Instructor: Hands-on with DNS. 2 2
In this video, I'm going to take you a little bit 3 3
inside of the network and we're going to use a tool 4 4
called packet tracer from Cisco 5 5
so we can actually watch the packets 6 6
and then see exactly what's going to happen 7 7
as packets go across the network 8 8
when we do our DNS resolution 9 9
to be able to pull up a website. 10 10
When we go in the environment, 11 11
you can see on my left side, I have a sample network. 12 12
I have a client and I have a local DNS server, 13 13
both attached to switch zero, 14 14
then those attached to that company's router. 15 15
That company's router has a serial connection, 16 16
indicated in red, that's connecting to an internet router. 17 17
And this would usually be shown as a big cloud 18 18
with a lot of different routers and switches 19 19
in the real world, because the internet's a big place. 20 20
But in this case, I'm just going to use one router 21 21
so I can use that as my sample internet. 22 22
In that internet router or in that internet cloud, 23 23
if you will, there's also a DNS server there. 24 24
This is the root DNS server. 25 25
So you can think about something like the .com domain 26 26
or the .net domain. 27 27
That's what we're talking about here. 28 28
Now off to the right, you'll see 29 29
there's the Dion Training router. 30 30
Now this is our border gateway router 31 31
that's connected to the internet. 32 32
So when your company tries to access our company, 33 33
it goes over the internet and goes 34 34
from your company's router 35 35
through a bunch of internet routers 36 36
and eventually to the Dion Training router. 37 37
Now the Dion Training router is then connected 38 38
to our internal switch, known as switch one, 39 39
and that has two devices hanging off of it that you can see. 40 40
One is at the bottom of the screen, 41 41
called authority.diontraining.com. 42 42
This is our internal DNS server. 43 43
And then up top, you have server.diontraining.com, 44 44
which is acting as a web server in this example. 45 45
All right, the first thing I want to show you 46 46
is that all of these DNS servers right now 47 47
have empty caches because I haven't done anything 48 48
and it's a brand new network. 49 49
So if I click in here and go to services, 50 50
you can see under DNS that I have a couple of records here 51 51
and under my cache it is completely empty. 52 52
If it had something in there, 53 53
I could clear the cache from here. 54 54
Next, we're going to look at the root DNS server, 55 55
and I'm going to look at its DNS cache as well 56 56
and see that it is also clear. 57 57
Finally, I want to look 58 58
at the Dion Training authority DNS server. 59 59
And I'm going to look at that and see again that it's clear. 60 60
All right, so what happens when you, as a client, 61 61
want to go to Diontraining.com? 62 62
Well, you're going to go onto your client 63 63
and you are going to end up hitting desktop 64 64
and go to your web browser. 65 65
Just like you would at home, you'd open up 66 66
Google Chrome or Safari or something like that. 67 67
And we're just going to type in what we want to go to, 68 68
in this case, Diontraining.com, and then hit go. 69 69
Now, because this is a packet tracer 70 70
I'm going to step-by-step through each and every packet 71 71
as it moves across the network. 72 72
You can see when I hit go, two packets showed up, 73 73
one with that brownish color and one with the green. 74 74
So what I'm going to do is I'm going to minimize 75 75
the client right now because it's going to take 76 76
a lot of packets going back and forth 77 77
before we actually see anything in this web browser. 78 78
And I want you to see what I have on the right side 79 79
of the screen. 80 80
This is a list of all of the different clients 81 81
and the different packets going back and forth. 82 82
So at time 0.0 you can see there was no last device, 83 83
but the first device here is it is at the client. 84 84
So it created these new packets. 85 85
We have a DNS packet and an ARP packet. 86 86
Now why does this happen? 87 87
Well, when the client wants to look up something 88 88
through DNS, what does it do? 89 89
It first checks it's internal DNS cache. 90 90
And here we can see that this one has no internal DNS cache, 91 91
but we do have a DNS server 92 92
of 10.0.0.3 that we want to go to. 93 93
Now, our default gateway is 10.0.0.1 94 94
