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When is "default-information originate" needed?

CSCO12157625
Level 1
Level 1

I searched online for this, but probably wasn't wording my correction properly.  I did find lots of examples, but no why-explanations.

I would like to know that when I have a connection that uses BGP, how do I know if 'd-i o' (default-information orginate) is needed within its BGP?  If I have two connections that share the same BGP, how do I know which of those connections needs the 'd-i o' within the configuration?  If I move one of the connections that shares the BGP to another router, how do I know if the 'd-i o' command needs to move or stay?  Is there something I should look for at the other end of either connection that would tell me "this one needs it"?

What level of certifcation would teach me this? 

3 Replies 3

John Blakley
VIP Alumni
VIP Alumni

Default-information is nothing more than setting a default route to your neighbors. For example, if Router A is peered with Router B, then Router A can send router B a default route pointing back to itself. In bgp, it would look like this:

Router A

neighbor default-originate

Router B would see:

B 0.0.0.0 0.0.0.0 Router A

Not sure about the "level of certification". Reading up on routing in general should help since other routing protocols use this same concept (OSPF comes to mind). So, basically you're telling your neighbor to use you as a default gateway.

You "need" a default route to handle all traffic that the router doesn't know about. When you send traffic to a destination, the router does a lookup to see if it knows about the destination and where/how to send the traffic to get it to it's destination (next hop). If the router doesn't have a match at all, it will use the default gateway that states, "if I don't know how to get here, I'm sending it to my default route in hopes that it knows how to get there."

HTH,
John

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HTH, John *** Please rate all useful posts ***

I understand default routes.  That's all "I don't know where this goes, so I'll push it that way."

But this is "  default-information originate" within a BGP config, not a 'neighbor...'.

Ah, the global under the bgp process. That one is used for when you have a default route already in the table via a static route. The default-information orignate only works with a redistribute static, and the static default route must be present. The neighbor command does NOT require an existing default route in the routing table though.

HTH,
John

*** Please rate all useful posts ***

HTH, John *** Please rate all useful posts ***
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