When you summarize routes in RIP, IGRP, EIGRP, or OSPF, you're replacing a series of routes with a summary route and mask. With RIP, IGRP, and EIGRP, this actually lessens the size of the routing update packet itself – multiple routes are replaced with the summary route. For instance, the routes 8.0.0.0/8, 9.0.0.0/8, 10.0.0.0/8, and 11.0.0.0/8 can be summarized as 8.0.0.0 252.0.0.0. Only the summary address will be found in the update packet, making it concise yet complete.
Summarizing routes can also make the routing table smaller, yet still allow for complete IP connectivity when done correctly. Using the above example, the four more-specific routes will be replaced by a single summary route. Since the entire routing table is parsed before the routing process is complete, keeping the routing table as small as possible does help speed the routing process as a whole.
Here are some additional tips on route summarization.
With RIP version 2 and EIGRP, manual route summarization is configured on the interface that will be advertising the summary. This is done with the route summarization command "ip summary-address."
RIP version 2 and EIGRP also both perform autosummarization on routes that are advertised across classful network boundaries. This is disabled with the protocol-level command "no auto-summary".
OSPF offers two different route summarization commands. To summarize routes from one OSPF area to another, use the "area range" command to summarize routes learned via redistribution, use the "summary-address" command on the ASBR.
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your stuff is really great, but l think it would really be fantastic if you include some detail on how you get the summary route and its subnet mask.
very interesting, but I don’t agree with you
Idetrorce
Please give easy tips & tricks for route summarization
In the first paragraph, wouldn’t the route mask be 248.0.0.0?
There is a tutorial on how to get summary routes at http://searchwarp.com/swa45047.htm
Josef,
252.0.0.0 is the correct mask. If you used 248.0.0.0, it would also include the networks 12.0.0.0/8, 13.0.0.0/8, 14.0.0.0/8, and 15.0.0.0/8.
Hi,
Curious as to what I’m missing here as I set up a simulation of this in my lab. I have a router 7 (3640-ios 12.4) configured with 4 Ethernet interfaces with each connecting to a corresponding Ethernet interface on another router (routers 1-4) for five routers total.
For simplicity all routers are running
router rip
no auto
vers 2
net 192.168.0.0
net xxxx (as appropriate for the ip of lo0)
and router R7 has the addition of
net 172.16.0.0 to handle the serial connection to R21
On routers 1-4 I configured loopback0 as
R1: 8.8.8.8/8
R2: 9.9.9.9/8
R3: 10.10.10.10/8
R4: 11.11.11.11/8
I then have S1/0 (IP 172.16.1.2/30) on R7 acting as the outbound connection to S0 (IP 172.16.1.1/30) on my primary router (R21) that connects to my LAN and is the gateway router to the firewall and Internet.
I have the routers R1-R4 divided as various subnets of the address space 192.168.0.0/24. When I summarize this on the S1/0 interface as: #ip summary-address rip 192.168.0.0 255.255.255.0
it acts as expected and the routing table on R21 shows
R 192.168.0.0/24 [120/1] via 172.16.1.2, 00:00:09, Serial0
and all the various subnetted interfaces can be successfully pinged from R21.
However:
If I also try to summarize the loopback interfaces on S1/0 I get:
p1R4(config-if)#ip summary-address rip 8.0.0.0 252.0.0.0
Summary mask must be greater or equal to major net
If I redo this using
p1R4(config-if)#ip summary-address rip 8.0.0.0 255.0.0.0
the router is happy but of course this doesn’t summarize the address space of 8.0.0.0/8-11.0.0.0/8
What am I missing/need to change to get this working?
TIA!
Cheers!
Mike Shafer
Small Correction: (this should not be on R4)
If I redo this using
p1R4(config-if)#ip summary-address rip 8.0.0.0 255.0.0.0
Should read: (but on R7)
If I redo this using
p1R7(config-if)#ip summary-address rip 8.0.0.0 255.0.0.0
To continue on the above it appears that it’s a RIP thing in not allowing summarization less than the classful boundary.
I took my above configuration and changed it over to EIGRP and all worked just dandy! That is I was able to summarize the Class A addresses on the S1/0 interface using:
p1R7(config-if)#ip summary-address eigrp 100 8.0.0.0 252.0.0.0
and the routes were summarized on the routing table on R21 as expected showing:
D 8.0.0.0/6 [90/2323456] via 172.16.1.2, 00:00:15, Serial0
If anyone knows how to accomplish this using RIP v2 I would appreciate you’re letting me know. I’m taking the BSCI exam in the near future and it’s *my* $150 down the drain if I crash and burn!
Cheers!
MS
kindly favour me to understand the summerization of rputer IP
What is route summerization and how is work on routing protocol.