Introduction

Intermediate System-to-Intermediate Syste Hello PDUs (IIHs) are used to create adj between ISIS neighbors.

IIHs

• IIH include:
  • System ID
  • Assigned Area address
  • Known neighbors
• There are three types of IIHs:
  • Point to Point - send on point to point interfaces.
  • Level 1 LAN IIHs - send on multiaccess interfaces when operating as a Level 1 router.
  • Level 2 LAN IIHs - send on multiaccess interfaces when operating as a Level 2 router.
• Router that share the same area number in a Level 1 will come adj. Level 2 routers don't need to be in the same area.
• By default Hello PDUs have padding enabled. They will send the with maximum size of 1497.
• Default timers:
  • Hello interval is 10 seconds (fast hellos also supported).
  • Holdtime interval is 30 seconds (3 x hello).

Relevant Commands

isis hello-interval

Set the hello interval. Hello timer does not have to match, ISIS neighbor responds back right away. Minimal option will set the hold time to 1 second and hello-multiplier command defines how many hellos are sent in a second.

R1(config-if)#        isis hello-interval (sec) [level1 | level2]

R1(config-if)#        isis hello-interval min [level1 | level2]
R1(config-if)#        isis hello-multiplier

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