-: In the last lesson, I talked about the fact 2 2
that we can use dynamic routing protocols 3 3
so routers can tell each other the routes they know. 4 4
But I said we would talk more 5 5
about those specific writing protocols later on. 6 6
Well, in this lesson, we're going to cover 7 7
each and every one of those 8 8
that you're going to need to know for the Network+ exam. 9 9
Now there are two different types 10 10
of dynamic routing protocols. 11 11
There are internal ones and external ones 12 12
and these are the basic categories. 13 13
Now, interior ones are things like 14 14
interior gateway protocols that operate 15 15
within a network or within an autonomous system. 16 16
External gateway protocols will operate 17 17
between autonomous systems on those exterior networks. 18 18
So for example, the internet 19 19
is a really large exterior system 20 20
so it's going to be using exterior gateway protocols. 21 21
Your networks inside your intranet, 22 22
even if you have multiple routers and switches there, 23 23
are going to operate using interior gateway protocols. 24 24
And we're going to go through some examples 25 25
of both of these types of protocols in this lesson. 26 26
Now first, let's talk about the router advertisement method. 27 27
This is a characteristic of every routing protocol. 28 28
Every dynamic routing protocol is going to look at routing 29 29
just a little bit differently, though. 30 30
Some of them are going to use things 31 31
known as distance vectors and others 32 32
are going to use things known as link states. 33 33
Now some of them don't fit neatly 34 34
into either of these two categories 35 35
and they become a hybrid of both of them. 36 36
Now, what this means is that there's some method 37 37
for the route to be received, advertised, 38 38
and provided to somebody else. 39 39
And you have to figure out how you're going to do that. 40 40
There's different ways of doing it. 41 41
It can be based on the measurement of cost. 42 42
That would be something like a distance vector. 43 43
If could be based on how many routers 44 44
you have to go through, 45 45
it might be something based on the link state of it. 46 46
All of those are valid ways, 47 47
depending on the protocol you're using. 48 48
And this is where you become much more concerned 49 49
with the different ways of doing things. 50 50
For instance, if you're going to be using a link state vector, 51 51
this is where you're going to be concerned more with link speed 52 52
and what is the quickest method of getting there? 53 53
If you have to go through four routers, 54 54
but it's quicker than going through just one. 55 55
That's okay if we're dealing with link state, 56 56
but if we're dealing with distance, that would be backwards. 57 57
We only want to go through one router, even if it's slower. 58 58
This is the way we have to look at these different things 59 59
and figure out what's going to be best for us. 60 60
Now, we're going to talk about all of these 61 61
as we go through this video 62 62
and hopefully it'll make a little bit more sense to you. 63 63
First, let's talk about distance vectors. 64 64
Now, when you're dealing with a distance vector, 65 65
this is about the number of routers 66 66
you're going to be connecting through 67 67
for a particular route. 68 68
And so if you're dealing with a distance vector, 69 69
it's going to send a full copy of its routing table 70 70
to everybody else who's directly connected to it 71 71
at regular intervals. 72 72
Now, the bad thing about this is it has 73 73
what's known as a slow convergence time. 74 74
Now, what is convergence? 75 75
Well, convergence is the time it takes 76 76
for all of the routers to update their routing tables 77 77
in response to a topology change. 78 78
So if I add a router or I take one away, 79 79
how long is it going to take for everyone on the network 80 80
to know that happened? 81 81
So in this example, you'll see I have three routers. 82 82
I have routers one, two, and three. 83 83
And if I added a fourth router in, 84 84
it's going to take some amount of time for router four 85 85
to tell the other three routers that it's there 86 86
and how it's connected. 87 87
That's the idea of convergence time. 88 88
Now, once everybody knows all the same information 89 89
across all four routers 90 90
then you have what's known as a converged network. 91 91
Now, one of the ways that we can speed up 92 92
our convergence time is to actually use a hold-down timer. 93 93
So instead of updating our routing tables every 30 seconds, 94 94
we might update it every three minutes. 95 95
Now, by doing that, it's going to allow us 96 96
to converge faster 97 97
because there's less changes across the network. 98 98
Now, if there's more changes, 99 99
it's going to take us more time to converge. 100 100
So if we do less changes and we spread that out 101 101
from 30 seconds to three minutes, maybe to six minutes, 102 102
that's going to be better for us 103 103
in terms of convergence time. 104 104
Now, when we deal with a distance vector, 105 105
it's really also concerned about a thing known as hop count. 106 106
And this is how many times 107 107
I have to go through another router to get somewhere. 108 108
