1
00:00:00,000 --> 00:00:02,856
[MUSIC PLAYING]

2
00:00:02,856 --> 00:00:08,100

3
00:00:08,100 --> 00:00:11,250
So let's start off with
a nice introduction

4
00:00:11,250 --> 00:00:14,580
to some of the attributes
of Label Distribution

5
00:00:14,580 --> 00:00:17,430
Protocol, or LDP.

6
00:00:17,430 --> 00:00:21,000
Now, as we've
discussed, LDP is used

7
00:00:21,000 --> 00:00:26,460
to exchange labels between our
LSRs, the Label Switch Routers.

8
00:00:26,460 --> 00:00:28,620
The reason, of course,
we need to do this,

9
00:00:28,620 --> 00:00:31,440
is that the labels
generated on a router

10
00:00:31,440 --> 00:00:33,840
are not used by that router.

11
00:00:33,840 --> 00:00:36,960
Those labels are
used by the neighbors

12
00:00:36,960 --> 00:00:40,360
to send traffic to this LSR.

13
00:00:40,360 --> 00:00:42,510
Therefore, we need
a reliable method

14
00:00:42,510 --> 00:00:44,280
to exchange those labels.

15
00:00:44,280 --> 00:00:46,900
That's, of course,
where LSR comes in.

16
00:00:46,900 --> 00:00:49,470
So let's go ahead
and jump in, and get

17
00:00:49,470 --> 00:00:53,330
started by looking at
some of its attributes.

18
00:00:53,330 --> 00:00:58,750
So keeping in mind that
those MPLS labels are locally

19
00:00:58,750 --> 00:01:01,510
significant to the
router, we have

20
00:01:01,510 --> 00:01:04,250
to get the labels
to our neighbors.

21
00:01:04,250 --> 00:01:10,210
So first, keep in mind that a
label, by default, is created

22
00:01:10,210 --> 00:01:12,860
for every IP destination.

23
00:01:12,860 --> 00:01:17,170
And again, for this, it's going
to use the RIB, the Routing

24
00:01:17,170 --> 00:01:20,050
Information Base, or
the routing table.

25
00:01:20,050 --> 00:01:23,620
Neighbors actually
use these labels

26
00:01:23,620 --> 00:01:27,080
to forward the traffic
to their neighbors.

27
00:01:27,080 --> 00:01:30,430
So in order to do
that, these labels

28
00:01:30,430 --> 00:01:34,780
are going to have to be known
specifically by the directly

29
00:01:34,780 --> 00:01:36,410
connected neighbors.

30
00:01:36,410 --> 00:01:38,540
They don't have to go past that.

31
00:01:38,540 --> 00:01:42,340
But we have to know all of the
labels that are being generated

32
00:01:42,340 --> 00:01:43,870
by our neighbors.

33
00:01:43,870 --> 00:01:47,470
Because when we forward
traffic to that neighbor going

34
00:01:47,470 --> 00:01:49,780
to a specific
destination, we need

35
00:01:49,780 --> 00:01:52,690
to use its designated label.

36
00:01:52,690 --> 00:01:56,470
This is, of course, where
LDP comes into play.

37
00:01:56,470 --> 00:01:59,350
It's used to exchange
these labels,

38
00:01:59,350 --> 00:02:03,100
specifically that we're
using for IP forwarding.

39
00:02:03,100 --> 00:02:06,910
We've discussed previously that
there are different protocols

40
00:02:06,910 --> 00:02:10,840
used for other applications,
such as VPN and traffic

41
00:02:10,840 --> 00:02:11,810
engineering.

42
00:02:11,810 --> 00:02:15,100
But for IP forwarding,
we use LDP.

43
00:02:15,100 --> 00:02:17,830
Now, here's the
interesting thing.

44
00:02:17,830 --> 00:02:24,060
Routing protocols could
have been used instead.

45
00:02:24,060 --> 00:02:26,970
Why do I say that's such
an interesting concept?

46
00:02:26,970 --> 00:02:28,980
Well, think about
this for a moment.

47
00:02:28,980 --> 00:02:32,190
Our routing protocols already
run between directly connected

48
00:02:32,190 --> 00:02:33,000
neighbors.

49
00:02:33,000 --> 00:02:38,250
So LDP is really just adding
another protocol into the mix.

50
00:02:38,250 --> 00:02:40,560
To a certain extent,
it's one more thing

51
00:02:40,560 --> 00:02:42,570
to break on our network, right?

52
00:02:42,570 --> 00:02:46,530
But the reason that it was
done, at least originally,

53
00:02:46,530 --> 00:02:52,440
is it's a lot easier to make a
new protocol to do a new task

54
00:02:52,440 --> 00:02:56,280
than it is to modify all
of these existing routing

55
00:02:56,280 --> 00:02:58,890
protocols, get
everybody's code up

56
00:02:58,890 --> 00:03:02,260
to date on all of the updates,
and all that kind of thing.

