From: Kenneth Wygand (KWygand@customonline.com)
Date: Mon Jul 26 2004 - 11:02:13 GMT-3
Geert,
Sorry for the confusion. Yes, I did accidentally mention RIP the second time while the original question pertained to EIGRP. Behind the scenes I was actually testing out the differences between the way RIP and the way EIGRP handle the "auto-summary" functionality. While the command is the same, the result is not always the same, and the internal implementation in IOS is completely different.
Having that said, I will reveal the answers (in essence, the protocol differences) to my Quiz Question:
-- Rip will always automatically summarize into it's own internal rip database (show ip rip database). This is true even if you are running Rip Version 2 and have auto-summary disabled. The "no auto-summary" command prevents this automatically-summarized address from entering the RIB.
-- Eigrp will only enter the auto-summary address into it's own eigrp topology table when auto-summary functionality is enabled locally.
Auto-Summary Enabled (Default):
<snip>
R1(3620)#sh ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(13.13.13.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 13.0.0.0/8, 1 successors, FD is 128256
via Summary (128256/0), Null0
P 13.13.13.0/24, 1 successors, FD is 128256
via Connected, Loopback1
</snip>
Auto-Summary Disabled:
<snip>
R1(3620)#sh ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(13.13.13.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 13.13.13.0/24, 1 successors, FD is 128256
via Connected, Loopback1
</snip>
Everything you have stated is correct. One point I would like to add, however, is the following. Say you have 1.1.1.1/24 on a loopback interface and want to advertise it into Eigrp. If auto-summary is -disabled-, you do not need to include the subnet mask to have it advertised as a /24 route. The subnet mask is there to simply include all interfaces on which you wish to run Eigrp, however the original masks will be advertised:
<snip>
R1(3620)#sh run int lo1
!
interface Loopback1
ip address 13.13.13.1 255.255.255.0
end
!
R1(3620)#sh run | b router eigrp
router eigrp 1
network 13.0.0.0
no auto-summary
! <<snipped for brevity>>
!
R1(3620)#sh ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(13.13.13.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 13.13.13.0/24, 1 successors, FD is 128256
via Connected, Loopback1
</snip>
Hope this helps!
Ken
________________________________
From: Geert Nijs [mailto:geert.nijs@simac.be]
Sent: Mon 7/26/2004 3:03 AM
To: Kenneth Wygand
Cc: ccielab@groupstudy.com
Subject: RE: Quiz Question of the Day 20040725
Kenneth,
In your explanation below, you are suddenly taking about RIP ??? In the original Quiz Question, you mention EIGRP ???
So for point 2, in EIGRP you can advertise subnetworks into EIGRP without advertising the entire classfull address, using
the mask option in the network command :-)
Regards,
Geert
-----Original Message-----
From: Kenneth Wygand [mailto:KWygand@customonline.com]
Sent: maandag 26 juli 2004 2:00
To: Geert Nijs
Cc: ccielab@groupstudy.com
Subject: RE: Quiz Question of the Day 20040725
?
Geert,
1) Yes, you are correct that with "no auto-summary" on R1, R2 will only see the /24 route. I mis-spoke in my last email, as the route still shows up in the rip database (show ip rip database) as a /8 due to "auto-summary". It appears as if Rip will automatically auto-summarize into its own database. It seems that "no auto-summary" doesn't prevent Rip from putting the auto-summarized address into its own database, rather it prevents the auto-summarized addresses from entering the RIB from the Rip process.
2) Independent of whether or not auto-summary is disabled, you will not be able to introduct any subnetworks into Rip without advertising the entire classful address in the process. If you enter "network 1.1.1.0" into rip (which won't accept a subnet mask), and then do a "show run", you will see that your subnet was parsed out by the IOS and reverted to the major class, which in this case is "1.0.0.0" (again without the subnet mask).
3) You are correct in that you cannot use the "summary-address" command to advertise a longer-length mask when you already have a shorter-length mask in your routing protocol's database. This, in essence, would be a "specific-address" command (if one existed), whereas this would have the exact opposite effect.
Thanks for taking the time to participate!
Ken
________________________________
From: Geert Nijs [mailto:geert.nijs@simac.be]
Sent: Sun 7/25/2004 7:36 PM
To: Kenneth Wygand
Subject: RE: Quiz Question of the Day 20040725
My conclusions after some lab tests:
1) auto-summary enabled on both routers and "network 1.0.0.0" on R1
-> generates a 1.0.0.0/8 summary route (together with a specific /24 route)
-> disable auto-summary on R1 and summary disappears on R2, R2 only has 1.1.1.0/24
2) auto-summary enabled,
but if you advertise the network with: network 1.1.1.0 0.0.0.255
-> the summary is not generated, R2 only contains 1.1.1.0/24
-> even with auto-summary on
3) The solution:
ip summary-address eigrp 1 1.1.1.0 255.255.255.0
don't think, it will work, since you can't summarize a /8 route into a /24 route
Regards,
Geert
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Kenneth Wygand
Sent: zondag 25 juli 2004 23:53
To: Georg Pauwen; ccielab@groupstudy.com
Subject: RE: Quiz Question of the Day 20040725
?
Hey Georg,
Have you labbed this up? I'm sure you'd be interested to find that either of this configurations will still yield a /8 route on R2. Surprised? ;-)
Ken
________________________________
From: Georg Pauwen [mailto:pauwen@hotmail.com]
Sent: Sun 7/25/2004 5:51 PM
To: Kenneth Wygand; ccielab@groupstudy.com
Subject: RE: Quiz Question of the Day 20040725
Hello,
auto-summary needs to be turned off on R1, the other way to advertise the
address is to use the ip summary-address eigrp 1 1.1.1.0 255.255.255.0
command on the R1 interface connected to R2. Not sure though if that second
way is the CCIE lab allowed way...
Regards,
Georg
>From: "Kenneth Wygand" <KWygand@customonline.com>
>Reply-To: "Kenneth Wygand" <KWygand@customonline.com>
>To: <ccielab@groupstudy.com>
>Subject: Quiz Question of the Day 20040725
>Date: Sun, 25 Jul 2004 17:10:15 -0400
>
>?
>Quiz Question of the Day 20040725:
>
>I have two routers back to back, R1 and R2. Both routers are running EIGRP
>on the interface between them. R1 also has a loopback interface it is
>advertising throughout the EIGRP domain natively (network command). The
>address of this loopback address is 1.1.1.1 /24.
>
>If I want R2 to receive 1.1.1.1 /24 in both its EIGRP topology table and
>RIB table, one way I can do this is by turning off the "auto-summary"
>feature within the EIGRP routing protocol.
>
>1) Which router do I need to turn off the "auto-summary" feature to have R2
>see this as a /24 route?
>
>2) Are there any other ways I can accomplish this within the "standard
>confines" of the CCIE lab?
>
>Good Luck!
>Ken
>
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