The ppp decapsulator in tcpdump 4.9.3 can be convinced to allocate a large amount of memory.
{ "availability": "Available with Ubuntu Pro (Infra-only): https://ubuntu.com/pro", "ubuntu_priority": "low", "binaries": [ { "binary_version": "4.9.3-0ubuntu0.16.04.1+esm1", "binary_name": "tcpdump" }, { "binary_version": "4.9.3-0ubuntu0.16.04.1+esm1", "binary_name": "tcpdump-dbgsym" } ] }