Re: Auto Summary Revisited

Dear Bilal,

Autosummary takes the prefix back to its classful form for instance if
autosummary is enabled and you have any prefixes begining with 10.*.*.* on
the remote router they will be present as 10.0.0.0/8 (regardless if they
share the 2nd/3rd 8 bits the same). If it were 172.16.*.* it will be summed
back to 172.16.0./16(since 172 is in the Class B range). EIGRP will do
autosummary when crossing a classful boundary as per my memory, i.e. if the
scenario is as follows:

172.16.1.0 (R1)--172.16.2.0--(R2)--

Even if autosummary is enabled it will not kickoff and R2 will see the route
unsummarized (172.16.1.0/24)

However if you change the subnet connecting R1/R2 (10.10.10.0/24)
autosummary will kickoff and you will find the route on R2 summarized back
to (172.16.0.0/16)

I hope I got it right..

Best Regards,

On Sat, Sep 4, 2010 at 4:44 PM, Bilal Hansrod <bilal.hansrod_at_gmail.com>wrote:

> Hello Team,
>
> I'm trying to get my head around to understand EIGRP auto-summary. I have
> read some archive and various material, but unable to understand in detail.
> What I understood so far is that, EIGRP auto-summary will summarise routes
> that have same first 8 bit, For example,
>
> R1 has multiple loopbacks 10.0.0.0/24, 10.0.1.0/24, 10.1.0.0,
> 10.2.0.0/24,11.0.0.0/24, 11.1.0.0/24, 12.1.1.0/24, 12.2.2.0./24, so if the
> auto-summary is enabled, it will create a summary route in it's routing
> table and point to null interface to as a loop prevention technique.
> Then it will advertise 10.0.0.0/8, 11.0.0.0/8, 12.0.0.0/8 to neighbour
> routers. Is this correct understanding, if not can anyone please explain.
> What will happen if that was RIP with auto summary enabled.
>
> Regards,
>
> Bilal
>
>
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-- 
KJ
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