GRE fields to match GRE flag bits to match Header includes optional key field Header does not include optional key field Header includes optional checksum Header does not include optional checksum Header includes a sequence number field Header does not include a sequence number field EtherType of encapsulated packet ip ip6 arp 802.1q 802.1ad u32:0-65535 Ethernet protocol number u32:0x0-0xffff Ethernet protocol number (hex) ip IPv4 ip6 IPv6 arp Address Resolution Protocol 802.1q VLAN-tagged frames (IEEE 802.1q) 802.1ad Provider Bridging (IEEE 802.1ad, Q-in-Q) gretap Transparent Ethernet Bridging (L2 Ethernet over GRE, gretap) (ip|ip6|arp|802.1q|802.1ad|gretap|0x[0-9a-fA-F]{1,4}) #include GRE Version gre Standard GRE pptp Point to Point Tunnelling Protocol (gre|pptp)