why summary-address command in ospf result an O type route not OE2?

[rookie R]

Hi all!

I configured the

summary-address 172.18.0.0 255.255.0.0 

command in the OSPF process on an OSPF ASBR router to summarize the routes that redistributed from EIGRP and found out the type of that summaries route is type O in the routing table on this device. Why is that? I mean, that route redistributes from the EIGRP protocol it should be an OE2-type route, right? And I looked up the OSPF database, it's a type-5 AS external link. I googled it for a long time, trying to find Cisco documents to explain it, but found nothing. Can someone send me the link of the documents about that? 

Thanks so much!

[David Ruess · Accepted solution]

Hello,

It could be to do with the summary itself and which router originated it. When you create a summary address (regardless of where it came from) the router you are implementing the summary on becomes the new originator of the route suppressing the more specific (Type 5 includes) routes. So since it is originating the summary route it will have it as an O route on the device. With summary address keep in mind there is a loss of path information as the newly created summarized route suppresses all of that. You wouldn't see the type 5 route because its being suppressed in place of the summary as a whole. 

May have to lab this up in a bit.

Hope that helps.

-David

[MHM Cisco World]

I send you private message 

[David Ruess · Accepted solution]

To further elaborate on my fist response what you are observing is correct. When you redistribute and summarize on the router it creates a Null 0 route of the summary address. When a router creates a local route its an Internal O route. To further add it could also be used to prevent loop. In terms of the OSPF path selection process the O route is chosen first so it would make sense to install the Null 0 route (bit bucket) as this route. If it installed the summary route as lets say an external route but a higher priority route (lets say Default Route) exists then it could use that unintended path and cause a loop.

However when the router ADVERTISES the summary route it does so as an external route as you would expect. See my lab below:

R1#debug ip ospf lsa-generation 
OSPF LSA generation debugging is on
R1#
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router ospf 1
R1(config-router)#redistribute connected
R1(config-router)#
*Nov 17 16:20:06.437: OSPF-1 LSGEN: Scheduling rtr LSA for area 0, build flag 0x41 (from 0x308D0D9)
*Nov 17 16:20:06.939: OSPF-1 LSGEN: Build router LSA for area 0, router ID 1.1.1.1, seq 0x80000004
*Nov 17 16:20:07.439: OSPF-1 LSGEN: Build external LSA 5.5.5.5, mask 255.255.255.255, type 5, age 0, seq 0x80000001
*Nov 17 16:20:07.439: OSPF-1 LSGEN: MTID Metric Metric-type FA Tag Topology Name
*Nov 17 16:20:07.439: OSPF-1 LSGEN: 0 20 2 0.0.0.0 0 Base

R1(config-router)#summary-address 5.5.5.0 255.255.255.0 
R1(config-router)#
*Nov 17 16:20:43.949: OSPF-1 LSGEN: Build external LSA 5.5.5.0, mask 255.255.255.0, type 5, age 0, seq 0x80000001
*Nov 17 16:20:43.949: OSPF-1 LSGEN: MTID Metric Metric-type FA Tag Topology Name
*Nov 17 16:20:43.949: OSPF-1 LSGEN: 0 20 2 0.0.0.0 0 Base

*Nov 17 16:20:43.952: OSPF-1 LSGEN: Build external LSA 5.5.5.5, mask 255.255.255.255, type 5, age 3600, seq 0x80000002
*Nov 17 16:20:43.952: OSPF-1 LSGEN: MTID Metric Metric-type FA Tag Topology Name
*Nov 17 16:20:43.952: OSPF-1 LSGEN: 0 16777215 2 0.0.0.0 0 Base
R1(config-router)#

As you can see our router creates the Type 5 LSA. Then, once I enter the summary address command it sends the Summary address as an External Type 5 LSA to its neighbor AND withdraws the original Type 5 route by giving it a Maximum metric and Maximum age-out time. As you can see on the neighbor router is shows as an External E2 route.

R2#sh ip route
Codes: L - local, 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, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
O E2 1.1.1.1 [110/20] via 10.10.12.1, 00:47:06, GigabitEthernet0/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/2] via 192.168.23.3, 00:46:11, GigabitEthernet0/1
5.0.0.0/24 is subnetted, 1 subnets
O E2 5.5.5.0 [110/20] via 10.10.12.1, 00:47:06, GigabitEthernet0/0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.10.12.0/24 is directly connected, GigabitEthernet0/0
L 10.10.12.2/32 is directly connected, GigabitEthernet0/0
192.168.23.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.23.0/24 is directly connected, GigabitEthernet0/1
L 192.168.23.2/32 is directly connected, GigabitEthernet0/1
R2#

Hope this helps

-David

[rookie R]

Thanks so much, dude. That is an excellent explanation. I got that.

