IPv6 has a traffic class field. According to the specification it is an IPv6 length, out of which first 6 bits are called code point or differential services code point (DSCP) and the last 2 bits are used for explicit congestion notification(ECN). These 6 bit combinations (DSCP) are used to classify IP packets so that one class of IP packet can receive precedence over the other in a network.

IPv4 has a field, called type of service (ToS). According to some references it is also used to carry DSCP and ECN bits (as for example explained in a video). However according to my professor IPv4 packets have no priority, which implies that this field is used for something else.

What is correct?

  • There is such a thing as overdoing formatting. Your question doesn't get more readable by using different types of fonts, bold and italic text all mixed up. Please consider applying formatting only where it has a real use.
    – Teun Vink
    Sep 14, 2021 at 13:22
  • It is DSCP (Differentiated Services Code Point), not DSCN.
    – Ron Maupin
    Sep 14, 2021 at 13:29
  • and please provide references to the sources of your information
    – Effie
    Sep 14, 2021 at 13:42
  • @effenok see this video
    – S. M.
    Sep 14, 2021 at 14:11
  • who said that IPv4 packets have no priority?
    – Effie
    Sep 14, 2021 at 14:16

1 Answer 1


why Ipv4 packets have no priority but Ipv6 packets have priority.

Both IPv4 and IPv6 packets use DSCP the same way. Neither IP actually uses the DSCP or ECN. Network devices can be configured to use those in various ways when there is congestion on an interface, but that is up to the network administrators. By default, network devices ignore DSCP and ECN. Neither field is used on the public Internet for either IP.

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    – Ron Maupin
    Sep 26, 2021 at 16:16

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