Subject: Type-7 to Type-5 translation issue

From: Santosh Esale <[email-masked]>
Date: Sat, 14 May 2005 20:40:58 +0530

Hi guys,
           Mine topology is as below-

R1----Area 1 ------R2--------Backbone Area------R3

Initially Area 1 was type-5 capabale area and i was redistributing RIP
routes into area 1 on R1, so R2 and R3 have type-5 LSAs for all the
RIP routes.Now i changed
Area 1 to NSSA , So R1 is now orginating type-7 LSAs for all the RIP
routes into area 1 with P-bit set.

Now mine question is should R2 -

 1.     Prefer type 7 LSA over type-5 .
Convert type-7 LSA into type-5 LSA  and flood into backbone, which
aleardy have  type-5 LSAs for the same netwroks earlier orginated by
R1(not yet flushed as it will remain in backbone for MAX AGE)
(According to RFC 3101. section 2.5 stp 6 (e) ).

Disadvantage: The LSP database size will be doubled till MAX AGE time.
Advantage : simplicity

2. Prefer type-5 over type-7 .
Use type-5 LSA for calculating external routes till type-5 LSAs
advertised by R1 exists in backbone(MAX Age) , and once type is
flushed because of MAX age , USE type -7 now to calculate external
routes , and translate at this point from type-7 to type-5(RFC 1587
3.5 step 5)

Advantage : LSP database size is small.
Disadvantage: bit complex,but not much.

3. or its Implementations Specific.

Thanks in Advance

-- 
Santosh Esale

Member - Technical Staff

Riverstone Networks India Pvt. Ltd.

Email: [email-masked]

---

From: sujay <[email-masked]>
Date: Mon, 16 May 2005 15:33:31 +0530

I guess the point is whether to defer the Type-7 to 5 conversion until
Type 5 expires, to save database size.

In case if the Type-7 carries a forwarding address, it should be
converted into the correct Type-5 without delay.

Best regds,
~Sujay

-----Original Message-----
From: Mailing List [mailto:[email-masked]] On Behalf Of
Santosh Esale
Sent: Saturday, May 14, 2005 8:41 PM
To: [email-masked]
Subject: Type-7 to Type-5 translation issue

Hi guys,

Initially Area 1 was type-5 capabale area and i was redistributing RIP
routes into area 1 on R1, so R2 and R3 have type-5 LSAs for all the RIP
routes.Now i changed Area 1 to NSSA , So R1 is now orginating type-7
LSAs for all the RIP routes into area 1 with P-bit set.

 1.     Prefer type 7 LSA over type-5 .
Convert type-7 LSA into type-5 LSA  and flood into backbone, which
aleardy have  type-5 LSAs for the same netwroks earlier orginated by
R1(not yet flushed as it will remain in backbone for MAX AGE) (According
to RFC 3101. section 2.5 stp 6 (e) ).

2. Prefer type-5 over type-7 .
Use type-5 LSA for calculating external routes till type-5 LSAs
advertised by R1 exists in backbone(MAX Age) , and once type is flushed
because of MAX age , USE type -7 now to calculate external routes , and
translate at this point from type-7 to type-5(RFC 1587 3.5 step 5)

Thanks in Advance

-- 
Santosh Esale

Member - Technical Staff

---

From: Acee Lindem <[email-masked]>
Date: Mon, 16 May 2005 06:24:35 -0400

Hi Santosh,

Whether or not R1 purges its AS-external-LSAs prior to area 1 being
coverted from a regular area to an NSSA is implementation specific. 
However, the
timing of the conversion may be such that R1 is unable to purge them 
from the
OSPF routing domain. In all cases, R1 should immediately originate 
NSSA-LSAs
(type-7s) for redistributed routes. When R2 computes its external/NSSA 
routes
it should not use R1's AS-external-LSA since its path to the ASBR is not 
through
a regular area (see section 2.5 in RFC 3101).

Hope this helps,
Acee

---

From: Santosh Esale <[email-masked]>
Date: Mon, 16 May 2005 16:13:23 +0530

Hi Acee,
            U mean i should check whether the ASBR path is via type-5
capable area, and if its not USE NSSA external lsa for calculation and
do the type-7 to type-5 conversion immediately.

I do agree with this...but we are doubling the LSP database size, how
to slove it?

Thanks
Santosh

-- 
Santosh Esale

Member - Technical Staff

---

From: Acee Lindem <[email-masked]>
Date: Mon, 16 May 2005 10:20:49 -0400

Santosh,
See inline.

>do the type-7 to type-5 conversion immediately.
I'm saying that you should not use the AS-external-LSA if the path to
the ASBR is not
through a regular area (RFC 3101 uses the term Type-5 capable which I
really don't
like since we have descriptive names for the LSAs). If there is an
NSSA-LSA originated
by R1 it will be used by other routers in area 1 and R2 will do the
translation.

>I do agree with this...but we are doubling the LSP database size, how
You don't :^) In your example, R1 could attempt to flush all its
AS-external-LSAs prior
to converting to area 1 to a regular area. However, the network
administrator would have
to time the conversion such that the MAXAGE'ed AS-external-LSAs get
flooded to other
routers in area 1 prior to conversion (since AS scoped LSAs are not
flooded over NSSA
interfaces). In any case, they will not be used and it may be easier to
allow them to just
age out.

Hope this helps,
Acee

---

From: Santosh Esale <[email-masked]>
Date: Mon, 16 May 2005 20:00:14 +0530

Thankyou Acee.

Regards
Santosh

-- 
Santosh Esale

Member - Technical Staff