1
00:00:00,000 --> 00:00:05,000
Classless routing protocols, on the other hand, do advertise the subnet mask.

2
00:00:05,000 --> 00:00:15,000
So as an example, they would advertise network 10.0.0.0/24 or 10.0.0.0/30

3
00:00:15,000 --> 00:00:18,000
They are advertising both the network and the subnet mask

4
00:00:18,000 --> 00:00:21,000
in the routing protocol advertisements

5
00:00:21,000 --> 00:00:25,000
routers are therefore able to see the exact network mask

6
00:00:25,000 --> 00:00:30,000
and do not have to assume what the network mask is

7
00:00:30,000 --> 00:00:33,000
on routing updates received from neighbors

8
00:00:33,000 --> 00:00:40,000
classless routing protocols also support Variable Length Subnet Mask or VLSM

9
00:00:40,000 --> 00:00:45,000
in other words, the mask of interfaces do not have to be the same.

10
00:00:45,000 --> 00:00:48,000
one interface could have a mask of /24

11
00:00:48,000 --> 00:00:52,000
and another interface could have a mask of /20

12
00:00:52,000 --> 00:00:57,000
as an example on serial interfaces or serial links

13
00:00:57,000 --> 00:01:03,000
you may want to use a /30 mask on a loopback interface on a router

14
00:01:03,000 --> 00:01:08,000
you may wanna use a /32 mask and on networks

15
00:01:08,000 --> 00:01:12,000
where hosts reside you may wanna use /24 mask

16
00:01:12,000 --> 00:01:17,000
in other words, on routers, Variable Length Subnet Mask are supported

17
00:01:17,000 --> 00:01:20,000
different interfaces can have different masks.

18
00:01:20,000 --> 00:01:27,000
Classless routing protocols also support manual summarization of routes.

19
00:01:27,000 --> 00:01:30,000
This depends on the routing protocol as an example

20
00:01:30,000 --> 00:01:37,000
OSPF supports summarization on what are called Area Border Routers or ABR's

21
00:01:37,000 --> 00:01:41,000
as well as Autonomous System Border Routers or ASBR's

22
00:01:41,000 --> 00:01:45,000
EIGRP supports summarization on any interface

23
00:01:45,000 --> 00:01:50,000
examples of classless routing protocols include RIP version 2, EIGRP, OSPF and ISIS.