Explain why the Telnet session was established to one of the hosts with the duplicate address and not the other. Explain why the Telnet session was established at all and did not result in an error message. Use the ARP cache and the captured packets to support your explanation.
What will be an ideal response?
When a host tries to establish telnet connection, it first checks its to see if the host with which it is
trying to establish telnet connection is present in the ARP cache. If there is no cache information,
then an ARP request is broadcasted through the network. Here there are two hosts(PC1 & PC4) with
the same IP address. PC3 receives an ARP reply from PC1 first and hence establishes the telnet
connection. PC4’s ARP response which comes in later is ignored by PC3 (determined by checking
the ARP cache). There is exactly one telnet session and that is between PC3 and PC1. Henceforth
whatever IP datagrams are sent by PC3 will uniquely identify PC1 as they will contain both the IP
address and MAC address of PC1, PC4 will not read the packets as the destination MAC address of
the IP datagrams will not match with its own and there will not be any errors.
The first few packets which concern with establishment of the session are included :–
No. Time Source Destination Protocol Info
1 0.000000 00:50:bf:75:1f:32 ff:ff:ff:ff:ff:ff ARP Who has 10.0.1.11? Tell 10.0.1.13
2 0.000095 00:50:bf:75:16:95 00:50:bf:75:1f:32 ARP 10.0.1.11 is at 00:50:bf:75:16:95
3 0.000116 10.0.1.13 10.0.1.11 TCP 34605 > 23 [SYN] Seq=1563346678 Ack=0 Win=5840 Len=0
4 0.000100 00:50:bf:74:ff:90 00:50:bf:75:1f:32 ARP 10.0.1.11 is at 00:50:bf:74:ff:90
5 0.000413 10.0.1.11 10.0.1.13 TCP 23 > 34605 [SYN, ACK] Seq=1118469189 Ack=1563346679
Win=5792 Len=0
6 0.000457 10.0.1.13 10.0.1.11 TCP 34605 > 23 [ACK] Seq=1563346679 Ack=1118469190
Win=5840 Len=0
The ARP cache is:
? (10.0.1.11) at 00:50:BF:75:16:95 [ether] on eth0
```
Frame 1 (42 on wire, 42 captured)
Arrival Time: Aug 1, 2003 23:52:27.026932
Time delta from previous packet: 0.000000 seconds
19
Time relative to first packet: 0.000000 seconds
Frame Number: 1
Packet Length: 42 bytes
Capture Length: 42 bytes
Ethernet II
Destination: ff:ff:ff:ff:ff:ff (ff:ff:ff:ff:ff:ff)
Source: 00:00:c0:a1:4f:00 (00:00:c0:a1:4f:00)
Type: ARP (0x0806)
Address Resolution Protocol (request)
Hardware type: Ethernet (0x0001)
Protocol type: IP (0x0800)
Hardware size: 6
Protocol size: 4
Opcode: request (0x0001)
Sender hardware address: 00:00:c0:a1:4f:00
Sender protocol address: 10.0.1.13
Target hardware address: 00:00:00:00:00:00
Target protocol address: 10.0.1.11
Frame 2 (60 on wire, 60 captured)
Arrival Time: Aug 1, 2003 23:52:27.026932
Time delta from previous packet: 0.000000 seconds
Time relative to first packet: 0.000000 seconds
Frame Number: 2
Packet Length: 60 bytes
Capture Length: 60 bytes
Ethernet II
Destination: 00:00:c0:a1:4f:00 (00:00:c0:a1:4f:00)
Source: 00:50:bf:73:4e:5c (00:50:bf:73:4e:5c)
Type: ARP (0x0806)
Trailer: 7A12F598801816A0D54300000101080A...
