From: Yves Fauser (Yves@xxxxxxxxx)
Date: Wed Aug 08 2001 - 11:35:06 GMT-3
Rick, Group,
I just build a routing loop that is kinda funny :
R4
/ \
172.16.2.0/24 / \ 172.16.3.0/24
/ \
/ \
R3--------R2---------------- R1 ----- l0 10.1.1.1 /8
172.16.1.0/24 192.168.1.0/24 (ospf netw point-to-point)
On R1 run OSPF only
On R2 run OSPF to R1 and IGRP to R3 and R4
On R3 run IGRP to R4 and R2
On R4 run IGRP to R3 and R2
On R2 make the link to R4 a passive interface in IGRP
R1 advertises 10.0.0.0/8 to R2, R2 advertises 10.0.0.0/8 as an IGRP system rout
e
to R3, R3 advertises 10.0.0.0/8 as an IGRP system route to R2 (!passive
interface on R2!). Since IGRP has a higher AD, R4 is selected as the best route
to 10.0.0.0/8. The loop circles around one more time, R4 finds out that he gets
fooled by R3 (!counting to infinity!) and sends the route as inaccessible to R2
.
R2 enters into holddown. When holddown timer expires 10.0.0.0/8 via R4 gets
flushed. R2 enters 10.0.0.0/8 in its route table via OSPF and the whole process
restarts any.
Funny routing loop "perpedo mobile" !
Yves
Rick Foltz wrote:
> does anyone have a good example of a scenerio where a routing loop will form
> using 3 or 4 routers, and without messing with default timers and AD.
>
> Richard Foltz, CCNP-Voice, CCDP, MCSE+I, Network+, A+
> Project Team Leader, Network Services
> Smith Datacom
> 713-430-2184
> 3rd Attempt in RTP 11/2 and/or 3rd (CCIE with a * I Guess)
> **Please read:http://www.groupstudy.com/list/posting.html
**Please read:http://www.groupstudy.com/list/posting.html
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