If you are interested in Part 1 of this blog series – click here.
Question 2 of 105
Given the topology and configurations shown in the exhibits. Which devices will receive EIGRP Query packets if R1 loses its route information for the 10.10.10.0/24 prefix?
a) None of the devices
b) R2, R3, R4, R5, R6, R7
c) R2, R3, R6, R7
d) R2, R3, R4, R5
e) R2, R3
Exhibit 1
Exhibit 2
R2#show run Building configuration... Current configuration : 877 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R2 ! boot-start-marker boot-end-marker ! no aaa new-model memory-size iomem 5 ip cef ! no ip domain lookup ip auth-proxy max-nodata-conns 3 ip admission max-nodata-conns 3 ! interface FastEthernet0/0 description Link to R1 ip address 10.20.20.2 255.255.255.0 duplex auto speed auto ! interface FastEthernet0/1 description Link to R4 ip address 10.24.24.2 255.255.255.0 duplex auto speed auto ! interface FastEthernet1/0 description Link to R5 ip address 10.25.25.2 255.255.255.0 duplex auto speed auto ! router eigrp 100 network 10.0.0.0 auto-summary ! ip forward-protocol nd ! ip http server no ip http secure-server ! control-plane ! line con 0 exec-timeout 0 0 logging synchronous line aux 0 line vty 0 4 ! end
Exhibit 3
R3#show run Building configuration... Current configuration : 982 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R3 ! boot-start-marker boot-end-marker ! no aaa new-model memory-size iomem 5 ip cef ! no ip domain lookup ip auth-proxy max-nodata-conns 3 ip admission max-nodata-conns 3 ! interface FastEthernet0/0 description Link to R1 ip address 10.30.30.3 255.255.255.0 duplex auto speed auto ! interface FastEthernet0/1 description Link to R6 ip address 10.36.36.3 255.255.255.0 ip summary-address eigrp 100 10.0.0.0 255.0.0.0 5 duplex auto speed auto ! interface FastEthernet1/0 description Link to R7 ip address 10.37.37.3 255.255.255.0 ip summary-address eigrp 100 10.0.0.0 255.0.0.0 5 duplex auto speed auto ! router eigrp 100 network 10.0.0.0 no auto-summary ! ip forward-protocol nd ! ip http server no ip http secure-server ! control-plane ! line con 0 exec-timeout 0 0 logging synchronous line aux 0 line vty 0 4 ! end
In order to solve this question, we must remember the various options for Query Scoping that were covered in the CCIE R/S Written Class On Demand, and in Petr’s excellent blog post. Remember, summarization, multiple EIGRP ASes, EIGRP Stub, and prefix filtering are all methods of scoping queries.
In this example, we examine R2′s configuration and learn that automatic summarization is left on. But this has no effect whatsoever in this scenario as all devices are numbered in the same major classful network space. On R3, we notice that manual summarization is being accomplished, but notice that will scope the queries at R6 and R7. So any devices BEYOND R6 and R7 will not receive the queries for this subnet, but those devices will indeed receive them.
In summary (no pun intended), we just need to remember here two basic concepts from the course. What are the options to scope queries? How will they impact the query behavior once implemented.
So our answer – option b – R2, R3, R4, R5, R6, and R7 all receive query packets for this network.
About INE Instructor:
You can leave a response, or trackback from your own site.
8 Responses to “CCIE R/S Written Sample Question – Part 2”
Leave a Reply
Excelent post,
Thanks to your post and the one of Petr, I fixed my knowledge about EIGRP query scope.
Very good.
When you stated “…On R3, we notice that manual summarization is being accomplished” you meant that:
on R3, ‘no auto-summary’ disables summarization, but then you entered ’10.0.0.0′ and that applied a manual summarization.
Petr article makes more sense to me know.
i know that when a router receive a query about a network, sees its routing table for that. if it find a summarized network of that queired network, or if it was configured to be stub, thst router sends a reply message and never distribute the query message. but if my thinkings are true, then routers R4, R5, R6, R7 must not receive the query message because both of routers R2 and R3 have the summarized route (10.0.0.0/8) on its tables.
R2 and R3 do not possess the summaries – they pass the summaries to the routers below. They will possess the summaries and represent the scope of the queries.
when auto-summary command was issued on the router, does the router creates a summary (10.0.0.0/8) route to “Null” interface? …. is this route makes the router to reply the Query message and not distribute it?
No – the reason a summary scopes the query is because the router does not have an entry for the SPECIFIC subnet in its topology database. It responds to the query and does not forward it as a result.
as you said, router R2 has the summary route and then must not pass he query to downstream routers. so why routers R4 and R5 receive this queries?
R2 has automatic summarization enabled – but it does NOT possess a summary route in this case.