06-19-2012 10:15 AM - edited 03-04-2019 04:43 PM
Hi,
If R1<-----> R2<-------> R3 are running EIGRP.
R1- configured with no-auto-summary
R2 and R3 : auto-summary (default).
R1 is publishing 10.1.1.0/24 , 10.1.2.0/24 and 192.168.1.0 / 26 , 192.168.1.64 /26 networks on R3 it was expeted that routing table will have only 10.0.0.0/8 and 192.168.1.0/24 but it was still showing routes with small subnets.
Please share the experience.
Thanks in advance.
Subodh
06-19-2012 10:21 AM
Hello Subodh,
In EIGRP, the rules for automatic summarization are somewhat different from RIP. EIGRP will automatically summarize networks from a particular major network only if there also is a directly connected subnet from that same major network. Otherwise, it is not going to modify those networks.
I assume that on R2, you are seeing the networks 10.1.1.0/24, 10.1.2.0/24 and 192.168.1.0/26. In addition, I assume that there are no other directly connected subnets of either 10.0.0.0/8 or 192.168.1.0/24 on R2. That causes R2 to skip autosummarizing these three networks.
Can you please post the show ip route output from R2 and R3? Thank you!
Best regards,
Peter
06-19-2012 11:00 AM
Here is the output of show int brief and ip route
R1 (fa0/0) <---------------------> R2(fa0/0) | R2(fa0/1)<----------------------> R3(fa0/1)
10.1.100.0/24 172.16.1.0/24
R1:
##############
R1#sh ip inter
R1#sh ip interface bri
R1#sh ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 10.1.100.1 YES manual up up
FastEthernet0/1 unassigned YES unset administratively down down
Loopback0 10.1.1.1 YES manual up up
Loopback2 10.1.2.1 YES manual up up
Loopback5 192.168.1.65 YES manual up up
Loopback50 192.168.1.1 YES manual up up
R1#
R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
D 172.16.0.0/16 [90/307200] via 10.1.100.2, 00:07:56, FastEthernet0/0
10.0.0.0/24 is subnetted, 3 subnets
C 10.1.2.0 is directly connected, Loopback2
C 10.1.1.0 is directly connected, Loopback0
C 10.1.100.0 is directly connected, FastEthernet0/0
192.168.1.0/26 is subnetted, 2 subnets
C 192.168.1.64 is directly connected, Loopback5
C 192.168.1.0 is directly connected, Loopback50
R1#
#############
R2
R2#sh ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 10.1.100.2 YES manual up up
FastEthernet0/1 172.16.1.1 YES manual up up
R2#
R2#
R2#sh ip rou
R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D 172.16.0.0/16 is a summary, 00:09:59, Null0
C 172.16.1.0/24 is directly connected, FastEthernet0/1
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
D 10.1.2.0/24 [90/409600] via 10.1.100.1, 00:08:45, FastEthernet0/0
D 10.1.1.0/24 [90/409600] via 10.1.100.1, 00:08:45, FastEthernet0/0
D 10.0.0.0/8 is a summary, 00:09:59, Null0
C 10.1.100.0/24 is directly connected, FastEthernet0/0
192.168.1.0/26 is subnetted, 2 subnets
D 192.168.1.64 [90/409600] via 10.1.100.1, 00:03:23, FastEthernet0/0
D 192.168.1.0 [90/409600] via 10.1.100.1, 00:05:20, FastEthernet0/0
R2
##################
R3
R3#sh ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES unset administratively down down
FastEthernet0/1 172.16.1.2 YES manual up up
R3#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 1 subnets
C 172.16.1.0 is directly connected, FastEthernet0/1
D 10.0.0.0/8 [90/307200] via 172.16.1.1, 00:07:38, FastEthernet0/1
192.168.1.0/26 is subnetted, 2 subnets
D 192.168.1.64 [90/435200] via 172.16.1.1, 00:04:13, FastEthernet0/1
D 192.168.1.0 [90/435200] via 172.16.1.1, 00:06:10, FastEthernet0/1
R3#
06-19-2012 11:23 AM
Hello Subodh,
So this confirms my previous assumption and analysis.
On R2, there are two directly connected networks: 10.1.100.0/24 and 172.16.1.0/24. R2 learns about unsummarized networks 10.1.1.0/24, 10.1.2.0/24, 192.168.1.0/26 and 192.168.1.64/26 through EIGRP from R1.
