Routing Protocols
A generic term that refers to a formula, or protocol, used by a router to determine the accepted path over which data is transmitted. The routing protocol also specifies how routers in a network share data with each other and narrative changes. The routing protocol enables a network to make dynamic adjustments to its conditions, so routing decisions do not have to be predetermined and static.
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Routing, Routed and Non-Routable Protocols
Routing | Routed | Non-Routable
Routing Protocols
Routing Protocols are the software that allow routers to dynamically advertise and learn routes, determine which routes are ready and which are the most efficient routes to a destination. Routing protocols used by the Internet Protocol suite include:
· Routing data Protocol (Rip and Rip Ii).
· Open Shortest Path First (Ospf).
· Intermediate ideas to Intermediate ideas (Is-Is).
· Interrior Gateway Routing Protocol (Igrp).
· Cisco's Enhanced Interior Gateway Routing Protocol (Eigrp).
· Border Gateway Protocol (Bgp).
Routing is the process of captivating data across two or more networks. Within a network, all hosts are directly accessable because they are on the same
Routed Protocols
Routed Protocols are nothing more than data being movable across the networks. Routed protocols include:
· Internet Protocol
o Telnet
o Remote procedure Call (Rpc)
o Snmp
o Smtp
· Novell Ipx
· Open Standards institute networking protocol
· Decnet
· Appletalk
· Banyan Vines
· Xerox Network ideas (Xns)
Outside a network, specialized devices called Routes are used to achieve the routing process of forwarding packets in the middle of networks. Routers are related to the edges of two or more networks to supply connectivity in the middle of them. These devices are usually dedicated machines with specialized hardware and software to speed up the routing process. These devices send and receive routing data to each other about networks that they can and cannot reach. Routers discover all routes to a destination, determine which routes have the best metric, and insert one or more routes into the Ip routing table on the router. By maintaining a current list of known routes, routers can quicky and efficiently send your data on it's way when received.
There are many clubs that yield routers: Cisco, Juniper, Bay, Nortel, 3Com, Cabletron, etc. Each company's goods is distinct in how it is configured, but most will interoperate so long as they share common physical and data link layer protocols (Cisco Hdlc or Ppp over Serial, Ethernet etc.). Before purchasing a router for your business, all the time check with your Internet supplier to see what tool they use, and choose a router, which will interoperate with your Internet provider's equipment.
Non-Routable Protocols
Non-Routable Protocols cannot survive being routed. Non-routable protocols calculate that all computers they will ever characterize with are on the same network (to get them working in a routed environment, you must bridge the networks). Todays contemporary networks are not very tolerant of protocols that do not understand the opinion of a multi-segment network and most of these protocols are dying or falling out of use.
· NetBeui
· Dlc
· Lat
· Drp
· Mop
Rip (Routing data Protocol)
Rip is a dynamic internetwork routing protocol original used in interior routing environments. A dynamic routing protocol, as opposed to a static routing protocol, automatically discovers routes and builds routing tables. Interior environments are typically secret networks (autonomous systems). In contrast, exterior routing protocols such as Bgp are used to change route summaries in the middle of autonomous systems. Bgp is used among autonomous systems on the Internet.
Rip uses the distance-vector algorithm advanced by Bellman and Ford (Bellman-Ford algorithm).
Routing data Protocol
Background
The Routing data Protocol, or Rip, as it is more commonly called, is one of the most enduring of all routing protocols. Rip is also one of the more actually confused protocols because a variety of Rip-like routing protocols proliferated, some of which even used
the same name! Rip and the myriad Rip-like protocols were based on the same set of algorithms that use distance vectors to mathematically assess routes to recognize the best path to any given destination address. These algorithms emerged from scholastic explore that dates back to 1957.
Today's open accepted version of Rip, sometimes referred to as Ip Rip, is formally defined in two documents: ask For Comments (Rfc) 1058 and Internet accepted (Std) 56. As Ip-based networks became both more numerous and greater in size, it became apparent to the Internet Engineering Task Force (Ietf) that Rip needed to be updated. Consequently, the Ietf released Rfc 1388 in January 1993, which was then superceded in November 1994 by Rfc 1723, which describes Rip 2 (the second version of Rip). These Rfcs described an extension of Rip's capabilities but did not effort to obsolete the former version of Rip. Rip 2 enabled Rip messages to carry more information, which permitted the use of a straightforward authentication mechanism to gain table updates. More importantly, Rip 2 supported subnet masks, a needful feature that was not ready in Rip.
This part summarizes the basic capabilities and features related with Rip. Topics contain the routing update process, Rip routing metrics, routing stability, and routing timers.
Routing Updates
Rip sends routing-update messages at quarterly intervals and when the network topology changes. When a router receives a routing update that includes changes to an entry, it updates its routing table to reflect the new route. The metric value for the path is increased by 1, and the sender is indicated as the next hop. Rip routers vocalize only the best route (the route with the lowest metric value) to a destination. After updating its routing table, the router immediately begins transmitting routing updates to forewarn other network routers of the change. These updates are sent independently of the usually scheduled updates that Rip routers send.
Rip Routing Metric
Rip uses a particular routing metric (hop count) to quantum the distance in the middle of the source and a destination network. Each hop in a path from source to destination is assigned a hop count value, which is typically 1. When a router receives a routing update that contains a new or changed destination network entry, the router adds 1 to the metric value indicated in the update and enters the network in the routing table. The Ip address of the sender is used as the next hop.
