This topic is to discuss the following lesson:
I did not understand this
“As soon as router John receives the hello packet from Jack it will respond by sending update packets that contain all the routing information that it has in its routing table. The only routes that are not sent on this interface are the one that John learned on this interface because of split-horizon”
router will send an UPDATE without forming a neighbor relationship??
Jack has not shared any update to john, then how john will come to know the prefix of jack so there is no point of split horizon here.
please correct me if am wrong…
You would expect that the routers would send 1 hello, receive 1 hello and then exchange routing information but it’s not the way it works with EIGRP. Once an EIGRP-enabled router receives a hello packet, it will send an update packet. A good way to see this in action is to configure EIGRP on two routers and then use an inbound access-list on one router that filters traffic destined for 126.96.36.199. If you do this, one router will filter all hello packets and you’ll see that its neighbor will still send update packets.
Forming the neighborship doesn’t really have anything to do with split horizon, I just mentioned it but could get rid of it in this example.
On below config advertisement
John(config)#router eigrp 1 John(config-router)#no auto-summary John(config-router)#network 188.8.131.52 0.0.0.255 John(config-router)#network 192.168.12.0 John(config-router)#exit
if i add below config on it
John(config)#router eigrp 1 John(config-router)#passive-interface loopback 0
That means traffic for network 184.108.40.206/24 and 192.168.12.0 won’t pass on interface loop back 0 ?
If you use the passive-interface command then it will no longer send EIGRP hello packets on that interface, that’s it. Here’s an example:
Thank You very much Rene for a nice elaboration. kindly share also the detail on how redistribute and connected command work on EIGRP.
You are welcome Dani. Here are two posts on EIGRP redistribution that should help:
Redistribute connected is used to redistribute directly connected networks in a routing protocol, it’s an alternative to the network command.
Thank Bro Rene.
Do you have the book for CCNP R& S v2 which is plain and simple?
Also you site for labs gns3vault.com is not opening.
I do you can find them here:
Just checked and the site is up and running, my monitoring software also doesn’t report any downtime.
Rene I saw the book on amazon.com but it has published Paperback – August 28, 2013 while ccnp route v2 was out on December 2014
This is the latest version, it was updated a few months ago. I updated the PDF files for the print but Amazon always shows the original print date.
Thank you for the nice explanation.
I’ve a question in my mind. In order to fulfill the neighborship what are the parameters that need to matched at both the router ?
Can you please explain this
There are a couple of parameters that have to match:
- AS Number
- K values
What are the EIGRP Neighbor Parameters for building adjacency.
You can find it in the answer right above your question. Authentication, AS number, K values and subnet are the required parameters that have to match on both ends.
Thanks for your explanation.
I just want to ask you, why you added the subnet mask for network 220.127.116.11 while you did not for network 192.168.12.0 as below:
Thanks in advance.
R1(config)#router eigrp 1 R1(config-router)#no auto-summary R1(config-router)#network 18.104.22.168 0.0.0.255 R1(config-router)#network 192.168.12.0 R1(config-router)#exit
If you don’t supply a wildcard then EIGRP will assume you want the whole network to be advertised. Here’s an example:
Router(config)#router eigrp 1 Router(config-router)#no auto-summary Router(config-router)#network 22.214.171.124
This is what is stored in the running config:
Router#show run | begin router eigrp router eigrp 1 network 126.96.36.199
188.8.131.52 falls under the class A 184.108.40.206/8 range so that’s what EIGRP adds to the running config. If you don’t want this, you have to add a wildcard:
Router(config)#router eigrp 1 Router(config-router)#no network 220.127.116.11 Router(config-router)#network 18.104.22.168 0.0.0.255
And you will get:
Router#show run | begin router eigrp router eigrp 1 network 22.214.171.124 0.0.0.255
Even without the wildcard, it would have worked but enabling EIGRP for all 1.x.x.x networks might not be what you want.
I didn’t have to do this for 192.168.12.0 since that’s a class C network. If I used a /25 - /30 subnet mask then I would have to add the correct subnet mask.
Hope this helps!
I got it. Thanks a lot Rene for your reply.
Your site is great and easy to understand.
In this topic i understand the part which you had mention if you don’t specify the wild card which command is stated below :
! no auto- summary router eigrp 1 network 126.96.36.199 **0.0.0.255** !
then in result, you’ll find “network 188.8.131.52/8” in your show run.
However when i read about the topic on RIP - “How to configure RIP on cisco router”
In the statement
“You can see that R2 has learned about network 172.16.1.0 /24 and 172.16.2.0 /24. This is because R1 and R3 are advertising 172.16.1.0 /24 and 172.16.2.0 /24, not 172.16.0.0 anymore. R1 and R3 also have learned about each other’s networks.”
I am abit confused because i realize there is no wildcard added for the network command.
Is there a difference in concept for RIP and EIGRP regarding the network and wildcard command ?
I mean in another word, no auto-summary for RIP, why i see there is no wildcard 0.0.0.255 for 172.16.1.0/24 and 172.16.2.0/24 network ?
In EIGRP, if you don’t use the
no auto-summary command, the router will assume a classful network address regardless of the wildcard mask you enter.
Once you enter the
no auto-summary command, EIGRP will begin sending the wildcard mask information as well.
As for RIP, version 1 will send classful routing information. In order to send classless routing information, RIP must be configured to use Version 2 AND must include the
no auto-summary command.
Now the difference between EIGRP and RIP is that when you configure the network command for RIP, you don’t input a wildcard mask. It won’t let you. Take a look at this output:
Router# Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#router rip Router(config-router)#version 2 Router(config-router)#network 172.16.0.0 ? <cr> Router(config-router)#network 172.16.0.0 Router(config-router)#
The only option it gives you after the network address is
So in RIP, if you configure version 2 and
no auto-summary, the router will use the subnet mask configured on the interface associated with the network. So for the example you used, if you have two interfaces with IP addresses 172.16.1.1/24 and 172.16.2.1/24 respectively and you configure those networks using RIP, it will use the subnet masks (/24) configured on the interfaces themselves.
I hope this has been helpful!