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Webcast-Catalyst9k
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Default-network with or without default route ?

Is it needed to set a default route, i.e:

ip route 0.0.0.0 0.0.0.0 ISP_Address or Exit_interface

before issuing a default network command:

ip default-network subnet_number_of_connection_to_ISP

Or it is sufficient enough to let only the "ip default-network ..."?

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Hall of Fame Super Bronze

Re: Default-network with or without default route ?

Acknowledged...

I wanted to expand on what you wrote.

__

Edison.

7 REPLIES
Hall of Fame Super Bronze

Re: Default-network with or without default route ?

Please refer to the documentation and look under examples on the differences while performing either option:

http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_pi1.html#wp1012319

HTH,

__

Edison.

New Member

Re: Default-network with or without default route ?

Could you give me some more details, as I miss the difference?

Ex:

1) If a router has an interface declared with IP@ 10.10.0.2/16 connected to another router with IP@10.10.0.1, what is the difference between:

a)ip route 0.0.0.0 0.0.0.0 10.10.0.1

ip default-network 10.10.0.0

and

b)ip default-network 10.10.0.0

2) If a router has no directly connected interface in the 10.10.0.0 subnet, what is the difference between the 2 cases listed above?

Hall of Fame Super Bronze

Re: Default-network with or without default route ?

As per your example, the second option will only generate a default route when 10.10.0.0/16 is in the routing table.

The first option is generating a default route with the Quad 0 statement (first line of the command). The second line will only generate a default route if 10.10.0.0/16 is in the routing table so you need ip route 10.10.0.0 255.255.0.0 ISP_Gateway for the second line to work as intended.

__

Edison.

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New Member

Re: Default-network with or without default route ?

I hope I get it right, please correct me if I'm wrong:

1) There is no difference between the cases a) and b), the same router behavior will be observed in both cases

2) Case b) won't work as intended, i.e the default network won't be advertised nor used as a default route. However, it could work but only in case additionally there is a static route (not a default route) towards that default network defined. That is to say for point 2) if we use a default route or a static route together with the "ip default-network" won't make any difference.

Hall of Fame Super Bronze

Re: Default-network with or without default route ?

Basically a conditional advertisement of a default route, the default network command - that is.

It will advertise the Quad 0 to the rest of devices only when the default network is on the router's routing table.

Inserting a Quad 0 statement won't force a default network Quad 0 origination but the static Quad 0 on itself is doing it.

Keep in mind, the default network send the default route advertisement by using an IGP while the static route needs to be manually redistributed into the IGP for advertisement.

HTH,

__

Edison.

New Member

Re: Default-network with or without default route ?

Edison, sorry I didn't really catch the exact meaning...my level is quite basic, just started to read the CCNA books.

Could you please acknowledge/deny directly the statements I made in my previous post?

Thanks.

Hall of Fame Super Bronze

Re: Default-network with or without default route ?

Acknowledged...

I wanted to expand on what you wrote.

__

Edison.

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