this video is module 13 in the intro to networks video series for the Cisco
Networking Academy this video is going to be covering ICMP we only have a few
objectives for this video ICMP messages and ping and traceroute
testing so what are IC MPF messages internet control message protocol our
ICMP provides feedback about issues related to the processing of IP packets
under certain conditions ICMP v4 is the messaging protocol for
ipv4 and icmpv6 is the messaging protocol for you guessed it I have a vc
ipv6 and it includes additional functionality as well on the ipv6 side
the ICMP messages common to both the ICMP v4 and v6 I'm just gonna say v4 and
v6 they have host reach ability the destination or service unreachable and
time exceeded and there's a note about the v4 is that messages are not required
and are often not allowed within a network for security reasons for host
reach ability the ICMP echo message can be used to test the reach ability of a
host on an IP network in this example the loca host the local host sends an
ICMP echo request to a host and if the host is available the destination host
responds with an echo reply for destination or service unreachable an
ICMP destination unreachable message can be used to notify the source that a
destination or service is unreachable unreachable the ICMP message will
include a code indicating why the packet could not be delivered a few destination
unreachable codes are for v40 is net unreachable one is host is unreachable
in other words the networks working but we just don't see the host protocol is
unreachable or the port is on reach and on the v6 side zero is no route to
destination which is kind of the same as net unreachable one communication with
the destination is administratively prohibited in other words it's hitting a
firewall to beyond scope of the source address or three address unreachable or
for the port is unreachable and v6 has similar but slightly different codes for
destination unreachable messages just so you'll you'll need to know both of these
going into any type of testing for the CCNA time exceeded or time to live so
when the time to live filled in a packet is decremented to zero an ICMP v4 time
exceeded message will be sent to the source host so when the time deliver the
TTL dies or is decremented to zero I always call it dying because time to
live dying get it it sends a message back so icmpv6 also sends a time
exceeded message instead of the the for TTL feed TTL filled the v6 uses the v6
hop limit field to determine if the packets expired so it gets to the end of
its hop limits and then it sends a message back saying the time was
exceeded and it time exceeded messages are used by the trace route tool as well
icmpv6 messages v6 has new features and some improved functionality not found in
v4 including four new protocols as part of the neighbor discovery protocol I
always want to call it neighborhood but its neighbor discovery protocol or in dr
NDP so you'll see it you'll see it you'll see it said some ways is indy and
sometimes you'll see it as NDP so messaging between an ipv6 router and a
v6 device including dynamic address allocation as as follows you get the
router solicitation and you have the router at advertisement i can't say that
for some reason the messaging between v6 devices including duplicate address
detection and address resolution or you get the neighbor solicitation an in s
message or a neighbor advertisement or an na message so if it's the router it's
a router solicitation and a router advertisement
and if it's a device it's a neighbor solicitation or a neighbor advertisement
so icmpv6 indy also includes the redirect message which has a similar
function to the degree direct message used in the ICMP v4 continuing on with a
v6 messages are a messages are sent by v6 enabled routers every 200 seconds to
provide addressing information to v6 enabled hosts an RA message can include
addressing information for the host such as the prefix the prefix length DNS
address and domain name and a host using stateless address auto-configuration or
slack will set its default gateway to the link local address of the router
that sent the RA a v6 enabled router will also send out an RA message in
response to an RS message in this figure over here on the right
PC one sends an RS message to determine how to receive its v6 address
information dynamically and it gets a response back with an RA message a
device assigned a global v6 unicast or link local unicast address may perform
duplicate address detection or dad we learned about that in the previous
module to ensure that the v6 address is unique to check you the unit to check
the uniqueness of an address the device will send an NS message with its own v6
address as the targeted v6 address and if another device on the network has
that address it will respond with an na message notifying the sending device
that the address is unused or in use and then the dad book you'll get that
response back and then it'll change its IP address dad is not required but RFC
48 61 recommends that it is performed on unicast addresses and finally 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 v6 address the device that has the targeted v6 address will respond
with an na message containing its Ethernet MAC address
and in this figure figure here on the right we see that our one sends an NS
message to this v6 address asking for its MAC address ping and traceroute test
first let's take a look at ping test connectivity the ping command is a v4
and v6 testing utility that uses ICMP echo request and echo reply messages to
test connectivity between hosts and provides a summary that includes the
success rate and average round-trip time to the destination over here on the
right we see that someone did a ping on a server on a switch what they ping to
192.168 22 and they got they sent five they had a success rate of 80% and the
round-trip average was that if a reply is not received within the timeout ping
provides a message indicating the response was not received it's common
for the first ping to timeout if the address resolution your ARP or your indi
needs to be performed before sending the ICMP echo request so if you do a ping
and the ARP table is not built or the MDM informations not there it's going to
fail out and then if you do it again it'll work so sometimes you have to run
it a second time pinging the loopback ping can be used to test the internal
configuration of v4 v6 on the local host to do that you just ping the one 2700
dot one for v4 r : : one for v6 if you get a response back that means that the
IP is properly installed on the host if you don't get a response back you get an
error that indicates that your TCP IP is not operational in the host that
something is not correct with your internal network interface card you can
then ping the default gateway the ping command can be used to test the ability
of a host to communicate on the local network so you can ping your default
gateway to make sure that you're connected to the default gateway it
doesn't tell you that you're connected outside it's just that you have a
connection from your NIC card to your default gateway and that'll also let you
know that if you if you've got any switches involved it'll let you know
that you're going through any switches as well so in this one here we have a
P protocol set up we have our IP address our default gateway we can ping that
default gateway and we should get a response back then we can ping a remote
host and this gets us on the routing side of it ping can be used to test the
ability of a local host to communicate across an intra network intern network
or routed a local PO you can successfully ping across the internet
work it confirms that communication on the local network is working and you're
getting through your default gateway many network administrator's limit or
prohibit the entry of ICMP messages though and the lack of ping response
could be due to security restrictions so if you're pinging and you get ever
secured if you get a response back don't just assume that something's down it
could be a security setup on routers now the traceroute command is your testing
the path trace route trace cert is a utility that's used to test the path
between two hosts and provide a list of hops on the route trace route provides
provides a round-trip time for each hop along the path and it indicates if a hop
fails to respond an asterisk is used to indicate a lost or Unruh plied packet
that information that you get back from a trace route is used to locate a
problematic router in the path or it may indicate that the router is configured
not to reply so just because you don't get a reply from it doesn't mean it's
not working it just could be a security setting and if your hops keep working
then you know that it got past that router traceroute makes use of a
function of the TTL field in v4 and the hop limit failed in v6 in the layer 3
headers along with ICMP time exceeded message so the first message sent from
trace route will have a TTL field of 1 this causes the TTL to timeout at the
first router this router then responds with the ICMP v4 time exceeded message
trace route then progressively increments the TTL field for each
sequence of messages this provides the trace with the address of each hop as
the packet times out further down the path and the TTL field continues to be
increased until the destination is reached or it's incremented to a
predefined maximum so if you're wanting to see what routes you have between you
and another IP address you can use the traceroute to do that okay so
what did we cover in this module we looked at ICMP we looked at ICMP v4 and
v6 we also took a look at the ping command and the traceroute command hope
this information is helpful for you be safe and be excellent to each other