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Bug #5367
closedgsmtap_log not taking into account MTU size and ip fragmentation occurring.
Start date:
12/21/2021
Due date:
% Done:
0%
Spec Reference:
Description
When printing a huge line using gsmtap_log, using something like osmo_hexdup(data, 999):
LOGP(DLLSK, LOGL_DEBUG, "llsk_rx_cb() SAP=%u (%u bytes): %s\n", oph->sap, msgb_length(oph->msg), osmo_hexdump(msgb_data(oph->msg), msgb_length(oph->msg)));
It can be seen in wireshark how it is sent in 3 packets because the MTU size of 1520 is not enough. As a result, one sees a gsmtap_log message followed by 2 "fragmented IP protocol" packets.
148 15:54:25.323044 Dec 21, 2021 16:54:25.323044000 CET 172.18.33.20 49279 172.18.33.203 4729 GSMTAP 1520 llsk_rx_cb() SAP=3 (991 bytes): 1e 00 00 00 28 23 00 01 ac 12 21 cb 00 00 00 00 00 00 00 00 00 00 00 00 00 00 03 00 03 03 51 00 67 00 3c 00 00 00 00 00 00 00 00 00 27 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 149 15:54:25.323046 Dec 21, 2021 16:54:25.323046000 CET 172.18.33.20 172.18.33.203 IPv4 1520 Fragmented IP protocol (proto=UDP 17, off=1480, ID=9f09) 150 15:54:25.323046 Dec 21, 2021 16:54:25.323046000 CET 172.18.33.20 172.18.33.203 IPv4 194 Fragmented IP protocol (proto=UDP 17, off=2960, ID=9f09)
I attach a pcap with the related 3 packets.
Ideally, gsmtap_log should take into account (at least the local) MTU and split the log line into UDP messages, each one with a gsmtap_log header.
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