From: Denise Donohue (fradendon@xxxxxxxxxxx)
Date: Mon Aug 05 2002 - 22:44:44 GMT-3
My favorite way to do this is to assign secondary addresses to the
interfaces that have subnet masks different from IGRP's. In your example
below, you'd assign a secondary to S1 of R4. Of course, you can only do
this if it won't overlap any other addresses on the router. Don't try to
assign the secondaries to the IGRP link - that leads to the issues you've
outlined
Denise
#9566
----- Original Message -----
From: "Volkov, Dmitry (Toronto - BCE)" <dmitry_volkov@ca.ml.com>
To: <ccielab@groupstudy.com>
Sent: Monday, August 05, 2002 8:48 PM
Subject: secondary on IGRP, redistr classless/IGRP
> Hello,
>
> Thinking about secondaries in IGRP as way to redistribute classles to
> classfull routing protocols,
> I came to intersting conclusion:
>
> Let say we have the following:
>
> 1) case r8(s0)-----igrp---/24----(s0)r4(s1)-----ospf--/29---- or even vice
> versa:
> 2) case r8(s0)-----igrp---/29----(s0)r4(s1)-----ospf--/24----
>
> several methods exist:
> 1) ospf piggy back on r4 - drawback - second routing process
> 2) tunnel between r8 & r4 with the same mask as ospf - drawback -
additional
> interfaces
> 3) secondary addresses between r8 & r4 ro reflect ospf prefix lengths -
> drawback - split horizon issue
> 4) making r4 ABR and use area range - not always possible...(ABR must be
> connected to area 0...)
> 5) summarize somewhere inside ospf if it possible...- not always possible
or
> permitted
> 6) static routes - usually not allowed in the lab.
>
> Usually in such scenarios we do mutual redistribution igrp <--> ospf...
> Taken into consideration that after 12.1(3) redistribute connected will
not
> work, because ospf is running on s1(r4),
> we can do the following : assign secondary address on s0(r4) ONLY !!!
> We can put many secondary there actually.
>
> Igrp is running on this secondary address, redistributes it to OSPF, it
> appears as LSA 5,
> after that we can put summary-address with any mask we want - shorter or
> longer than original ospf network -
> depending on which case we have 1) or 2) , no discard route external if
You
> want, and this summary will be
> redistributed to IGRP. Now R8 will know required network.
> Care should be taken to avoid black holes on R4.
>
> I think this way more clean than using tunnels or piggy back...
>
> I tried it using 12.1(15) - works fine.
>
> What do You think about it ? Did I miss something ??
>
>
> Thanks,
>
> Dmitry
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