Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

How to control OSPF NSSA Area type-7 LSAs P-bit?

It seems should use "summary-address network-address network-mask not-advertise"command.But when I use this command in ASBR,even the neighbours in NSSA area could not received the type-7 LSA,it seems this command didn't set the P-bit,but filtered the type-7 LSA?

1 ACCEPTED SOLUTION

Accepted Solutions
Purple

Re: How to control OSPF NSSA Area type-7 LSAs P-bit?

Yes, unfortunately... that's the same conclusion I reached.

The workaround here is to create a summary-address on the NSSA ABRs (that matches the summary-address on the NSSA ASBR) for the prefixes that we wish to suppress type-5 LSA generation for using the no-advertise keyword. In that case, the NSSA ASBR (which is not also an ABR) will generate type-7 LSAs for the required prefixes. The ABR (configured with no-advertise) will receive these type-7s and not translate them to type-5s (since we have configured the no-advertise keyword).

Hope that helps - pls rate posts that help.

Paresh.

5 REPLIES

Re: How to control OSPF NSSA Area type-7 LSAs P-bit?

Hello,

In "OSPF: Frequently Asked Questions" there is a question relating to your problem:

Q. Can I control the P-bit when importing external routes into a not-so-stubby area (NSSA)?

A. When external routing information is imported into an NSSA in a type 7 link-state advertisement (LSA), the type 7 LSA has only area flooding scope. To further distribute the external information, type 7 LSAs are translated into type 5 LSAs at the NSSA border. The P-bit in the type 7 LSA Options field indicates whether the type 7 LSA should be translated. Only those LSAs with the P-bit set are translated. When you redistribute information into the NSSA, the P-bit is automatically set. A possible workaround applies when the Autonomous System Boundary Router (ASBR) is also an Area Border Router (ABR). The NSSA ASBR can then summarize with the not-advertise keyword, which results in not advertising the translated type 7 LSAs.

So you should see the route in the NSSA.

There is also a stement in "Filtering in NSSA"

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a88.shtml#filternssa

Another case of filtering is when you need to prevent the type 7 LSAs from being translated outside the NSSA. In other words, when you want to control which type 7 LSAs get translated into type 5. For example, we have a RIP learned route 141.108.10.0/24 that is being injected into the OSPF NSSA area 1. We do not want this route to be leaked into the rest of the OSPF areas. We achieve this using the following configuration on either the NSSA ASBR or the NSSA ABR.

router ospf 1

summary-address 141.108.10.0 255.255.255.0 not-advertise

So you could give it a try on the ABR and see whether this works.

Hope this helps! Please rate all posts.

Regards, Martin

Purple

Re: How to control OSPF NSSA Area type-7 LSAs P-bit?

Hi,

While the CCO doco seems to suggest that the use of the 'no-advertise' keyword can be used to selectively set the P-bit, this does not work as expected. As the original poster observed, the 'no-advertise' keyword results in prefixes matching the summary-address being completely suppressed.

I have tested this "feature" with various IOS releases (up to 12.4) and have never been able to get it to work as I expect.

Hope that helps - pls rate the post if it does.

Regards,

Paresh

New Member

Re: How to control OSPF NSSA Area type-7 LSAs P-bit?

so we have the same conclusion and there is no way for IOS to set the P-bit?

Purple

Re: How to control OSPF NSSA Area type-7 LSAs P-bit?

Yes, unfortunately... that's the same conclusion I reached.

The workaround here is to create a summary-address on the NSSA ABRs (that matches the summary-address on the NSSA ASBR) for the prefixes that we wish to suppress type-5 LSA generation for using the no-advertise keyword. In that case, the NSSA ASBR (which is not also an ABR) will generate type-7 LSAs for the required prefixes. The ABR (configured with no-advertise) will receive these type-7s and not translate them to type-5s (since we have configured the no-advertise keyword).

Hope that helps - pls rate posts that help.

Paresh.

New Member

Would the Nssa-only work for

Would the Nssa-only work for this?

3660
Views
4
Helpful
5
Replies