Routing protocols

Tecvic · New Member Joined: Feb 03, 2006 Posts: 1

What is the primary purpose of the Routing process?

dwyane · Occasional Member Joined: Oct 17, 2004 Posts: 40

Hi tecvic..
i think u shld elaborate ur question more, which routing ur taking about?
if ur taking abt routing term in general,

The job of a router is to connect two different networks, this is where routing comes into picture, a routing process includes sendig and recieving packets between different networks in a efficient manner.

tHe-SwItCh · New Member Joined: Apr 04, 2006 Posts: 18

To simplify things ... well...... you move any form of data/ traffic from PC A to PC B it is 'Switching'. In essence, you switch data between two endpoints. From a simplified viewpoint, 'Routing' is the same, you still are switching data between two endpoints, howsoever far apart they might be.

Now, onto what makes 'Routing' different from 'Switching' ....essentially this distinction also underlines the functional difference between a 'Router' and a 'Switch'.

'Switching' happens at Layer 2 & 'Routing' happens at Layer 3. IP networks are defined at Layer 3. Hence it naturally follows that 'Routing' is nothing but 'Switching' at Layer 3.

Short and sweet, you need to 'Switch' data between endpoints, if the endpoints are within the same network (Layer 2), 'Switching' is needed and if these data points happen to be on different networks (with respect to IP addressing schemes), 'Routing' is implicitly required !

At layer 3 however, 'Switching' (or Routing) needs to take into consideration many factors when transporting data. These points include ...... link availablity, link cost (low cost routing), traffic shaping considerations, Shortest Path routing and so on. Layer 2 'Switching' is bereft of these know-hows .......

Cheerz n Beerz

Arani · Posted: Tue Apr 04, 2006 6:56 pm Post subject: routing

lets take the term routing by the horns...

In computer networking the term routing refers to selecting paths in a computer network along which to send data.

Routing directs forwarding, the passing of logically addressed packets from their source toward their ultimate destination through intermediary nodes (called routers). The routing process usually directs forwarding on the basis of routing tables within the routers, which maintain a record of the best routes to various network destinations. Thus the construction of routing tables becomes very important for efficient routing.

Routing differs from bridging in its assumption that address-structures imply the proximity of similar addresses within the network, thus allowing a single routing-table entry to represent the route to a group of addresses. Therefore, routing outperforms bridging in large networks, and it has become the dominant form of path-discovery on the Internet.

Small networks may involve hand-configured routing tables. Large networks involve complex topologies and may change constantly, making the manual construction of routing tables very problematic. Nevertheless, most of the public switched telephone network (PSTN) uses pre-computed routing tables, with fallback routes if the most direct route becomes blocked; see routing in the PSTN. Dynamic routing attempts to solve this problem by constructing routing tables automatically, based on information carried by routing protocols, and allowing the network to act nearly autonomously in avoiding network failures and blockages.

Dynamic routing dominates the Internet. However, the configuration of the routing protocols often requires a skilled touch; one should not suppose that networking technology has developed to the point of the complete automation of routing.

Packet-switched networks, such as the Internet, split data up into packets, each labeled with the complete destination address and each routed individually. Circuit switched networks, such as the voice telephone network, also perform routing, in order to find paths for circuits (such as telephone calls) over which they can send large amounts of data without continually repeating the complete destination address.

routing forms several protocols, namely under IPv4, they are:

Unicast routing protocols
IS-IS—Intermediate System-to-Intermediate System is a link-state interior gateway protocol (IGP) for IP networks that uses the shortest-path-first (SPF) algorithm, which also is referred to as the Djikstra algorithm, to determine routes. The JUNOS IS-IS software is a new and complete implementation of the protocol, addressing issues of scale, convergence, and resilience.
OSPF—Open Shortest Path First, Version 2, is an IGP that was developed for IP networks by the Internet Engineering Task Force (IETF). OSPF is a link-state protocol that makes routing decisions based on the SPF algorithm. The JUNOS OSPF software is a new and complete implementation of the protocol, addressing issues of scale, convergence, and resilience.
RIP—Routing Information Protocol, Version 2, is an IGP for IP networks based on the Bellman-Ford algorithm. RIP is a distance-vector protocol. RIP dynamically routes packets between a subscriber and a service provider without the subscriber having to configure BGP or to participate in the service provider's IGP discovery process.
ICMP—Internet Control Message Protocol router discovery allows hosts to discover the addresses of operational routers on the subnet.
BGP—Border Gateway Protocol, Version 4, is an exterior gateway protocol (EGP) that guarantees loop-free exchange of routing information between routing domains (also called autonomous systems). BGP, in conjunction with JUNOS routing policy, provides a system of administrative checks and balances that can be used to implement peering and transit agreements.

Multicast routing protocols
DVMRP—Distance Vector Multicast Routing Protocol is a dense-mode (flood-and-prune) multicast routing protocol.
PIM sparse mode and dense mode—Protocol-Independent Multicast is a multicast routing protocol. PIM sparse mode routes to multicast groups that might span wide-area and interdomain internets. PIM dense mode is a flood-and-prune protocol.
MSDP—Multicast Source Discovery Protocol allows multiple PIM sparse mode domains to be joined. A rendezvous point (RP) in a PIM sparse mode domain has a peer relationship with an RP in another domain, enabling it to discover multicast sources from other domains.
IGMP—Internet Group Management Protocol, Versions 1 and 2, is used to manage membership in multicast groups.
SAP/SDP—Session Announcement Protocol and Session Description Protocol handle conference session announcements.

MPLS applications protocols
MPLS—Multiprotocol Label Switching, formerly known as tag switching, allows you to manually or dynamically configure label-switched paths (LSPs) through a network. It lets you direct traffic through particular paths rather than rely on the IGP's least-cost algorithm to choose a path.
RSVP—The Resource Reservation Protocol, Version 1, provides a mechanism for engineering network traffic patterns that is independent of the shortest path decided upon by a routing protocol. RSVP itself is not a routing protocol; it operates with current and future unicast and multicast routing protocols. The primary purpose of the JUNOS RSVP software is to support dynamic signaling for MPLS label-switched paths (LSPs).
LDP—The Label Distribution Protocol provides a mechanism for distributing labels in nontraffic-engineered applications. LDP allows routers to establish LSPs through a network by mapping network-layer routing information directly to data-link layer switched paths. LSPs created by LDP can also traverse LSPs created by RSVP.

hope all of this is not an information overload for you Smile

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TheBishop · Posted: Wed Apr 05, 2006 8:18 am Post subject: Routing

Nice post arani!

Arani · Posted: Wed Apr 05, 2006 2:05 pm Post subject: thanks

thanks bishop,
i couldn't help resist myself in indulging into a comprehensive explanation of such a fundamental term in networking. and added to that, i simply hate half baked explanations Laughing

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