Now, for a network X to be automatically summarized in EIGRP, all these conditions must be met:
Note that these two conditions are met for subnets 10.1.1.0/24 and 10.1.2.0/24, as they are being advertised out an interface located in a different major network 172.16.0.0/16 and there is a directly connected network 10.1.100.0/24 present in R2's routing table which is in the same major network 10.0.0.0/8 as the two subnets 10.1.1.0/24 and 10.1.2.0/24. On R3, you can see the automatic summary 10.0.0.0/8 learned via EIGRP.
The second condition is not met for the subnets 192.168.1.0/26 and 192.168.1.64/26. Therefore, they are not summarized when advertised to R3. However, they would be advertised if you caused a directly connected network from the major network 192.168.1.0/24 to appear in R2's routing table. For example, try creating a loopback interface 192.168.1.254 255.255.255.255. You do not need to include it into EIGRP. That should cause R2 to start autosummarizing the 192.168.1.0/26 and 192.168.1.64/26.
Best regards,
Peter
06-19-2012 12:02 PM
R2
R2#sh ip interface bri
R2#sh ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 10.1.100.2 YES manual up up
FastEthernet0/1 172.16.1.1 YES manual up up
Loopback2000 192.168.1.254 YES manual up up
R2#
R2#sh ip rou
R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D 172.16.0.0/16 is a summary, 01:17:04, Null0
C 172.16.1.0/24 is directly connected, FastEthernet0/1
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
D 10.1.2.0/24 [90/409600] via 10.1.100.1, 00:02:27, FastEthernet0/0
D 10.1.1.0/24 [90/409600] via 10.1.100.1, 00:02:27, FastEthernet0/0
D 10.0.0.0/8 is a summary, 01:17:04, Null0
C 10.1.100.0/24 is directly connected, FastEthernet0/0
192.168.1.0/24 is variably subnetted, 3 subnets, 2 masks
D 192.168.1.64/26 [90/409600] via 10.1.100.1, 00:02:28, FastEthernet0/0
D 192.168.1.0/26 [90/409600] via 10.1.100.1, 00:02:28, FastEthernet0/0
C 192.168.1.254/32 is directly connected, Loopback2000
R2#
IP-EIGRP neighbors for process 10
IP-EIGRP neighbors for process 200
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 172.16.1.2 Fa0/1 11 00:02:45 47 282 0 20
0 10.1.100.1 Fa0/0 12 00:02:45 40 240 0 17
R2#
############
R3
R3#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 1 subnets
C 172.16.1.0 is directly connected, FastEthernet0/1
D 10.0.0.0/8 [90/307200] via 172.16.1.1, 00:03:04, FastEthernet0/1
192.168.1.0/26 is subnetted, 2 subnets
D 192.168.1.64 [90/435200] via 172.16.1.1, 00:03:02, FastEthernet0/1
D 192.168.1.0 [90/435200] via 172.16.1.1, 00:03:02, FastEthernet0/1
R3#
R3#
06-19-2012 07:24 PM
Hello Subodh,
Hmmm, you're right here, I've tested that in Dynamips and also arrived to the same results. The 192.168.1.0/26 and 192.168.1.64/26 do not appear to get auto-summarized. My previous explanation was not correct.
Let me research this further. I will be back with any information I can get. And there is a gentleman around - Donald Slice - who is intimately familiar with EIGRP internals so I hope he joins this thread as well!
Best regards,
Peter
06-19-2012 08:36 PM
Hi Guys!
You are advertising routes under the "no auto" eigrp process. Test this under the auto-summary eigrp to get the results.
Advetise the routes on R3 so it will auto summarise.
use "debug ip eigrp summary" and "debug ip eigrp"
Nandan.
06-19-2012 09:15 PM
Hello Nandan,
Running auto-summary on R1 is not the point here. What we are looking at is why R2 does not summarize the 192.168.1.0/26 and 192.168.1.64/26 into 192.168.1.0/24 when advertising them out the interface in the 172.16.x.x network. RIP would have summarized those networks immediately. What prevents EIGRP from doing that?