and this particular client, 95 95
it has an IP address of 10.0.0.2. 96 96
So when it says I want to go to Diontraining.com, 97 97
it's first going to say, hey, I need to look this up in DNS. 98 98
So I'm going to go to my DNS server, 99 99
which is shown here as 10.0.0.3, 100 100
which is this DNS server down at the bottom of the diagram. 101 101
And you can see here, it's on fast ethernet zero, 102 102
it's link is up and it's 10.0.0.3/24, 103 103
which is this particular DNS server. 104 104
But my client doesn't know where that is yet 105 105
because it only talks to things using Mac addresses. 106 106
And since I've never talked to the DNS server before 107 107
'cause this is a brand new network or just created 108 108
it doesn't know where to go. 109 109
So it's going to send out an ARP packet 110 110
and that's why you see that green ARP packet. 111 111
Now, as you can expect, 112 112
that ARP packet is going to go from the Mac address 113 113
of my client and it's going to go to FF FF FF FF FF FF, 114 114
which is the broadcast at layer two. 115 115
So when that packet goes to the switch, 116 116
which we're going to see here in a second, 117 117
what is the switch going to do? 118 118
It's going to broadcast it out to everybody. 119 119
So we see that art packet going from the client 120 120
to the switch. 121 121
Once it gets to the switch, the switch is going to look at it 122 122
and it's going to say, do I know who FF FF FF FF FF FF is? 123 123
In this case, they do. 124 124
It knows that it goes to the broadcast. 125 125
So it's going to send out every other switch port it has. 126 126
In this case, it's going to go to the company router 127 127
and the local DNS server. 128 128
They're going to receive that. 129 129
And inside that art packet, they're going to see, 130 130
hey, is this for me? 131 131
So if I look at this art packet, 132 132
you can see the inside of it is asking, 133 133
do you know where the 10.0.0.3 address is? 134 134
And it's going to say, yes, I do. 135 135
I'm that guy. 136 136
And so local DNS is going to answer up 137 137
back to the switch and say, 138 138
I'm the device you're looking for. 139 139
Now on the company router side, it's going to look at that 140 140
and go, you're looking for 10.0.0.3. 141 141
That's not me. 142 142
I'm a router and I host the 10.0.0.0/24 network, 143 143
but that means I don't need to take this traffic 144 144
and pass it outward because in my network. 145 145
So I'm just going to drop this packet 146 146
because it's not really meant for me. 147 147
All right, once we do that, 148 148
we're going to go to the next packet that happens. 149 149
This time, the DNS server is going to send the message back 150 150
to the switch and say, yes, I'm the guy you're looking for. 151 151
I am 10.0.0.3. 152 152
And the switch says, okay, 153 153
let me tell that back to the client. 154 154
So the client now knows what the Mac address is 155 155
for that local DNS server, 156 156
because it reports it inside of that ARP message. 157 157
Now the client, when it receives that goes, 158 158
great, now I know who to send my DNS traffic to. 159 159
So I'm going to create a new DNS message, 160 160
which you can see here in brown, 161 161
and I'm going to send that back to the switch 162 162
and the switch is going to send it to the DNS server, 163 163
because it knows that Mac address 164 164
was addressed from the client to the DNS server. 165 165
At this point, the DNS server looks at it 166 166
and it has to see what do I do with this message? 167 167
So the first thing we're going to do 168 168
when we look at that message is we have to check 169 169
our own DNS records. 170 170
So as the DNS server, when I see that 171 171
I'm going to say, do I know what to do with Diontraining.com? 172 172
So I check my DNS records and here they are. 173 173
I have two records. 174 174
I have one for com and one for root. 175 175
Now the com one is a name server for the .com domain. 176 176
And it says, if you get something that ends in com, 177 177
go to the route server here on the right. 178 178
Well, that then looks in the record, says, 179 179
okay, where is the root server? 180 180
I have an A record for that and it's 10.2.0.2. 181 181
So where is that device? 182 182
Well, it's not on this network 183 183
because that's a different local area network. 184 184
So I'm going to have to send this message to my gateway, 185 185
