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• Packet or connection marks (on the same machine only)
• Type of Service (ToS) or Differentiated Services (DiffServ) Field (IP packet)
• Priority Code Point (PCP) Field (Ethernet frame)

There's Traffic Server offers more than one way to set some of these marks and some ways don't work in all scenarios:

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These marks work only when Traffic Server and iproute2 etc. are on the same machine, they aren't communicated to a separate device, however a separate device can might want to copy marks from the ToS/DiffServ or PCP fields to the connection mark to mark traffic sent *from* the origin. iproute2, iptables/ip6tables, and ebtables all support the packet mark:

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The ToS Field was originally specified in RFC 791. Both it and the IPv6 Traffic Class Field were superseded by the DiffServ Field specified in RFC 2474. The IPv4 socket option is setsockopt(sockfd, IPPROTO_IP, IP_TOS, &optval, optlen). The and the IPv6 socket option is setsockopt(sockfd, IPPROTO_IPV6, IPV6_TCLASS, &optval, optlen)

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