Solved

Network Advertisement and Summarization

Posted on 2014-07-19
4
205 Views
Last Modified: 2014-07-20
I have seen in some configuration where they Advertise the Network with a prefix different than the Interface IP mask.
They also summarize the network different than the interface IP mask.

Example:

Let's say I have R1 connected to R2 through serial interfaces on each router.
R1 serial interface has Ip address 10.10.10.1/24 and R2 serial interface has ip address 10.10.10.2/24
when Network is advertised  in EIGRP for instance, they use the command:
EIGRP 90
Network 10.0.0.0
** I believe The Network command above will by default add a mask of /8 , it is like typing 255.0.0.0
which is different than /24  mask of the serial interface.
So what would be the impact in that case?

another scenario is Summarization,example :
Interface serial 1/0
ip summary-address EIGRP 90 10.10.0.0 255.255.0.0

I see the summarization is based on /16 , so how this would impact the /24 configured on the serial interfaces ?


Thank you
0
Comment
Question by:jskfan
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2
  • 2
4 Comments
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 500 total points
ID: 40206872
when Network is advertised  in EIGRP for instance, they use the command:
EIGRP 90
Network 10.0.0.0

The network statement is EIGRP (and OSPF) does not define how a network is advertised.  It simply defines which interfaces are classified as EIGRP member interfaces. Which means that EIGRP will attempt to create adjacencies through these interfaces.  For example if this router had interfaces with IP addresses of 10.1.1.1/24, 10.2.2.2/24 and 10.3.3.3/24, all of those interfaces would have EIGRP hellos sent out.

another scenario is Summarization,example :
Interface serial 1/0
ip summary-address EIGRP 90 10.10.0.0 255.255.0.0

I see the summarization is based on /16 , so how this would impact the /24 configured on the serial interfaces ?
Now this actually does affect how an advertisement is sent.  If there was a 10.10.1.0/24 network in the topology table, a summary route of 10.10.0.0/16 would be sent instead.
0
 

Author Comment

by:jskfan
ID: 40207166
<<The network statement is EIGRP (and OSPF) does not define how a network is advertised>>
Sometimes they add the Wild card mask and sometimes not.
if interface is configured with 10.10.10.1/24 and the Network is advertised without mask, then there is no Impact if I understand your comment

EIGRP 90
Network 10.0.0.0
(This implicitly will look just for the first octet to be matched, the rest of the octets do not matter)


****for the Summary , let's say we have a bunch of Loopback interfaces :
2.2.2.1/24
2.2.2.2/24
2.2.2.3/24
2.2.2.4/24

if I am not wrong ,The IP summary has to match the first 3 octets otherwise , the router receiving the summary routes will not be able to reach the loopbacks… Correct ?

it has to be:
ip summary-address EIGRP 90 2.0.0.0 255.255.255.0

and Not:
ip summary-address EIGRP 90 2.0.0.0 255.255.0.0
0
 
LVL 50

Accepted Solution

by:
Don Johnston earned 500 total points
ID: 40207259
Like I said before, the network statement has no bearing on how the network is advertised.

For example, You have a router with four interfaces:
E0: 10.0.0.1/24
E1: 10.1.1.1/24
E2: 10.1.2.1/24
E3: 10.3.3.1/24
And an EIGRP network statement of: network 10.0.0.0

The router will attempt to form an adjacency on every single interface.  Once those adjacencies are formed, the four networks will be advertised (10.0.0.0/24,  10.1.1.0/24, 10.1.2.0/24 and 10.3.3.0/24).

If you don't want E1 and E2 to play EIGRP, then you can use:
network 10.0.0.0 0.0.0.255
network 10.3.3.0 0.0.0.255

The router will only attempt to form adjacencies on E0 and E3. Once those adjacencies are formed, only 10.0.0.0/24 and 10.3.3.0/24 will be advertised since E1 and E2 are not participating in EIGRP.

There's a bit more (passive interfaces and auto summary) but we're just talking about network statements, right? ;-)
0
 

Author Closing Comment

by:jskfan
ID: 40207878
Thanks
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

We've been using the Cisco/Linksys RV042 for years as: - an internet Gateway - a site-to-site VPN device - a leased line site-to-site subnet-to-subnet interface (And, here I'm assuming that any RV0xx behaves the same way as an RV042.  So that's …
Getting hacked is no longer a matter or "if you get hacked" — the 2016 cyber threat landscape is now titled "when you get hacked." When it happens — will you be proactive, or reactive?
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
Suggested Courses
Course of the Month10 days, 19 hours left to enroll

628 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question