From: Volkov, Dmitry (Toronto - BCE) (dmitry_volkov@xxxxxxxxx)
Date: Mon Aug 05 2002 - 19:56:56 GMT-3
Hello group,
It was mentioned many times, that placing secondary ip addresses with longer
mask f.e /29 on
interfaces /24 between igrp router and redistr router (running ospf/igrp)
could help to redistribute longer prefixes
from classless prot like OSPF to IGRP.
According to http://www.cisco.com/warp/public/105/41.html
Table 4: IGRP updates with secondary address on same major network as
primary
Split horizon Update source Update contents
Enabled Primary Subnets of primary/secondary (if known
through non-source interfaces). Other major networks, known through
non-source interface, summarized to major net
boundary.
Enabled Secondary None - No updates source from secondary.
So untill we disable split horizon on interfaces - NO updates source from
secondary.
Obviously, split horizon has to be disabled.
Somehow i got opposite result after putting secondary addresses /30:.
I have primary address 165.10.16.0/24 and secondary 165.10.1.4/30
and r8 gets ALL from r4 routes with mask /30.
I don't know why it's like that, but not /24
I have r8----/24 prim, /30 sec-------(igrp)-----r4-----ospf
major class (B) is the same everywhere.
So I got updates from secondary but nothing from primary.... IOS 12.1.(15)
ANY comments ???
Now I have the main question: How to better organize route filtering to
avoid loops, etc. in this case when we disable split horizon.
It's OK in the lab with a couple routes to make filtering on r4 to prevent
learning routes from r8 if these
routes were sent from r4 to r8 earlier and vice versa:
I guess it can be done using distribute list on each router with keyword
"gateway prefix-list in" -
something like that. However this way seems to be very not efficient when
You have a lot of routes.
What would be adequate way to do route filtering when You have to deal with
split horizon disabled ???
Thanks,
Dmitry
This archive was generated by hypermail 2.1.4 : Sat Sep 07 2002 - 19:48:17 GMT-3