which is the company router, 186 186
which will then forward it out 187 187
to the appropriate network where 10.2.0.2 is. 188 188
Now 10.2.0.2 in this example 189 189
is simulating the top level domain for.com 190 190
because we don't own this name 191 191
and we don't know where it goes. 192 192
So we're going to go to .com and ask them 193 193
for the authoritative name server for it. 194 194
Alright, 10.2.0.2 is actually going to be 195 195
this root DNS server right here. 196 196
And you can see right here, it is 10.2.0.2/24, 197 197
and it is up and available. 198 198
So we want to get that message over to this server 199 199
and then we're going to check our DNS records on this server. 200 200
So you're going to watch that brown packet, 201 201
and it's going to go up to the switch. 202 202
And the switch is then going to send an ARP message 203 203
out to the company and out to the client, 204 204
because again, nobody knows where 10.2.0.2 is yet. 205 205
Now when it gets to the client, 206 206
the client says that's not me and drops the message. 207 207
The router on the other hand says, hey, 208 208
I know how to get to 10.2.0.2. 209 209
So I'll answer up for that and say any local area traffic 210 210
that's destined for that address comes to me 211 211
and then I'll forward it using layer three IP addresses 212 212
out to the internet to get it over there. 213 213
So it's going to send that message back to the switch 214 214
and the switch sees it, and then it sends it back 215 215
to the local DNS server. 216 216
The local DNS server says, great, 217 217
now I know how to get there. 218 218
I'm going to send all those requests for 10.2.0.2 219 219
over to the company router, which is my default gateway. 220 220
So that's what's going to happen. 221 221
We see that go up. 222 222
We see it hit the switch, 223 223
and then it goes from the switch over to the company. 224 224
Now, once it gets to the company router, 225 225
we need to get that over to the 10.2.0.2 device. 226 226
So it's going to look at it and say, not part of my network. 227 227
Let me send it out my default gateway to the internet. 228 228
So it does that and sends it over to the ISP's router. 229 229
The ISP's looks at and goes, 230 230
Hmm, where is this thing located? 231 231
And in this case, we have it 232 232
directly attached to that router. 233 233
So it's going to drop that DNS packet 234 234
and it's going to change it into an ARP packet, 235 235
'cause again, we always send things to the final device 236 236
using layer two, using ethernet, 237 237
and that's going to require a Mac address. 238 238
And so we have to use our ARP 239 239
to do the IP and Mac address binding. 240 240
So the internet routers then can go down to the DNS server. 241 241
When it hits there the DNS server says, 242 242
oh, I know what that is. 243 243
That's me, I'm 10.2.0.2. 244 244
So it sends that message back to the internet router 245 245
and the internet router is going to send that message 246 246
back over to the company, and in turn, 247 247
they're going to say, okay, I know how to get there. 248 248
Now at this point, the local DNS server 249 249
hasn't gotten its message over to that final server yet. 250 250
And it's going to then send it again to the company. 251 251
So in this case, it sends it up to the switch zero, 252 252
from switch zero to company, and now at this point, 253 253
the company router knows what to do with it. 254 254
It sends it over to the internet router 255 255
and the internet router knows what to do with it as well. 256 256
It's going to send it down to the root DNS server. 257 257
So we're now going to look at that message, which says, 258 258
hey, where is this address for www.Diontraining.com 259 259
or Diontraining.com, like we entered in the browser. 260 260
Now we're going to look at our DNS records on this server 261 261
and see if we have one for it. 262 262
So as we go here and we look at our DNS records, 263 263
we can see there's nothing in its cache. 264 264
And we see three records. 265 265
First we have an SOA record, or a start of authority. 266 266
Now the start of authority record 267 267
is going to have these things about it, 268 268
like saying, when does it expire, when does it refresh, 269 269
when do you want to retry, what's the minimum time to live 270 270
and all those details. 271 271
Now this authority record says who owns the authority name. 272 272
