Clarification on EIGRP stub - query scoping

Answered Question
Sep 17th, 2009

Imagine I have the following:

CorporateRouter1-------(S0/0)EIGRP-STUB-BranchRouter

Advertising:172.16.1.0/24

192.168.1.0/24

10.0.0.0/24

CorporateRouter2-------(S0/1)EIGRP-STUB-BranchRouter

Advertising:10.0.0.0/24

192.168.1.0/24

Let's say that due to a misconfiguration, 172.16.1.0/24 is not being advertised on CorporateRouter2.

So both Corporate Routers connected to the branch office EIGRP-Stub routers.

Let's say CorporateRouter1 dies for good. Since we have a stub configured on EIGRP-STUB-BranchRouter, the branch router will not query CorporateRouter2 in order to learn route 172.16.1.0/24 no matter what, right?

I have this problem too.
0 votes
Correct Answer by Peter Paluch about 7 years 4 months ago

Hello Rick,

Are you sure about this? I have a different experience and the debug eigrp packet update query reply confirms that: while a stub router routinely answers with destination unreachable to all queries, the stub functionality does not prevent it from sending queries itself.

I could provide some debugs here but I don't want to do it right now. I'd like to just highlight another thread where this topic was also discussed:

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=WAN%2C%20Routing%20and%20Switching&topicID=.ee71a06&fromOutline=&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.2cd44205

Best regards,

Peter

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Richard Burts Thu, 09/17/2009 - 07:56

Marlon

There are some details in your question that are not clear to me, especially about the possible configuration error. But it is clear that the effect of configuring the Branch router as a stub is that if it loses a route that it learned then it will not generate a query for that route.

HTH

Rick

Correct Answer
Peter Paluch Thu, 09/17/2009 - 13:37

Hello Rick,

Are you sure about this? I have a different experience and the debug eigrp packet update query reply confirms that: while a stub router routinely answers with destination unreachable to all queries, the stub functionality does not prevent it from sending queries itself.

I could provide some debugs here but I don't want to do it right now. I'd like to just highlight another thread where this topic was also discussed:

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=WAN%2C%20Routing%20and%20Switching&topicID=.ee71a06&fromOutline=&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.2cd44205

Best regards,

Peter

news2010a Thu, 09/17/2009 - 20:22

Peter, no problem after this excellent explanation I took the time to build the lab and verify this; Yes I can see that once I shut the connection between CorporateRouter1 to the Stub router(R3 below) the second Corporate Router receives a QUERY from the stub router. Perfect! Thanks all.

R1#debug eigrp packets reply

EIGRP Packets debugging is on

(REPLY)

R1#debug eigrp packets query

EIGRP Packets debugging is on

(QUERY)

R1#

00:25:52: EIGRP: Received QUERY on FastEthernet1/0 nbr 192.168.1.3

00:25:52: AS 100, Flags 0x0, Seq 24/0 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely

0/0

R3#debug eigrp packets query

EIGRP Packets debugging is on

(QUERY)

R3#debug eigrp packets reply

EIGRP Packets debugging is on

(REPLY)

R3#

R3#ping 2.2.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 48/90/120 ms

R3#config t

Enter configuration commands, one per line. End with CNTL/Z.

R3(config)#

R3#

00:20:20: %SYS-5-CONFIG_I: Configured from console by console

00:20:48: EIGRP: Received REPLY on FastEthernet1/0 nbr 192.168.1.1

00:20:48: AS 100, Flags 0x0, Seq 9/24 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely

0/0

R3#show ip route

Richard Burts Fri, 09/18/2009 - 07:12

Peter and Marlon

Thank you for improving my understanding of EIGRP stub. Sorry that my initial response was off the mark. It is always good to learn things and improve understanding on the forum.

HTH

Rick

Peter Paluch Fri, 09/18/2009 - 11:02

Hello Rick,

You are heartily welcome, and absolutely no apologies are necessary. And I'm sure I am going to learn a lot from you.

Best regards,

Peter

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