1
00:00:00,000 --> 00:00:04,710
[MUSIC PLAYING]

2
00:00:04,710 --> 00:00:07,070

3
00:00:07,070 --> 00:00:09,440
So now we've been
through almost all

4
00:00:09,440 --> 00:00:12,780
of the OSPF path
selection criteria.

5
00:00:12,780 --> 00:00:15,410
We just have one thing left.

6
00:00:15,410 --> 00:00:19,940
When we get to the end, if what
we have are external routes,

7
00:00:19,940 --> 00:00:23,300
it depends if they're normal
external routes coming

8
00:00:23,300 --> 00:00:29,840
from a type 5 LSA, or if they're
in NSSA external route coming

9
00:00:29,840 --> 00:00:31,610
from a type 7.

10
00:00:31,610 --> 00:00:35,930
And as we've discussed,
it does depend on which

11
00:00:35,930 --> 00:00:39,720
RFC is in effect on the router.

12
00:00:39,720 --> 00:00:42,080
So what we're going
to do in this video

13
00:00:42,080 --> 00:00:45,080
is we're going to
focus in on router 6

14
00:00:45,080 --> 00:00:49,700
because this is only ever
going to happen on an ABR

15
00:00:49,700 --> 00:00:52,760
with an SSH area involved.

16
00:00:52,760 --> 00:00:55,520
Otherwise, there
would be no type 7s.

17
00:00:55,520 --> 00:00:58,100
So we're going to
do this on router 6.

18
00:00:58,100 --> 00:01:03,620
And we're going to start off
with the default RFC 3101.

19
00:01:03,620 --> 00:01:05,690
We'll see how that behaves.

20
00:01:05,690 --> 00:01:09,410
And then we'll switch
it to RFC 1587.

21
00:01:09,410 --> 00:01:12,600
And we see how that
changes the behavior.

22
00:01:12,600 --> 00:01:14,690
So let's jump in
and get started.

23
00:01:14,690 --> 00:01:16,482
We'll, again, look
at our topology

24
00:01:16,482 --> 00:01:18,440
just so we have a quick
idea of what's going on

25
00:01:18,440 --> 00:01:20,000
and where the routes
are coming from.

26
00:01:20,000 --> 00:01:23,180
And then we'll jump
into our command line.

27
00:01:23,180 --> 00:01:25,310
So again, for this
demonstration,

28
00:01:25,310 --> 00:01:28,360
we will be dealing with
the loopback on router 10,

29
00:01:28,360 --> 00:01:32,020
and the loopback on router,
which both represent that same

30
00:01:32,020 --> 00:01:39,050
address the 100.100.100.0/24.

31
00:01:39,050 --> 00:01:41,260
These are both
going to be arriving

32
00:01:41,260 --> 00:01:45,130
as external routes on router 6.

33
00:01:45,130 --> 00:01:50,560
Now of course, the one coming
from EIGRP 100, so the router

34
00:01:50,560 --> 00:01:56,290
2 side, this is going to be
coming in as an E, external.

35
00:01:56,290 --> 00:01:58,960
And for this other
route, area 200

36
00:01:58,960 --> 00:02:02,170
has been converted to an NSSA.

37
00:02:02,170 --> 00:02:04,150
And therefore, this
one will be coming

38
00:02:04,150 --> 00:02:07,810
in as an N route or a type 7.

39
00:02:07,810 --> 00:02:10,509
So we'll be focusing
again on router 6, which

40
00:02:10,509 --> 00:02:12,400
is acting as the ABR.

41
00:02:12,400 --> 00:02:15,430
And we'll begin by making
sure that those two

42
00:02:15,430 --> 00:02:16,820
routes are equal.

43
00:02:16,820 --> 00:02:19,630
Now at this point, they
have been manipulated

44
00:02:19,630 --> 00:02:21,340
so that they should
be showing up

45
00:02:21,340 --> 00:02:24,520
is equal entries on router 6.

46
00:02:24,520 --> 00:02:27,260
Now it's not going
to be using both.

47
00:02:27,260 --> 00:02:29,170
So we'll have to
look at the database

48
00:02:29,170 --> 00:02:30,700
to ensure that they're equal.

49
00:02:30,700 --> 00:02:33,170
Number two here has
actually already been done.

50
00:02:33,170 --> 00:02:37,150
We did change area
200 to an NSSA.

51
00:02:37,150 --> 00:02:40,840
So we're already receiving
the type 7 LSA on router 6.

52
00:02:40,840 --> 00:02:43,630
And of course, we're going to
be looking at the results here.

53
00:02:43,630 --> 00:02:48,550
And specifically what happens as
we change the rules on router 6

54
00:02:48,550 --> 00:02:50,200
as far as the RFC.

55
00:02:50,200 --> 00:02:54,590
So let's jump into router
6 and see how this works.

56
00:02:54,590 --> 00:02:56,800
So the first thing we
want to do on router 6

57
00:02:56,800 --> 00:03:01,450
is ensure that we are, in
fact, getting both LSA types,

58
00:03:01,450 --> 00:03:03,850
the type 5 and the type 7.

59
00:03:03,850 --> 00:03:07,300
So let's start with a
show IP OSPF database.

