An intoroduction to the IS-IS IGP routing protocol
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The document provides an overview of the Intermediate System to Intermediate System (IS-IS) routing protocol. It describes key IS-IS concepts like neighbor discovery using hello messages, flooding of link state packets (LSPs) to share routing information, synchronization of the link state database, and running shortest path first (SPF) calculations to determine optimal routes. Pseudo-nodes and designated routers are used on broadcast networks to represent the entire network topology. Sequence numbers, checksums, and hold timers ensure freshness and accuracy of routing data.
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An intoroduction to the IS-IS IGP routing protocol
- 1. IS-IS An introduction to IGP routing protocols Hagai Kahana
- 2. Compass-EOS Confidential 156.10.24.1 16.55.42.10 57.13.29.2
- 14. IS-IS Common Header Compass-EOS Confidential Packet Data … Definition Values network layer identifier assigned to IS-IS (ISO 9577) 0x83 Length of the packet header fields in octets Variable Version 0x1 Indicates length of the source ID (SysID) field 0x0 -> 6 byte IS-IS packet type (3 bits reserved) Hello, LSP or SNP Version 0x1 Reserved 0 Number of area addresses permitted for this intermediate system’s area 0x0 = max 3 areas
- 19. IIH – LAN Level 1 and Level 2 Compass-EOS Confidential Field Definition Circuit type Level 1, Level 1-2, or Level 2 only (6 bit reserved) Source ID System ID of the router that generated packet Holding time Maximum interval between two consecutive hello packets before the router is considered no longer available PDU length Length of the entire PDU, including header Priority designates the DIS (Level 1 or Level 2) on the LAN LAN ID SysID of the DIS plus an octet-long unique ID for this router assigned by the DIS. TLV fields Type 1 - Area Addresses Type 6 - IS Neighbors Type 8 - Padding Type 10 - Authentication Type
- 22. Flooding
- 29. Link state database Synchronization.
- 34. SPF (short path first) calculation.
- 37. Thank you Compass-EOS Confidential
Editor's Notes
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- In OSPF all timers must align with the DR (designated router) July 10, 2000
- Any change in network conditions causing changes in TLV information advertised in the most recent hello transmitted ID length in the IIH. This field indicates the length of the SysID and the SysID must be consistent on all routers across the domain Maximum number of areas. addresses supported in a single router configuration must match between adjacent neighbors, default maximum value of 3. July 10, 2000
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- POP - close collection of routers July 10, 2000
- POP - close collection of routers July 10, 2000
- If pseudo-node ID is 00 it means that this is a real router. Since IS-IS is on layer 2 there is no fragmentation service, do it is part of the IS-IS itself July 10, 2000
- If pseudo-node ID is 00 it means that this is a real router. Since IS-IS is on layer 2 there is no fragmentation service, do it is part of the IS-IS itself July 10, 2000
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- Synchronizing DB and resulting routing tables is crucial for bringing packets closer to their destination. CSNP by default is sends every 10 seconds. Can be configured. CSNP can be more than one packet. Start and end LAN-ID is used to identify it: 0000.0000.0000.00-00 to ffff.ffff.ffff.ff-ff SRM – set on a link the corresponding LSP has to be sent out on that link. SSN – the corresponding LSP should be included in the next PSNP Behavior when CSNP reporting an older version of the LSP\\a more recent version of LSP\\ an unknown LSP July 10, 2000
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- TLV - Type Length Value Authentication is applied on the entire PDU July 10, 2000