SCION and In-band Network Telemetry Layers for Scapy

Scapy is an interactive packet manipulation program/library for Python. This repository contains Scapy packet header definitions ("layers") for SCION and In-band Network Telemetry (INT) on top of SCION. Just start Scapy by running sudo ./scapy_scion.py and the new headers are available at the interactive command line.

Supported headers:

• SCION (with path types EmptyPath, SCION, and OneHopPath)
• SCION Hop-by-Hop and End-to-End Options Header
• SCMP (only Echo Request and Reply)
• BFD over SCION
• INT-MD over UDP
• Inter-domain INT for SCION

Some SCION tools built with Scapy are available in tools.

Dependencies

• Python 3
• Scapy (2.5.0)
• Additional Python packages:
  • cryptography (39.0.0)

Installation on Ubuntu 22.04.1:

sudo apt-get install python3 python3-pip
sudo pip install --pre scapy[basic]
pip install cryptography

Run Unit Tests

python -m unittest

Getting Started: Craft and Send a SCION Packet

1. Ping the target AS.

Replace 127.0.0.27:30255 with the address of your SCION daemon and the destination AS with the AS you want to send packets to.

bin/scion ping --sciond 127.0.0.27:30255 2-ff00:0:211,127.0.0.1

2. Launch Scapy in a second terminal and capture one of the echo requests.

Replace IP 127.0.0.25 and port 31014 with the internal address of your border router.

sudo ./scapy_scion.py
bind_layers(UDP, SCION, dport=31014)
bind_layers(UDP, SCION, sport=31014)
pkts = sniff(iface="lo",
    filter="host 127.0.0.25 and port 31014",
    lfilter=lambda pkt: pkt.haslayer(SCMP) and pkt[SCMP].Type==128,
    prn=lambda pkt: pkt.summary(), count=1)

3. Extract the IP/UDP underlay and the SCION header.

p = pkts[0][IP]
p[SCION].remove_payload()
del p[IP].len
del p[IP].chksum
del p[UDP].len
del p[UDP].chksum
del p[SCION].NextHdr
del p[SCION].HdrLen
del p[SCION].PayloadLen

4. Build a new packet (e.g., a new echo request) and send it.

Changing conf.L3Socket to L3RawSocket is required in order to send packets to local applications. Refer to this FAQ.

req = p/SCMP(Message=EchoRequest(Identifier=0xabcd, Data=b"Hello!"))
req[SCION].DstHostAddr = "127.0.0.2"
conf.L3socket = L3RawSocket
resp = sr1(req, iface="lo", timeout=1)
resp.show()