60
00:03:07,300 --> 00:03:09,340
We'll do external first.

61
00:03:09,340 --> 00:03:12,340
And of course, we'll filter
for that specific prefix.

62
00:03:12,340 --> 00:03:16,300
What we see here is that we
are, in fact, getting the type 5

63
00:03:16,300 --> 00:03:20,290
LSA from the advertising
router 10.2.2.2.

64
00:03:20,290 --> 00:03:22,780
And it has a metric of 20.

65
00:03:22,780 --> 00:03:25,000
And it has a
forwarding address set.

66
00:03:25,000 --> 00:03:28,030
Also note, if we
scroll down, we also

67
00:03:28,030 --> 00:03:33,040
have a type 5 LSA here that's
being generated by this router.

68
00:03:33,040 --> 00:03:36,400
The advertising
router is 10.6.6.6.

69
00:03:36,400 --> 00:03:41,380
So this indicates that we are,
in fact, translating the type

70
00:03:41,380 --> 00:03:43,150
7 to the type 5.

71
00:03:43,150 --> 00:03:45,010
Now that's a pretty
good indicator

72
00:03:45,010 --> 00:03:46,780
that we're already
getting the type 7.

73
00:03:46,780 --> 00:03:48,920
But of course, we
want to verify that.

74
00:03:48,920 --> 00:03:51,010
So let's change this to NSSA.

75
00:03:51,010 --> 00:03:54,460
And here we can see that we are,
in fact, getting the type 7.

76
00:03:54,460 --> 00:03:58,630
This type 7 is coming from
advertising router 10.10.10.10.

77
00:03:58,630 --> 00:04:01,030
It also has a metric of 20.

78
00:04:01,030 --> 00:04:04,180
And it has the
forwarding address set.

79
00:04:04,180 --> 00:04:08,770
NSSA always sets the forwarding
address just as a note.

80
00:04:08,770 --> 00:04:13,220
Now let's see which route
we're actually using.

81
00:04:13,220 --> 00:04:16,850
Here what we see is that we're
actually following the route

82
00:04:16,850 --> 00:04:17,899
to router 10.

83
00:04:17,899 --> 00:04:22,820
That means that we're preferring
the N route over the E route.

84
00:04:22,820 --> 00:04:25,880
We're preferring the
type 7 over the type 5.

85
00:04:25,880 --> 00:04:30,110
We can actually verify this
if we do a show IP OSPF,

86
00:04:30,110 --> 00:04:34,250
and include RFC, we
can actually see here

87
00:04:34,250 --> 00:04:41,420
that for NSSA, it is currently
being compatible with RFC 3101.

88
00:04:41,420 --> 00:04:45,080
Keep in mind that our
router 6 is running iOS XE.

89
00:04:45,080 --> 00:04:47,100
And it's following
our newer method.

90
00:04:47,100 --> 00:04:51,410
However, we can change this
to be backwards compatible.

91
00:04:51,410 --> 00:04:54,320

92
00:04:54,320 --> 00:04:57,260
We simply go into
our OSPF process.

93
00:04:57,260 --> 00:05:01,280
And we say compatible RFC 1587.

94
00:05:01,280 --> 00:05:03,410
If we look at our
command now, we

95
00:05:03,410 --> 00:05:07,310
see that it says it's
compatible with RFC 1587 now.

96
00:05:07,310 --> 00:05:11,220
And that also means we
look at our routing table,

97
00:05:11,220 --> 00:05:15,740
notice we are now following
the type 2 external,

98
00:05:15,740 --> 00:05:18,740
in other words, the type 5 LSA.

99
00:05:18,740 --> 00:05:23,500
It has changed the behavior
just as we would expect it to.

100
00:05:23,500 --> 00:05:28,120
In this video, we simply looked
at how the router handles

101
00:05:28,120 --> 00:05:32,470
an N route or a type
7 LSA, versus an E

102
00:05:32,470 --> 00:05:35,500
route or a type 5 LSA.

103
00:05:35,500 --> 00:05:40,720
If we're following RFC
3101, we prefer the N route.

104
00:05:40,720 --> 00:05:46,330
If we're following RFC
1587 we prefer the E route.

105
00:05:46,330 --> 00:05:50,650
And as we can see on iOS XE,
we can switch back and forth

106
00:05:50,650 --> 00:05:53,860
between which one we want
to be compatible with.

107
00:05:53,860 --> 00:05:57,920
On iOS XR, keep in
mind, at this point,

108
00:05:57,920 --> 00:06:01,510
it will only follow RFC 1587.

109
00:06:01,510 --> 00:06:06,100
Again NSSA, probably
not a very high priority

110
00:06:06,100 --> 00:06:09,340
on the iOS XR code chain.

111
00:06:09,340 --> 00:06:11,900
So that may be
changed in the future.

112
00:06:11,900 --> 00:06:16,690
But as of right now, it
simply follows RFC 1587.

113
00:06:16,690 --> 00:06:18,880
I hope this has been
informative for you.

114
00:06:18,880 --> 00:06:21,960
And I'd like to thank
you for viewing.

115
00:06:21,960 --> 00:06:25,000