Learning IOS and JUNOS

Appendix A. IS-IS Packet Formats IS-IS Packet Fields (Alphabetical Order) ATT— Attachment Bits (Flags attachment to other areas) Checksum— Checksum of contents of LSP from source ID field to the end Circuit Type— Defines whether link is Level-1 and Level-2 End LSP— LSP ID of last LSP in CSNP Holding Time— Defines how long to wait for a hello from this system before clearing the adjacency ID Length— Length of the System ID field in an NSAP(NET) Intradomain Routing Protocol Discriminator— Network layer protocol identifier IS Type— Defines type of router, Level-1 or Level-2 LAN ID— LAN Identifier, Consists of the System ID of the designated intermediate system plus a unique number Length Indicator— Length of the fixed header of the packet in bytes Local Circuit ID— Unique identifier for a link LSP ID— Identifier for router's LSP, consisting of the System ID of the router, fragment number, and a nonzero octet for pseudonode number in case of pseudonode LSP Maximum Area Addresses— Numbe...

Using the IS-IS Attach-Bit Control Feature Introduction In Intermediate System-to-Intermediate System (IS-IS) networks, routing inter-area traffic from Layer 1 areas is accomplished by sending the traffic to the nearest Layer 1/Layer 2 router. A Layer 1/Layer 2 router identifies itself by setting an attach-bit (ATT-bit) in its Layer 1 link-state packet (LSP). In some situations, however, it might not be desirable to set the ATT-bit. For example, if there are multiple Layer 1/Layer 2 routers within a Layer 1 area and one of the Layer 1/Layer 2 routers loses its backbone connection, continuing to send inter-area traffic to this Layer 1/Layer 2 router can cause the traffic to be dropped. Cisco IOS® Software now introduces a new capability to allow network administrators to control when a Layer 1/Layer 2 router should set the ATT bit and avert dropped traffic. Overview In networks running hierarchical routing protocols—IS-IS or Open Shortest Path First (OSPF) Protocol, for example—it is ...

Introduction This Tech Note describes the line-state packet (LSP) pseudonode. A pseudonode is a logical representation of the LAN which is generated by a Designated Intermediate System (DIS) on a LAN segment. The document also describes the propagation of information to the routers. What is the DIS? On broadcast multi-access networks, a single router is elected as the DIS. There is no backup DIS elected. The DIS is the router that creates the pseudonode and acts on behalf of the pseudonode. The DIS There are two major tasks performed by the DIS: ．Creating and updating pseudonode LSP for reporting links to all systems on the broadcast subnetwork. See the Pseudenode LSP section for more information. ．Flooding LSPs over the LAN. The flooding over the LAN means that the DIS sends periodic complete sequence number protocol data units (CSNPs) (default setting of 10 seconds) summarizing the following information: ．LSP ID ．Sequence Number ．Checksum ．Remaining Lifetime The DIS is responsible f...

1.0 Abstract This document describes extensions to the IS-IS protocol to support Traffic Engineering [1]. The IS-IS protocol is specified in [2], with extensions for supporting IPv4 specified in [3]. This document extends the IS-IS protocol by specifying new information that a Intermediate System (IS) [router] can place in Link State Protocol Data Units (LSPs). This information describes additional information about the state of the network that is useful for traffic engineering computations. 2.0 Introduction An IS-IS LSP is composed of a fixed header and a number of tuples, each consisting of a Type, a Length, and a Value. Such tuples are commonly known as TLVs, and are a good way of encoding information in a flexible and extensible format. The changes in this document include the design of new TLVs to replace the existing IS Neighbor TLV, IP Reachability TLV and add additional information. Mechanisms and procedures to migrate to the new TLVs are not discussed in this document. The pr...

在Link-State Routing Protocol兩兄弟OSPF, IS-IS之間，有很多地方相似及相異之處，我這次特別將OSPF Designated Router(DR)/Backup Designated Router(BDR)及IS-IS Designated Intermediate System(DIS)這兩個同為SPF algorithm中在MultiAccess網路中必須存在的角色分別說明它們之間的相異點，希望可以為大家省去一一比對的麻煩。(如附圖)