From: ccie2be (ccie2be@nyc.rr.com)
Date: Mon Jun 27 2005 - 08:15:41 GMT-3
Hey George et el,
Did you see this link?
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122
t/122t15/ftoadsup.htm
This is what got me thinking about these issues. I'm trying to better
understand how to recognize scenarios where I might need to use this
command, area X nssa translate, and it occurred to me that maybe if I'm
summarizing routes from the nssa, this command would be needed.
But, apparently not, unless maybe the ip address (or router-id) of the ASBR
is included as part of the summary. I'm not sure.
I saw one example where this command is needed but that scenario was so
contrived I couldn't imagine anything like that being on the lab.
In that very contrived example, filtering was configured on the ABR (the
router between the nssa and the backbone) so that the address of the ASBR
wasn't known to other routers in the backbone. Because of that filtering,
routes redist into the nssa became unreachable from the backbone.
To get around this, the area X nssa translate suppress-fa was used. What
this command did was change the fa (forwarding address) from the actual
address of the ASBR to 0.0.0.0 and by doing so made redist routes reachable
again because routers in the backbone will now forward traffic using the ABR
instead of the address of the ASBR which they don't know.
Personally, I thought this was an interesting issue and it highlighted
issues concerning what routes get advertised into the backbone from the stub
area which is probably a good to know before taking the lab.
Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
George Cassels
Sent: Monday, June 27, 2005 6:24 AM
To: 'ccie2be'; 'Sila Moni'; 'Group Study'
Subject: RE: using nssa and area X range together
Tim I would agree that the area range command could be used to summarize
the routes that are internal to the NSSA area to the backbone and could
also summarize routes coming from area 0 to the NSSA area since type 3s
are still allowed into that area.
George
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Sunday, June 26, 2005 8:18 PM
To: 'George Cassels'; 'Sila Moni'; 'Group Study'
Subject: RE: using nssa and area X range together
Hi guys,
Thanks for getting back to me on this.
So, here's my summary from your posts:
1. The area X range command can only summarize internal ospf routes
regardless of what type of stub network is configured.
2. Configuring any type of stub area doesn't prevent the use of the
area X
range command. The command can still summarize the ospf routes internal
to
that area.
Do you all agree with this?
Tim
-----Original Message-----
From: George Cassels [mailto:glcassels3@nc.rr.com]
Sent: Sunday, June 26, 2005 8:45 PM
To: 'Sila Moni'; 'ccie2be'; 'Group Study'
Subject: RE: using nssa and area X range together
Sila,
Take a look at my response to Tim...I used the summary-address
command and it aggregated the routes going to another ospf area 0
router.
George
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Sila Moni
Sent: Sunday, June 26, 2005 7:31 PM
To: ccie2be; Group Study
Subject: Re: using nssa and area X range together
You can't summarize external routes (I don't have a
rack to lab it out to confirm). Since R2 has only one
exit point, you can use LSA 3 filter to deny all
routes except for the default prefix. Example:
ip prefix-list LSA-FILTER deny x.x.x.x/24
ip prefix-list LSA-FILTER permit 0.0.0.0/0 le 32
!
router ospf 1
area 1 filter-list prefix LSA-FILTER in
--- ccie2be <ccie2be@nyc.rr.com> wrote:
> Hi guys,
>
> This is an interesting scenario - at least I hadn't
> thought much about this
> previously.
>
> Let's say you have this topology:
>
> IGP R1 nssa R2 area 0 R3
>
>
> R1 is redist routes from another IGP into OSPF. Can
> I use the area X range
> command on R2 to summarize routes learned from the
> IGP redist into the nssa
> area so that the backbone doesn't have all those
> specific routes from the
> other routing protocol?
>
>
> And, more generally, do I need to be concerned about
> any restrictions on
> using the area X range command to summarize routes
> into the backbone area
> depending upon what type of stub area is configured?
>
> What I find interesting about this scenario is that
> typically when I think
> about what type of stub area to configure, I'm
> concerned about what routes
> are advertised into the stub area from the backbone.
>
> In this scenario, it's just the opposite. Here the
> concern is what routes
> area advertised from the stub area into the backbone
> area.
>
> (I don't have access to any routers at the moment to
> lab this up.
>
> TIA, Tim
>
>
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