Route Summerisation - Help!!

Hi Guys,

I need a bit of help with a question I am struggling with.

I have been aske to provide route summaries for a router with 3 interfaces.

interface 0:

200.60.32.0/24 through 200.60.35.0/24

Answer = 200.60.32.0/22

interface 1:

200.60.36.0/24 through 200.60.39.0/24

Answer = 200.60.36.0/22

Now this is where I come unstuck:

200.60.40.0/24 through 200.60.50.0/24

The only summary that I can come up with that covers the whole ip address range is:

200.60.40.0/19 but that conflicts with the other 2.

Any help would be appreciated.

Thanks

Jon

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Comments

blackmage439

I think this is right...

I usually figure these out by just converting the octet you're trying to figure out into binary form. Obviously, the third octect is being used in your problem.

200.60.40.0/24 = 00101000 through
200.60.50.0/24 = 00110010

The subsequent summarized route would be:

001|01000 \ Common bits
001|10010 /

200.60.32.0/19 = 00100000

It's on a completely different subnet, so it does not conflict with the other two routes.

mwgood

Try this:

200.60.40.0 /21 &
200.60.48.0 /23 &
200.60.50.0 /24

You've got 11 subnets to summarize - so I don't see that ONLY these subnets can be summarized in a single subnet.

If you stick to only these subnets - it looks to me like this is the best that can be done.

georgemc

mwgood wrote:

Try this:

200.60.40.0 /21 &
200.60.48.0 /23 &
200.60.50.0 /24

You've got 11 subnets to summarize - so I don't see that ONLY these subnets can be summarized in a single subnet.

If you stick to only these subnets - it looks to me like this is the best that can be done.

I agree, the /19 as suggested by blackmage439 would include subnets not assigned to the router.

I would probably summarize the entire router as:

200.60.32.0 /20 for 200.60.32.0 - 200.60.47.255
200.60.48.0 /23 for 200.60.48.0 - 200.60.49.255
200.60.32.0 /24 for 200.60.50.0 - 200.60.50.255

This would cover all subnets on the router without encroaching on any unassigned subnets. I don't see any way to summarize further.

Of course, if I were to be configuring a router I probably wouldn't place multiple contiguous /24 subnets on the same interface. I'd assign them as the way you summarized interface 0 and 1, and the way that mwgood summarized for interface 2.

to clarify, I'd do something such as:

interface ethernet 0
ip address 200.60.32.0 255.255.252.0

Interface ethernet 1
ip address 200.60.36.0 255.255.252.0

Interface ethernet 2
ip address 200.60.40.0 255.255.248.0
ip address 200.60.248.0 255.255.254.0 secondary
ip address 200.60.250.0 255.255.255.0 secondary

If I'm way out in left field with this and misunderstood the question, someone please let me know.

If you've got a lab, you can try setting up EIGRP with route summarization turned on and see what it does with it. It's kinda neat to watch...

emsrescue

Thanks for you input guys.

I think I will need to clarify the question with my tutor.

If you've got a lab, you can try setting up EIGRP with route summarization turned on and see what it does with it. It's kinda neat to watch...

Hadnt thought of that. I am going to try it now.

Jon

emsrescue

OK, I have set up the following network:

3 x 2500 routers attached via serial crossover cables to a 4000 router.
4000 router connected to 1721 via crossover cable.

Each 2500 has the ip addresses listed above assigned to loopback interfaces.

Eigrp is running on all routers and each router has all of the routes in its table.

How do I get auto summerization to work.

I have issued:

conf t
network eigrp 1
auto-summary

on all of the routers but I am not seeing any auto summerized routes in the routing tables.

Any ideas?

Thanks

Jon

georgemc

I'm gonna fire up some of my routers and see if I can figure it out. I need a short break from studying anyway. I'll let you know how it goes.

Georgemc

NightShade1

emsrescue wrote:

Hi Guys,

I need a bit of help with a question I am struggling with.

I have been aske to provide route summaries for a router with 3 interfaces.

interface 0:

200.60.32.0/24 through 200.60.35.0/24

Answer = 200.60.32.0/22

interface 1:

200.60.36.0/24 through 200.60.39.0/24

Answer = 200.60.36.0/22

Now this is where I come unstuck:

200.60.40.0/24 through 200.60.50.0/24

The only summary that I can come up with that covers the whole ip address range is:

200.60.40.0/19 but that conflicts with the other 2.

Any help would be appreciated.

Thanks

Jon

If you wanna learn how to do some routing summerazation then click on my tech notes on my signature... and look for the message in which i give a tutorial of how to do routing summerzation....
Cheers!

emsrescue

Hi Nightshade,

Thanks for the tips, thats the technique that I have been using. I think my confusion comes from the question I have been set asks for a route summerisation of 3 groups of networks that over lap.

I also have the problem with trying to replicate the network in my lab as I have just destroyed my 4000 router! It wont event boot into rommon now, it just throws up an error about a compressed image checksum and reboots.

Jon

mwgood

How about this?

config t

int interface0
ip address 192.168.14.2 255.255.255.0 (whatever you want here)
ip summary-address eigrp 1 200.60.32.0 255.255.254.0

int interface1
ip address 192.168.15.2 255.255.255.0 (whatever you want here)
ip summary-address eigrp 1 200.60.36.0 255.255.252.0

int interface2
ip address 192.168.16.2 255.255.255.0 (whatever you want here)
ip summary-address eigrp 1 200.60.40.0 255.255.248.0
ip summary-address eigrp 1 200.60.48.0 255.255.254.0
ip summary-address eigrp 1 200.60.50.0 255.255.255.0

router eigrp 1
network x.x.x.x (desired connected networks)

rossonieri#1

hello,

basically, there are 2 types of network summarization :
1. done in routing protocol (as global)
2. done in perinterface basis.

cheers.