Convergence describes the process of when routers notice change in the network, exchange the information about the change, and perform necessary calculations to reevaluate the best routes.
A converged network describes the state of the network in which all routers have the same view on the network topology. Convergence is the normal and desired state of the network, and it is achieved when all routing information is exchanged between routers participating in the routing protocol. Any topology change in the network temporarily breaks the convergence until the change is propagated to all routers and best paths are recalculated.
By using a specific destination IP address type, the device can send traffic to one recipient, to selected recipients, or to all devices within a subnet at the same time. Routing protocols use different traffic types to control how routing information is exchanged. Selecting a destination IP according to different address types enables a device to send different types of traffic:
* Unicast: Unicast addresses are used in a one-to-one context. Unicast traffic is exchanged only between one sender and one receiver. Source addresses can only be a unicast address.
* Multicast: Multicast addresses identify a group of interfaces across different devices. Traffic that is sent to a multicast address is sent to multiple destinations at the same time. An interface may belong to any number of multicast groups. In IPv4, the reserved address space range for multicast addresses is 188.8.131.52–184.108.40.206. IPv6 reserved multicast addresses have the prefix FF00::/8.
* Anycast: An anycast address is assigned to an interface on more than one node.
When a packet is sent to an anycast address, it is routed to the nearest interface that
has this address. The nearest interface is found according to the measure of distance
of the particular routing protocol. All nodes that share the same address should
behave the same way so that the service is offered similarly regardless of the node
that services the request. A common use case for anycast is the Internet DNS server.
There are several instances of the same server across the world, and anycast enables
you to reach the nearest one by simply using the anycast destination address. The
arrows in the figure for anycast indicate that one destination is closer than the other.
* Broadcast: IPv4 broadcast addresses are used when sending traffic to all devices in the subnet. Information is transmitted from one sender to all connected receivers. Local broadcast address 255.255.255.255 is used when you wish to communicate with all devices on the local network. The directed broadcast address, which is the last IPv4 address in each subnet, allows a device to reach all devices in a remote network. IPv6 does not use a broadcast address, but uses multicast addresses instead.
IPv6 Address Types
2000::/3 to be global unicast address space that the IANA may allocate to the regional Internet Registries (RIRs). A global unicast address is an IPv6 address from
the global unicast prefix, equivalent to a public IPv4 address. These addresses are unique and globally routable.
FE80::/10 IPv6 link-local addresses. Any device that is an IPv6 device must at least have a link-local address, which is automatically configured by default using EUI-64 or the privacy extension, although the link-local address can be statically configured. Routers typically have statically configured link-local addresses to make the address more easily recognizable when looking at IPv6 routing tables and examining IPv6 routing protocol information. Nodes on a local link can use link-local
addresses to communicate; the nodes do not need globally unique addresses to communicate. Link-local addresses are not routable, therefore only stay on the link or network.
FF00::/8 Multicast addresses are heavily used in IPv6 as there are no broadcast addresses. There are both assigned and solicited node multicast addresses. Routing protocols make extensive use of the assigned multicast addresses. Assigned multicast addresses are similar to well-known multicast addresses. in IPv4 used by routing protocols such as EIGRP and OSPF. Solicited node multicast addresses are used by ICMPv6 Neighbor Discovery (ND) address resolution. Similar to ARP for IPv4, ND address resolution is used to map a Layer 2 MAC address to a Layer 3
FC00::/7 prefix is used to identify the unique local IPv6 unicast addresses. Unique local addresses are IPv6 unicast addresses that are globally unique and are intended for local communications. It is not expected to be routable on the global Internet and is routable inside of a limited area, such as a site. It may also be routed between a limited set of sites.
::1/128 The loopback address (0:0:0:0:0:0:0:1)
::/0 unspecified address.