From: zhuqingliu (zql@xxxxxxxxxx)
Date: Thu Feb 08 2001 - 11:06:59 GMT-3
> Justin,
>
> IGRP will send the default route to another router?
> If r1 has an default-network route to e1, then how to configure the router
s to let r2 and r3 learn that default-network? Suppose that all routers' interf
aces are in the same major network, such as 145.100.0.0.
>
> (e1)r1(s0)----(s0)r2(s1)---(s1)r3
>
> Thanks,
>
> Perry Zhu
>
> ----- Original Message -----
> From: Justin Menga <Justin.Menga@computerland.co.nz>
> To: <erickbe@yahoo.com>; Justin Menga <Justin.Menga@computerland.co.nz>; 'Chu
ck Larrieu' <chuck@cl.cncdsl.com>; CCIE_Lab Groupstudy List <ccielab@groupstudy
.com>
> Sent: Thursday, February 08, 2001 7:14 PM
> Subject: RE: Default routes and default networks - some experiments
>
>
> > Yep, I agree, this is what I found......the way that IGRP marks a
> > default-network is by marking the route as an EXTERIOR route. So if in the
> > scenario below R1 (S0) is the default network, of course R1 never sends thi
s
> > route to R2 (as it is the local connected network), hence R2 doesn't receiv
e
> > an EXTERIOR route.
> >
> > Regards,
> >
> > Justin Menga CCIE #6640 MCSE+I CCSE
> > WAN Specialist
> > Computerland New Zealand
> > PO Box 3631, Auckland
> > DDI: (+64) 9 360 4864 Mobile: (+64) 25 349 599
> > mailto: justin.menga@computerland.co.nz
> > web: http://www.computerland.co.nz
> >
> >
> > -----Original Message-----
> > From: Erick B. [mailto:erickbe@yahoo.com]
> > Sent: Thursday, 8 February 2001 7:50 p.m.
> > To: Justin Menga; 'Chuck Larrieu'; CCIE_Lab Groupstudy List
> > Subject: RE: Default routes and default networks - some experiments
> >
> >
> > Justin and Chuck,
> >
> > Was the directly connected network you had set as a
> > default-network a directly connected network in the
> > neighboring router or a IGRP learned route?
> >
> > If you have:
> >
> > (e1)r1(s0)----(s0)r2(s1)---(s1)r3
> >
> > If s0 subnet is default-network on r1, r2 will have it
> > as a directly connected network - not from IGRP. No
> > routes will be marked as gateway of last resort on r2
> > since the IGRP route isn't in main routing table
> > because the directly connected route has a lower admin
> > dist. r3 would see all routes but not have a gateway
> > of last resort either since r2 has no IGRP route
> > flagged as default in its main routing table.
> >
> > If e1 on r1 is default-network, and in IGRP process
> > then r2 will have a IGRP learned route in its table
> > and this will become the gateway of last resort. This
> > will also get passed along to r3 with r2 as next hop.
> >
> > In summary, if you're using default-network statements
> > then the route *has* to be learned dynamically
> > (IGRP/EIGRP) in the main routing table for the gateway
> > of last resort to be set or passed on to other
> > neighboring routers part of the IGRP/EIGRP process.
> >
> > HTH, Erick Bergquist - take 2 in May
> >
> > --- Justin Menga <Justin.Menga@computerland.co.nz>
> > wrote:
> > > Hi Chuck,
> > >
> > > I just tested your theory - doesn't sound right - I
> > > had a connected network
> > > configured as a default-network, no static or
> > > default routes - this was
> > > propagated to other IGRP neighbors.........
> > >
> > > You do have to wait for the next IGRP update for
> > > this change to propagate -
> > > or you can 'clear ip route *'
> > >
> > > Regards,
> > >
> > > Justin Menga CCIE #6640 MCSE+I CCSE
> > > WAN Specialist
> > > Computerland New Zealand
> > > PO Box 3631, Auckland
> > > DDI: (+64) 9 360 4864 Mobile: (+64) 25 349 599
> > > mailto: justin.menga@computerland.co.nz
> > >
> > >
> > > -----Original Message-----
> > > From: Chuck Larrieu [mailto:chuck@cl.cncdsl.com]
> > > Sent: Wednesday, 7 February 2001 6:49 p.m.
> > > To: CCIE_Lab Groupstudy List
> > > Subject: Default routes and default networks - some
> > > experiments
> > >
> > >
> > > Trying to pare down my inbox by getting rid of
> > > threads I have saved for
> > > experimentation. This one has me, and I am ashamed
> > > to admit it, but I can't
> > > figure out why.
> > >
> > > ISIS domain ----------------------------- Other
> > > Protocol Domain
> > > Ip route 0.0.0.0 0.0.0.0 --> <- default route or
> > > default network depending
> > >
> > > Ok, work out the bugs in my design. Everything is
> > > what it should be. Now
> > > then....
> > >
> > > When "other domain" is RIP and I do a
> > > default-information originate, I can
> > > ping all over the place and life is good.
> > >
> > > Same thing when "other domain" is OSPF
> > >
> > > But when "other domain" is IGRP, life is hell. Pings
> > > go nowhere. I can get
> > > to the other side of the connection to the ISIS
> > > domain but not beyond. I can
> > > get from the ISIS domain to the other edge of the
> > > IGRP domain but not
> > > beyond. The candidate default route is in all of the
> > > IGRP router routing
> > > tables.
> > >
> > > Same when "other domain" is EIGRP
> > >
> > > No changes were made on the ISIS side of the fence
> > > during any of these
> > > tests.
> > >
> > > I conclude that the problem is my misunderstanding
> > > of the ip default-network
> > > mechanism. Until this moment, I had believed that
> > > all that was required was
> > > that the default network be part of the routing
> > > process and appear in the
> > > routing table. This does not appear to be true. I am
> > > certain this is not a
> > > classful / classless issue because I am only using
> > > classful networks
> > >
> > > Well, a bit of research, and here is what I come up
> > > with. I don't like it,
> > > if for no other reason than it has been said here
> > > and elsewhere that this is
> > > grounds for losing points in the Lab:
> > >
> > > If the default network is a directly connected
> > > network, then the router
> > > itself still needs a default route.
> > > So, you must have an ip route 0.0.0.0 0.0.0.0
> > > [network]
> > > And then an ip default-network [network]
> > >
> > > Only in this manner can (E)IGRP then propogate the
> > > default.
> > >
> > > This also explains why my grand WAN in the brokerage
> > > firm actually worked
> > > the way it was supposed to, even though I was
> > > running EIGRP. I had the
> > > 0.0.0.0 0.0.0.0 static on each and every router.
> > >
> > > Obviously there are ways around this. Route maps of
> > > various flavors. Policy
> > > routing of varying degrees of cleverness. But this
> > > is one hell of a "gotcha"
> > > / "pitfall"
> >
> >
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