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Bronze

use of summary-address command to flood default route

Hi everybody.

Let me start with an apology for repeating the question;  I am at totally lost as to how " system-address  0.0.0.0 0.0.0 " can be used to flood default route as my CCNP book has suggested.      Most of you have  mentioned  " default-information originate " command to flood default route in ospf domain,however it is not my goal.  The goal is  to see how  System-address command can be used to flood default route.

Below is my set up:

R1---200.200.200.0--ripv2--R2--199.199.199.0--ospf area 1----R3---198.198.198.0  ospf area 0---R4

R2 is AsBr, R3 is ABR connecting area 0 and 1.R4 is internal route in area 0.

R2  was creating lsa5 and flooding external routes(10.10.10.0/24,10.10.20.0/24)  in Ospf domain. However, When I configured " Summary-address 0.0.0.0 0.0.0.0" on R2 ,the routers(R3,R4) stopped learning external routes.

R2's routing table:

C    200.200.200.0/24 is directly connected, Serial0/0

O IA 198.198.198.0/24 [110/128] via 199.199.199.3, 00:01:22, Serial0/1

C    199.199.199.0/24 is directly connected, Serial0/1

     10.0.0.0/24 is subnetted, 2 subnets

R       10.10.10.0 [120/1] via 200.200.200.1, 00:00:03, Serial0/0

R       10.10.20.0 [120/1] via 200.200.200.1, 00:00:03, Serial0/0

R2's config:

router ospf 1

log-adjacency-changes

summary-address 0.0.0.0 0.0.0.0 not-advertise

redistribute rip subnets

network 199.199.199.0 0.0.0.255 area 1

!

router rip

version 2

network 200.200.200.0

no auto-summary

!

My question are:

1)  When I use " Summary-address 0.0.0.0 0.0.0.0"   , does it not  summarize  the routes 10.10.10.0/24,10.10.20.0/24 ?

2)  Why  the default route is not flooded when I  configure "  summary-address 0.0.0.0 0.0.0.0 command on R2 ?

Thanks and have a nice week

3 ACCEPTED SOLUTIONS

Accepted Solutions
Bronze

use of summary-address command to flood default route

Hi,

OSPF doesn't support "summary-address 0.0.0.0 0.0.0.0". So the above command cannot summarize your routes 10.10.x.0/24. Instead you have to explicity provide the summarized network for the summary-address command,

In this case you can issue command "summary-address 10.10.0.0 255.255.0.0" and the routes will be summarized to 10.0.0.0/16 network.

To flood default route into rip, on R2 you should use "default-information originate" under rip process.

Hope this helps.

Hall of Fame Super Gold

use of summary-address command to flood default route

Manju

I stand corrected (and +5 for you). I thought that the command was supported and just did not do what the original poster wanted it to do. The Command Reference in the URL that you supplied is clear in its statement that summary-address 0.0.0.0 0.0.0.0 is not supported.

Am I correct in assuming that you have tested and discovered that trying to use the summarization command for 0.0.0.0 results in no advertisement of redistributed routes? I am not authoritative on this but I believe that what is happening is this:

- there is code in processing summaries in OSPF that supresses advertisement of component routes when a summary address is configured. That code executes and  OSPF does not advertise the individual redistributed routes when summary-address 0.0.0.0 0.0.0.0 is configured.

- but the OSPF code does not support the summary-address 0.0.0.0 0.0.0.0 so that summary is not advertised.

HTH

Rick

Bronze

use of summary-address command to flood default route

- there is code in processing summaries in OSPF that supresses advertisement of component routes when a summary address is configured. That code executes and  OSPF does not advertise the individual redistributed routes when summary-address 0.0.0.0 0.0.0.0 is configured.

- but the OSPF code does not support the summary-address 0.0.0.0 0.0.0.0 so that summary is not advertised.

Thanks Rick for letting know this code 

7 REPLIES
Bronze

use of summary-address command to flood default route

Hi,

OSPF doesn't support "summary-address 0.0.0.0 0.0.0.0". So the above command cannot summarize your routes 10.10.x.0/24. Instead you have to explicity provide the summarized network for the summary-address command,

In this case you can issue command "summary-address 10.10.0.0 255.255.0.0" and the routes will be summarized to 10.0.0.0/16 network.

To flood default route into rip, on R2 you should use "default-information originate" under rip process.

Hope this helps.

Hall of Fame Super Gold

use of summary-address command to flood default route

I will take a somewhat different approach in answering this question. And I do not agree with Manju assertion that OSPF does not support summary-address 0.0.0.0 0.0.0.0. I believe that the command is supported but that it does not do what you want it to do.

The key thing to understand about summary-address in OSPF is that it is used to summarize routes being redistributed into OSPF on ASBR (and not anywhere else in the network). So if you configure summary-address 0.0.0.0 0.0.0.0 it will summarize any external routes being redistributed into OSPF to the 0.0.0.0/0 route. But it will NOT treat that as a default route.

summary-address 0.0.0.0 0.0.0.0 may work in other routing protocols (such as EIGRP) to advertise a default route but it does not have this function in OSPF. The specification of OSPF is very clear that to advertise a default route to neighbors you need to use default-information originate. You can find more explanation of OSPF summarization and default route in the OSPF Design Guide at this URL

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml#t28

HTH

Rick

Bronze

use of summary-address command to flood default route

Hi Richard,

I agree with you, OSPF does accepts the command summary-address 0.0.0.0 0.0.0.0 but it does not do what we want it to do.

This below link of command reference also says OSPF does not support summary-address 0.0.0.0 0.0.0.0

http://www.cisco.com/en/US/docs/ios/12_2/iproute/command/reference/1rfospf.html#wp1029504

On issuing command "summary-address 0.0.0.0 0.0.0.0" on ASBR, the redistributed routes are no more sent to ospf neighbors. Not sure why they are not sent, i believe(my guess) that this command behaves negatively, meaning, not to summarize or advertise any network (0.0.0.0) to neighbor .....some kind of implict deny(not-advertise).......

So we have to explicitly specify the networks we need to summarize and we get the summarized network to ospf neighbors.

Any views from your side would be much appreciated Richard, it will be good learning for me on understanding OSPF behaviours.

Thank you.

Hall of Fame Super Gold

use of summary-address command to flood default route

Manju

I stand corrected (and +5 for you). I thought that the command was supported and just did not do what the original poster wanted it to do. The Command Reference in the URL that you supplied is clear in its statement that summary-address 0.0.0.0 0.0.0.0 is not supported.

Am I correct in assuming that you have tested and discovered that trying to use the summarization command for 0.0.0.0 results in no advertisement of redistributed routes? I am not authoritative on this but I believe that what is happening is this:

- there is code in processing summaries in OSPF that supresses advertisement of component routes when a summary address is configured. That code executes and  OSPF does not advertise the individual redistributed routes when summary-address 0.0.0.0 0.0.0.0 is configured.

- but the OSPF code does not support the summary-address 0.0.0.0 0.0.0.0 so that summary is not advertised.

HTH

Rick

Bronze

use of summary-address command to flood default route

- there is code in processing summaries in OSPF that supresses advertisement of component routes when a summary address is configured. That code executes and  OSPF does not advertise the individual redistributed routes when summary-address 0.0.0.0 0.0.0.0 is configured.

- but the OSPF code does not support the summary-address 0.0.0.0 0.0.0.0 so that summary is not advertised.

Thanks Rick for letting know this code 

Bronze

use of summary-address command to flood default route

Thanks Manjo

Bronze

use of summary-address command to flood default route

Thanks Rick

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