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Interior Gateway Protocol |
Exterior Gateway Protocols |
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Distance Vector |
Link-State |
Path Vector |
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IPv4 |
RIPv2 |
EIGRP |
OSPFv2 |
IS-IS |
BGP-4 |
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IPv6 |
RIPng |
EIGRP for IPv6 |
OSPFv3 |
IS-IS For IPv6 |
BGP-MP |
Part 1: IS-IS Fundamentals (ISO 10589)
The protocol is designed to operate in an OSI Connectionless Network Service (CLNS) environment.
The features of IS-IS include the following:
- Hierarchical routing
- classless behavior
- Rapid flooding of new information
- fast convergence
- very scalable
- Flexible timer tuning
| OSI Reference Model | OSI Protocol Suit |
| Application | ASES CMIP DS FTAM MHS VTP |
| Presentation | Presentation Service / Presentation Protocol |
| Session | Session Service / Session Protocol |
| Transport | TP0 TP1 TP2 TP3 |
| Network | IS-IS CONP/CMNS ES-IS CLNP/CLNS |
| Data Link | IEEE 802.2 IEEE 802.3 IEEE802.5 FDDI X.25 |
| Physical | IEEE 802.3 Hardware Toking Ring Hardware FDDI Hardware |
CLNS(Connectionless Network Service)
OSI CLNS is a network layer service similar to bare IP service.
Connectionless Network Protocol (CLNP) is an OSI network layer protocol that carries upper layer data and error indications over connectionless links. CLNP provides the interface between CLNS and upper layers. A CLNS entity communicates over CLNP with its peer CLNS entity. CLNP is the OSI equivalent of IP.
OSI Network Layer Addressing
- NSAP (Network Service Access Point)
- NET(Network Entity Titles)
Comparing IP and OSI Services
| IP Services | OSI Services |
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Basic Connectoinless Servcies: IP (RFC 791) |
CLNS(ISO 8473) |
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Neighbor greeting and error reports to source about packet dilivery: ICMP (RFC 792) ARP(RFC 826). IRDP (RFC 1256) |
CLNP(ISO 8743) ES-IS(9542) |
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Routing: Intergrated IS-IS(RFC 1195) Participants are routers and hosts |
IS-IS(ISO 10589) Participants are ISs and ESs |
| IP autonomous System | ISO Routing Doamin |
| IGP | Introdomain routing protocol |
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EGP BGP for IP (RFC 1105) Static IP routes |
Interdomain Routing Protocol(IDRP) ISO IDRP(proposal) Static CLNS routes |
OSPF vs IS-IS
OSPF and IS-IS Similarities
- classless
- Link-state databases and Dijkstra‘s algorithm
- Hello packets to form and maintain adjacencies
- use areas to form hierarchial topologies
- support address summarization between areas
- Elect DR on multi-access netwok
- Link-state representaion, aging, and metrics
- update, decision, and flooding processes
- convergence capabilities
- deployed on ISP backbones
OSPF and IS-IS DR Differences
- IS-IS does not elect a BDR
- IS-IS repeats the election process whenever a new router becomes active
- if the new router has a higher priority or the same priority and a higher system ID, it will take over as the DR
- Designed to be deterministic, the same set of router always produces the same DR.
- Every time the DR changes, a new set of LSPs must be flooded.
- IS-IS routers form adjacencies with all neighobrs, not just DR.
OSPF and IS-IS Area Differences
OSPF and IS-IS Resource Usage Differences
OSPF and IS-IS Scalability Differences