used to test the ability of a local host to communicate across an internetwork. -The local host can ping an operational IPv4 host of a remote network -The router uses its IP routing table to forward the packets -If this ping is successful, the operation of a large piece of the internetwork can be verified. -A successful ping across the internetwork confirms: * communication on the local network * the operation of the router serving as the default gateway * the operation of all other routers that might be in the path between the local network and the network of the remote host. * and successful functionality of the remote host. because if the RH was not functional, it would not reply back.

NS msg (neighbor solicitation) and NA msg (neighbor advertisement)

1st use -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. -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. 2nd use -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. I.e. R1 sends an NS message to 2001:db8:acad:1::10 asking for its MAC address.