Original subtitles

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Classless routing protocols, on the other hand, do advertise the subnet mask.

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So as an example, they would advertise network 10.0.0.0/24 or 10.0.0.0/30

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They are advertising both the network and the subnet mask

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in the routing protocol advertisements

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routers are therefore able to see the exact network mask

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and do not have to assume what the network mask is

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on routing updates received from neighbors

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classless routing protocols also support Variable Length Subnet Mask or VLSM

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in other words, the mask of interfaces do not have to be the same.

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one interface could have a mask of /24

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and another interface could have a mask of /20

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as an example on serial interfaces or serial links

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you may want to use a /30 mask on a loopback interface on a router

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you may wanna use a /32 mask and on networks

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where hosts reside you may wanna use /24 mask

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in other words, on routers, Variable Length Subnet Mask are supported

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different interfaces can have different masks.

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Classless routing protocols also support manual summarization of routes.

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This depends on the routing protocol as an example

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OSPF supports summarization on what are called Area Border Routers or ABR's

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as well as Autonomous System Border Routers or ASBR's

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EIGRP supports summarization on any interface

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examples of classless routing protocols include RIP version 2, EIGRP, OSPF and ISIS.