Now the next one we have is authority.diontraining.com. 273 273
And we have an A record associated with that, 274 274
which says this address of authority.diontraining.com 275 275
goes to 10.4.0.2. 276 276
That is not the same as diontraining.com. 277 277
It's not the same as www.diontraining.com. 278 278
This is a sub domain called authority. 279 279
And so authority.diontraining.com 280 280
would be at that server's IP. 281 281
Now, if we go to the last thing, 282 282
we do see that there's Diontraining.com there, 283 283
and this is actually a name server record. 284 284
So who owns all of the Diontraining.com name server records? 285 285
Well, it's owned by what we see on the right, 286 286
which is authority.diontraining.com. 287 287
So if somebody wants to look up beta.diontraining.com, 288 288
wwww.diontraining.com, support.diontraining.com, 289 289
they're going to go from this record to that name server 290 290
at diontraining.com, which is located 291 291
at the authority.diontraining.com 292 292
or 10.4.0.2. 293 293
So let's look and see, where is 10.4.0.2 on this diagram? 294 294
Well, here it is. 295 295
It's authority.diontraining.com, 296 296
and you can see it's 10.4.0.2. 297 297
So again, this root DNS server is now going to send the traffic 298 298
over there and to do that, 299 299
it's going to have to do that at layer three. 300 300
So first we're going to have to go 301 301
through the ARP process again, 302 302
because we just found a new IP address 303 303
that nobody knew of before 304 304
and we have to figure out where it's going to be located. 305 305
So up we go with the DNS to the internet router, 306 306
and then that's going to get sent over to the next router, 307 307
which is Diontraining.com. 308 308
Now, once it's there, it's now going to have to get delivered 309 309
that final leg to that server. 310 310
And this is where we have to again use ARP. 311 311
So the router is going to drop that message 312 312
because it doesn't know what to do with it, 313 313
and instead it's going to start sending out 314 314
the ARP broadcast again. 315 315
So out goes the broadcast to the switch, 316 316
the switch then broadcasts it up. 317 317
And it goes to server.Diontraining.com, 318 318
which is my web server and authority.diontraining.com, 319 319
which is my name server. 320 320
Now in this case, we were looking for 10.4.0.2, 321 321
which happened to be the authority.diontraining.com server, 322 322
so server.diontraining.com is going to drop that ARP packet 323 323
and not respond to it because it's not meant for them. 324 324
Instead, the DNS server is going to respond 325 325
back to the switch and say, I'm who you're looking for. 326 326
And the switch is going to send that back to the router 327 327
at Dion Training. 328 328
Now the Dion Training router knows 329 329
where the authority.Diontraining.com server is, 330 330
and it knows how to address it using its Mac address 331 331
because we just did this ARP broadcast. 332 332
So the next time we get the retransmit of that DNS request, 333 333
it's going to go and it's going to come 334 334
from the client to the switch. 335 335
The switch says, I know what to do with that. 336 336
I'm going to send it over to the DNS server 337 337
because I always use my local DNS server first. 338 338
Now my local DNS server is going to check its cache. 339 339
Again, do we have anything in our cache yet? 340 340
Let's take a look. 341 341
Right now we don't, because we never got a message 342 342
back to this server yet 343 343
to know where the final destination is. 344 344
So what is it going to do? 345 345
If it's not my cache, I'm going to send it 346 346
to the next higher DNS server, 347 347
which happens to be the root DNS server. 348 348
So off it goes. 349 349
It transfers it up to the switch, 350 350
over to the company router. 351 351
That's going to say and take it over to the internet. 352 352
The internet's going to deliver it down to the root DNS server. 353 353
So the root DNS server is now I'm going to send that message 354 354
up to the internet router. 355 355
The internet router is going to send it over to Dion Training 356 356
and then Dion Training is going to send it over to the switch. 357 357
The switch knows where to send it now 358 358
because of that ARP broadcast we just did. 359 359
And so it's going to send it down 360 360
to the authority.diontraining.com. 361 361
