2019-10-20
The network shown in FIG.
please answer the following question:
(1) When configuring the host IP address, the correct subnet mask and default gateway respectively?
(2) If the router R in a forward Internet sent by the host to 192.168.1.5, ID = 12345, length = 500B, when the packet IP DF = 1, then the IP packet header fields which will be modified? How to modify?
(3) If the host to the internet 192.168.1.10 ID = 6789, length = 1500B, DF = IP 0 when the packet, the router needs the IP packet into several pieces (each maximum possible package sheet)? The results are given fragment, each comprising a sheet ID, DF, MF, length, offset values.
my answer
1) subnet mask: 255.255.255.240
The default gateway address: 130.11.22.254
2) the source IP address is modified as: 130.11.22.3;
Router to forward a packet, TTL will change: TTL minus 1
3) DF = 0, fragmentation is allowed, the number of IP router packet fragmentation is:
(IP packet total length of the header bytes -20) / per a maximum amount of data can be packaged MTU = (1500-20) /512=2.890625 ≈ 3 pieces of fragmented;
Fragmentation results:
ID=6789 DF=0 MF=1 length=512 offset=0
ID=6789 DF=0 MF=1 length=512 offset=(512-20)/8*(2-1)=61.5
ID=6789 DF=0 MF=0 length=476 offset=(512-20)/8*(3-1)=123
standard answer
no