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This chapter is from the book

This chapter is from the book

Rules for IS-IS Adjacencies

  • L1 routers form L1 adjacencies with L1 and L1-L2 routers in their area.
  • L2 routers form L2 adjacencies with L2 and L1-L2 routers in their area or another area.
  • L1/L2 routers form L1 and L2 adjacencies with each other in their area or another area.
  • An L1 router does not form an adjacency with an L2 router, regardless of area.
  • The system ID must be unique to each router.
  • Hello intervals and hold times do not have to match.
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