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Secondary IP Address

Discussion in 'General Cisco Certifications' started by Macfly!, Mar 9, 2011.

  1. Macfly!

    Macfly! Bit Poster


    have been using the network simulator software from cisco press to prep for my ICND2 exam and came accross one of the labs today where I had to enter in a secondary IP address to an interface, the lab didnt really explain much about it.

    So now I am thinking that I can have 2 PC on completely different subnets, both cannected to the same switch with different default gateways set i.e the IP of each, main and secondary on the router interface and I should be able to route between the 2 and over the network?

    I plan to hook this up with some real kit tomorrow to test, but it got me thinking because this is the first time I have come accross this, I had a one week ICND2 course and dont recall it mentioned then, or in anything else I have read so far, also thinking could something like this come up during the exam, and would this type of thing be used for real?

    A lot of the teachings have basically led me to believe that everything should be in the same subnet per interface, other than vlans and sub interfaces, so would be good if anyone here in the know could explain a little more?

    Certifications: CCENT
  2. Simonvm

    Simonvm Kilobyte Poster

    The ICND2 book presents it as one of the ways to expand your network without the need to change the IP addressing scheme already in place.

    Sounds pretty correct.

    That said, you already know enough about it for the exams I guess.
    The only difference is you configure two IP addresses, the second having "secondary" after the command.
    Certifications: MCITP: EST, MCDST, MCTS, A+, N+, CCNP, CCNA Wireless
  3. BosonMichael
    Highly Decorated Member Award

    BosonMichael Yottabyte Poster

    There's one big thing you need to remember with secondary IP addresses: although EIGRP supports routing over secondary IP addresses, EIGRP will not establish a neighbor relationship over secondary IP addresses: link
    Certifications: CISSP, MCSE+I, MCSE: Security, MCSE: Messaging, MCDST, MCDBA, MCTS, OCP, CCNP, CCDP, CCNA Security, CCNA Voice, CNE, SCSA, Security+, Linux+, Server+, Network+, A+
    WIP: Just about everything!
  4. Macfly!

    Macfly! Bit Poster

    Thanks for the info guys, will read up on this in more detail. I didnt get time today to hook this up for real, so tried to do it in packet tracer only to find out that Packet Tracer doesnt support secondary IP addresses :cry::cry:


    Certifications: CCENT

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