[paul driver]

Hello

---

@rookie R wrote:
summaries route is type O in the routing table on this device. Why is that?

---

Are you sure your not looking at the OSPF code which will be O and not the lsa which will be external E2 from an ASBR ( O E2 ) and as stated already, by default when you perform summarisation the summarising rtr will by default create a discard route (NULL0) to avoid routing loops ( basically the same summary route being advertised  back into rtr that initially created)

This discard route (internal/external) can be removed if desired
router ospf x
no discard-route (internal/external)
discard-route (internal/external) 255

[rookie R]

@paul driver @MHM Cisco World 

Sorry for replying so late guys,I was on vacation back then,here is my lab：

3 Routers,R1 and R2's E0/0 running the OSPF,R2's E0/1 and R3 running the EIGRP, I configured the summary-address command on R2, here is my configuration:

R1:

interface Loopback0
ip address 1.1.1.1 255.255.255.255
ip ospf 1 area 0
!
interface Ethernet0/0
ip address 192.168.12.1 255.255.255.0
ip ospf 1 area 0
duplex auto
!

router ospf 1
router-id 1.1.1.1




R2:

interface Loopback0
ip address 2.2.2.2 255.255.255.255
ip ospf 1 area 0
!
interface Ethernet0/0
ip address 192.168.12.2 255.255.255.0
ip ospf 1 area 0
duplex auto
!
interface Ethernet0/1
ip address 192.168.23.2 255.255.255.0
duplex auto
!

router eigrp ccie
!
address-family ipv4 unicast autonomous-system 10003
!
topology base
exit-af-topology
network 192.168.23.0
exit-address-family
!
router ospf 1
router-id 2.2.2.2
summary-address 10.6.0.0 255.254.0.0
redistribute eigrp 10003 subnets
!


R3:

interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Loopback23
ip address 10.6.0.1 255.255.0.0
!
interface Loopback24
ip address 10.7.0.1 255.255.0.0
!
interface Ethernet0/0
ip address 192.168.23.3 255.255.255.0
duplex auto
!

router eigrp cisco
!
address-family ipv4 unicast autonomous-system 10003
!
topology base
exit-af-topology
network 10.0.0.0
network 192.168.23.0
exit-address-family
!


Here is the route table, OSPF database and neighbor status:


R2#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/BDR 00:00:34 192.168.12.1 Ethernet0/0




R2#show ip eigrp neighbors
EIGRP-IPv4 VR(ccie) Address-Family Neighbors for AS(10003)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 192.168.23.3 Et0/1 10 00:23:23 8 100 0 2




R2#show ip route
Codes: L - local, 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, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/11] via 192.168.12.1, 00:20:57, Ethernet0/0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
O 10.6.0.0/15 is a summary, 00:22:17, Null0
D 10.6.0.0/16 [90/1024640] via 192.168.23.3, 00:23:40, Ethernet0/1
D 10.7.0.0/16 [90/1024640] via 192.168.23.3, 00:23:40, Ethernet0/1
192.168.12.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.12.0/24 is directly connected, Ethernet0/0
L 192.168.12.2/32 is directly connected, Ethernet0/0
192.168.23.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.23.0/24 is directly connected, Ethernet0/1
L 192.168.23.2/32 is directly connected, Ethernet0/1




R2#show ip ospf database

OSPF Router with ID (2.2.2.2) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 1317 0x80000004 0x0059C2 2
2.2.2.2 2.2.2.2 1313 0x80000005 0x004DBE 2

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
192.168.12.2 2.2.2.2 1318 0x80000001 0x008F1F

Type-5 AS External Link States

Link ID ADV Router Age Seq# Checksum Tag
10.6.0.0 2.2.2.2 1383 0x80000001 0x00DCAC 0
192.168.23.0 2.2.2.2 1383 0x80000001 0x00FB1C 0

[MHM Cisco World]

Sorry I make you retrun to this issue'

When you share self originate show ip ospf db I was not see summary?

Can I know why?

