Eigrp summary route

phoeneous

Just checking my work here. If I wanted to summarize 10.100.0.0/30, 10.100.0.4/30, and 10.100.0.8/30, would the summary route be 10.100.0.0/28? And then f0/0 on Interwebs would be ip summary-address eigrp 1 10.100.0.0 255.255.255.240?

Chris_

Yes, that would be the most efficient single summary address for these networks - just bear in mind that this wastes the .12 - .15 addresses, or keeps them in reserve for future use behind that summary address.

Your summary cmd looks good to me.

phoeneous

Chris_ wrote: »

Yes, that would be the most efficient single summary address for these networks - just bear in mind that this wastes the .12 - .15 addresses, or keeps them in reserve for future use behind that summary address.

Your summary cmd looks good to me.

To eliminate waste would a /29 be better? I'll lab it up later, at work right now.

vinbuck

Depends on your design goals. If this is just for a lab, then a /28 would cover everything you currently have in place. However, in IP planning, it is common to allocate beyond what you need in your IP reservations so you won't have to re-address anything should you add more links (or go around changing masks). It also depends on your equipment too. There are only so many hours in the day and you have to decide if there is enough of a performance/stability increase to justify spending the time on it. To be honest, I would definitely spend the time summarizing 4 subnets if it was a 2600 chassis, but put it on the back burner if it's on a 7600. Also depends on whether it's public or private. Public addresses seem to be easier to summarize because they have to be purchased in blocks and accounted for...so they don't get used and abused the way private subnets do.

The thing about summarizing is that it works great in a lab environment because you can arrange subnets however you want to. In a production envrionment though (where subnets get scattered about and broken up for various reasons), you usually only have the luxury of having enough contiguous subnets to warrant summarizing at a handful of routers.

EDIT: Ooops...i was thinking /28 but I had a PEBKAC error ...fixed it.

DPG

phoeneous wrote: »

To eliminate waste would a /29 be better? I'll lab it up later, at work right now.

A /29 would not work with your address scheme.
You are correct in using a /28 for the most efficient summary route.

phoeneous

DPG wrote: »

A /29 would not work with your address scheme.
You are correct in using a /28 for the most efficient summary route.

You're right. /29 does not include 10.100.0.8/30.

WEST#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
     172.16.0.0/30 is subnetted, 1 subnets
C       172.16.80.0 is directly connected, FastEthernet0/0
     22.0.0.0/32 is subnetted, 1 subnets
C       22.22.22.22 is directly connected, Loopback22
     10.0.0.0/29 is subnetted, 1 subnets
D       10.100.0.0 [90/2195456] via 172.16.80.1, 00:00:25, FastEthernet0/0
     11.0.0.0/32 is subnetted, 1 subnets
D       11.11.11.11 [90/409600] via 172.16.80.1, 01:54:07, FastEthernet0/0
WEST#ping 10.100.0.10
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.100.0.10, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
WEST#ping 10.100.0.8
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.100.0.8, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
WEST#ping 10.100.0.7
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.100.0.7, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/42/68 ms
WEST#