Address Resolution Protocol (reply)
Hardware type: Ethernet (0x0001)
Protocol type: IP (0x0800)
Hardware size: 6
Protocol size: 4
Opcode: reply (0x0002)
Sender hardware address: 00:50:bf:73:4e:5c
Sender protocol address: 10.0.1.11
Target hardware address: 00:00:c0:a1:4f:00
Target protocol address: 10.0.1.13
Frame 3 (74 on wire, 74 captured)
Arrival Time: Aug 1, 2003 23:52:27.026932
Time delta from previous packet: 0.000000 seconds
Time relative to first packet: 0.000000 seconds
Frame Number: 3
Packet Length: 74 bytes
Capture Length: 74 bytes
Ethernet II
Destination: 00:50:bf:73:4e:5c (00:50:bf:73:4e:5c)
Source: 00:00:c0:a1:4f:00 (00:00:c0:a1:4f:00)
Type: IP (0x0800)
20
Internet Protocol, Src Addr: 10.0.1.13 (10.0.1.13), Dst Addr: 10.0.1.11 (10.0.1.11)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 60
Identification: 0xf681
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x2e23 (correct)
Source: 10.0.1.13 (10.0.1.13)
Destination: 10.0.1.11 (10.0.1.11)
Transmission Control Protocol, Src Port: 1025 (1025), Dst Port: 23 (23),
Seq: 2332344669, Ack: 0
Source port: 1025 (1025)
Destination port: 23 (23)
Sequence number: 2332344669
Header length: 40 bytes
Flags: 0x0002 (SYN)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...0 .... = Acknowledgment: Not set
.... 0... = Push: Not set
.... .0.. = Reset: Not set
.... ..1. = Syn: Set
.... ...0 = Fin: Not set
Window size: 5840
Checksum: 0x92c9 (correct)
Options: (20 bytes)
Maximum segment size: 1460 bytes
SACK permitted
Time stamp: tsval 14300, tsecr 0
NOP
Window scale: 0 bytes
Frame 4 (60 on wire, 60 captured)
Arrival Time: Aug 1, 2003 23:52:27.026932
Time delta from previous packet: 0.000000 seconds
Time relative to first packet: 0.000000 seconds
Frame Number: 4
Packet Length: 60 bytes
Capture Length: 60 bytes
Ethernet II
Destination: 00:00:c0:a1:4f:00 (00:00:c0:a1:4f:00)
Source: 00:00:c0:3f:4f:00 (00:00:c0:3f:4f:00)
Type: ARP (0x0806)
21
Trailer: 00000000000000000000000000000000...
Address Resolution Protocol (reply)
Hardware type: Ethernet (0x0001)
Protocol type: IP (0x0800)
Hardware size: 6
Protocol size: 4
Opcode: reply (0x0002)
Sender hardware address: 00:00:c0:3f:4f:00
Sender protocol address: 10.0.1.11
Target hardware address: 00:00:c0:a1:4f:00
Target protocol address: 10.0.1.13
Frame 5 (74 on wire, 74 captured)
Arrival Time: Aug 1, 2003 23:52:27.026932
Time delta from previous packet: 0.000000 seconds
Time relative to first packet: 0.000000 seconds
Frame Number: 5
Packet Length: 74 bytes
Capture Length: 74 bytes
Ethernet II
Destination: 00:00:c0:a1:4f:00 (00:00:c0:a1:4f:00)
Source: 00:50:bf:73:4e:5c (00:50:bf:73:4e:5c)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.1.11 (10.0.1.11), Dst Addr: 10.0.1.13 (10.0.1.13)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 60
Identification: 0x0000
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x24a5 (correct)
Source: 10.0.1.11 (10.0.1.11)
Destination: 10.0.1.13 (10.0.1.13)
Transmission Control Protocol, Src Port: 23 (23), Dst Port: 1025 (1025),
Seq: 2497906152, Ack: 2332344670
Source port: 23 (23)
Destination port: 1025 (1025)
Sequence number: 2497906152
Acknowledgement number: 2332344670
Header length: 40 bytes
Flags: 0x0012 (SYN, ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...1 .... = Acknowledgment: Set
22
.... 0... = Push: Not set
.... .0.. = Reset: Not set
.... ..1. = Syn: Set
.... ...0 = Fin: Not set
Window size: 5792
Checksum: 0x2718 (correct)
Options: (20 bytes)
Maximum segment size: 1460 bytes
SACK permitted
Time stamp: tsval 381183, tsecr 14300
NOP
Window scale: 0 bytes
Frame 6 (66 on wire, 66 captured)
Arrival Time: Aug 1, 2003 23:52:27.026932
Time delta from previous packet: 0.000000 seconds
Time relative to first packet: 0.000000 seconds