Originally, I thought it was an internal protection of EIGRP to disallow summarizing those subnetworks for which there is no certainty that we are the owner of the entire major network (this is recognized by not having any directly connected network from this major network). However, this does not seem to be the case.
Best regards,
Peter
06-19-2012 09:29 PM
Hello Pete,
I tried some different options and i came to following conslusion.
For router that is EIGRP default - auto-summary
1. If the updates are received on the interface that is not from the same major subnet here in example the link between R1 and R2 is 10.....some thing some thing and update received are 192.168.1.0 /26 192.168.1.64 /26.
AND
2. Second condition is updates are sent to 172.16.some thing some thing subnet... this is different than the 192.168.1.0/26 etc.. then router will do auto summarization.
I was able to see 192.168.1.0/24 single subnet on the R3 routing table.
Only thing I could not verify is what if the link between R2 and R3 is say 192.168.1.192/ 26 ? In this case what will be routing table or R3?
I think it will have two routes for 192.168.1.192 directly connected and one more sent by R2 192.168.1.0/24
Please share the experience.
Thanks!
Subodh
06-19-2012 10:19 PM
Subodh,
But this is the scenario from the first experiment, and we both have agreed that surprisingly, the 192.168.1.0/26 and 192.168.1.64/26 do not get autosummarized when advertised to R3. How come you were suddenly been able to see them summarized to 192.168.1.0/24 on R3? What exact configuration changes did you perform?
Best regards,
Peter
06-19-2012 10:33 PM
Hi Peter!
As per my observation when you have disabled auto-summary (R1 ) and advertise routes to the router with auto-summary (R2) , R2 will not make any changes. Thats because only originating routers attach the mask or default mask as per the auto-summary or no auto-summary command. Then the routers which are re-advertising the routes dont make any changes to the subnet mask information.
E.G
R1 (no auto) -- R2 (auto) -- R3 (auto)
R1 sends a route with 192.168.1.0/26 mask information R2 just forwards this information to R3 without any changes.
But if you configure the 192.168.1.0/26 network on R3 which has auto-summary it will summarise and send the routes to R2 with /24 .
As per my thought only originating router summarieses based on the auto-summary feature.
Let me know if you think otherwise.
Thanks,
Nandan Mathure
06-19-2012 10:50 PM
Hello Nandan,
As per my observation when you have disabled auto-summary (R1 ) and advertise routes to the router with auto-summary (R2) , R2 will not make any changes. Thats because only originating routers attach the mask or default mask as per the auto-summary or no auto-summary command. Then the routers which are re-advertising the routes dont make any changes to the subnet mask information.
I respectfully disagree. It is an inherent nature of distance-vector protocols that you can summarize at any point in the network topology (as opposed to link-state protocols where summarization is allowed only between areas or during redistribution). The fact that R1 does not summarize the networks does not prevent R2 from performing the summarization itself. The basic rule for automatic summarization is that if a network X is going to be advertised through an interface in network Y and major_network(X) != major_network(Y), then instead of advertising the network X, the router will advertise major_network(X). This condition applies on R2 to both 10.1.x.0/24 and 192.168.1.x/26 when being advertised to R3. However, in original Subodh's configuration (and in my config as well!), R2 created a summary 10.0.0.0/8 but left the 192.168.1.x/26 unsummarized. The question is - what is the difference between these two networks?
I shall emphasize that with RIPv1 or RIPv2 and auto-summary on, R2 would advertise 10.0.0.0/8 and 192.168.1.0/24 without any hesitations.
Best regards,
Peter
06-19-2012 11:03 PM
Hi Peter,
You are absolutely right on that. I got it wrong.
Thanks for the refresher.
5 points. I need to lab this up now and look for packet data.
thanks,
Nandan.
06-20-2012 04:44 AM
Here are the configurations and details :
R1#sh runn
Building configuration...
