IS-IS(IE)

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CLNS: is like generic TCP/IP

CSNP: the protocol used for data transfer

packet capture will show data link layer header and then ISIS header. no IP header

- router: intermediate system

- host: end system

- Link state protocol like OSPF. use LSP(link state PDUs)

- use SFP

-like ospf DR is elected as DIS

- IS_IS AD = 115

- ISIS : whole router is in single area

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Level 1:

- its like totally NSSA in OSPF

- sends L1 hello

-learns intra area routes

- level 1 router dynamically creates a default route upon detecting a level1-2 router in their area. but Level1-2 router should set a "attach" bit while sending level 1 LSPs. level1-2 router will set "attach" bit only when it is connected to a L1-2 or L2 router in different area.

- learns redistributed routes

- L1 routers will form adjacancy with only llevel1 router in same area

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Level 2:

- its like ABR in ospf

- sends L2 hello

-keeps track of inter-area routing

- will form adjacency only with Level 2(same area or different area)

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Level1-2:

- maintains different L1/L2 database and different SPF algorithm

- send L1 and l2 hello

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LSPs

Level 2 LSP:

- Level 2 or Level 1-2 creates Level2 LSP

- Level 2 LSPs contain prefix via:

directly connected to this router

if router is L1/2 , learned by L2

like type 5 LSA

- learned by Level 1 router (if router is L1/2)

- router sends one LSP for all prefixes learned unlike OSPF where for each network we have LSA

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Level 1 LSP:

- each Level 1 router will create 1 LSP

- all routers which are Level1 and Level1/2 will share Level 1 LSPs

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SPF:

-SPF will run twice for level1-2 router. once for Level1 LSPs and one for Level2 LSPs

- routes of Level1 will be preferred than Level2

Router ID

in IS-IS is called NET

NET: Network entity title

- manually configured

- variable in size ( 8 to 20 octets)

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NET = IDP + DSP

IDP: only when running ISIS between 2 routing domains. like customer and ISP. optional

IDP = AFI + IDI

- AFI is 49. its a local address.

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Psuedonodes and DIS:

- on broadcast networks, all IS form adjacancy

DIS is elected :

- highest priority

- highest MAC

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-all IS routers exchange level1 LSPs in a broadcast domain

- 1 DIS is selected per broadcast domain

- IS routers exchange Level 1 LSPs with all routers along with DIS

- DIS create a pseudo router called psuedonode who creates copy of each LSP he received from all the routers along with LSP he generated

- this LSP is not used for routing computation purpose.

- any other router receive this LSP and checks for networks he has advertised, if router doesnt find the network - he assumes network has been lost and send a new LSP to L2 MAC broadcast address.

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