So in this example, what's the quickest way 109 109
to get from router three to router two? 110 110
Well, if you're only concerned with hops 111 111
or the number of routers you have to go through, 112 112
you're going to go directly from three over to two 113 113
over that slow, one-megabit-per-second connection. 114 114
Now, if you're concerned with link state on the other hand, 115 115
you're going to be concerned with the fastest way 116 116
to get there by going where the most bandwidth is available. 117 117
And that would actually be going 118 118
across the 100-megabit-per-second connections. 119 119
So I go from router three to router one to router two, 120 120
and that will be much faster than going directly 121 121
to router two from router three. 122 122
Now that's again not going to account for the fact 123 123
that if we're doing a distance or link state vector. 124 124
If we're using a distance vector, we don't consider speed. 125 125
We just count the hops. 126 126
So we're going to go direct from two to three, 127 127
but if we're dealing with a link state vector, 128 128
we're going to go based on speed. 129 129
And that's the big difference here. 130 130
So you have to think about that as you're figuring out 131 131
which protocol you're going to use 132 132
and which is going to be the best way 133 133
for you to have information flow in your network. 134 134
Now, when we deal with link state, we start worrying 135 135
about the cost and the speed of all these connections. 136 136
This is going to require all of our routers 137 137
to know about all the paths of all the other routers as well 138 138
so it can figure out what the best path is 139 139
to send the information around. 140 140
Now, this information is flooded out 141 141
through the link state domain when you're using OSPF, 142 142
which is one of our routing protocols. 143 143
Another one we can use is IS-IS 144 144
and this again is a link state protocol 145 145
to ensure the routers have a synchronized information 146 146
inside their routing tables. 147 147
Now, with that synchronized information, 148 148
they can then make the best routing decisions. 149 149
Now, we're going to talk specifically 150 150
about these two protocols in just a little bit here 151 151
so hang in with me. 152 152
Now, the link state does have a faster convergence time 153 153
than distance vectors and it does use that cost 154 154
and other factors as metrics 155 155
when it figures out what the best way of routing traffic is. 156 156
Now, this also includes things like your link speed, 157 157
because the link speed is really important 158 158
of how much bandwidth you have to send the data across. 159 159
Each router is going to construct 160 160
its own relative shortest path based 161 161
on where it sees itself in the logical diagram 162 162
and then it calculates the distance 163 163
of how it's going to get to the other places. 164 164
So let's take an example of you sitting in Florida, 165 165
and I'm sitting here in Washington, DC, 166 166
and we both want to get to California. 167 167
Now we can have different methods to get there based 168 168
on where we sit in the typology of the United States, right? 169 169
If we're both going to get in our car and drive there, 170 170
we have to figure out based on the highway speeds 171 171
and the slowness of those speeds 172 172
and which traffic there is 173 173
and how many states we have to go through 174 174
and which highways we're going to go to get over there. 175 175
So let's say we had to go 3,000 miles 176 176
to get to California from Washington or from Florida. 177 177
Well, if I can go 60 miles an hour the whole time, 178 178
but you can only go 30 miles an hour, 179 179
well, I'm going to get there a lot faster, right? 180 180
Because I can go two miles for every one that you go. 181 181
Now that's the idea. 182 182
So as we start figuring out 183 183
how we're going to go through this using link state, 184 184
we can start taking speeds into account and figuring out, 185 185
hey, maybe I'm going to take this highway 186 186
versus that back road. 187 187
Or, there's a lot of traffic on that highway 188 188
so I'm going to take the back roads instead. 189 189
Well, our routers do the same exact thing 190 190
using those links state protocols. 191 191
Now let's talk about the first routing protocol here. 192 192
This one is known as RIP, R-I-P, 193 193
and it's one of the oldest routing protocols out there. 194 194
It stands for the Routing Information Protocol 195 195
and it is an interior gateway protocol 196 196
that is used internal to your networks. 197 197
This is a distance vector protocol 198 198
and so it's going to rely on hop count 199 199
to figure out the fastest path. 200 200
Now it's all about how many routers 201 201
we're going to have to go through 202 202
and the maximum number of hops you can hit is 15 with RIP. 203 203
Now, if you hit 16 or more routers, 204 204
the connection is going to be considered dead 205 205
and it's just going to drop the packet 206 206
and wait for you to retransmit it. 207 207
Now, again, this is the oldest dynamic routing protocol 208 208
out there and it does provide updates every 30 seconds 209 209
and so it becomes really hard to maintain convergence 210 210
