IS-IS multi-area and static route redistribution

IS-IS multi-area and static route redistribution


In this project our task is to implementing the IP protocol intermediate system to intermediate system (IS-IS) with multi area routing and static route redistribution by using of four routers. In this report we will discuss IS-IS features, different routing levels and static route redistribution in IS-IS. We will also provide details and configurations results of our task in the paper.


When IS-IS used to support IP is called integrated IS-IS. It supports a two level hierarchy all routers are reside in one area and level 1-2 router act as border area router as ABRs in OSPF routing protocol and the level 1-2 routers are also called backbone routers. Level 1 routers are used for inter area routing. Both level 1 and level 2 run SPF algorithm to find best path for their routing table and fast for fast convergence.

In our project the main task is to configure IS-IS and redistribute a static route. We will configure a static route in one area on loopback interface and then redistribute it in other area so that networks in other area can access this loopback interface.

We divide four routers in two areas. Area 1 and area 2, two routers in each area become level 1-2 router and reaming two level 1 router.

Intermediate System-to-intermediate System (IS-IS)

IS-IS is an Interior Gateway Protocol (IGP) developed in the 1980s by DEC (Digital Equipment Corporation )and submitted to [3](ISO) the International Organization for Standardization as the routing protocol for Open System Interconnection (OSI). The creation of IS-IS,[3] was part of an attempt to produce an international standard protocol suite that could compete with TCP/IP [1]

IS-IS become very popular routing protocol among ISPs because of fast convergence flexibility and support to MPLS. IS-IS features are as follows.

* Hierarchical routing

* Classless behavior

* Rapid flooding of new information

* Fast convergence

* Very scalable

* Flexible timer tuning

* Protocol independent [2].


Both OSPF and IS-IS support a two-level hierarchy. OSPF has a central area (Area 0) to which all other areas attach. OSPF interfaces belong in an area; routers that straddle two areas are called Area Border Routers (ABR).In IS-IS the router is wholly in a Level 1 area. Level 1-2 routers, which are similar to OSPF ABRs, are in one area at Level 1 and also route separately at Level 2. IS-IS Level 2 may wind through Level 1 areas. Level 1 router must be in the same area to exchange local routes and receive a default route from a Level 1-2 router. Level 2 routers send Level 2 updates across the backbone.

Level 0 Routing

OSI routing begins with ES-IS, when the ES discovers the nearest IS by listing to ISH packets when an ES needs to send a packet ES, it sends the packet to an IS on an attached network. This process known as L0 routing.

Level 1 Routing

Level 1 routing is in one intermediate system and is also called intra area routing. Level 1 Router is the device that routes traffic within OSI area. Level 1 router uses IS-IS protocol to route traffic inside the area. Many routers using IS-IS protocol can do both intra-area and inter-area routing. In this case it is called level 1-2 router [4]

Level 2 routing

Level 2 routing is called inter area routing and level 2 or level 1-2 routers are used for inter area routing when in one area router find an IP packet with address who's destination is in other area router then send it to destination level 2 router in the other area and then IP packet send to the destination on the best path based on the system ID.

Level 3 routing

Level 3 routing is used between different domains. It is comparable with BGP inter domain routing in IP. It also used in passing traffic between different autonomous systems.

Integrated or Dual IS-IS

IS-IS routing protocol support both IP and OSI and is used as an IGP. It is mostly used in large ISP's. It can work with pure IP and pure OSI based networks. When IS-IS used to support IP networks is called integrated networks.

OSI Addressing

OSI address are used for the router ID in the IS-IS as OSPF use IP address as router ID. These addresses are dependent on the device like

* Network Service Access Point(NSAP)

* Network entity title (NET)

There are three major parts of the OSI address are given bellow

* Area

* ID



Inter domain part used for the autonomous system routing. IDP is further divided into two parts




The authority and format identifier (AFI) first octet identifies the authority that dictates the address format and issues addresses. This byte is typically either 39(Country Code), 47 (International Code), or 49 (private) [1]


Initial domain identifier is the sub part of AFI it is related to US government for the civilian departments.


Domain specific part is used inside the autonomous system and further divided into three parts.

* Higher order DSP

* System ID


High Order DSP is typically the area within the autonomous system.

System ID identifies the device. Cisco use 6 byte as system ID.

NSEL is one byte. It is used to recognize the service to which the packet handout. It works on the network layer.

IS-IS Operation

In IS-IS enabled network routers send hello packets to their neighboring routers to make adjacencies. Routers that are directly connected to each other become neighbors if their hello packets have necessary information that can allow them to accept directly connected router as neighbor. The adjacencies depend on the IS-type, MTU size and authentication. Link state packets (LSP) build by the routers on the basis of interfaces which are configured as IS-IS and prefixes gained from adjacent routers. Routers flood LSP to all adjacent routers. From these LSP's link state data base build by the routes that are flooded from the neighbor routers. And then SPT shortest path tree created and from this tree all routes make their routing table.

IS-IS MD5 Authentication

The purpose of authentication implementation is to protect the network from unwanted and illegal communication. Message digest MD 5 is used in IS-IS PDU. HMAC is method known as message validation code and it use hash functions. It is used for authentication at protocol level. HMAC-MD5 is more scour then the clear text because it is in encrypted form and password protected.

Clear Text Authentication

In clear text authentication passwords or keys are not in plain text format and can be hacked easily. If few extra commands are used while configuration it encrypt the and this mechanism make easy to manage passwords and keys.


IS-IS developed by ISO and OSPF developed by internet engineering task force (IETF). Both protocols are very similar to each other. The partial difference is there like resources and ability to customize their behavior.

In both protocols more similarities as compared to dissimilarities. Both have the following similar characteristics

* Open-standard link-state routing protocols

* Support VLSM

* Support route summarization between areas

* Similar mechanisms to maintain the health of the LSDB (link-state advertisements [LSAs], link-state aging timers, and LSDB synchronization)

* Use the shortest path first (SPF) algorithm, with similar update, decision, and flooding processes

* Successful in the largest and most demanding ISP networks

* Converge quickly after network changes [3]

The dissimilarities are do exist in the IS-IS and OSF like area border routers. In IS-IS exist in inside the area but in OSPF its one interface is in one area and other interface exist in the other area.

In our topology we have four routers R1, R2, R3 and R4. R1 and R2 are in area 1. R3 and R4 are in area 2.

R1 and R4 are only performing level 1 routing. R2 and R 4 are Area Border Routers and performing Level 1-2 routing.

Connections details are

1. R1> S1/0 connected R2>S1/0, R1> S1/0 is DCE

2. R2> S1/1 connected R3>S1/1, R2> S1/1 is DCE

3. R3> S1/0 connected R4> S1/0, R3> S1/0 is DCE

IP Addressing


Network 1 (R1 and R2)

Network 2 (R2 and R3)

Network 3 (R3 and R4)

Network 4 (Loopback 1 on R1)

Network 5 (Loopback 4 on R4)

Interface IP Address

R1> S1/0

R1> Lo 1

R2> S1/0

R2> S1/1

R3> S1/1

R3> S1/0

R4> S1/0

R4> Lo 4

CLNS Addressing

R1: 49.0001.0000.0000.1111.00

R2: 49.0001.0000.0000.2222.00

R3: 49.0002.0000.0000.3333.00

R4: 49.0002.0000.0000.4444.00

We have configured all routers with IS-IS. We don't enable IS-IS on loopback interfaces on R1 and R4. We have configured static route on R2 and R3 to reach the networks of Loopback interface on R1 ( and R4 ( We redistribute the static routes on R2 and R3. After these configurations we can reach on all the networks from all routers.

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