Second IP on Interface Why?

ULWizULWiz Member Posts: 722
in CCNA & CCENT
So as you can see my title pretty much explains it all. I am wondering why someone would set a second ip address to a interface? Is there a special reason being this and has anyone done this and why.

Thanks for the info ahead of time.
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  • mattrgeemattrgee Member Posts: 201
    There is a few reasons really, the most common you are likely to come across in the near future is for Frame Relay. A physical interface can be divided into multiple sub interfaces indicated with the .x notation, an ip address is then assigned to each sub interface.
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  • mikej412mikej412 Member Posts: 10,086 ■■■■■■■■■■
    http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfipadr.html#wp1001012

    https://supportwiki.cisco.com/ViewWiki/index.php/A_network_that_belongs_to_a_secondary_IP_address_is_not_advertised
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  • boostinbadgerboostinbadger Member Posts: 256
    You would run into this configuring router on a stick too; configuring one interface with several sub interfaces.
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  • AaronfbAaronfb Member Posts: 10 ■□□□□□□□□□
    We do it on one of our routers as a means of seperating two network IP ranges that use the same interface on the router. I work in a retail environment and our Corporate office is next to one of our stores. Our office runs using the private ip range 198.232.234.x while our store runs the private range 10.124.1.x. On our inside interface we have the ip 10.124.1.1 and 198.212.234.1 assigined. Works fine. We treat as two seperate networks - tho really they are the same.
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  • LBC90805LBC90805 Member Posts: 247
    Aaronfb wrote: »
    We do it on one of our routers as a means of seperating two network IP ranges that use the same interface on the router. I work in a retail environment and our Corporate office is next to one of our stores. Our office runs using the private ip range 198.232.234.x while our store runs the private range 10.124.1.x. On our inside interface we have the ip 10.124.1.1 and 198.212.234.1 assigined. Works fine. We treat as two seperate networks - tho really they are the same.

    Are you sure that is a Private Address???
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  • Gat0rveanGat0rvean Member Posts: 5 ■□□□□□□□□□
    LBC90805 wrote: »
    Are you sure that is a Private Address???

    The 198.x.x.x is not reserved for private addressing.
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  • TurgonTurgon Banned Posts: 6,308 ■■■■■■■■■□
    ULWiz wrote: »
    So as you can see my title pretty much explains it all. I am wondering why someone would set a second ip address to a interface? Is there a special reason being this and has anyone done this and why.

    Thanks for the info ahead of time.

    Useful when migrating from one IP address range to another across a site. Used it for this very same purpose years back.
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