BGP network command

Answered Question
Jul 22nd, 2010
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If I enter the following two network commands:


network 172.20.0.0

network 172.16.3.0


Will BGP pick up that the 172.20.0.0 network is a /16 and that the 172.16.3.0 is a /24 or do i need to use the mask portion of this command?


Thanks

Correct Answer by francisco_1 about 7 years 6 days ago

The behavior of the network command varies depending on whether auto-summary is enabled or disabled. When auto-summary is enabled, it summarizes the locally originated BGP networks (network x.x.x.x) to their classful boundaries (auto-summary is enabled by default in BGP).


When auto-summary is disabled, the routes introduced locally into the BGP table are not summarized to their classful boundaries.


Francisco.


See this http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800945ff.shtml


Francisco

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milan.kulik Thu, 07/22/2010 - 08:26
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Hi,


BGP network command is expecting a classful network used.

network 172.20.0.0

is OK, as 172.20.0.0 is a class-B network.

For a classless prefix, you need to use

network 172.16.3.0 mask 255.255.255.0

command form.


IMHO,

network 172.16.3.0

is treated as a configuration error - surprisingly does not bring any error message/warning unlike "network 172.16.3.0 mask 255.255.0.0" does.


HTH,

Milan

Correct Answer
francisco_1 Thu, 07/22/2010 - 08:42
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The behavior of the network command varies depending on whether auto-summary is enabled or disabled. When auto-summary is enabled, it summarizes the locally originated BGP networks (network x.x.x.x) to their classful boundaries (auto-summary is enabled by default in BGP).


When auto-summary is disabled, the routes introduced locally into the BGP table are not summarized to their classful boundaries.


Francisco.


See this http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800945ff.shtml


Francisco

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