Frame Number: 6
Packet Length: 66 bytes
Capture Length: 66 bytes
Ethernet II
Destination: 00:50:bf:73:4e:5c (00:50:bf:73:4e:5c)
Source: 00:00:c0:a1:4f:00 (00:00:c0:a1:4f:00)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.1.13 (10.0.1.13), Dst Addr: 10.0.1.11 (10.0.1.11)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 52
Identification: 0xf682
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x2e2a (correct)
Source: 10.0.1.13 (10.0.1.13)
Destination: 10.0.1.11 (10.0.1.11)
Transmission Control Protocol, Src Port: 1025 (1025), Dst Port: 23 (23),
Seq: 2332344670, Ack: 2497906153
Source port: 1025 (1025)
Destination port: 23 (23)
Sequence number: 2332344670
Acknowledgement number: 2497906153
Header length: 32 bytes
Flags: 0x0010 (ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
23
...1 .... = Acknowledgment: Set
.... 0... = Push: Not set
.... .0.. = Reset: Not set
.... ..0. = Syn: Not set
.... ...0 = Fin: Not set
Window size: 5840
Checksum: 0x55ad (correct)
Options: (12 bytes)
NOP
NOP
Time stamp: tsval 14300, tsecr 381183
Frame 7 (78 on wire, 78 captured)
Arrival Time: Aug 1, 2003 23:52:27.046932
Time delta from previous packet: 0.020000 seconds
Time relative to first packet: 0.020000 seconds
Frame Number: 7
Packet Length: 78 bytes
Capture Length: 78 bytes
Ethernet II
Destination: 00:00:c0:a1:4f:00 (00:00:c0:a1:4f:00)
Source: 00:50:bf:73:4e:5c (00:50:bf:73:4e:5c)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.1.11 (10.0.1.11), Dst Addr: 10.0.1.13 (10.0.1.13)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x10 (DSCP 0x04: Unknown DSCP; ECN: 0x00)
0001 00.. = Differentiated Services Codepoint: Unknown (0x04)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 64
Identification: 0xd516
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x4f7a (correct)
Source: 10.0.1.11 (10.0.1.11)
Destination: 10.0.1.13 (10.0.1.13)
Transmission Control Protocol, Src Port: 23 (23), Dst Port: 1025 (1025),
Seq: 2497906153, Ack: 2332344670
Source port: 23 (23)
Destination port: 1025 (1025)
Sequence number: 2497906153
Next sequence number: 2497906165
Acknowledgement number: 2332344670
Header length: 32 bytes
Flags: 0x0018 (PSH, ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
24
...1 .... = Acknowledgment: Set
.... 1... = Push: Set
.... .0.. = Reset: Not set
.... ..0. = Syn: Not set
.... ...0 = Fin: Not set
Window size: 5792
Checksum: 0x1e84 (correct)
Options: (12 bytes)
NOP
NOP
Time stamp: tsval 381185, tsecr 14300
Telnet
Command: Do Terminal Type
Command: Do Terminal Speed
Command: Do X Display Location
Command: Do New Environment Option
Frame 8 (66 on wire, 66 captured)
Arrival Time: Aug 1, 2003 23:52:27.046932
Time delta from previous packet: 0.000000 seconds
Time relative to first packet: 0.020000 seconds
Frame Number: 8
Packet Length: 66 bytes
Capture Length: 66 bytes
Ethernet II
Destination: 00:50:bf:73:4e:5c (00:50:bf:73:4e:5c)
Source: 00:00:c0:a1:4f:00 (00:00:c0:a1:4f:00)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.1.13 (10.0.1.13), Dst Addr: 10.0.1.11 (10.0.1.11)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 52
Identification: 0xf683
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: TCP (0x06)
Header checksum: 0x2e29 (correct)
Source: 10.0.1.13 (10.0.1.13)
Destination: 10.0.1.11 (10.0.1.11)
Transmission Control Protocol, Src Port: 1025 (1025), Dst Port: 23 (23),
Seq: 2332344670, Ack: 2497906165
Source port: 1025 (1025)
Destination port: 23 (23)
Sequence number: 2332344670
Acknowledgement number: 2497906165
Header length: 32 bytes
25
Flags: 0x0010 (ACK)
0... .... = Congestion Window Reduced (CWR): Not set
.0.. .... = ECN-Echo: Not set
..0. .... = Urgent: Not set
...1 .... = Ac
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