GroupStudy.com GroupStudy.com - A virtual community of network engineers
 Home  BookStore  StudyNotes  Links  Archives  StudyRooms  HelpWanted  Discounts  Login
RE: OSPF external type-2 route load balance posted 08/31/2007
[Chronological Index] [Thread Index] [Top] [Date Prev][Date Next] [Thread Prev][Thread Next]


Actually, section 16.4 (16.4.1 as well) describes the process quite well
about External LSA Path selection...

http://www.faqs.org/rfcs/rfc2328.html

Every once and a while, it's good to look at the rules.  When in doubt, they
win.  :)

 
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
VP - Technical Training - IPexpert, Inc.
IPexpert Sr. Technical Instructor
 
A Cisco Learning Partner - We Accept Learning Credits!
 
smorris@xxxxxxxxxxxx
 
Telephone: +1.810.326.1444 
Fax: +1.810.454.0130
http://www.ipexpert.com
 

-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of Gary
Duncanson
Sent: Friday, August 31, 2007 3:58 PM
To: Scott Smith
Cc: ccielab@xxxxxxxxxxxxxx; Sadiq Yakasai; ISolveSystems; Herbert Maosa;
Joseph Brunner
Subject: Re: OSPF external type-2 route load balance

Thanks for that Scott.

Looks like this demonstrates this rather well, at least how I read it.

>From OSPF Design Guide on CCO.

sic 'External routes fall under two categories, external type 1 and external
type 2. The difference between the two is in the way the cost (metric) of
the route is being calculated. The cost of a type 2 route is always the
external cost, irrespective of the interior cost to reach that route.'

Rgds
Gary
----- Original Message -----
From: "Scott Smith" <hioctane@xxxxxxxxx>
To: "Sadiq Yakasai" <sadiqtanko@xxxxxxxxx>
Cc: "Joseph Brunner" <joe@xxxxxxxxxxxxxxxxxxx>; "Herbert Maosa" 
<asawilunda@xxxxxxxxxxxxxx>; "ISolveSystems" <support@xxxxxxxxxxxxxxxxx>;
"Cisco certification" <ccielab@xxxxxxxxxxxxxx>
Sent: Friday, August 31, 2007 7:49 PM
Subject: Re: OSPF external type-2 route load balance


> Bingo!
>
> A1 learns 100.100.100.0 from both 10.43.1.61 & 10.43.1.73.
>
> Before - BW 1536 to both ASBRs
>
> A1(config-router)#do sh ip route ospf
>     100.0.0.0/24 is subnetted, 1 subnets
> O E2    100.100.100.0 [110/20] via 10.43.1.61, 00:00:36, Serial1/0.1
>                                 [110/20] via 10.43.1.73, 00:00:36,
> Serial1/0.2
>
>
> After - Dropped BW to 512 on s1/0.1
>
> A1(config-subif)#do sh ip route ospf
>     100.0.0.0/24 is subnetted, 1 subnets
> O E2    100.100.100.0 [110/20] via 10.43.1.73, 00:00:06, Serial1/0.2
>
>
> Then changed BW back to 1536 on s1/0.1 (now both are equal again)
>
> A1(config-subif)#do sh ip route ospf
>     100.0.0.0/24 is subnetted, 1 subnets
> O E2    100.100.100.0 [110/20] via 10.43.1.73, 00:00:02, Serial1/0.2
>                                 [110/20] via 10.43.1.61, 00:00:02,
> Serial1/0.1
>
> The metric is a constant 20, however, for the externals OSPF also uses 
> the cost to the ASBR.
>
> --
> Scott
> CCIE #17040 (R&S)
>
>
> On 8/31/07, Sadiq Yakasai <sadiqtanko@xxxxxxxxx> wrote:
>> Can you show the Type 4 LSA database as well?
>>
>> I think the cost to the ASBR has a role to play in selecting 2 Type 5 
>> LSA's reporting the same prefix.
>>
>> I am not quite sure about this though.
>>
>> _____________________________________________________________________
>> __ Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>
> ______________________________________________________________________
> _ Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

_______________________________________________________________________
Subscription information may be found at: 
http://www.groupstudy.com/list/CCIELab.html