Chapter 9: Fowarding ip packets



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Chapter 9: Fowarding IP Packets


1. Which router, based on the architecture in the figure, is probably a small site router? Which is probably a large Internet backbone router?

Although architectures vary, the router with only memory is likely to be a smaller site router. The router with separate hardware forwarding and control plane is likely the backbone router.

2. Which output interface, based on the routing table shown in the figure, will packets arriving from the directly attached host for IPv4 address 10.10.11.1 use for forwarding? Assume longest match is used.

64 is 0100 0000, 128 is 1000 0000, and 11 is 0000 1011. All three routes match the first 16 bits. The /18 masks (01 and 10) do not match the address bit pattern (00) in positions 17 and 18. So 10.10.0.0/16 is the longest match and the packet will use output interface #1.

3. Which output interface will packets for 10.10.192.10 use? Assume longest match is used.

192 is 1100 0000. Again, all three routes match the first 16 bits. The /18 masks (01 and 10) do not match the address bit pattern (11) in positions 17 and 18. So 10.10.0.0/16 is again the longest match and the packet will use output interface #1.

4. Is 6to4 tunneling automatic? How many bits will be used for the subnet identifier?

Yes, 6to4 automatic tunnels are defined in RFC 3065. Sixteen bits are used for subnet ID. See Figure 9-9.



5. Do the routers require IPv6 support to deliver packets between the two hosts?

No. If IPv6 is not supported on the routers, 6to4 tunneling can be used to deliver packets.


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