Discover how the four traffic types—unicast, broadcast, multicast, and anycast—vary. Understand the fundamental differences between the three dynamic routing protocol types—distance-vector, link-state, and path-vector.
- [Instructor] Routing protocols fall into a few different categories. Distance vector, link state and path vector. Distance vector protocols like the routing information protocol are based on a hop count and in RIP the network link tops out at 15 hops. They also send the full route table to peers at regular intervals, whether there is a need for updates or not. Distance vector protocols also generally have a much longer convergence time.
Cisco's once proprietary Enhanced Interior Gateway Routing Protocol is considered an advanced distance vector or hybrid distance vector protocol. While other vendors are free to utilize EIGRP, it doesn't behoove them to spend time or money to implement it in their systems, so it is effectively Cisco only. It is considered hybrid because it not only converges quickly but also only sends routing table updates when triggered.
EIGRP also uses bandwidth and delay in its metrics as opposed to just the standard hop count. Due to the broadcast nature of the routing updates, distance vector protocols employ a couple of techniques that help prevent loops, namely Split Horizon and Poison Reverse. Split Horizon prevents any routes learned on a specific interface from being advertised back out that same interface. Poison Reverse, however, advertises a route back out of an interface it was learned on with a metric that makes it infinite and thus, unused.
Link state protocols exchange link state information among neighbors. This link state info is then used to compute the best routes to be installed into the local router. All routers will compute best path from their personal place in the network. On initial peering, full information is exchanged between neighbors. Those subsequent updates are exchanged on a triggered basis. This generally allows link state protocols to converge more quickly than a traditional distance vector protocol.
Example protocols are open shortest path first, which is universally the most used IGP and intermediate system to intermediate system. OSPF and IS-IS offer vendor interoperability, but IS-IS isn't nearly as widely adopted. The third and final type discussed are Path Vector Protocols. While distance vector protocols look up a hop count based on individual routers, path vector protocols focus on hop count based on autonomous systems.
An autonomous system is a collection of routers under the control of a single organization. This could be one router or 10,000. The Border Gateway Protocol is a prime example of a path vector protocol. When determining which route among many to use one of the primary factors is how many AS hops away the subnet is sourced from. Multiple traffic types exist. Unicast, Broadcast, Multicast and Anycast.
Unicast traffic will be any that is sourced from a single host and is destined to a single host. This is going to be the majority of network traffic. Broadcast traffic is going to be traffic destined to 255.255.255.255. Also known as all listing hosts on a subnet. Some early routing protocols, like RIP and IGRP use Broadcast to disseminate routing information. Multicast traffic is one host sending to multiple specific hosts simultaneously.
A common use is video streaming in a network where many specific users want to receive the same video feed. It's also often seen with Telecom PA style systems where audio messages can be broadcast to multiple destinations at the same time. Since Multicast can efficiently distribute information to multiple hosts, its employed by routing protocols like OSPF. Anycast is well-known in IPv6, though the concept does exist in IPv4, despite what some sources may say.
Anycast is where multiple devices have the same IP address. When a host makes a request to an Anycast IP, generally the closest geographically located Anycast device will answer the request. This concept will not only choose the closest device, but can also offer some redundancy in the case of an Anycast host failure. There are also a few network architecture types Cisco wants you to be aware of. Point-to-point networks are pretty much just as they sound.
Two devices only connected to each other. These were once seen on serial links. Broadcast connections are network segments allowing Broadcast traffic to be sent between neighbors. This can be two devices or this could be a 100 devices. Nonbroadcast Multi Access networks are those that don't allow broadcasts, but connect to more than one device together. These were popular on older frame relay and ATM networks. This network access method is still used a bit in mixed vendor environments for fixed base wireless providers.
NBMA usually requires static neighbor configuration when using dynamic routing protocols. Choosing an internal routing protocol can be difficult, but you should now have a bit better understanding of each.