Everything we did so far was just to establish 362 362
that initial connection and get that first DNS request 363 363
over to the name server, 364 364
who is the authority for this Diontraining.com name. 365 365
So now that we're there, what is this server going to do? 366 366
It's going to take it, 367 367
and it looks at the request and the request said, 368 368
I want to know where Diontraining.com is. 369 369
So it's going to check its DNS records, 370 370
and in its DNS records, does it have an A record 371 371
for Diontraining.com or a C name record 372 372
for Diontraining.com? 373 373
Well, yes it does. 374 374
You can see that record number two is Diontraining.com 375 375
and it's an A record that points to 10.4.0.3. 376 376
Now that same IP address is also going to be used 377 377
for server.Diontraining.com. 378 378
And there's an A record for that. 379 379
And then finally, you see a C name record at the end, 380 380
which says www.Diontraining.com, 381 381
and that is going to be pointing to server.Diontraining.com. 382 382
So if I went in my web browser and asked 383 383
for www.Diontraining.com, 384 384
it's going to use the C name record 385 385
and point me to server.Diontraining.com, 386 386
which points me to this A record, 387 387
which points me to this IP address. 388 388
And you can see how these things linked together, 389 389
but when I typed it in, 390 390
I just typed in directly Diontraining.com. 391 391
So I'm only going to be looking at record number two here, 392 392
which is the A record with the IP address we want to go to. 393 393
So the question is where is 10.4.0.3? 394 394
Well, if we look at that, 395 395
it's up here and it's server.Diontraining.com. 396 396
So now what we want to happen 397 397
is once the client finds out where the server is located, 398 398
it's going to start sending all this traffic 399 399
to the IP address of server.diontraining.com. 400 400
And we're going to go from the client to the switch 401 401
across the network, to the other switch, 402 402
and then up to server.Diontraining.com. 403 403
So let's see what happens as this DNS message goes back. 404 404
So it's going to go back to the switch. 405 405
It's going to give the reply and say, 406 406
here's the IP address you were looking for. 407 407
Then it's going to go over to the Dion Training router. 408 408
From the Dion Training router it's going to go 409 409
back to the internet router, 410 410
and now it's going to send it back to the root DNS server, 411 411
because we want them, that lower level server, 412 412
to know where is Diontraining.com 413 413
so if anybody else asks in the future, 414 414
they can just tell them where it is 415 415
using that .com domain name 416 416
instead of having to go all the way back 417 417
to my individual DNS server. 418 418
So when I do this, you're going to see 419 419
that we're going to actually get a cache 420 420
happening inside this root DNS server. 421 421
So there we go. 422 422
Now we've got the root DNS server and it knows where it is. 423 423
So if I go to services and look at my DNS cache, 424 424
you're going to see that it now knows that there's an A record 425 425
for Diontraining.com at this timestamp, 426 426
and it's going to be going to 10.4.0.3. 427 427
Now, depending on the time to live for this DNS record, 428 428
it's going to stay in this cache. 429 429
And then once that cash is going to expire, 430 430
it's going to go back and ask again directly from the server 431 431
instead of using its cache in the future. 432 432
All right, once we have that, 433 433
you can see though it did not add that as an A record 434 434
in its DNS. 435 435
The reason for this is that this A record 436 436
is not owned by this root server. 437 437
It's owned by the authoritative name server, 438 438
authority.Diontraining.com 439 439
over on the right side of our screen. 440 440
So it only can cache it. 441 441
It can't add the A record automatically. 442 442
All right, once it gets that we still need to go 443 443
and tell the lower level DNS server what's going on. 444 444
So it's now going to send a message 445 445
up to the internet router, over to the company router, 446 446
which sends it over to the switch. 447 447
The switch knows where it needs to go. 448 448
So it sends it down to the local DNS server. 449 449
And now if we check the local DNS server, 450 450
we're going to see that its cache 451 451