Thanks

MHM

[rookie R]

@MHM Cisco World You are right. The OSPF database has no type 1 LSA entry of the 10.6.0.0/15. I didn't notice that until you asked. I also turned on the debug as David said, and here are they:

R2(config-router)# summary-address 10.6.0.0 255.254.0.0
R2(config-router)#
*Dec 3 03:20:11.099: OSPF-1 LSGEN: Build external LSA 10.6.0.0, mask 255.255.0.0, type 5, age 3600, seq 0x80000004
*Dec 3 03:20:11.099: OSPF-1 LSGEN: MTID Metric Metric-type FA Tag Topology Name
*Dec 3 03:20:11.099: OSPF-1 LSGEN: 0 16777215 2 0.0.0.0 0 Base
*Dec 3 03:20:11.099: OSPF-1 LSGEN: Build external LSA 10.7.0.0, mask 255.255.0.0, type 5, age 3600, seq 0x80000002
*Dec 3 03:20:11.099: OSPF-1 LSGEN: MTID Metric Metric-type FA Tag Topology Name
*Dec 3 03:20:11.099: OSPF-1 LSGEN: 0 16777215 2 0.0.0.0 0
R2(config-router)#Base
*Dec 3 03:20:11.099: OSPF-1 LSGEN: No change in ext LSA 192.168.23.0, mask 255.255.255.0, type 5, age 1201, seq 0x80000001
*Dec 3 03:20:11.099: OSPF-1 LSGEN: Rate limit LSA generation for 5/10.6.0.0/2.2.2.2
*Dec 3 03:20:11.099: OSPF-1 LSGEN: No change in ext LSA 192.168.23.0, mask 255.255.255.0, type 5, age 1201, seq 0x80000001
R2(config-router)#
*Dec 3 03:20:16.103: OSPF-1 LSGEN: Build external LSA 10.6.0.0, mask 255.254.0.0, type 5, age 0, seq 0x80000005
*Dec 3 03:20:16.103: OSPF-1 LSGEN: MTID Metric Metric-type FA Tag Topology Name
*Dec 3 03:20:16.103: OSPF-1 LSGEN: 0 20 2 0.0.0.0 0 Base
R2(config-router)#
*Dec 3 03:30:28.766: OSPF-1 LSGEN: Update external LSA 5/192.168.23.0/2.2.2.2 0x80000001
*Dec 3 03:30:28.766: OSPF-1 LSGEN: Build external LSA 192.168.23.0, mask 255.255.255.0, type 5, age 0, seq 0x80000002
*Dec 3 03:30:28.766: OSPF-1 LSGEN: MTID Metric Metric-type FA Tag Topology Name
*Dec 3 03:30:28.766: OSPF-1 LSGEN: 0 20 2 0.0.0.0 0 Base
R2(config-router)#
*Dec 3 03:34:40.669: OSPF-1 LSGEN: Update router LSA 1/2.2.2.2/2.2.2.2 0x80000006
*Dec 3 03:34:40.669: OSPF-1 LSGEN: Build router LSA for area 0, router ID 2.2.2.2, seq 0x80000007
*Dec 3 03:34:40.669: OSPF-1 LSGEN: Update network LSA 2/192.168.12.2/2.2.2.2 0x80000001
*Dec 3 03:34:40.669: OSPF-1 LSGEN: Build network LSA for Ethernet0/0, router ID 2.2.2.2
R2(config-router)#

The router created two LSAs, 10.6.0.0/24 and 10.7.0.0/24, the age of these two LSA is 3600, which means OSPF removed these two 5 type LSAs from the OSPF database and then created the type 5 LSA of 10.6.0.0/15, but no other LSA debug of the route 10.6.0.0/15, and I tried another show command:

R2#show ip route 10.6.0.0 255.254.0.0
Routing entry for 10.6.0.0/15
Known via "ospf 1", distance 254, metric 20, type intra area
Routing Descriptor Blocks:
* directly connected, via Null0
Route metric is 20, traffic share count is 1

The output said the type of it is intra area, so that proved what David said is correct. That route is generated in this router, so it's a type O route, but I don't know why there is no type 1 LSA in the OSPF database but only type 5 there. ChatGPT said it's because it was generated in this very router to avoid loop routing, so the type must be O in the routing table, but an ASBR generates it, so it must be type 5 LSA in the OSPF database. I can take it as the right answer.

[MHM Cisco World]

Hi
I know it late reply 
I go furthered 
the summary add three prefix 
two LSA4/LSA5  E1/E2 <- this advertise to other OSPF peers 
one LSA1 O <- this only appear in RIB and not appear in OSPF and nor advertise to other OSPF Peers

I check RFC and could not find notes about why it not advertise nor why it not appear in OSPF DB
update you if I found something 
MHM

[rookie R]

Thanks so much for your reply, I am impressed by your attitude toward tech, I should be more like you. 

And would you please tell me the details of the 3 prefix?

[MHM Cisco World]

keep study and sure you will be better than Me
MHM