GGSN operation / feature

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Keith keith at rhizomatica.org
Sun Nov 1 02:27:34 UTC 2020


Hi All,

I have scanned 3GPP documents for info on the GGSN IP network facing
side, IIUC how the GGSN responds there is "out of scope" - I'm
specifically wondering about sending ICMP host unreachable messages in
response to packets for IPs that are not currently active in the pool.

Sometimes it would happen where I was pinging an IP assigned to an MS
while looking at other things in the SGSN and PCU but in the meantime
the MS would cycle the PDP context and have a new IP.

For this and maybe other reasons I wrote a proof of concept, probably
not great code, but working, patch to have the GGSN send ICMP host
unreachable.

Do you think this is a desirable feature?

If so I would try to clean it up and submit to code review.

Also if in agreement, would it be worth making it switchable via a vty
param? I am thinking of where one might not want the IP space to be
probable, although I would assume that kind of thing is best left to the
local firewall implementation.

Patch here: http://git.osmocom.org/osmo-ggsn/?h=keith%2Ficmp

Thanks.

K.






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