57
00:03:02,260 --> 00:03:07,080
However, time has passed
since all of this was done.

58
00:03:07,080 --> 00:03:09,930
Now, it's obviously
not our current topic.

59
00:03:09,930 --> 00:03:14,340
But in this course, we will
be covering segment routing.

60
00:03:14,340 --> 00:03:16,800
And in segment
routing, we, in fact,

61
00:03:16,800 --> 00:03:20,430
do use the routing protocols
to exchange the labels.

62
00:03:20,430 --> 00:03:23,790
So just so we're clear, it
can, of course, be done.

63
00:03:23,790 --> 00:03:25,840
I just mentioned that.

64
00:03:25,840 --> 00:03:29,070
But we're going to
focus on LDP here first.

65
00:03:29,070 --> 00:03:33,510
And I guess we could call it
traditional MPLS forwarding.

66
00:03:33,510 --> 00:03:36,990
And again, I just summarized
this whole last point here,

67
00:03:36,990 --> 00:03:41,970
that, yeah, a separate protocol
was chosen in order to minimize

68
00:03:41,970 --> 00:03:45,300
the changes needed to the IGPs.

69
00:03:45,300 --> 00:03:48,450
And again, it wasn't necessarily
that we didn't want to do it.

70
00:03:48,450 --> 00:03:51,150
Because again, ultimately,
we sort of did.

71
00:03:51,150 --> 00:03:54,420
It's just, it's a lot quicker
to create a new protocol

72
00:03:54,420 --> 00:03:56,280
to do something
when you're trying

73
00:03:56,280 --> 00:03:58,940
to create a new technology.

74
00:03:58,940 --> 00:04:01,180
Now, LDP is a standard.

75
00:04:01,180 --> 00:04:05,080
It's referenced in RFC 3036.

76
00:04:05,080 --> 00:04:10,270
This actually replaces Cisco's
proprietary Tag Distribution

77
00:04:10,270 --> 00:04:14,100
Protocol, or TDP.

78
00:04:14,100 --> 00:04:15,750
Just as a quick note here.

79
00:04:15,750 --> 00:04:19,649
Some devices do actually
still support TDP.

80
00:04:19,649 --> 00:04:20,610
It still works.

81
00:04:20,610 --> 00:04:22,019
It still functions.

82
00:04:22,019 --> 00:04:23,940
You could still use it.

83
00:04:23,940 --> 00:04:26,460
They are not,
however, compatible.

84
00:04:26,460 --> 00:04:29,410
They operate on different
port numbers, and so on.

85
00:04:29,410 --> 00:04:31,420
They're not compatible
with each other,

86
00:04:31,420 --> 00:04:33,990
but they do an equivalent job.

87
00:04:33,990 --> 00:04:35,490
Needless to say
though, we should

88
00:04:35,490 --> 00:04:37,750
be using the standard today.

89
00:04:37,750 --> 00:04:39,990
Now, what's
interesting about LDP

90
00:04:39,990 --> 00:04:43,890
is it uses both UDP and TCP.

91
00:04:43,890 --> 00:04:47,070
We'll see this in our
traffic captures later.

92
00:04:47,070 --> 00:04:50,970
Although, it does use the
same port on both protocols.

93
00:04:50,970 --> 00:04:53,910
And as we've mentioned,
this is generally

94
00:04:53,910 --> 00:04:56,910
used on directly
connected neighbors.

95
00:04:56,910 --> 00:04:59,830
In which case, it
uses multicast.

96
00:04:59,830 --> 00:05:05,580
However, it can be targeted
to go to routed neighbors.

97
00:05:05,580 --> 00:05:07,930
We can use this for
a variety of reasons.

98
00:05:07,930 --> 00:05:09,660
And we'll talk
about some of those

99
00:05:09,660 --> 00:05:12,780
as we move through this skill.

100
00:05:12,780 --> 00:05:16,880
In this video, we just got
an introduction to LDP,

101
00:05:16,880 --> 00:05:19,640
or Label Distribution
Protocol, which

102
00:05:19,640 --> 00:05:23,210
is what we use to exchange
labels between our routers

103
00:05:23,210 --> 00:05:26,180
that are going to be
used for IP forwarding.

104
00:05:26,180 --> 00:05:28,460
Now, this is
generally used, again,

105
00:05:28,460 --> 00:05:30,320
directly between neighbors.

106
00:05:30,320 --> 00:05:34,490
However, it can be targeted
to get to a routed neighbor

107
00:05:34,490 --> 00:05:36,000
if we need to.

108
00:05:36,000 --> 00:05:38,540
Now we have to
discuss neighborships.

109
00:05:38,540 --> 00:05:41,400
And that's exactly
what we get to do next.

110
00:05:41,400 --> 00:05:45,020
Until then, I hope this has
been informative for you,

111
00:05:45,020 --> 00:05:48,130
and I'd like to thank
you for viewing.

112
00:05:48,130 --> 00:05:52,000