Support for pvcX (Frame Relay) interfaces

[mnhauke]

Starting with a recent commit to the Linux kernel any ethertypes are now passed from hdlcX to the pvcX sub-interfaces.

After the initial setup with with:

# sethdlc hdlc0 fr lmi ansi
# sethdlc hdlc0 create 102
# ip link set hdlc0 up
# ip link set pvc0 up
# ip address add 1.1.1.2 peer 1.1.1.1 dev pvc0

those network interfaces look like this:

$ ip -d l l dev hdlc0
9: hdlc0: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 50
    link/frad  promiscuity 0 minmtu 68 maxmtu 1500 addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535

$ ip -d l l dev pvc0
10: pvc0: <POINTOPOINT,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
    link/dlci 00:66 peer 18:61 promiscuity 0 minmtu 68 maxmtu 1500 addrgenmode eui64 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535

It would be interesting to have support for these non-ethernet pvcX interfaces.

Here are some pcaps with LLDP frames passing through hdlc0 and pvc0 interfaces from a Linux system connected to a HP Procurve router:
hdlc0.pcap.gz

$ sudo tcpdump -ihdlc0 -s0 -n -w /tmp/hdlc0
tcpdump: listening on hdlc0, link-type FRELAY (Frame Relay), capture size 262144 bytes

pvc0.pcap.gz

$ sudo tcpdump -ipvc0 -n -s0 -w /tmp/pvc0.pcap
tcpdump: listening on pvc0, link-type RAW (Raw IP), capture size 262144 bytes

I recently posted some information about the Linux generic HDLC layer (including Frame Relay) on the osmocom wiki:
https://osmocom.org/projects/e1-t1-adapter/wiki/Linux_generic_HDLC_layer_+_DAHDI/

[vincentbernat]

This is not trivial as Ethernet is quite hard-coded for LLDP, but there could be an abstraction to support other encapsulations. Wireshark is able to decode HDLC, but not PVC. Looking at the bytes, I don't see the SNAP header with 0x88cc as Ethernet type.