CCNA-200-301- aaa5GITTC-Unlocked

grows. It has been said that if there were no route summarization, the Internet backbone
would have warped from the total size of its own routing tables back in 1997.

Routing updates, whether done with a distance vector or link-state protocol, grow with the number
of routes you need to advertise. In simple terms, a router that needs to advertise ten routes needs
ten specific lines in its update packet. The more routes you have to advertise, the bigger the packet.
The bigger the packet, the more bandwidth the update takes, reducing the bandwidth available to
transfer data. But with route summarization, you can advertise many routes with only one line in
an update packet. This reduces the size of the update, allowing you more bandwidth for data
transfer.

Summarization allows you to create a more efficient routing environment by providing the
following advantages:

 It reduces the size of routing tables, requiring less memory and processing.

 It reduces the size of updates, requiring less bandwidth.

 It contains network problems

Example of VLSM

Above image shows several branch offices using subnetted Class C (/26) addresses that provide
each branch with 62 possible host IPs. The branches are connected to the central office via point-
to-point WAN links. The ideal mask to use for such a link is /30 because it provides only 2 hosts,
one for each end of the link. The problem arises when the routing protocols are configured: Prior
to VLSM, the /30 networks could not be used because the /26 networks existed in the same
system and the classful routing protocols could only advertise one mask per class of address. All
networks, including the little /30 links, had to use the same mask of /26. This wastes 60 IP
addresses on each WAN link.