VOS>ping 192.168.12.9 Pinging host 192.168.12.9 : 192.168.12.9 ping: No reply. Time Out !! ping: No reply. Time Out !! ping: No reply. Time Out !! ping: No reply. Time Out !! Host 192.168.12.9 replied to 0 of the 4 pings ready 20:48:13 VOS> |
The following trace implies that it is. There could be many reasons for the VOS system to not see the replies.
No. Time Source Destination Protocol Info 1 0.000000000 192.168.1.137 192.168.12.9 ICMP Echo (ping) request Internet Control Message Protocol Type: 8 (Echo (ping) request) Code: 0 () Checksum: 0x4bb3 [correct] Identifier: 0x0000 Sequence number: 11437 (0x2cad) Data (64 bytes) 2 0.050319672 192.168.12.9 192.168.1.137 ICMP Echo (ping) reply Internet Control Message Protocol Type: 0 (Echo (ping) reply) Code: 0 () Checksum: 0x8d64 [correct] Identifier: 0xc64e Sequence number: 11437 (0x2cad) Data (64 bytes) 3 15.000925064 192.168.1.137 192.168.12.9 ICMP Echo (ping) request Internet Control Message Protocol Type: 8 (Echo (ping) request) Code: 0 () Checksum: 0x4bb3 [correct] Identifier: 0x0000 Sequence number: 11437 (0x2cad) Data (64 bytes) 4 15.050540924 192.168.12.9 192.168.1.137 ICMP Echo (ping) reply Internet Control Message Protocol Type: 0 (Echo (ping) reply) Code: 0 () Checksum: 0x8d64 [correct] Identifier: 0xc64e Sequence number: 11437 (0x2cad) Data (64 bytes) 5 30.001644134 192.168.1.137 192.168.12.9 ICMP Echo (ping) request Internet Control Message Protocol Type: 8 (Echo (ping) request) Code: 0 () Checksum: 0x4bb3 [correct] Identifier: 0x0000 Sequence number: 11437 (0x2cad) Data (64 bytes) 6 30.051267624 192.168.12.9 192.168.1.137 ICMP Echo (ping) reply Internet Control Message Protocol Type: 0 (Echo (ping) reply) Code: 0 () Checksum: 0x8d64 [correct] Identifier: 0xc64e Sequence number: 11437 (0x2cad) Data (64 bytes) 7 45.002258301 192.168.1.137 192.168.12.9 ICMP Echo (ping) request Internet Control Message Protocol Type: 8 (Echo (ping) request) Code: 0 () Checksum: 0x4bb3 [correct] Identifier: 0x0000 Sequence number: 11437 (0x2cad) Data (64 bytes) 8 45.051847458 192.168.12.9 192.168.1.137 ICMP Echo (ping) reply Internet Control Message Protocol Type: 0 (Echo (ping) reply) Code: 0 () Checksum: 0x8d64 [correct] Identifier: 0xc64e Sequence number: 11437 (0x2cad) Data (64 bytes) |
Now the question is why do the replies not match the requests. Tracing each leg of the network it was determined that an F5 BIG-IP running the Local Traffic Manager application release 9.1.3 Build 39.0 was changing the ICMP packet before it forwarded it on to the 192.168.12.0 subnet. The 192.168,12,9 host saw the ping with the changed Identifier field and correctly responded to the ping that it received. It appears that the F5 device only makes the change only when the Identifier field is zero, non-zero fields are not changed.
Since the F5 device correctly updates the checksum in the ICMP and IP packet headers I have to assume that it is changing the Identifier field on purpose although I do not understand why. According to the Internet Control Message Protocol RFC (792) the Identifier field may be 0. If the device felt that the ICMP packet was invalid I could understand it discarding the packet but I do not understand why it would change it.