Bob obtained the following information from a workstation: C:\\>ipconfig Windows
ID: 3536939 • Letter: B
Question
Bob obtained the following information from a workstation:
C:>ipconfig
Windows IP Configuration
Ethernet adapter El90x 1:
IP Address : 10.0.0.98
Subnet Mask : 255.255.0.0
Default Gateway : 10.0.250.254
He checked his arp table with the following entry:
C:>arp -a
Interface: 10.0.0.98 on Interface 2
Internet Address Physical Address Type
10.0.250.254 00-eO-bO-ac-ac-a8 dynamic
Next, he executed the following command:
C:>ping 10.0.255.255
And received the following reply:
Pinging 10.0.255.255 with 32 bytes of data:
Reply from 10.0.255.255: bytes=32 time<10ms ttl="255" p="">
Reply from 10.0.255.255: bytes=32 time<10ms ttl="255" p="">
Reply from 10.0.255.255: bytes=32 time<10ms ttl="255" p="">
finally he obtained the following:
C:> arp-a
Interface: 10.0.0.98 on Interface 2
Internet Address Physical Address Type
10.0.116.21 00-00-f4-a9-9d-d4 dynamic
10.0.224.34 00-00-ld-Of-4b-71 dynamic
10.0.108.2 00-00-f4-a9-98-21 dynamic
10.0.17.129 00-00-f4-b1-b6-57 dynamic
10.0.7.141 00-10-5a-05-ef-f9 dynamic
10.0.0.153 00-60-bO-79-c3-80 dynamic
10.0.3.3 00-eO-34-8b-2f-ff dynamic
10.0.1.250 00-00-Oc-4e-32-90 dynamic
10.0.1.251 00-00-Oc-4e-32-90 dynamic
10.0.250.254 00-eO-bO-ac-ac-a8 dynamic
169.254.0.1 00-00-09-6c-4b-58 dynamic
a. How can Bob account for the new entries in his arp table?
b. How would you explain the arp entry for 10.0.1.250 and 10.0.1.251?
c. How would you explain the arp entry for 169.254.0.1?
Explanation / Answer
a) arp tables are maintained as and when ip's are discovered.
These new values came, because they were discovered along the route taken when Bob pinged 10.0.255.255
b) arp entry for 10.0.1.250 and 10.0.1.251 have the same physical address because they possibly both belong to a router on the network, which routes for these two ip's. Arp only shows the physical address of the first encountered device to an ip address, i.e, unless these ip's are separately reached, their physical address will refer to the router's physical address.
c)ARP entry 169.254.0.1 possibly refers to a smaler virtual network within Bob's larger network, where the computers have assigned themselves ip's from a different scheme.
Another possibility is, it refers to an external LAN (other than the one bob is on) which was visited (i.e, the route was taken which went throught it) when the ip 10.0.255.255 was pinged.
The latter is more probable.
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