EIGRP Summarization question

Watching a video for BSCI and they do a route summary for the following

loop1 101.1.0.1
loop2 102.1.0.1
loop3 103.1.0.1
loop4 104.1.0.1
loop5 105.1.0.1
loop6 106.1.0.1
loop7 107.1.0.1

So the summary address/mask is 100.0.0.0 255.248.0.0

This part I understand.

They show the ip route on the sending router and it has a line of

D 100.0.0.0/13 is a summary , Null0

Now my question is if a packet comes into the router for address 100.0.0.1 would get droppped?

And if so why would you want to send out a summary address to the adj routers giving it a route which would lose data since that address is not on the sending router?

I think I am missing the point but after watching the video 3 times now I am not understanding or missing somthing.

Thank you

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Comments

jason_lunde

The summarizing router should have a longer prefix in its routing table for each of the summarized routes. This is a built-in loop prevention mechanism; the route to null0 will drop any traffic destined for the summary address that does not match a more specific route in the table.

burbankmarc

The reason you would do this is because if the destination doesn't exist then it doesn't matter if the traffic gets dropped. The router should never advertise routes to existing networks that it doesn't know.

georgemc

Can you please let me know what video you're getting this example from? Is this Jeremy or Chris, or possibly someone else? Unless I'm a lot more tired than I think I am right now, the mask you've isn't summarizing any of those addresses.

100.0.0.0 /13 = 100.0.0.0 - 100.7.255.255?

240.0.0.0/4 - 96.0.0.0 - 111.255.255.255?

If I'm completely off track here then please forgive me.

Thanks,
George

Dilbert65 wrote: »

Watching a video for BSCI and they do a route summary for the following

loop1 101.1.0.1
loop2 102.1.0.1
loop3 103.1.0.1
loop4 104.1.0.1
loop5 105.1.0.1
loop6 106.1.0.1
loop7 107.1.0.1

So the summary address/mask is 100.0.0.0 255.248.0.0

This part I understand.

They show the ip route on the sending router and it has a line of

D 100.0.0.0/13 is a summary , Null0

Now my question is if a packet comes into the router for address 100.0.0.1 would get droppped?

And if so why would you want to send out a summary address to the adj routers giving it a route which would lose data since that address is not on the sending router?

I think I am missing the point but after watching the video 3 times now I am not understanding or missing somthing.

Thank you

Dilbert65

It was Chris Bryant, trainsiganl video.

agent2592

The summary route you have given will not create a summary route for the loopbacks.

I will answer your question, since I think understand the point you are getting at but I would go back to make sure that the video is really attempting to do a summary for that entire range.

The summary route required to supernet that entire range is 96.0.0.0 /4 which is a huge waste of a address space.

>>>Now my question is if a packet comes into the router for address 100.0.0.1 would get droppped?

Assuming there is nothing in that range in the routers forward information base (routing table) and using a route summary, the packet will go to the "bit bucket" and be unequivocally "dropped".

So, yes, summarization does require thoughful consideration since it is one of the few instanced when a router may advertise a range of networks even if they do not exist.