Even though Based on your previous comments, in this thread and others, it seems to me that you think that because 10 and 11 are in the same class ie, both are from class A networks they are not a boundary point. A,C, and D would all represent classful boundaries because each side of R1 is a different network when taken back to it's classful boundary.
So if I restated the answer options like this taking them back to the classful boundary in which they belong :. It would be very easy to look at that and say that A, C and D are not the same on both sides of R1 thus, a boundary and B and E are the same on both sides of R1 not a boundary. In this case it would be a bad idea for R1 to auto-summarize in the case of B and E because. To answer that question, try this exercise. Spin up a router in your lab and give it two interfaces.
Assign "ip address A,C, and D would all represent classful boundaries. And as Anthony pointed out, classfull addresses withing the same network. By this i mean:. These are all Class A networks but each is a different class A network. So if you assigned the addresses as follows. There are no subnets, dividing the classful boundaries. However, if we were to subnet that Class A This would be discontiguous. The Class A This is a contiguous network as there are no subnets, separating the classfull Again, these are all Class B addresses, but again, different Class B networks.
So RIP and IGRP only work with classful addresses, as in that only advertise classful addresses as it doesn't advertise the subnet mask of a route, so if you have a bunch of subnets on Special thanks for you Steven.
Steven Davidson. I was getting trolled so I decided to take a break. I did reach out to you via e-mail but perhaps you forgot. I just noticed that you sent me an e-mail.
If you have been sending me other e-mails perhaps they were not getting through or were but going to spam. In any case, take a look at the document and see if any of it makes sense to you. You seem to be struggling quite a bit with auto-summary. In this topology, subnets Link to download the discontiguous network topology. In this network topology, if a host wants to communicate with other hosts of the same network, it has to go through another network's subnet.
For example, if PC1 wants to communicate with PC7, it has to cross a subnet of a different network. Since PC1 and PC7 belong to two different subnets As you can see in the above image, packets exchanged between PC1 If all subnets of a network are organized in such a way that their hosts can communicate with each other without going outside the network, the network is contiguous.
If a host takes a route to communicate with other hosts of the same network that belongs to a different network, the network is discontiguous. The following image shows one contiguous network When designing a network, you should always arrange subnets in a contiguous way. Contiguous subnets have several advantages over discontiguous subnets. If subnets are contiguous, routing protocols summarize them before advertising. I will explain this feature through examples in the next article.
That's all for this tutorial. Router B advertises that it can get to networks To understand why the prefix length is 20, convert the network numbers to binary. Because classless routing protocols understand prefixes of any length not just 8, 16, or 24 , the routers in Figure can route to discontiguous subnets, assuming they are running a classless routing protocol, such as OSPF or EIGRP. To configure the devices in the previous example with an old-style subnet mask rather than a prefix length, use a mask of The first 4 bits of the third octet are set to 1s.
A trick for determining the value of the relevant octet in a subnet mask is to subtract the number of summarized subnets from
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