DSCP Propagation and Default CoS on ACX Series Routers
Junos OS Evolved uses default CoS and rewrite functions on ACX Series routers. As a result, Differentiated Services code point (DSCP) can't propagate from the native payload to the VXLAN tunnel header.
Starting in Junos OS Evolved release 22.1R1, use our new command set system
packet-forwarding-options no-ip-tos-rewrite to allow DSCP propagation for VXLAN
traffic. When you configure or delete DSCP propagation, the evo-pfemand
process restarts.
The new CLI command can handle IP code point propagation, but VLAN Priority Code Point (PCP) propagation is not supported.
Benefits of DSCP Propagation and Default CoS Support for EVPN VXLANs
The set system packet-forwarding-options no-ip-tos-rewrite command enables
the DSCP field from the incoming packet to propagate to the VXLAN encapsulated packet. This
allows CoS to be applied to VXLAN encapsulated packets as they traverse the network.
Default CoS and DSCP propagation on VXLAN interfaces
In previous releases, the DSCP information in the incoming (native) payload does not propagate to the VXLAN tunnel header. Therefore, the DSCP of the VXLAN packet is set to zero. With the new CLI command, the DSCP of the native payload propagates to the VXLAN tunnel header.
The Layer 3 classifier (inet-precedence, DSCP, DSCPv6) at the ingress interface classifies packets to a forwarding class and loss priority. With the new command, the Layer 3 classifier classifies packets using the DSCP of the native packet since the DSCP of the native payload is always retained.
The Table 1 provide a summary of the CoS, Layer 3, and L3 and L2 classifier behavior when you enable the CLI command.
|
CoS Behavior with CLI Command |
CoS Behavior without CLI Command |
|---|---|
|
Disables L3 rewrite |
Existing CoS function |
|
Retains the DSCP of the native payload |
Retains the DSCP of the native payload |
|
Enables DSCP propagation for both VXLAN L2 and VXLAN L3, with the L3 classifier explicitly attached to the user-to-network (UNI) interface for an L2. |
DSCP of the VXLAN packet is set to zero |
Layer 3 Classifier Behavior
|
Ingress Classifier Type |
Egress Rewrite Type |
Ingress Packet DSCP |
Support for Rewrite as per Configured Rewrite |
|---|---|---|---|
|
L3 (DSCP, DSCP IPv6, IP Precedence) on L2 or L3 IFL |
L3 |
not applicable |
Preserves only the configured rewrite |
|
L3 (DSCP, DSCP IPv6, IP Precedence) on L2 or L3 IFL |
IEEE 802.1p/ad, EXP |
not applicable |
Preserves only the configured rewrite Does not allow rewrite or preserve the configured rewrite for IEEE 802.1p and IEEE 802.1pad/EXP |
|
L2 (IEEE 802.1p/ad) on L2 IFL |
IEEE 802.1p/ad |
not applicable |
Supports rewrite and preserves if DSCP is present |
|
MPLS EXP |
IEEE 802.1p/ad, MPLS EXP |
not applicable |
Yes |
|
L3 (DSCP, DSCP IPv6, IP Precedence) |
IEEE 802.1p/ad, EXP |
0 to 7 |
The rewrite configuration is preserved if the ingress DSCP matches the forwarding class id used in the rewrite rule. For IEEE 802.1p, EXP rewrite occurs per the rewrite rule IEEE 802.1p, EXP rewrite occurs as per the rewrite rule (forwarding class, loss priority to IEEE 802.1p/EXP). For IEEE 802.1p, the EXP bits are set to zero. |
|
L3 (DSCP, DSCP IPv6, IP Precedence) |
IEEE 802.1p/ad, EXP |
More than 7 |
For IEEE 802.1p, the EXP bits are set to zero |
The Table 3 provides a summary of the L3 and L2 classifier behavior when you enable the CLI command.
|
Input Packet |
Type of Interface at UNI |
Classifier |
User Configuration |
Ingress Remark |
Egress Rewrite |
VXLAN Encapsulated Packet DSCP |
Description |
|---|---|---|---|---|---|---|---|
|
L3 IPv4 and IPv6 |
IRB/L3 UNI |
DSCP default |
None |
No |
No |
PCP/DEI of inner packet |
None |
|
L2 carrying IPv4 and IPv6 |
L2 |
PCP default |
DSCP classifier |
No |
No |
PCP/DEI of inner packet |
User needs to configure DSCP classifier explicitly on L2 UNI. |
|
Pure L2 (no IP payload) |
L2 |
PCP default |
DSCP classifier |
No |
No |
PCP /DEI of inner packet having VLAN tag Example: PCP/DEI bits = 100/1 => DSCP = 1001 =9 (decimal); DSCP =0 with untagged packet; DSCP=0 with native tagging |
User needs to configure DSCP classifier explicitly on L2 UNI; On QFX, DSCP=0 on VXLAN encapsulated packet irrespective of single tagged, untagged and native tagged packets at L2 UNI. |
Limitations
When you enable the new CLI command on an ACX Series router:
-
The IP DSCP or IP Precedence rewrite is disabled in the system and network. As a result, you can't execute L3 rewrite (DSCP, DSCP IPv6, IP precedence).
-
IEEE 802.1p code point bits in the packet header retain their original header. IEEE 802.1p propagation is not supported.