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0:00:13
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Now, the very last network type loopback
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0:00:16
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we talked a little about this before
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0:00:18
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where it's a special case for loopback and hardware looped-back interfaces,
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0:00:25
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where if you have a...
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0:00:27
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analogue circuit, let's say you have a DS3 link
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0:00:31
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that you're link that you're trying to figure out where the failure is in the provider network,
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0:00:37
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so they're looping back different portions of the circuits.
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0:00:40
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When the interface goes into the hardware loopback state,
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0:00:44
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OSPF runs this as network type loopback,
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0:00:48
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which advertises it as a /32 host route.
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0:00:52
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So, from other portions of the network, you're able to still test connectivity
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0:00:56
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to see if a packet can go out that link and then loop back in.
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0:01:01
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Now, from our perspective, since we're not really gonna be dealing with hardware loopbacks in the exam,
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0:01:06
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the effect of this is that on a software loopback,
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0:01:09
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so when we say Interface Loopback 0,
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0:01:12
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this is the default network type.
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0:01:14
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So, as we saw, if we look at router 5, and Show Run Interface Loopback 0,
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0:01:21
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the link here is configured a /24,
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0:01:24
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but when we go to someone else's routing table,
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and Show IP Route 150.42.5.5,
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0:01:31
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this appears as a /32 host route.
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0:01:35
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The reason why is that on router 5, if we Show IP OSPF Interface Loopback 0,
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0:01:40
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the network type is loopback.
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So, it's treated as a stub host that's advertised as a /32.
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0:01:48
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So, if we do not want to advertise this as /32,
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0:01:52
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and have it matched with the actual mask,
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0:01:54
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then, we need to disable this network type.
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0:01:57
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So, at the link level of the loopback, we would say, IP OSPF network is point-to-point.
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0:02:04
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Then, when we look at the Show IP OSPF Interface Loopback 0,
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0:02:10
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now, it is no longer a loopback interface or loopback network type,
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0:02:14
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and if we look at on router 4,
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0:02:18
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we could see that mask is now /24
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0:02:22
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as opposed to the previous /32.
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