EIGRP IP Default-Network - Confusion Reigns !!!

Hello All,

We have had numerous discussions on the use of the IP Default-network
command in EIGRP, but I would like to ask a couple of questions which I
couldn't find answers to anywhere on the web.

1) Cisco's documentation and quite a few books say that with EIGRP, the
network which has been configured as the default-network is advertised and
flagged as an external route. Here is a link to the Cisco Doc -

http://www.cisco.com/en/US/docs/ios/iproute_pi/configuration/guide/iri_ip_prot_indep_ps6441_TSD_Products_Configuration_Guide_Chapter.html#wp1056283

This does not seem correct to me . If you read Narbik's puzzles about this
command a couple of weeks back or simply connect two routers back to back
running EIGRP, you would find that the network being advertised as a
candidate-default is being sent and learned as an EIGRP internal route.
Please note that the network is being advertised using the network statement
so i am not talking about routes being genuinely advertised as external
routes using redistribute commands. So the question is- what am I missing
here ?

2) Considering the above is incorrect and the candidate default route can be
an internal route, what bit in the update packet tells the receiving router
that the route is a candidate default. An EIGRP update having an external
TLV contains the Flag field which tells the receiving router whether the
route is supposed to be a candidate default. Doing a packet dissection using
wireshark , I don't seem to find anything in an Internal EIGRP update that
would make the router decide whether to insert the route as a candidate
default or not.

Awaiting your valuable responses !!

Regards,
Ravi

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Received on Sat Dec 04 2010 - 04:15:30 ART