From: ccie candidate (ccie1@xxxxxxxxx)
Date: Sat Jul 13 2002 - 06:30:51 GMT-3
the wrong mask which you have used is actual create a summary address for the
default route .
0.0.0.255 if you match it against the subnet you used ..it will lead to 0.0.0.0
/0.
the comment of Mas kato is worth to try if other masks will create also the sam
e default network
--On Fri, 12 Jul 2002 13:58:22 Mayande P.Gowon wrote: >I'm hoping someone will be able to provide me with some insight >on the following: > I was working on a redistributing IGRP & OSPF lab the other night when I came >across something that I'm unclear about any thoughts or explanations would be >appreciated: > > lo0--A----B----C-----D----lo0 >There were 4 routers - A, B, C, D. The serial interfaces between A & B are in >OSPF area 1, the serial interfaces between B & C are in OSPF area 0, and the >link between C and D are IGRP. >This is a VLSM/FLSM scenario (IGRP has /24 mask, and OSPF has various). The >lo0 of A is being redistributed (redistribute connected subnets) into OSPF, >because it is a /28 I performed a summary-address command to advertise it as a >/24 to IGRP. All of this worked fine in the end without issue...but the first >time I performed the summary command I accidently used the wrong subnet mask. > > Instead of "summary-address 152.1.11.0 255.255.255.0" I typed >"summary-address 152.1.11.0 0.0.0.255". This created a default null route >(0.0.0/0) which propogated across the entire OSPF network! In other words >routers B and C now had a default gateway pointing to the null route 0.0.0.0/0 >on router A. >This seems like a neat trick as this default gateway gets propogated across >the OSPF network and without creating a static route. I however don't really >understand what caused this to happen...any insight?
This archive was generated by hypermail 2.1.4 : Sat Sep 07 2002 - 19:36:28 GMT-3