Original subtitles

So now on 37 51 the switch that the monitoring station is connected to confetti monitor session.

We want to configure a spend session so we use the session command on do the switch 66 span sessions

could be configured if we wanted to configure span on the twenty nine fifty switch it doesn't support

the same number of sessions on the switch it only supports two sessions the number of active span sessions

however is switch dependent.

Have a look at the documentation of the switch here we'll simply configure session one to keep it simple

we need to specify a source as well as a destination of the span session so the source in our example

will be the LAN one and I want to capture traffic both sent and received in VLAN 1 you need to be careful

spanning a v lan if a lot of traffic is transmitted and received on that VLAN you could oversubscribed

the port as an example of the switch had 24 ports and you spanned all of those ports to this single

interface you would possibly overwhelm this physical interface as another example you don't want to

span a gigabit port to 100 make port and in the same way you need to make sure that your capturing device

can handle the traffic that it's receiving you don't want to as an example forward one gigabits per

second of traffic to P.C. with a slow CPSU that can't capture or handle the amount of traffic that you

throwing at it as an analogy we as people may drink water from a gloss or from a tap but generally not

from a fire hydrant because the rate of water that's sent out of a fire hydrant is far more than you

can drink so don't overload or overwhelm the port as well as the P.C. by sending too much spam traffic

out of this port so now monitor session we need to specify the same session no and we're going to specify

a destination in this case it's going to be a local interface on the switch fast ethernet 1 0 5 I'll

talk about the encapsulation and ingress options in a moment.

For now we're just going to forward the traffic out of the port so do show run pipe include monitor

we configured this command as well as this command on the switch show monitor

we can see that we have one active session it's a local session it's looking at traffic sent and received

on VLAN 1 that's the source destination is Port Fost Ethan at 1 0 5 we're using the native a villain

as the encapsulation ingress traffic is disabled so now on the capturing P.S. we'll filter for ICMP

and let's restart that capture

and en route a one all ping routed to and notice we can see the traffic which we weren't able to see

before.

Here is a source ICMP packet from router 1 Notice the MAC address ending in 0 1.

Going to write it to it's a unit cost here the IP addresses a 10 1 1 1 going to 10 1 1 2 it's an echo

request.

Here's the reply It's also a unique cost frame from Rod a 2 to write a 1 unit cost IP addresses it's

a ping reply now if write a 1 Telnet to write a 2 and logs in we should be able to see that telnet traffic

on the capturing device and we can so notice as an example he has some telnet information I'll scroll

down the road is asking for a password he has the password C I S CEO We could also follow the DCP stream

and we'll be able to see the password in this example because we are capturing traffic sent and received

on the V Line.

We're getting some duplicates but as an example if on top enable password show run and look at the running

config of that router if I fall to 4 telnet traffic again we'll be able to see the line Viti Y and the

password is shown on the line Viti y in the running config of the Rada.

So that's the conflict on the router and here it's seen in the wash out capture.

I could once again follow the TCB stream and I'll see the full configuration of the rudder as captured

on the monitoring station.

So what's happening now is when traffic is received or sent on VLAN 1 it's been forwarded out of this

port and the capturing device running why shark is able to view the traffic.

So what we did is create a monitoring session monitor session 1 capturing on VLAN 1 and the destination

as fast Ethernet.

1 05 if we remove the monitoring session so do show run pipe include monitor we can see that there's

no output in other words the monitoring session has been removed.

Now when we do the capture

and we for instance filter for ICMP traffic and paying a T from Route 1 we don't see any output.

So no ICMP traffic is shown if we fall to 4 telnet

and then Telnet to 10 1 1 2.

We don't see anything but if we put to the monitoring session back so monitor session choose a number

one.

And in this case all monitor and interface if one 0 3 which is this interface over here and we'll do

both and then we'll specify a destination of first Ethan at 1 0 5 what we should see now is once that

kicks in as you can see over there we are able to see the Telnet information so there's the prompt of

wrote it to and if I scroll up we can see the password.

So the right is asking for a enabled password and he has the password that I typed which Cisco and then

I pressed into once again if we follow that stream you can see the password that was typed so it's as

simple as that to create a monitoring session to show.

Monitor in this example we've got session one which was a local session capturing traffic in and out

of this port and it's going to this destination port 1 0 5 encapsulation is native English traffic is

disabled.

So let's talk about ingress traffic when you enable span on a switch as we've got over here the switch

no longer learns mac addresses on the span destination port it also doesn't allow traffic to be received

from that port.

So if road A one pings write a t it works

and the MAC addresses are shown in the MAC address table but rather one is not able to ping the capturing

device.

So filtering for ICMP the pings are being received from Radio a 1 to the P.C. but no replies are being

accepted by the switch.

So in other words the ping from rudder one to the capturing device is received on this port and because

of the port mirroring or span the traffic is being sent out of this port and is received by the capturing

device.

But when the capturing device replies that traffic is not accepted on the destination spend port.

So the pings are failing

so once again notice there were no successes on the ping from of one to the capturing device.

And just to confirm that is the IP address of the capturing device if we want to allow that device to

send traffic we have to configure the monitoring session to receive that traffic.

So destination interface is fast ethernet 1 0 5

and we have to add this option ingress to enable ingress traffic forwarding

and to specify that is on tagged traffic in VLAN 1.

So I'll start the capture again

and let's see if Rada one is able to ping that capturing station notice the pings succeed here's the

ping from Route One to the capturing device here's the reply and the pings succeeded.

So just to prove that again I'll do a repeat of just one

play the one shall capture one ping.

There's the ping sent from Rada one he has the reply we've seen duplicates because we are looking at

traffic sent and received on this port.

So we are receiving duplicates because we are sending traffic to the monitoring station that's received

or transmitted on this port.

So we get some duplicates but they point to remember is that if we don't use the ingress command the

monitoring station is not able to participate in the network.

Essentially the Mac address is removed from the Mac address table so the Mac addresses is not learnt

as you can see over here.

Traffic is not allowed to be received on this interface but with the ingress option it can be received

and the device is allowed to participate in the network.