What are the effects of enabling RFC4821 on the VCS

[Michael Rubin]

                   Was wondering what network effects would occur from enabling IP RGC4821 Mode on the VCS?  Does this pose a security risk? Would any other changes need to be made on VCS for normal communication?  Currently firwall is giving an error to PMTU-D.  Call connects but no video is sent.  It only works if call is forced to SIP.

[Michael Rubin]

RFC 4821 is what I want to enable.

[mahkrish]

Hi Michael,

Please refer to the following document on PMTUD https://supportforums.cisco.com/docs/DOC-23594

HTH.

BR, Mahesh Adithiyha

[sagsheth]

Hi Michael,

RFC4821 provide mechanism to detect unreachable UDP port, for if there is link congestion.

It uses ICMP Type 3 code 3 -Destination not reachable when a UDP port is blocked.

If there is congestion on link, far-end or intermidiate devices does not support the MTU as present value, it will send ICMP type 3 code 4 fragmentation needed.

If DF bit (dont fragmnet bit) is set in IP header flag, it will be informed as well.It does not pose any security threat from what i know and it will not affect the normal communication of the VCS.

Hope it helps

Regards,

Sagar

[ahmashar]

what is your end goal as a result of enabling RFC4821?