Is Supernetting the same as Route Summarization?

abefroman

Is Supernetting the same as Route Summarization?

If not, what is the difference?

Pash

Tell us what you think both of those items mean. Maybe that may answer the question for you

Pash

Forsaken_GA

abefroman wrote: »

Is Supernetting the same as Route Summarization?

If not, what is the difference?

Functionally, they're the same thing, though you reasons for doing so may not the same.

You generally summarize (though I prefer the term aggregate) your routes in order to reduce routing table size. You could also need a supernet because you discovered that the amount of space you allocated for a subnet wasn't enough, and that the easiest way to grow it is to give a bit back and add the next contiguous subnet assuming it's available.

Let me give you a functional example -

I have a customer that has 10 servers and wants their own IP allocation, so I give them a /28. Then later on down the line, they add 15 more servers. Well, now that /28 isn't big enough. If the next contiguous subnet is still available, I can give them a /27 and renumber the mask on all of their servers. This would be supernetting.

As far as summarization goes.... internally, I have a whole bunch of /24's and /23's an so on. When I advertise that IP space out to the rest of the internet though, I'm advertising the smallest route I possibly can (which is usually a /1. I could advertise all of the smaller routes if I wanted, but this is unncessary, as they all lead to the same location, and each route announced eats up router memory and processing time in the event of a flap.

Bonus points - In the first example, I could have also added an additional allocation to the customer's SVI as a secondary IP address. Why would it be preferable to supernet their allocation if possible instead of simply adding another /28 and having them address their servers with that? (Hint: the servers transfer large amounts of traffic between themselves, and there are other customers on the switch that all of these are connected to)

Pash

I still prefer summarization as the used word. Aggregate is more of a total.

But yeh, very good example. My boss always has a go at me for using the same terms for describing the same items, maybe this example would give his argument some weight.

Pash

Forsaken_GA

Pash wrote: »

I still prefer summarization as the used word. Aggregate is more of a total.

It's one of those word usage things, in the BGP world it's usually termed aggregation (the command is even called aggregate-address), and I can honestly say that the only place on my network that we're doing summary routes is when we originate our prefixes, so it just kind of sticks.

mella060

abefroman wrote: »

Is Supernetting the same as Route Summarization?

If not, what is the difference?

As had been said. Funtionally the same.

A supernet is a group of major networks.

A route summary is a group of subnets.

A major network is any classful network, along with its native mask.

10.0.0.0/8 (255.0.0.0) is a major network
11.0.0.0/8
12.0.0.0/8

172.16.0.0/16 (255.255.0.0) is a major network
172.17.0.0/16
172.18.0.0/16

192.168.1.0/24 (255.255.255.0) is a major network
192.168.2.0/24
192.168.3.0/24

These are all major networks

For example....10.0.0.0/7 is a supernet, which is a group of the major networks 10.0.0.0/8 and 11.0.0.0/8

Supernetting is basically going the other way to subnetting