Loopback interface with 32 bit mask

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Aug 27th, 2012
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Can any one explain me , why do we use loopback interfaces with 32 bit subnet mask only?  Is there any special reason behind that.

Likewise we use loopback interface IP addresses  in BGP network config and we advertise it using network command . why ?



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cadet alain Mon, 08/27/2012 - 10:36
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we usually use /32 to not waste ip addresses. in BGP loopabcks are used for the peering between iBGP peers or sometimes netween eBGP peers having redundant connection but it's not mandatory to announce the loopback into BGp process.



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Alessio Andreoli Mon, 08/27/2012 - 10:38
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Hi Ajay,

the loopback is not only an interface or a logical host or a tool for troubleshooting. A loopback is a TYPE OF NETWORK  as much as a point-to-point network, point-to-multipoint network and so on. This is mainly a cisco implementation of it and especially works in this way with OSPF.

It is a curios experiment you can do to set a loopback with a /24 address and to see on the other end of your OSPF domain how the same loopback is advertised. You will find that, if you do not further modify the loopback configuration, your /24 subnet will be advertised as a /32!!!

hope being clear enough!!





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