Current configuration : 904 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
hostname R1
boot-start-marker
boot-end-marker
no aaa new-model
resource policy
memory-size iomem 5
ip cef
no ip domain lookup
interface Loopback1
ip address 192.168.1.1 255.255.255.192
interface Loopback2
ip address 192.168.1.65 255.255.255.192
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
duplex auto
speed auto
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
router eigrp 10
network 10.1.1.0 0.0.0.255
network 192.168.1.0 0.0.0.63
network 192.168.1.64 0.0.0.63
no auto-summary
no 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
R1#
R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
D 172.16.0.0/16 [90/307200] via 10.1.1.2, 00:03:10, FastEthernet0/0
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, FastEthernet0/0
192.168.1.0/26 is subnetted, 2 subnets
C 192.168.1.64 is directly connected, Loopback2
C 192.168.1.0 is directly connected, Loopback1
R1#
R1#show cdp ne
R1#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Intrfce Holdtme Capability Platform Port ID
R2 Fas 0/0 153 R S I 2691 Fas 0/0
R1#
R1#
R1#sh ip eig
R1#sh ip eigrp n
R1#sh ip eigrp neighbors
IP-EIGRP neighbors for process 10
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.1.1.2 Fa0/0 14 00:05:02 53 477 0 5
R1#
#########################################
R2 Details
show runn
R2#show running-config
Building configuration...
Current configuration : 757 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
resource policy
memory-size iomem 5
ip cef
no ip domain lookup
interface FastEthernet0/0
ip address 10.1.1.2 255.255.255.0
duplex auto
speed auto
interface FastEthernet0/1
ip address 172.16.1.1 255.255.255.0
duplex auto
speed auto
router eigrp 10
network 10.1.1.0 0.0.0.255
network 172.16.1.0 0.0.0.255
auto-summary
no ip http server
no ip http secure-server
control-plane
line con 0
exec-timeout 0 0
logging synchronous
line aux 0
R2#
R2#sh ip route
R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D 172.16.0.0/16 is a summary, 00:04:18, Null0
C 172.16.1.0/24 is directly connected, FastEthernet0/1
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.1.1.0/24 is directly connected, FastEthernet0/0
D 10.0.0.0/8 is a summary, 00:04:18, Null0
192.168.1.0/26 is subnetted, 2 subnets
D 192.168.1.64 [90/409600] via 10.1.1.1, 00:05:57, FastEthernet0/0
D 192.168.1.0 [90/409600] via 10.1.1.1, 00:05:59, FastEthernet0/0
R2#
R2#sh ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 10.1.1.2 YES manual up up
FastEthernet0/1 172.16.1.1 YES manual up up
R2#sh c ip eig
R2#sh ip eigrp n
R2#sh ip eigrp neighbors
IP-EIGRP neighbors for process 10
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 172.16.1.2 Fa0/1 14 00:04:37 1283 5000 0 4
0 10.1.1.1 Fa0/0 11 00:06:16 51 306 0 3
R2#
R2#
R2#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Intrfce Holdtme Capability Platform Port ID
R3 Fas 0/1 155 R S I 2691 Fas 0/1
R1 Fas 0/0 155 R S I 2691 Fas 0/0
R2#
##############
R3
Building configuration...
Current configuration : 719 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
resource policy
memory-size iomem 5
ip cef
no ip domain lookup
interface FastEthernet0/0
no ip address
shutdown
duplex auto
speed auto
interface FastEthernet0/1
ip address 172.16.1.2 255.255.255.0
duplex auto
speed auto
router eigrp 10
network 172.16.1.0 0.0.0.255
auto-summary
no 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
R3#
R3#sh ip rou
R3#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 1 subnets
C 172.16.1.0 is directly connected, FastEthernet0/1
D 10.0.0.0/8 [90/307200] via 172.16.1.1, 00:05:51, FastEthernet0/1
192.168.1.0/26 is subnetted, 2 subnets
D 192.168.1.64 [90/435200] via 172.16.1.1, 00:05:51, FastEthernet0/1
D 192.168.1.0 [90/435200] via 172.16.1.1, 00:05:51, FastEthernet0/1
R3#
R3#sh ip interface bri
R3#sh ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES unset administratively down down
FastEthernet0/1 172.16.1.2 YES manual up up
R3#sh ip eig
R3#sh ip eigrp n
R3#sh ip eigrp neighbors
IP-EIGRP neighbors for process 10
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 172.16.1.1 Fa0/1 13 00:06:06 66 396 0 8
R3#
R3#
R3#show cdp n
R3#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Intrfce Holdtme Capability Platform Port ID
R2 Fas 0/1 150 R S I 2691 Fas 0/1
04-15-2014 09:39 AM
Hey guys, Peter had it half way right. But R2 needs to have a 192.x interface participating in EIGRP.
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