The way I always understood it was that the default-information originate
command was used as a way to implement a default route in a single IS-IS
area network or to override the ATT default by the level 2 router connected
to another area. In an IS-IS network a level 2 router with an active level
2 adjacency with another area will send level 1 updates with the ATT bit
set. All level 1 routers that receive that update will install a default
route to the originator. This allows for inter area routing. However, if
there are multiple level 2 exit points within the area then a level 1 router
will always install a default to the closest exit point when only using the
ATT bit. This is not always the most efficient routing since level 1
routers have no idea about anything outside of their area and could send
traffic to the closest exit point instead of the shortest path. There are 2
ways around this. First, by using default-information originate you can
override which default gets installed in level 1 routers. Using this
command overrides defaults implemented with the ATT bit. Secondly you can
use route leaking which allows you to redistribute level 2 (backbone routes)
into level 1 areas.
HTH,
-Michael Cohen CCIE #6080
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
aaa aaa
Sent: Monday, April 30, 2001 12:17 AM
To: [EMAIL PROTECTED]
Subject: Re: IS-IS: Default route for L1 router [7:2485]
The adjancencies are formed, here clns routing is
automatically enabled when you enter routing isis, but
actually clns routing is not enabled at any interface,
so it will not try to build clns routing table.
According to Doyle's book, you need to do something to
let L1 knows the default route, for example, have clns
routing command *on* interface level. Or have L1L2
router generate a default route, but I have neither
one configured here.
Probably it's a new enhancement after 11.2. I don't
know.
--- andyh wrote:
> I'm not convinced that you have L1-L2 adjancencies
> as you think - you have a
> fairly random mix of circuit-types on the interfaces
> and is-types on the
> isis processes. Might want to do a "sh clns
> neighbors" on each router to
> see that the adjancencies are as you think they are.
> Don't recall quite how
> default/unspecified circuit-types will behave, but
> prolly worth checking
>
> Also, you *do* have clns routing enabled on all the
> routers.
>
> As far as loopbacks go, I would always run
> link-state protocols off Lo
> interfaces, even in the lab - gives you a few extra
> routes in the table to
> play with, nice to have non-direct-link routes in
> there to check your
> connectivity.
>
> This may well be a bug - as per Control Program, but
> good to be certain of
> what we're actually looking at first-off
>
> Andy
>
> ----- Original Message -----
> From: "Jerry Seven"
> To:
> Sent: Monday, April 30, 2001 3:30 AM
> Subject: Re: IS-IS: Default route for L1 router
> [7:2485]
>
>
> > Actually I have 1 L1/L2 which is in 12.1, and two
> L1 routers, one is in
> > 11.3, another is also in 12.1 same as L1/L2, same
> result, no luck.
> >
> > Here is the topology, the links are all ethernet:
> >
> > E0/1 F2/3
> G1/2
> > G1/2
> > ---------- NSX(L1) ----------- Corvette(L1/L2)
> --------------
> > Boxster(L1) ----------
> >
> > Here is related config(trimmed):
> > For NSX:
> >
> > version 11.3
> > clns routing
> > interface Ethernet0/1
> > ip address 192.20.20.2 255.255.255.0
> > ip router isis
> > router isis
> > net 01.0050.731d.1941.00
> > is-type level-1
> > NSX#show ip ro
> > i*L1 0.0.0.0/0 [115/10] via 192.20.20.1,
> Ethernet0/1
> > NSX#
> >
> > For Corvette:
> > version 12.1
> > clns routing
> > interface GigabitEthernet1/2
> > ip address 118.60.0.2 255.255.0.0
> > ip router isis
> > isis circuit-type level-1
> > interface FastEthernet2/3
> > ip address 192.20.20.1 255.255.255.0
> > ip router isis
> > isis circuit-type level-1
> > router isis
> > net 01.0030.b636.fe61.00
> >
> > For Boxster:
> > version 12.1
> > clns routing
> > interface GigabitEthernet1/2
> > ip address 118.60.0.1 255.255.0.0
> > ip router isis
> > router isis
> > net 01.00d0.97f2.8c8c.00
> > is-type level-1
> > Boxster#sh ip ro
> > i*L1 0.0.0.0/0 [115/10] via 118.60.0.2,
> GigabitEthernet1/2
> > Boxster#
> >
> > I have loopback if defined in each router, but I
> don't think it's related
> to
> > this.
> >
> > Thanks,
> > Jerry
> >
> > ----- Original Message -----
> > From: "andyh"
> > To: "Jerry Seven" ;
> > Sent: Sunday, April 29, 2001 6:36 PM
> > Subject: Re: IS-IS: Default route for L1 router
> [7:2485]
> >
> >
> > > I would go with what works in your lab!!
> > >
> > > seriously - try putting 11.3 on both routers,
> then 12.1 on both, and
> then
> > > reverse the 11.3/12.1 (so 12.1 on L1 and 11.3 on
> L2) and see what
> happens.
> > > I would imagine that you can get away with not
> enabling CLNS if you have
> > > IS-IS on just a P2P link - maybe not in a
> multi-router environment - are
> > you
> > > running off loopback interfaces, or just the
> physicals?
> > >
> > > I have had trouble with this in the past -
> albeit in a lab environment.
> I
> > > am always dubious about adding
> default-originates to Link-State
> protocols,
> > > especially in an ISP enviroment where you want a
> default-free
> > environment -
> > > messing with outbound route-maps is a pain in
> the arse .
> > >
> > > I will set this up in the lab again and see if I
> can nail it down once
> and
> > > for all.
> > >
> > > hth
> > >
> > > Andy
> > >
> > >
> > > ----- Original Message -----
> > > From: "Jerry Seven"
> > > To:
> > > Sent: Sunday, April 29, 2001 11:08 PM
> > > Subject: IS-IS: Default route for L1 router
> [7:2485]
> > >
> > >
> > > > Hi,
> > > >
> > > > I have a question on case study on Doyle
> P.655. It says that in order
> > to
> > > > have a default route for IS-IS L1 router, the
> L1/L2 can have CLNS
> > routing
> > > > enabled, or have the following command:
> > > >
> > > > default-information originate
> > > >
> > > > My question is after tried this in my lab, I
> found even WITHOUT this
> > > command
> > > > L1 router still got the L1 0.0.0.0/0 created,
> after I checked with
> IS-IS
> > > > database, L1/L2 router actually doesn't have
> it included in LSP, so it
> > > seems
> > > > that L1 router is able to parse that ATT bit
> and automatically create
> it
> > > in
> > > > routing table. I don't have CLNS routing
> enabled either. The IOS
> > version
> > > > on L1 router is 11.3 and on L1/L2 is 12.1.
> > > >
> > > > After searching on CCO, the explaination of
> "default-information
> > > originate"
> > > > command made me more confused, it says the
> default is only advertised
> in
> > > L2
> > > > LSPs if without a route-map, but in Doyle's
> case study router Brussels
> > > uses
> > > > this command and send it to Amsterdam which is
> a L1 route, which one
> is
> > > > correct ...
> > > >
>
=== message truncated ===
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