when you're dealing with a RIP network. 211 211
Now, RIP is really easy to configure 212 212
and it sends out its information using UDP as its protocol 213 213
and so it does have that fire and forget method. 214 214
The next routing protocol we have is known as OSPF 215 215
which is really popular. 216 216
This is known as Open Shortest Path First. 217 217
OSPF is another interior gateway protocol, 218 218
but unlike RIP it doesn't use distance vector. 219 219
It uses link state. 220 220
So it is concerned with costs and this way 221 221
it's going to be a lot more efficient. 222 222
Now, going back to our example of having the three routers, 223 223
router one, router two, and router three, 224 224
what is the shortest path for us to go 225 225
from router three to router two? 226 226
Well, it's actually going through router one 227 227
because the speed there is going 228 228
across a 100-megabit-per-second link 229 229
instead of going over a 10-megabit-per-second link. 230 230
Cost here is based on link speed not on hop count. 231 231
And so OSPF will help you get there fastest 232 232
using that link state variable. 233 233
Next, we have 234 234
the Intermediate System to Intermediate System 235 235
known as IS-IS. 236 236
This is another interior gateway protocol 237 237
and it functions a lot like OSPF. 238 238
It again is going to use cost as its link state measurement. 239 239
And this cost is based on link speed between two routers. 240 240
It functions a lot like OSPF, 241 241
but OSPF is still dominant in the marketplace 242 242
and used very widely where IS-IS 243 243
didn't really see widespread adoption. 244 244
The next routing protocol we have to discuss is EIGRP 245 245
or the Enhanced Interior Gateway Routing Protocol, 246 246
which you can probably guess 247 247
is the interior gateway protocol based on its name. 248 248
Now this is an advanced distance vector protocol 249 249
that uses both bandwidth and delay to make it a hybrid 250 250
of the distance and link state protocols. 251 251
It does count the delay that exists, 252 252
which is how many hops there are, 253 253
as well as the cost that's available 254 254
with each of those links to figure out their speed, 255 255
making it that nice hybrid. 256 256
Now, this hybrid protocol was developed by Cisco 257 257
as an upgrade to OSPF and it is very popular 258 258
if you're using a Cisco-only network. 259 259
Because it's proprietary, 260 260
meaning you can only use it with all Cisco products, 261 261
you're not going to see it a lot if you're using Juniper 262 262
or Brocade or other routers in your network. 263 263
Again, it hasn't gotten the widespread acceptance 264 264
that OSPF has because OSPF can be used on any device 265 265
in any networks, not just Cisco. 266 266
The last protocol we're going to talk about is BGP 267 267
or the Border Gateway Protocol. 268 268
This is an external gateway protocol and on the exam, 269 269
if you're asked which of these 270 270
is an exterior gateway protocol, 271 271
the only answer you should be looking for is BGP 272 272
because all the other protocols we talked about 273 273
are interior protocols. 274 274
Now this gateway protocol is going to use a path vector 275 275
to use a number of the autonomous system hops 276 276
that it needs to use instead of router hops. 277 277
Now, I'm not concerned with how many routers 278 278
I have to go through necessarily, 279 279
but I'm more concerned with how many systems 280 280
I have to go through. 281 281
Again, this makes sense when you start thinking 282 282
about the fact that BGP is used 283 283
as the backbone of the internet. 284 284
It's made up of lots of different autonomous systems 285 285
as we move from one ISP to another 286 286
and so this is what we want to think about 287 287
when we talk about autonomous systems. 288 288
Now this has gained widespread utilization 289 289
and is used all across the internet. 290 290
BGP makes the internet run. 291 291
The big problem with it is that 292 292
it doesn't converge very quickly 293 293
because of the large scale of all of these networks. 294 294
So if you add a new router or a new system to the internet, 295 295
it can take an hour or two 296 296
before it starts getting populated 297 297
and even more as it goes across the entire internet 298 298
to let them know that it now exists. 299 299
When we talk about these routers, 300 300
we have all of these different routes 301 301
and we have to think about the believability of a route. 302 302
Now, what exactly does that mean 303 303
when we talk about believability of a route? 304 304
Well, let's say I have a network that's using 305 305
more than one routing protocol 306 306
because my routers can support multiple protocols. 307 307
I might be running RIP, and I might have OSPF. 308 308
Both of them being used on the same router 309 309
in the same network. 310 310
Now, how do I know which one 311 311
I'm going to go with when I'm a packet 312 312
and the router needs to move me around the network? 313 313
Well, these routing protocols 314 314
are going to be considered more or less believable 315 315
based on some different factors that we have. 316 316
