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:
0.0.0.0 to 127.255.255.255
Private range: 10.0.0.0 – 10.255.255.255
Class B:
128.1.0.0 to 191.255.255.255
Private range: 172.16.0.0 to 172.32.255.255
Class C:
192.0.1.1 to 223.255.254.255
Private range: 192.168.0.0 to 192.168.255.255
Class D:
224.0.0.0 to 239.255.255.255
Class E:
240.0.0.0 to 254.255.255.255.255
VLSM
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.
Subnet Math: What are the network and broadcast addresses of the following range
192.168.12.0/28
/28 = 255.255.255.240
Network – 192.168.12.0, Broadcast 192.168.12.15
172.27.25.0/19
/19 = 255.255.224.0
Network – 172.27.0.0, Broadcast 172.27.31.255
ARP
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