type, let's move on and take a look at the link state request or LSR packet type.
This packet type is used to request specific LSAs from the neighboring device.
So in this case,
this would be a response directly to the comparison that was done
with the DBDs and the link state header information that they were
sent that we showed in the capture.
The LSR packet is rather simple compared to the
previously discussed packet types.
It contains three fields that match the information relayed in the DBD packet,
including the entry link state type, the link state id,
and the advertising device's router id.
Multiple triplets of these three fields can be included in a single IP packet,
depending on the number of requested LSAs.
The purpose of this packet type is to request the LSAs that a
device is missing and needs to retrieve.
So now let's move back into the capture and take a look at what this looks like.
So again we're going to use the same capture,
and we're going to take a look at the link state request packet,
and we see here these are the database descriptor packets,
there's one, two, three, and there's link state request.
We go to the top here so 10.10 .10 .1, this is Core 1 requesting,
making several requests here as we can see if we actually move this bigger.
We can see, as I noted in the slide there,
you can make several requests in the same packet,
but you have to send an individual packet for each request.
So you can send, okay,
I don't have any of these so I'm going to send a
big batch of link state requests,
and there's only three fields in that type of packet.
There's link state type; in this case it's an LSA,
router 1 is an router LSA, which is a type 1,
with a link state id of it in the advertising router.
So with this indexed information, anybody on this link that it's requesting,
in this case it's talking specifically to Core 2,
this is the information,
look it up and send me all the reachability information for this link
state entry so I can make my database mirror yours.
And this is done for all these.
So in the bottom here you're going to have more other different
types of LSA with slightly different information,
but the response to all this is going to be in the next packet
that we're going to talk about here in a second.
So in this case let's review,
this is just Core 1 in this case talking to Core 2 and saying I need all this,
all of your link state information or all of these different devices using this information.