For example, RIP is considered less believable than OSPF. 317 317
Now, why is that? 318 318
Well, this is because routers use an index of believability, 319 319
which we're going to call AD 320 320
or the administrative distance. 321 321
Now, if a route has a lower administrative distance, 322 322
it's going to be considered more believable, 323 323
and it's going to be better to have a lower number. 324 324
So I like to think about this like golf rules, 325 325
the lower the number, the better it is 326 326
in terms of believability. 327 327
Now here's a chart for you with the administrative distances 328 328
of the different protocols we talked about. 329 329
If you're dealing with a directly connected route, 330 330
this is going to be the most believable. 331 331
Why? 332 332
Because the router is directly connected 333 333
to another router so it knows itself 334 334
and it trusts its own opinion that it's connected. 335 335
Now, this makes a lot of sense, right? 336 336
So if I know you personally, we're holding hands, 337 337
we're both connected and therefore the trust would be zero. 338 338
That's the idea here with the directly connected route. 339 339
It is fully trusted. 340 340
Now a statically configured network 341 341
is going to have an AD of one. 342 342
That's the next most believable 343 343
because routers do what they're told. 344 344
And if you, as a network administrator 345 345
went in and configured a static route, you told that router, 346 346
I want you to believe this above everything else, 347 347
unless you're directly connected to somebody else. 348 348
Beyond that, you're always going to believe me. 349 349
After our directly connected routes and our static routes, 350 350
we're then going to trust EIGRP next. 351 351
After that we believe, OSPF and then RIP, 352 352
and then external EIGRP. 353 353
And then as we go all the way to the bottom of our chart, 354 354
we see the worst believability, the unknown or unbelievable, 355 355
which means that it's going to have a rate of 255 356 356
for its administrative distance. 357 357
The reason why we set it at 255 is basically we say, 358 358
I can't find this network anymore. 359 359
It is totally unbelievable 360 360
and so I don't want to run traffic that way. 361 361
Now for the exam, do you have to memorize all these numbers? 362 362
No, but you should have an idea that directly connected 363 363
is the most believable, then static, 364 364
then followed by things like EIGRP, OSPF and RIP. 365 365
If you think about the fact that RIP 366 366
was one of our earliest protocols, 367 367
it would be one of our least believable. 368 368
OSPF was an improvement to RIP 369 369
so it's a little bit more believable. 370 370
And then we had EIGRP, which was an improvement to OSPF. 371 371
So again, it's more believable. 372 372
This is kind of a memory game that I use 373 373
to try to remember which ones are most believable 374 374
and which ones are least believable. 375 375
Lastly, we have metrics associated with all of these routes. 376 376
And when we look at these metrics 377 377
and we look at these routes, 378 378
there's going to be a routing protocol 379 379
that's able to choose which path it's going to go on. 380 380
And we do this based on metrics. 381 381
These are things like hop count, believability, 382 382
reliability, bandwidth, delay, costs, or other metrics. 383 383
Each protocol uses a different metric 384 384
to determine which route it should use 385 385
and which one is it going to be considered faster or slower. 386 386
Depending on which route it is, 387 387
it's going to determine which metric you're going to use. 388 388
And so when we're dealing with metrics, 389 389
it's always going to be thinking about the fact 390 390
that lower numbers are better, higher numbers are worse, 391 391
when we deal with routing. 392 392
Anytime we talk about hop count, 393 393
we want the least number of routes. 394 394
If we start talking about bandwidth, 395 395
we want the lowest cost of bandwidth. 396 396
And that gives us the highest amount of bandwidth. 397 397
And so lower costs becomes better. 398 398
If we're dealing with delay, 399 399
we want the least amount of delay. 400 400
Believability, we want the lowest number. 401 401
We want a zero for directly connected, right? 402 402
Or one for static route or one of those lower numbers 403 403
for the administrative distance. 404 404
That's the idea here. 405 405
Lower numbers are always going to be better. 406 406
You see this trend in routing 407 407
where the metrics lower is always better. 408 408
And so remember that for the exam. 409 409
Lastly, I wanted to give you this summary slide 410 410
here on the screen. 411 411
This is one of those things I'd like you to write down 412 412
in your notes so you can remember 413 413
all about the routing protocols. 414 414
This summarizes everything nicely. 415 415
-: From RIP, OSPF, EIGRP. 416 416
IS-IS, and BGP. 417 417
It shows you which ones are interior, 418 418
which ones are exterior, which ones are distanced vectors, 419 419
which ones are link states. 420 420
And hopefully this will help you 421 421
as you study your different routing protocols 422 422
and remember the key facts and figures 423 423
for them before the exam.