[Lsr] 答复: Question about OSPF (transit area routing loop)

[Aijun Wang <[e-mail]>]

Hi, Sergey:

 

If so, ABR-3 should also receive this SumLSA-4 for the ASBR(with cost 300), and then prefer the path via ABR-2 to reach ASBR(with cost 20).

Then there will be no loop then?

 

Or, how many SumLAS-4 will be advertised by ABR-1? If it selects and advertises only one (3 or 300), then the loop will not be emerged. 

Currently, it seems it advertises this SumLAS-4 with the cost 300 to RT_1 and with the cost 3 to ABR-3?

 

 

Best Regards.

 

Aijun Wang

China Telecom

 

发件人: [e-mail] [mailto:[e-mail]] 代表 Sergey SHpenkov
发送时间: 2020年2月26日 15:20
收件人: [e-mail]
主题: Re: [Lsr] Question about OSPF (transit area routing loop)

 

Acee,

 

Because ABR_1 creates SumLSA-4 for the ASBR not from the backbone area. The cost of SumLSA-4 for ASBR is 300.

 

Thanks,

Sergey

 

вт, 25 февр. 2020 г. в 22:44, Acee Lindem (acee) <[e-mail]>:

Hi Sergey, 

I don’t see why RT_1 wouldn’t go through ABR_1 to get to the ASBR. 

Thanks,

Acee

 

From: Lsr <[e-mail]> on behalf of Sergey SHpenkov <[e-mail]>
Date: Tuesday, February 25, 2020 at 2:38 PM
To: "lsr@ietf..org <mailto:[e-mail]> " <[e-mail]>
Subject: [Lsr] Question about OSPF (transit area routing loop)

 

Hi,

In section 16.3 of the OSPF RFC 2328 standard, it is stated that all ABR routers 

connected to a transit area are required to check the sumLSA contained within

this area in order to possibly improve the intra-area and inter-area backbone routes

for themselves.


See the picture:

The RT_1 and ABR_3 routers will use different paths to the ASBR router:

ABR_3 -> RT_1 -> ABR_1 -> ASBR = cost 3
RT_1 -> ABR_3 -> ABR_2 -> ASBR = cost 21

route loop between RT_1 and ABR_3

Please explain this situation

Thanks,
Sergey