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Community Member

IP OPTIONS SELECTIVE DROP against fragmentation

Regarding the IP OPTIONS SELECTIVE DROP command in the IOS 12.0s. If the IGNORE preference was selected, which is said to pass the packet containing the unknown option as a pure IP ignoring but not removing the option, then what if the router also is to fragment this packet, should it copy this ignored option to each fragment or not?


Re: IP OPTIONS SELECTIVE DROP against fragmentation

As I understand it will copy the option in the fragmented packet also.

ip options {drop | ignore}

drop - Router drops all IP options packets that it receives.

ignore - Router ignores all options and treats the packets as though they do not have any IP options. (The options are not removed from the packetjust ignored.)

Community Member

Re: IP OPTIONS SELECTIVE DROP against fragmentation

Thank you very much for your answer. Ye,. I'm also at your side; (most probably the option would be copied at the line rate). Although it was not explicitly written in the feature overview of the (IP OPTIONS SELECTIVE DROP), but your answer could really be visioned more logic in accordance to the handling of the data stream from the hardware perspective. I want to say that since the hardware is directed to ignore the option and treat the header as a pure IP Header, then it should also deal with the IP header -when packet should be fragmented- the same way if would any other real pure IP.

However, there is also a contradicting vision which is:

May be the router's hardware in the case of (IGNORE), should be visioning the optioned IP header as a pure one (optionless), by confining to only 5 words which, results in excluding the ip options from any consideration, including fragmentation functions.

Any corrections or comments regarding this analysis.

Thank you all

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