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In the following network, why should we pick the subnet mask /30 for the internet port of Edge Router 1? Since the wireless access point Edge Router 1 needs to connect to 3 hosts in LAN 1, a subnet mask of /30 that can only cater to 2 hosts is certainly not enough, isn't it? Network architecture

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    This smells like homework so your question will more than likely be closed. However, its always best practise to only use exactly what you need in terms of IP space. The connection between Edge Router 1 and Wan Router 1 only needs an IP on each end, in theory you can use a /31 to achieve this too. It is assumed that Edge Router 1 here will perform NAT for all devices behind it on the LAN.
    – ditrapanij
    Oct 19 at 7:53
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    Sadly homework and certification questions are off topic here.
    – Ron Trunk
    Oct 19 at 12:01
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The /30 subnet mask provides the most efficient use of IP addresses by not wasting any IP addresses when it is applied to a point to point network connection.

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    A point-to-point network connection should use /31 rather than /30 subnet mask, isn't it? Oct 19 at 8:52
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    /30 gives you 2 usable IP addresses if you don't use the broadcast address you might use /31. packetlife.net/blog/2008/jun/18/… Oct 19 at 9:44
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    Some network devices (mostly older devices) don’t allow the use of /31, so /30 is more commonly used even in PTP scenarios as it’s an efficient and effective compromise.
    – Jesse P.
    Oct 19 at 11:41

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