[ovs-discuss] CDP (cisco discovery protocol) packets being dropped by OVS

Field, Brian Brian_Field at cable.comcast.com
Sun Mar 29 13:44:58 UTC 2015

I’ve noticed the CDP frames are being dropped by OVS:

# ovs-dpctl dump-flows

skb_priority(0),in_port(2),eth(src=52:54:00:d7:50:8e,dst=01:00:0c:cc:cc:cc),eth_type(0/0xffff), packets:0, bytes:0, used:never, actions:drop

In http://benpfaff.org/~blp/ovs-fields.pdf, it mentions “OpenFlow and Open vSwitch only support LLC headers with DSAP and SSAP 0xaa and control byte 0x03, which indicate that a SNAP header follows the LLC header. In turn, OpenFlow and Open vSwitch only support a SNAP header with organization 0x000000."

CDP frames use LLC/SNAP encapsulation with an organization code of (0xc).  So it would appear this is why CDP frames are being dropped by OVS.

Is the limitation to only support LLC/SNAP with org values of 0x0 a limitation imposed on OVS because OpenFlow doesn’t support or… ?



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