IS-IS facts for kids

IS-IS (which stands for Intermediate System to Intermediate System) is like a smart guide for computer networks. It's a special set of rules, called a routing protocol, that helps information travel quickly and efficiently. Think of it as a GPS for data packets, finding the very best path for them to reach their destination in a big network.

This protocol is an international standard, meaning it's recognized and used worldwide. Many large internet companies use IS-IS to manage their main networks because it's very good at handling lots of traffic.

What IS-IS Does

IS-IS is an "interior gateway protocol." This means it works inside one big network, like a school's computer system or a company's private network. It's different from protocols that connect completely separate networks, like the internet itself.

IS-IS is also a "link-state routing protocol." Imagine every computer or device in a network is a point, and the connections between them are lines. IS-IS shares information about the "state" of these connections (links). Every IS-IS device then builds its own map of the entire network.

Just like the OSPF protocol, IS-IS uses a clever math trick called Dijkstra's algorithm. This algorithm helps it figure out the shortest and fastest path for data to travel across the network. Once the best path is found, data packets are sent along that route to their final destination.

How IS-IS Started

The IS-IS protocol was first created by a company called Digital Equipment Corporation as part of their DECnet Phase V project. It became an official standard in 1992 by the ISO. Its main goal was to help network devices, called Intermediate Systems, send data using the OSI protocol stack.

Around the same time, another group called the Internet Engineering Task Force (IETF) was developing a similar protocol called OSPF. Later, IS-IS was updated to also work with Internet Protocol (IP), which is the main way data travels on the global internet. This updated version is often called Integrated IS-IS.

Types of IS-IS Messages

IS-IS devices talk to each other using different types of messages, like sending notes back and forth. Here are the main ones:

• Hello Packet: Devices send these messages regularly to find and connect with nearby IS-IS devices. It's like saying "hello, are you there?" If two devices agree to connect, one might become a "Designated IS" (DIS), which helps manage the network information.
• LSP (Link State Packet): These are the most important messages. They contain the actual information about the network's routes. Think of them as small maps showing which connections are available and how fast they are.
• CSNP (Complete Sequence Number PDU): The Designated IS (DIS) sends these messages regularly, usually every 10 seconds. They list all the LSPs it knows about, along with their version numbers. This helps other devices check if their maps are up-to-date.
• PSNP (Partial Sequence Number PDU): If a device receives a CSNP and notices it's missing some LSP information, it sends a PSNP. This is like saying, "Hey DIS, I need you to send me that specific LSP again!"

IS-IS vs. OSPF

Both IS-IS and OSPF are popular "link-state" protocols, and they both use the same Dijkstra algorithm to find the best paths in a network. They are quite similar in how they work. Both can find neighboring devices using "hello packets" and can secure their updates.

However, there are some key differences:

• Original Design: OSPF was built specifically for routing IP traffic. IS-IS was first made for a different type of network traffic (CLNS) but was later easily updated to handle both IPv4 and IPv6 traffic. OSPF needed a completely new version (OSPFv3) to support IPv6.
• Network Organization: Both protocols create a map of the network. But they organize networks into "areas" differently.

OSPF defines areas on the connections themselves. A router can be part of two or more areas at once, acting as a border. All traffic between areas usually has to pass through a central "Area 0." IS-IS defines areas between routers. An IS-IS router is usually only part of one area. It uses "Level 1" routers for inside an area and "Level 2" routers for connecting different areas. "Level 1-2" routers connect both. This creates a backbone of Level 2 routers with branches of Level 1 areas.

• Flexibility: IS-IS is often easier to expand and add new features to. It uses a flexible system called TLVs (Type-Length-Values) for its messages. This means engineers can add support for new technologies without completely changing the protocol. This flexibility helps IS-IS work well in very large networks, like those used by internet service providers.

Other Uses for IS-IS

IS-IS isn't just for routing IP traffic. It's also used in a technology called IEEE 802.1aq Shortest Path Bridging (SPB). SPB helps Ethernet networks (which are common in homes and offices) find the shortest paths and use multiple connections at the same time. This makes these networks faster and more reliable. IS-IS helps SPB by sharing information about the network's connections.

Related Protocols

• Fabric Shortest Path First (FSPF)
• Transparent Interconnect of Lots of Links (TRILL)

See also

In Spanish: IS-IS para niños