loop back advertisements

why do we advertise  loopback in interface on router for EIGRP? It make sense to advertise routers network with EIGRP, but why loopback0? 

Comments

  • MartinlMartinl ✭✭✭

    1. could be needed to connect to router from remote location. loopback is always up up, never down. advertise it and u will be able to connect to router.

    2. just to have  some networks in home lab. i.e., to practice summarization, add 10-20 loopbacks and advertise them thruough network

  • so there are many reasons to use the loopback function. My main reason for this is to make sure the router is functioning properly and that EIGRP is working properly. If you dont have any hosts connected to the router running EIGRP it is also good to think of that loopback as a host. this way, with two routers you can see if the neighbor relationship is working if the loopback of the other router shows up in the routing table (#show ip route).

  • leminhleminh ✭✭

    loopback is like an indetity of a specific router in the network. For example, a router has ten physical layer 3 interfaces, which interface you should remember to connect to this router? in this case, you can advertise the loopback of this router to the network so that it can be always referred back.

  • BugaziaBugazia ✭✭✭

    @Martinl said:
    1. could be needed to connect to router from remote location. loopback is always up up, never down. advertise it and u will be able to connect to router.

    1. just to have  some networks in home lab. i.e., to practice summarization, add 10-20 loopbacks and advertise them thruough network

    Advertising the Loopback has many Applications for it,some are really Advanced(like Multicast MSDP, or MPLS), and some are really simple:
    a Simple example would be BGP. and i will explain it:

    in the Fig. above, R1 and R2 are EIGRP Neighbors through both Fa0/0 and FA0/1 interfaces. and they have already advertised their Loopback0 interfaces (1.1.1.1, and 2.2.2.2) into EIGRP to each other.
    if Link Fa0/0 goes down, R1 can still reach Loopback0 through the other Interface, Fas0/1 (and Vice Versa )
    Now we wanna initiate BGP neighboring relationship between R1 and R2. and let's say that R2 is an ISP (internet Service Provider) and has access to the routes of the Entire Internet. and we wanna have R2 send all the Internet routes to R1 through BGP, we have 3 way for them to become neighbors:
    1) have a neighbor relationship through their Interface Fa0/0 IP addresses (but if FA0/0 goes down, all the Internet routes are gone, because the neighbor is gone)
    2) have a neighbor relationship through their Interface Fa0/1 IP addresses (but if FA0/1 goes down, all the Internet routes are gone)
    3) have a neighbor relationship through their Loopback 0 IP addresses :
    this is a viable solution, because BGP doesn't have to have a Direct link connection for a neighboring relationship (because it uses TCP for it's neighboring relationship), so this way if Fa0/0 goes down, R1 can still reach it's R2 neighbor (Loopback0 of R2) through FA0/1. and we have ourselves a backup .

    NOTE:
    this small article was intentionally wrote in simple words so that anyone can understand , even if they're new to Networking.

    If you need me, @Bugazia Me, and i'll be there .

  • IGP used Loopback IP as Router ID, so if you need particular router to be DR then you can assign higher IP for that domain, which can help granular Network design.

  • tmanitotmanito ✭✭✭

    Simply for management purposes

    Hope this helps!

    Timothy Q. Manito

  • Hi,
    Loopbacks is used for management,granular control and stability purposes.
    Example,
    do allow NTP or tacacs access only by one IP you define update source referencing loopback which is always UP.If you would use physical interface and when physical interface goes down you lose management to device.
    Another purpose is stability ,OSPF BGP EIGRP choose router-id using interfaces.When router-id is loopback it is stable.If it is physical interface address then device must elect new router-id.
    BGP runs over TCP sessions.If session is created between loopback it is stable,if between physical interfaces,disconnecting one cable could cause BGP to go down.

    HTH,

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