Subject: Re: [OSPF] issue for default route originate in NSSA

From: "Pat Murphy - (650)329-4044" <[email-masked]>
Date: Thu, 17 May 2007 06:25:54 -0700 (PDT)

Jin,

Regarding

>RFC3101 2.5 Calculating type-7 as external routes (3) states:

>Else if the destination is a Type-7 default route (destination
>          ID = DefaultDestination) and one of the following is true,
>          then do nothing with this LSA and consider the next in the
>          list:

>            o  The calculating router is a border router and the LSA has
>               its P-bit clear.  Appendix E describes a technique
>               whereby an NSSA border router installs a Type-7 default
>               LSA without propagating it.
>
>            o  The calculating router is a border router and is
>               suppressing the import of summary routes as Type-3
>               summary-LSAs.
>            [NSSA]
>Suppose user perform following steps in scenario(there is one ABR and ASBR 
>in NSSA area):
>1)ASBR generate type-7 default route LSA to redistribute default route 
>from static route source.
>2)In ABR,Create type 7 default route LSA via command like 
>"default-route-originate" for this NSSA area.

>After step 2),the ABR calculation also should not consider type-7 default 
>route LSA redistribted by ASBRs?
>Am I missing something?please correct me.

The answer is yes; but only if the P-bit is clear. From your text it would
seem that you are using Cisco equipment. As far as I know Cisco IOS has no
way of setting/clearing the P-bit in a route-map and its Type 7 LSAs almost
always have the P-bit set. So most likely your ASBR's default route has the
P-bit set and the ABR will install it.

Setting/clearing the P-bit is a very useful feature as it allows an LSA's
global propagation attribute to be set by its originating router. Without
the ability to clear the P-bit, DoNotAdvertise ranges must be configured
on every ABR when global propagation is not desired. Also since the default
setting of the P-bit in RFC 3101 is clear, a RFC 3101 consistant
implementation must have the ability to set the P-bit.

Pat

_______________________________________________
OSPF mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/ospf

---

From: "Jin Wang" <[email-masked]>
Date: Fri, 18 May 2007 09:36:56 +0800

Thanks pat's response.
Consider below case:
Suppose user want to propagate the type-7 default route generated by ASBR 
in the whole AS scope and translate it into type-5 in ABR,so p-bit must be 
set.
Now if ABR install this default route,then routing loop maybe 
generated,because ASBR is also learning and installing default route 
generated by ABR.
So my opinion is that no matter p bit is set or not,ABR or ASBR should not 
install default route as long as default route has been manually 
configured to be genereated by themselves.

Best regards,

Wangjin
Accton Technology China Company Ltd.
Shanghai R&D Center 
TEL:+86-021-64859922*6227
E-mail:[email-masked]
Web Site:www.accton.com.cn

"Pat Murphy - (650)329-4044" <[email-masked]>
2007-05-17 21:25
 
        收件人：        [email-masked]
        抄送： 
        主题：  Re: [OSPF] issue for default route originate in NSSA

Jin,

Regarding

The answer is yes; but only if the P-bit is clear. From your text it would
seem that you are using Cisco equipment. As far as I know Cisco IOS has no
way of setting/clearing the P-bit in a route-map and its Type 7 LSAs 
almost
always have the P-bit set. So most likely your ASBR's default route has 
the
P-bit set and the ABR will install it.

on every ABR when global propagation is not desired. Also since the 
default

Pat

-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.