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n-dhcp4: change the default DSCP value to 0

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Section 4.9 of RFC 4594 specifies that DHCP should use the standard
(CS0 = 0) service class. Section 3.2 says that class CS6 is for
"transmitting packets between network devices (routers) that require
control (routing) information to be exchanged between nodes", listing
"OSPF, BGP, ISIS, RIP" as examples of such traffic. Furthermore, it
says that:

      User traffic is not allowed to use this service class.  By user
      traffic, we mean packet flows that originate from user-controlled
      end points that are connected to the network.

Indeed, we got reports of some Cisco switches dropping DHCP packets
because of the CS6 marking.

For these reasons, change the default value to the recommended one,
CS0.
This commit is contained in:
Beniamino Galvani 2024-02-05 10:36:05 +01:00
parent d920b48a5f
commit d8b33e2a97
2 changed files with 2 additions and 2 deletions
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2
src/n-dhcp4/src/n-dhcp4-c-probe.c
View file

@ -198,7 +198,7 @@ _c_public_ void n_dhcp4_client_probe_config_set_init_reboot(NDhcp4ClientProbeCon
*
* This sets the DSCP property of the configuration object, which specifies
* the DSCP value to set in the first six bits of the DS field in the IPv4
* header. If this function is not called, the DSCP will be set to CS6.
* header. If this function is not called, the DSCP will be set to CS0.
*/
_c_public_ void n_dhcp4_client_probe_config_set_dscp(NDhcp4ClientProbeConfig *config, uint8_t dscp) {
config->dscp = dscp & 0x3F;

2
src/n-dhcp4/src/n-dhcp4-private.h
View file

@ -35,7 +35,7 @@ typedef struct NDhcp4LogQueue NDhcp4LogQueue;
#define N_DHCP4_NETWORK_CLIENT_PORT (68)
#define N_DHCP4_MESSAGE_MAGIC ((uint32_t)(0x63825363))
#define N_DHCP4_MESSAGE_FLAG_BROADCAST (htons(0x8000))
#define N_DHCP4_DSCP_DEFAULT (IPTOS_CLASS_CS6 >> 2)
#define N_DHCP4_DSCP_DEFAULT (IPTOS_CLASS_CS0 >> 2)
enum {
N_DHCP4_OP_BOOTREQUEST = 1,