Lectures notes for 2010 - KTH

Count to Infinity
C
network 1
network 2
network 3
Router A
TTL expires
Router B
• Router A advertises it knows about routes to networks 1 and 2
• Router B advertises it knows about routes to networks 2 and 3
• After one update cycles A and B know about all 3 routes.
If A’s interface to Network 1 goes down, then A learns from B - that B knows a
route to Network 1 ; so A now thinks it can reach Network 1 via B. So if D sends a
packet for C, it will simply loop back and forth between routers A and B, until the
TTL counts down to 0.
D
Maguire Count to Infinity 7: 16 of 70
maguire@kth.se 2010.03.21 Internetworking/Internetteknik