now has that same A record in it. 452 452
And so, again, we didn't add it as an A record here. 453 453
We added it as a cache, 454 454
and you can see now that we now have the cache name 455 455
for the name server on the way over, 456 456
and now we have the cash name for the IP address 457 457
for Diontraining.com. 458 458
So at this point our local DNS server 459 459
can now interrupt for anybody 460 460
who's asking where Diontraining.com is, 461 461
and we don't have to go through all those packets 462 462
we just did to get that information again, 463 463
because we already have it. 464 464
Now once the time to expire happens, 465 465
we're going to have to have that cache invalidated 466 466
and it happens automatically. 467 467
So then we would have to go all the way back to the server 468 468
and get a new copy because maybe I changed my IP address 469 469
or move that server. 470 470
All right, so now that the DNS server has it, 471 471
it can answer that back to the original requester, 472 472
which was our client. 473 473
So now our client knows where to go. 474 474
So now the client can actually start sending traffic 475 475
and we want to send on HTTP traffic 476 476
because that's what we were trying to do by going to a website. 477 477
Now first, you're seeing this ARP again. 478 478
This ARP is going to the switch, 479 479
and then that's going over to the company 480 480
and the DNS server, because we now know 481 481
what the IP address we want to go to is. 482 482
And that IP address was the IP address 483 483
for server.Diontraining.com. 484 484
But our switch doesn't know that 485 485
and our router doesn't know that. 486 486
So we again have to ARP to say, hey, 487 487
what is the Mac address for this IP address? 488 488
Both these things are going to get it. 489 489
And both of them are going to say, it's not me. 490 490
The company router on the other hand is going to say, 491 491
it's not me, but I know where to send it 492 492
so you can send that to me 493 493
and I'll send it out my default gateway. 494 494
So that's what's going to happen. 495 495
We get that ARP request going back to the switch. 496 496
The switch now knows anytime somebody's asking 497 497
for that server.Diontraining.com IP 498 498
that we were talking about, 499 499
it's going to go over to the company router 500 500
because that is considered the default gateway. 501 501
All right, now that we see that, 502 502
what's the next thing that's going to happen? 503 503
Well, the Dion Training router is also going to be doing 504 504
an ARP request on its side of the connection, 505 505
because it needs to know how to do that final delivery 506 506
to that server. 507 507
So it's doing an ARP broadcast. 508 508
It goes out to the switch, 509 509
the switch sends it to both the servers. 510 510
And then the one that it is, 511 511
is going to respond back to the switch, 512 512
in this case, server.Diontraining.com. 513 513
Now, as we do that, 514 514
the switch now gets that message 515 515
and it sends it back to Dion Training using ARP 516 516
to say, hey, I know where to send messages 517 517
for the server.Diontraining.com, 518 518
so go ahead and send it to me as a switch 519 519
and I'll deliver it on the local area network. 520 520
All right, so now that we did all of that, 521 521
our client knows where to go. 522 522
It's going to go to its local DNS server 523 523
for that address resolution. 524 524
Now that it knows the IP name, 525 525
anytime it wants to do things 526 526
to go to the server.Diontraining.com or Diontraining.com, 527 527
it can do that using the IP, 528 528
using its local cache on the client. 529 529
If it's client has expired on that cache, 530 530
it can then go to its local DNS server. 531 531
If the local DNS server is expired, 532 532
it's going to go back to the root server. 533 533
If the root server is expired, 534 534
it's going to go all the way back 535 535
to the authority.Diontraining.com name server 536 536
and we do this whole process again. 537 537
All right, so now I want to go ahead 538 538
and look at my browser and make sure 539 539
we can get traffic going back and forth 540 540
now that we've done the DNS part of this. 541 541
So I'm going to go to Diontraining.com and I'm going to hit go 542 542
and off it goes with the message. 543 543
And there we go: DNS, DNS. 544 544
We're going to go all through that process again 545 545
