CCIE – RS – L3 Technologies – Addressing Technologies – IPv4

In this section I assume that you have a CCNA level of understanding of IP addressing

Identify, Implement and Troubleshoot IPv4 Addressing and Subnetting

Address Types

Class A: to

Private range: –

Class B: to

Private range: to

Class C: to

Private range: to

Class D: to

Class E: to


Variable Length Subnet Mask

Allows for dividing ip addresses into subnets of different sizes

I make the following table before doing any subnetting math. This will help you figure out what the /cidr into subnet mask numbers will be without much effort. This will then help you figure out the network and broadcast range.

Screen Shot 2018-01-28 at 8.33.15 PM.png

Subnet Math: What are the network and broadcast addresses of the following range

/28 =

Network –, Broadcast

/19 =

Network –, Broadcast


Address Resolution Protocol

  • RFC 826
  • Protocol so that IP hosts can discover the MAC address of another device
  • L3 needs ARP to map IP network addresses to MAC hardware addresses so IP packets can be sent across networks
  • Cisco routers hold ARP entries for 4 hours by default
    • This can be changed under interface configuration: arp timeout ###

Proxy ARP

  • Allow L3 device to respond on behalf of actual destination for ARP
  • RFC 925 and 1027
  • Router makes itself available to hosts as a “gateway”
    • If a host is missing it’s default gateway the router will act as this
  • Enabled by default: disable on interface with – no ip proxy-arp

Reverse ARP (RARP)

  • Host attempting to find its own IP address, replaced DHCP
  • Maps IP address to known hardware address

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