neighbor maximum-prefix command

[ageorgan1]

Hi,

The Cisco document entitled "EIGRP Prefix Limit Support (http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/cs_epls.html) references a "neighbor maximum-prefix" command that that "limits the number of prefixes that are accepted from the specified EIGRP neighbor" when a particular neighbor is specified, and "limits the number of prefixes that are accepted from all EIGRP neighbors" when no particular neighbor is specified. Unfortunately, the phrase "limits the number of prefixes that are accepted from all EIGRP neighbors" is ambiguous and I have no means of testing the command to verify how it works. Therefore, I am hoping someone here can point me in the right direction.

There are two possible interpretations of the phrase "limits the number of prefixes that are accepted from all EIGRP neighbors" in the latter case when no neighbor is specified:

Interpretation 1: The "maximum-prefix" applies cumulatively to all EIGRP neighbors. Assume that the "maximum-prefix" is set to 1000, neighbor 1 has advertised 200 prefixes, neighbor 2 has advertised 200 prefixes, and neighbor 3 has advertised 600 prefixes. Under the first interpretation, the "maximum-prefix" of 1000 has been reached even though no single neighbor has individually advertised 1000 prefixes.

OR

Interpretation 2: The "maximum-prefix" applies individually to each EIGRP neighbor. Referring back to the example provided above, under the second interpretation, the "maximum-prefix" of 1000 has not been reached even though the three neighbors have cumulatively advertised 1000 prefixes, because no single neighbor has individually advertised 1000 prefixes.

Any help would be greatly appreciated.

Andrew

[Robert Hillcoat]

Hi Andrew with regards to the command 'maximum-prefix' this applies cumulatively to all neighbors.

Once the prefix limit has been reached the default behavior is for the router to tear down the neighbors. 

You will see messages like this from the router with the maximum prefix command set.  
%DUAL-5-NBRCHANGE: EIGRP-IPv4 101: Neighbor a.b.c.d (FastEthernet0/0) is down: prefix-limit exceeded. 

On the neighbor routers you will see messages like this. 
%DUAL-5-NBRCHANGE: IP-EIGRP(0) 101: Neighbor a.b.c.d (FastEthernet0/0) is down: Interface goodbye received

You can see how many prefixes each neighbor is advertising using the command 'show ip eigrp vrf xxx accounting'

hope this helps you. 

[rosaho]

This discussion has been reposted from Additional Communities to the WAN, Routing and Switching community.

[paul driver]

Hello

@Robert
"'maximum-prefix' this applies cumulatively to all neighbors."

I disagree on this statement  the neighbour x.x.x.x maximum-prefix is specifc to each eigrp neighbour
 

As i understand it if the router has multiple EIGRP peerings its limiting on the prefixes being recived on that particaulr nieghbour ONLY

And two options are available:

1) Issue a warning if the threshold is reached
2) tear down the adjecency if threshold is reached
 

res

Paul

[Robert Hillcoat]

@Paul if you read my post again, I didn't say anything about the command "neighbor x.x.x.x maximum-prefix" my exact statement was regarding the command "maximum-prefix"

I agree with you that the command "neighbor x.x.x.x maximum-prefix" applies to an individual neighbor, but that was not what I was stating. 

Perhaps i wasn't clear enough in stating that 2 commands exist under "router eigrp" one with neighbor and one without. One applies cumulatively and one applies individually.