Rip Stability Features
Rip prevents routing loops from lasting indefinitely by implementing a limit on the whole of hops allowed in a path from the source to a destination. The maximum whole of hops in a path is 15. If a router receives a routing update that contains a new or changed entry, and if addition the metric value by 1 causes the metric to be infinity (that is, 16), the network destination is carefully unreachable. The downside of this stability feature is that it limits the maximum diameter of a Rip network to less than 16 hops.
Rip includes a whole of other stability features that are common to many routing protocols. These features are designed to supply stability despite potentially rapid changes in a network's topology. For example, Rip implements the split horizon and holddown mechanisms to preclude incorrect routing data from being propagated.
Rip Timers
Rip uses numerous timers to regulate its performance. These contain a routing-update timer, a route-timeout timer, and a route-flush timer. The routing-update timer clocks the interval in the middle of periodic routing updates. Generally, it is set to 30 seconds, with a small random whole of time added whenever the timer is reset. This is done to help preclude congestion, which could corollary from all routers simultaneously attempting to update their neighbors. Each routing table entry has a route-timeout timer related with it. When the route-timeout timer expires, the route is marked invalid but is retained in the table until the route-flush timer expires.
Packet Formats
The following section focuses on the Ip Rip and Ip Rip 2 packet formats descriptive in Figures 44-1 and 44-2. Each illustration is followed by descriptions of the fields illustrated.
Rip Packet Format
· Command—Indicates either the packet is a ask or a response. The ask asks that a router send all or part of its routing table. The response can be an unsolicited quarterly routing update or a reply to a request. Responses contain routing table entries. Multiple Rip packets are used to transport data from large routing tables.
· Version number—Specifies the Rip version used. This field can signal distinct potentially incompatible versions.
· Zero—This field is not actually used by Rfc 1058 Rip; it was added solely to supply backward compatibility with prestandard varieties of Rip. Its name comes from its defaulted value: zero.
· Address-family identifier (Afi)—Specifies the address house used. Rip is designed to carry routing data for several distinct protocols. Each entry has an address-family identifier to indicate the type of address being specified. The Afi for Ip is 2.
· Address—Specifies the Ip address for the entry.
· Metric—Indicates how many internetwork hops (routers) have been traversed in the trip to the destination. This value is in the middle of 1 and 15 for a valid route, or 16 for an unreachable route.
Note: Up to 25 occurrences of the Afi, Address, and Metric fields are permitted in a particular Ip Rip packet. (Up to 25 destinations can be listed in a particular Rip packet.)
Rip 2 Packet Format
· Command—Indicates either the packet is a ask or a response. The ask asks that a router send all or a part of its routing table. The response can be an unsolicited quarterly routing update or a reply to a request. Responses contain routing table entries. Multiple Rip packets are used to transport data from large routing tables.
· Version—Specifies the Rip version used. In a Rip packet implementing any of the Rip 2 fields or using authentication, this value is set to 2.
· Unused—Has a value set to zero.
· Address-family identifier (Afi)—Specifies the address house used. Ripv2's Afi field functions identically to Rfc 1058 Rip's Afi field, with one exception: If the Afi for the first entry in the message is 0xFfff, the remainder of the entry contains authentication information. Currently, the only authentication type is straightforward password.
· Route tag—Provides a recipe for distinguishing in the middle of internal routes (learned by Rip) and external routes (learned from other protocols).
· Ip address—Specifies the Ip address for the entry.
· Subnet mask—Contains the subnet mask for the entry. If this field is zero, no subnet mask has been specified for the entry.
·Next hop—Indicates the Ip address of the next hop to which packets for the entry should be forwarded.
· Metric—Indicates how many internetwork hops (routers) have been traversed in the trip to the destination. This value is in the middle of 1 and 15 for a valid route, or 16 for an unreachable route.
Note: Up to 25 occurrences of the Afi, Address, and Metric fields are permitted in a particular Ip Rip packet. That is, up to 25 routing table entries can be listed in a particular Rip packet. If the Afi specifies an authenticated message, only 24 routing table entries can be specified. Given that individual table entries aren't fragmented into Multiple packets, Rip does not need a mechanism to resequence datagrams bearing routing table updates from neighboring routers.
Summary
Despite Rip's age and the emergence of more sophisticated routing protocols, it is far from obsolete. Rip is mature, stable, widely supported, and easy to configure. Its simplicity is well distinguished for use in stub networks and in small autonomous systems that do not have enough redundant paths to certify the overheads of a more sophisticated protocol.
Review Questions
Q—Name Rip's varied stability features.
A—Rip has numerous stability features, the most unavoidable of which is Rip's maximum hop count. By placing a finite limit on the whole of hops that a route can take, routing loops are discouraged, if not completely eliminated. Other stability features contain its varied timing mechanisms that help ensure that the routing table contains only valid routes, as well as split horizon and holddown mechanisms that preclude incorrect routing data from being disseminated throughout the network.
Q—What is the purpose of the timeout timer?
A—The timeout timer is used to help purge invalid routes from a Rip node. Routes that aren't refreshed for a given period of time are likely invalid because of some turn in the network. Thus, Rip maintains a timeout timer for each known route. When a route's timeout timer expires, the route is marked invalid but is retained in the table until the route-flush timer expires.
Q—What two capabilities are supported by Rip 2 but not Rip?
A—Rip 2 enables the use of a straightforward authentication mechanism to gain table updates. More importantly, Rip 2 supports subnet masks, a needful feature that is not ready in Rip.
Q—What is the maximum network diameter of a Rip network?
A—A Rip network's maximum diameter is 15 hops. Rip can count to 16, but that value is carefully an error health rather than a valid hop count.
Routing, Routed, and Non-Routable Protocols
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