Table of Contents
Why IS-IS is Layer 2 protocol?
Basically is because IS-IS has its own protocol stack callen CLNS, as this protocol does not uses IP to transport the routing information it cannot be considered an IP or layer 3 protocol, and is considered a layer 2 protocol.
What layer protocol is IS-IS?
Layer 3 protocol
IS-IS is an OSI Layer 3 protocol initially defined for routing CLNP. However, IS-IS is neutral regarding the type of network addresses for which it can route, and was easily extended to support IPv4 routing, using mechanisms described in RFC 1195, and later IPv6 as specified in RFC 5308.
What is L1 and L2 in IS-IS?
An ISIS router is in one area only, and cannot be in multiple areas like OSPF. An L1 adjacency is formed only with routers in the same area. An L2 adjacency is formed with routers in the same area or a different area. An ISIS router will form L1 and L2 adjacencies by default with a router in the same area.
Why is IS-IS protocol used?
I think there are several reasons:
- Stability. ISIS is based on CLNS, that is, it runs at the link layer.
- Scalability. In ISIS, all routing information is transmitted using TLVs (TYPE/LENGTH/VALUE), ensuring simple structure and providing easy scalability.
- Complexity.
- Convergence.
- Scale.
- In conclusion.
What is-IS-IS LSP?
ISIS (Intermediate System to Intermediate System) LSP (Link State Protocol Data Unit) publishing method and equipment.
What is-IS-IS protocol in networking?
The IS-IS (Intermediate System – Intermediate System) protocol is one of a family of IP Routing protocols, and is an Interior Gateway Protocol (IGP) for the Internet, used to distribute IP routing information throughout a single Autonomous System (AS) in an IP network.
Why do protocols have layers?
Layers provide a division of the work done by a network. Networks are set up with a protocol hierarchy that divides the communication task into several layers. A protocol is a set of rules for communication within a layer.
What is level in IS-IS?
Level 1 corresponds OSPF intra-area routing whereas Level 2 corresponds with the OSPF backbone Area 0 routing. Level 2 areas join all the areas with the backbone area. Every Cisco router comes by default as Level 1-2 (L1/L2) router to allow for easy configuration and deployment.
Why we use ISIS over OSPF?
OSPF is prone to attacks hence security overheads are required for protection. The possibility of attacks is very less in case of ISIS as it runs over Layer 2. OSPF designates a backbone area and standard or non-backbone area for inter-area advertisements whereas ISIS organizes the domain into different levels.
What is attach bit in IS-IS?
The purpose of an ATT-Bit is to accomplish Inter-Area Routing. When an L1/L2 router is connected to more than one area, it sets the ATT-bit on its L1 LSP. If multiple L1/L2 routers exist, then routers in L1 choose the nearest L1/L2 router.
IS-IS protocol vs OSPF?
Differences between OSPF and IS-IS Routing Protocols OSPF supports NBMA and point-to-multipoint links, whereas IS-IS does not support. IS-IS runs on the data link layer, whereas OSPF runs on the network layer. OSPF supports virtual link, whereas IS-IS does not support.