2
11.Destination address: 202.70.20.30
Mask: /26Mask: /25Mask: /24Mask: /22
Result: 202.70.20.0 Result: 202.70.20.0 Result: 202.70.20.0 Result: 202.70.20.0
No matchNo matchNo matchNo match
Next hop address: 180.70.65.200 (default router) → Interface: m2
13.A routing table for a LAN not connected to the Internet and with no subnets can
have a routing table with host-specific addresses. There is no next-hop addresssince all packets remain within the network.15.If the packet with destination address 140.24.7.194 arrives at R3, it gets sent to
interface m0. If it arrives at R2, it gets sent to interface m1 and then to router R3.The only way R1 can receive the packet is if the packet comes from organization 1,2, or 3; it goes to R1 and is sent out from interface m3.17.See Table 6.E17.
Table 6.E17Solution to Exercise 17
Mask
Network address120.14.64.0120.14.96.0120.14.112.00.0.0.0
Next-hop address
Interfacem0m2m3m4
/20/20/20/0
???
default router
19.See Table 6.E19.
Table 6.E19Solution to Exercise 19
Mask
Network address120.14.96.0120.14.100.0120.14.104.0120.14.108.00.0.0.0
Next-hop address
Interfacem0m1m2m3m4
/22/22/22/22/0
????
default router
3
21.See Table 6.E21.
Table 6.E21Solution to Exercise 21
Mask
Network address120.14.64.0120.14.64.4120.14.64.8120.14.64.12
Next-hop address
Interfacem0m1m2m3
/30/30/30/30…/30/0
…
120.14.65.252
0.0.0.0
????…?
default router
…
m127m128
4
CHAPTER 7
Internet Protocol Version 4 (IPv4)
Exercises
1.If no fragmentation occurs at the router, then the only field to change in the baseheader is the time to live field. If any of the multiple-byte options are present, thenthere will be changes in the option headers as well (to record the route and/or time-stamp). If fragmentation does occur, the total length field will change to reflect thetotal length of each datagram. The more fragment bit of the flags field and the frag-mentation offset fields may also change to reflect the fragmentation. If options arepresent and fragmentation occurs, the HLEN field of the base header may alsochange to reflect whether or not the option was included in the fragments.3.
Advantages of a large MTU:
Good for transferring large amounts of data over long distancesNo fragmentation necessary; faster delivery and no reassemblyFewer lost datagrams
More efficient (less overhead)Advantages of a small MTU:
Good for transferring time-sensitive data such as audio or videoBetter suited for multiplexing
5.In this case, we use a Loose Source Route option with only one entry as shown inFigure 7.E5. Figure 7.E5Solution to Exercise 5
~Base HeaderOp: 010000000110000000Length:7Code:1311000001100000111128.46.10.50010111000001010Pointer: 40000010000000101~1
2
7.The value of the header length field of an IP packet can never be less than 5because every IP datagram must have at least a base header that has a fixed size of20 bytes. The value of HLEN field, when multiplied by 4, gives the number ofbytes contained in the header. Therefore the minimum value of this field is 5. Thisfield has a value of exactly 5 when there are no options included in the header.9.If the size of the option field is 20 bytes, then the total length of the header is 40bytes (20 byte base header plus 20 bytes of options). The HLEN field will be thetotal number of bytes in the header divided by 4, in this case ten (1010 in binary).11.HLEN field: 5 = (0101)2
Total length field: 1044 = (00000100 00010100)2
13.If the fragmentation offset is 0 and the more fragment bit is off, this is not a frag-ment.15.
a.b.c.d.e.f.g.
There are no options.
The packet is not fragmented.
The packet carries 64 bytes of data. The header is 20 bytes long. The checksum is not used.
The packet may visit up to 32 more routers.
The identification number of the packet is 3 (decimal). The type of service isnormal.
TCPIP协议族第四版课后答案
