IPv4 Addressing Overview

IPv4 uses a 32-bit addressing system designed for use in packet-switched networks. IPv4 routing is enabled by default on SLX-OS devices that operate at Layer 3 and cannot be disabled.

IPv4 is an Internet protocol used to deliver packets of data from a source to a destination across an interconnected system of networks. IPv4 uses a fixed-length 32-bit addressing system and is represented in a 4-byte dotted decimal format: x.x.x.x.

IP uses four main mechanisms to provide service:

Type of Service (ToS)—Indicates the Quality of Service (QoS) required for a specific traffic type or network and enables a higher priority to be given to voice traffic, for example, that is more sensitive to dropped packets.
Time to Live (TTL)—The time period for which a packet can exist before it reaches its final destination. If the TTL expires before the packet reaches its destination, the packet is destroyed. The period is set by the packet sender.
Options—Control mechanisms such as timestamps, security, and other special routing functions that are optional.
Header Checksum—Used to verify that the packet contents have transmitted correctly. If the checksum algorithm fails, the packet is dropped immediately.

An IP address has two sections:

Network—Identifies the network on which the device is configured.
Host—Identifies the host device.

IPv4 does not provide a reliable communication function. No acknowledgments are sent and the only error control is the header checksum. There are no flow-control mechanisms or retransmissions. Internet Control Message Protocol (ICMP) may be used to report any errors.

IP interfaces

SLX-OS devices that operate at Layer 3 allow IP addresses to be configured on the following types of interfaces:

Ethernet ports
Virtual routing interfaces
Loopback interfaces

You can configure up to 128 IP addresses on each interface.

Note

After you configure a port as a "switchport," you cannot configure Layer 3 interface parameters on that port. The parameters must be configured on the appropriate virtual routing interface.

IP unnumbered interfaces

With large numbers of routers and redundant Layer 3 interfaces, many IP addresses are consumed just to configure the network itself. Using /31 masks reduces the consumption of addresses, but two IP addresses are still consumed per interface. Using unnumbered interfaces greatly reduces the number of IP addresses that are consumed in the configuration of the network.

For more information, see IP unnumbered interface.