From: Toh Soon, Lim (tohsoon28@gmail.com)
Date: Tue Sep 11 2007 - 23:52:12 ART
Hi NET HE,
I have labbed it up. My topo as follows:
-----Area0----- R5 -----Area 1 NSSA----- R7 -----Area 1 NSSA----- R8
R5 & R8 both have the "area 1 nssa default-information-originate" command.
R8 does not source the N2 default route until I configured a static default
route on it. You are right.
R5-R7 is FastEthernet. R7-R8 is a serial link.
R5#sh ip os da
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
0.0.0.0 5.5.5.5 713 0x80000001 0x00EADD 0
0.0.0.0 8.8.8.8 811 0x80000001 0x002830 0
R5#sh ip os b
i 8.8.8.8 [65] via 150.50.7.7, FastEthernet0/0, ASBR, Area 1, SPF 11
R7#sh ip os da
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
0.0.0.0 5.5.5.5 852 0x80000001 0x00EADD 0
0.0.0.0 8.8.8.8 950 0x80000001 0x002830 0
R7#sh ip os b
i 8.8.8.8 [64] via 150.50.5.69, Serial0/0, ASBR, Area 1, SPF 4
i 5.5.5.5 [1] via 150.50.7.5, FastEthernet0/0, ABR/ASBR, Area 1, SPF 4
Examing their routing tables, R5 learns O*N2 0.0.0.0/0 from R7. R7 learns
O*N2 0.0.0.0/0 from R5! I believe this is due to R7 choosing the lowest cost
to the advertising ASBR since it's an External Type-2 route. Obviously
routing loop is formed between R5-R7 for external addresses.
Any comments?
Thank you.
B.Rgds,
Lim TS
On 9/11/07, NET HE <he_net@hotmail.com> wrote:
>
> - ASBR does need have a default route first, then inject type-7 default
> route into NSSA area. And depends on metric-type, it can be N1 or N2.
> (nssa
> default-information originate)
> - ABR unconditionally inject a default route using "nssa
> default-information
> originate), it is a type-7 LSA as well.
> - ABR unconditionally inject a default route using "nssa no-summary", but
> it
> is a type-3 LSA.
>
> Best Regards,
> Net (Xin) He
>
> >X-OriginalArrivalTime: 11 Sep 2007 02:07:27.0120 (UTC)
> >FILETIME=[803CA900:01C7F418]
> >
> >Hi NET HE,
> >
> >Thanks for your reply.
> >
> >I have never tried configuring "area X nssa
> default-information-originate"
> >on an internal router (non-ABR) in an NSSA. When used on the ABR, it
> >unconditionally sources an N2 default route into the NSSA by default. If
> >applied on an internal router in the NSSA, does the router have to have a
> >default route (static route or learned from other IGP) in order to inject
> >the Type-7 default?
> >
> >
> >
> >Thank you.
> >
> >B.Rgds,
> >Lim TS
> >
> >
> >
> >On 9/11/07, NET HE <he_net@hotmail.com> wrote:
> > >
> > > In addition, cmd "area 23 nssa no-summary" can only be used at ABR
> > > routers,
> > > but cmd "area 23 nssa defalut-information-originate" can be used at
> ABR
> > > routers or ASBR routers, which are located in NSSA area, and inject
> >type-7
> > > LSA.
> > >
> > >
> > > Best Regards,
> > > Net (Xin) He
> > >
> > > >X-OriginalArrivalTime: 10 Sep 2007 23:08:20.0266 (UTC)
> > > >FILETIME=[7A9CE0A0:01C7F3FF]
> > > >
> > > >with the "no-summary" option, the ABR will inject a default route and
> > > >it will also block all LSA type 3s, therefore, the routers in the
> NSSA
> > > area
> > > >will NOT see the inter-area routes. But with the
> "default-information"
> > > >keyword, the ABR will inject a default route but it won't block LSA
> >type
> > > 3s
> > > >and as a result of that the routers within the NSSA area will still
> > > >maintain
> > > >LSA type 3s (Inter-Area routes).
> > > >
> > > >On 9/10/07, Carlos Trujillo Jimenez <nergal888@hotmail.com> wrote:
> > > > >
> > > > > Hi all.
> > > > >
> > > > > I have a NSSA area, the routers from the NSSA dont need
> reachability
> > > > > information about the external prefixes, that means I must inject
> a
> > > > > default
> > > > > route for the external prefixes reachability.
> > > > >
> > > > > I have two options to do it.
> > > > >
> > > > > at the area border router:
> > > > >
> > > > > area 23 nssa no-summary
> > > > >
> > > > > or
> > > > >
> > > > > area 23 nssa defalut-information-originate
> > > > >
> > > > > Is there any significant difference between both options?? both
> > > works,
> > > >by
> > > > > a
> > > > > show ip route at the internal routers of the nssa area I can see
> an
> > > > > external
> > > > > IA default route with both commands, theres is no difference, any
> > > ideas
> > > > > when
> > > > > one of these options can and cannot be used???
> > > > >
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