On ACX5448 after upgrading to Junos 23.4R2-S4, all IPv6 traffic stopped working when BGP-LU (BGP Labeled Unicast) is used.
No IPv6 traffic getting forwarded by the ACX.
Between ACX and peer device BGP-LU is configured for IPv6 traffic:-
group BGP-RR {
type internal;
description BGP-RR;
local-address 2.2.2.2;
family inet {
unicast;
}
family inet6 {
labeled-unicast {
explicit-null;
From peer device, push 2 is used:
user@router> show route forwarding-table destination 2001::105
Routing table: default.inet6
Internet6:
Destination Type RtRef Next hop Type Index NhRef Netif
2001::105/127
user 0 indr 1051121 5
1.1.1.1 Push 2 7558 2 ae11.100
On ACX:
user@router# run show route table mpls.0
mpls.0: 11 destinations, 11 routes (11 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
0 *[MPLS/0] 00:21:03, metric 1
to table inet.0
0(S=0) *[MPLS/0] 00:21:03, metric 1
to table mpls.0
1 *[MPLS/0] 3d 22:33:15, metric 1
Receive
2 *[MPLS/0] 00:21:03, metric 1
to table inet6.0
2(S=0) *[MPLS/0] 00:21:03, metric 1
13 *[MPLS/0] 3d 22:33:15, metric 1
Multiple traffic items may experience packet loss due to incorrect handling of label routes. The issue stems from a change in the label route processing path (create/delete/rebake) that introduces a conditional check to skip label routes where the bottom-of-stack (S) bit is 0. This inadvertently filters out explicit null labels label 0 (IPv4) and label 2 (IPv6)which are required for proper forwarding in 6vpe configurations. As these labels are essential for signaling implicit null behavior in SR-MPLS, their exclusion causes the Packet Forwarding Engine (PFE) to drop IPv6 VPN traffic (IPv6 over MPLS), leading to loss of service connectivity.
This is tracked via https://prsearch.juniper.net/problemreport/PR1853294
And its fixed in: