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Extended ping question....

For a lab we had use the extended ping command with the Record option.

Question.....the first set is always 0.0.0.0, why is that?  Part of my output is below.

I have already checked out : http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f22.shtml, but that didnt yield any answers.

SanJose2# ping
Protocol [ip]:
Target IP address: 192.168.100.1
Repeat count [5]: 2
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: 172.16.32.1
Type of service [0]:
Set DF bit in IP header? [no]:
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]: record
Number of hops [ 9 ]:
Loose, Strict, Record, Timestamp, Verbose[RV]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.100.1, timeout is 2 seconds:
Packet has IP options: Total option bytes= 39, padded length=40
Record route: <*>
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)
(0.0.0.0)

Reply to request 0 (48 ms). Received packet has options
Total option bytes= 40, padded length=40
Record route:
(172.16.1.2)
(192.168.1.6)
(192.168.100.1)

Thank you,

Jimmy

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Extended ping question....

Hi Jimmy,

IP packets using the Record Route option contain extra fields in their IP headers to store the individual traversed IP addresses into (at most 9). RFC 791 is specific about this:

        The originating host must compose this option with a large
        enough route data area to hold all the address expected.  The
        size of the option does not change due to adding addresses.  The
        intitial contents of the route data area must be zero.

In other words, sender of this IP packet extends its IP header with a sufficient number of bytes to hold the necessary count of traversed IP addresses, and they should be filled with zeros. This is why you see the first ping request being sent with all zeros.

The question is actually, why does the extended ping send subsequent ping requests with this area being non-zero and instead containing the list of IP addresses from the last reply (at least it says it is doing so), thereby conflicting the RFC 791. Nevertheless, the initial value of this field is actually uninteresting, as this field is simply overwritten each time the packet traverses a network, so I would personally find this a nuisance, not a real problem.

Best regards,

Peter

3 REPLIES
Cisco Employee

Re: Extended ping question....

Hi Jimmy,

IP packets using the Record Route option contain extra fields in their IP headers to store the individual traversed IP addresses into (at most 9). RFC 791 is specific about this:

        The originating host must compose this option with a large
        enough route data area to hold all the address expected.  The
        size of the option does not change due to adding addresses.  The
        intitial contents of the route data area must be zero.

In other words, sender of this IP packet extends its IP header with a sufficient number of bytes to hold the necessary count of traversed IP addresses, and they should be filled with zeros. This is why you see the first ping request being sent with all zeros.

The question is actually, why does the extended ping send subsequent ping requests with this area being non-zero and instead containing the list of IP addresses from the last reply (at least it says it is doing so), thereby conflicting the RFC 791. Nevertheless, the initial value of this field is actually uninteresting, as this field is simply overwritten each time the packet traverses a network, so I would personally find this a nuisance, not a real problem.

Best regards,

Peter

Re: Extended ping question....

Good explanation, thank you.

New Member

Re: Extended ping question....

Hi Pete,

Noted with Thanks.

Ever Friendly,

ThiyaguVG.

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