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OSPF Summarization

i have 3 routers( 1601-Area0,2610-Area0 and Area 10,1603-Area 10 and Area 11):

Cisco1601#sh ip int brief

Interface IP-Address OK? Method Status Protocol

Ethernet0 A.B. C.D YES NVRAM up up

Loopback0 131.108.2.1 YES manual up up

Loopback1 131.108.3.1 YES manual up up

Loopback2 131.108.4.1 YES manual up up

Loopback3 131.108.5.1 YES manual up up

Loopback4 131.108.6.1 YES manual up up

Loopback5 131.108.7.1 YES manual up up

Loopback6 131.108.8.1 YES manual up up

Loopback7 131.108.9.1 YES manual up up

Loopback8 131.108.10.1 YES manual up up

Loopback9 131.108.11.1 YES manual up up

Loopback10 131.108.12.1 YES manual up up

Loopback11 131.108.13.1 YES manual up up

Loopback12 131.108.14.1 YES manual up up

Loopback13 131.108.15.1 YES manual up up

Serial0 unassigned YES NVRAM up up

Serial0.1 192.168.1.77 YES NVRAM up up

Serial1 unassigned YES NVRAM up up

Serial1.1 192.168.100.2 YES NVRAM up up

----

From 1601 config-

!

router ospf 1

log-adjacency-changes

network 131.108.0.0 0.0.255.255 area 0

network 192.168.100.0 0.0.0.255 area 0

!

--------------

--------------

2610#sh ip int brief

Interface IP-Address OK? Method Status Protocol

Ethernet0/0 A.B.C.1 YES NVRAM up up

Serial0/0 unassigned YES NVRAM up up

Serial0/0.1 A.B.C.22 YES NVRAM up up

Serial0/0.2 192.168.100.1 YES NVRAM up up

Serial0/0.3 unassigned YES unset up up

Loopback0 192.168.18.1 YES manual up up

-----------------

From 2610 config-

!

router ospf 2

log-adjacency-changes

area 0 range 131.108.0.0 255.255.224.0

area 10 virtual-link 192.168.16.1

network 192.168.18.0 0.0.0.255 area 10

network 192.168.100.0 0.0.0.255 area 0

network A.B.C.0 0.0.0.255 area 10

!

----------------

----------------

c1603#sh ip int brief

Interface IP-Address OK? Method Status Protocol

Ethernet0 A.B.C.111 YES NVRAM up up

Loopback3 192.168.16.1 YES manual up up

---------------

!

router ospf 3

network 192.168.16.0 0.0.0.255 area 11

network A.B.C.0 0.0.0.255 area 10

area 10 virtual-link A.B.C.22

!

----------

As you can see i've made OSPF summarization at 2610 for routes from 1601 ( because 2610 ABR). But that i still see in the routing table:

2610#sh ip route ospf

131.108.0.0/16 is variably subnetted, 15 subnets, 2 masks

O 131.108.14.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.15.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.12.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.13.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.10.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.11.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.8.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.9.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.6.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.7.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.4.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.5.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.2.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.3.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

O 131.108.0.0/19 is a summary, 00:12:50, Null0

192.168.16.0/32 is subnetted, 1 subnets

O IA 192.168.16.1 [110/11] via A.B.C.111, 00:12:50, Ethernet0/0

-----------

Why i have

O 131.108.0.0/19 is a summary, 00:12:50, Null0

I suppose that it must be

O 131.108.0.0/19 is a summary, 00:12:50, Serial0/0.2

instead 13 lines like

O 131.108.5.1/32 [110/782] via 192.168.100.2, 00:12:50, Serial0/0.2

Why?

4 REPLIES
Bronze

Re: OSPF Summarization

I believe the summarization configuration on the 2610 only affects what it announces to other routers rather than what it puts in its own routing table.

New Member

Re: OSPF Summarization

But anyway how to reduce the size of routing tables. I think summarization is used for it!

Bronze

Re: OSPF Summarization

Summarization is done at abrs to reduce the routes downstream. If you want to reduce the routes on the 2600 remove the network statement from the 1600 for the loopbacks and redist connected. Then summarize in the 1600 since it will now be a asbr.

Re: OSPF Summarization

I agree.

Just an explanation "Why i have

O 131.108.0.0/19 is a summary, 00:12:50, Null0"

This is a discard route feature of route summarization.

See http://www.cisco.com/warp/customer/104/3.html#12.0 for details.

Regards,

Milan

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