Osmocom Libraries » libosmocore

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.