so you can see what it looks like, 546 546
going through, getting to the root DNS server, 547 547
back to the router, back over to Dion Training's router, 548 548
back to the switch, down to the authority.DNS 549 549
and up to the server.DNS. 550 550
It drops it at the server 551 551
because there's no DNS record there. 552 552
And then the authority one sends back its message 553 553
and says, here is what we have. 554 554
And so when it does that it goes back through 555 555
to one router, to the second router, 556 556
to the root DNS, back to the internet router, 557 557
over to the company router, over to the company switch 558 558
and then down to the local DNS server. 559 559
And then that goes all the way back up to our client. 560 560
All right, that is the DNS process 561 561
as we're looking at using hierarchies 562 562
and going from our local to our root DNS 563 563
and then over to our authoritative name servers. 564 564
So at this point, we want to send out a request 565 565
back to that HTTP server, which is holding Diontraining.com. 566 566
And at this point, we will be able to send our get message 567 567
using HTTP and we'll receive the webpage back. 568 568
So we create our packet. 569 569
We address it with the Mac address of our default gateway. 570 570
And that way our company router will send it out 571 571
to the Dion Training router across the internet. 572 572
So here we go. 573 573
We're going to send that HTTP traffic. 574 574
It goes over to switch zero. 575 575
From switch zero is going to send it to the company router. 576 576
The company routers is going to then readdress it, 577 577
using the IP address that we want to go to, 578 578
which happens to be the IP address 579 579
for server.Diontraining.com. 580 580
And it sends it out to the internet. 581 581
The internet then says, where does this belong? 582 582
Finds the right network as it passes it 583 583
from router to router and eventually getting 584 584
to the Dion Training router, 585 585
which hosts the network for server.Diontraining.com. 586 586
Once it gets to that router, 587 587
it's going to strip it down to layer two 588 588
and start using ethernet as it goes to the switch 589 589
and using Mac addresses. 590 590
So it does the IP to Mac address conversion using ARP. 591 591
Once it does that, it hits the switch. 592 592
The switch knows where it goes and sends it 593 593
up to the server. 594 594
Notice it only went from the client to the server. 595 595
It never touched those DNS servers again, 596 596
'cause we already did the DNS part. 597 597
We know what the IP address is. 598 598
Now, once it gets to the server, 599 599
the server is going to process that message. 600 600
In this case, it was a get message saying 601 601
give me the website. 602 602
And so it's going to send back the website 603 603
in a series of packets. 604 604
In this case, it's only one packet 605 605
because it's a very small website I'm sending 606 606
and it goes back across the internet to the company, 607 607
over to the switch and then up to our client. 608 608
Now, once I do that, 609 609
we can go and look at what page it was that we received. 610 610
This would happen all in the background 611 611
and you'd see it on your web browser. 612 612
And there it is. 613 613
So in this case, I have server.Diontraining.com, 614 614
also known as www.Diontraining.com. 615 615
And this is used to simulate the Dion Training homepage 616 616
within my lab environment. 617 617
Now, if I actually put pictures on there 618 618
and things like that, 619 619
it would make this a much bigger website 620 620
and it would be a lot of different packets 621 621
and this purple packet going back and forth 622 622
would just keep on happening. 623 623
I would send the one packet over and say, 624 624
give me the website. 625 625
And then I would get a whole series of packets back 626 626
from the web server, 627 627
with the videos and images and texts that I need 628 628
to build that website at layer seven, 629 629
the presentation layer on my client. 630 630
And that's how you get to see the webpage 631 631
once you go to something like Diontraining.com. 632 632
Hopefully this explanation helped you understand 633 633
a little bit more about how DNS works in the background 634 634
and how these things layer upon each other 635 635
from the local to the top level domain 636 636
and to the authoritative servers.