This article describes why ISIS IPv4 route tags are lost while IPv6 tags are preserved when traffic-engineering is disabled. This behavior is expected.
SRX-1 ge-0/0/0------------------------------------ge-0/0/0 SRX-2
SRX-1 and SRX-2 are running ISIS routing protocol for both IPv4 and IPv6, initially with traffic engineering enabled.
SRX-2 is redistributing static routes with tags into ISIS by routing policy:
root@SRX-2# show routing-options
rib inet6.0 {
static {
route 2001:9999:8888:7777::/64 {
reject;
tag 200;
}
}
}
static {
route 192.168.0.0/24 {
reject;
tag 100;
}
}
On SRX-1 they are seen with corresponding route-tag:
root@SRX-1# run show route protocol isis
inet.0: 8 destinations, 8 routes (8 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
2.2.2.2/32 *[IS-IS/18] 00:28:52, metric 10
> to 10.10.10.2 via ge-0/0/0.0
192.168.0.0/24 *[IS-IS/165] 00:10:20, metric 10, tag 100
> to 10.10.10.2 via ge-0/0/0.0
iso.0: 1 destinations, 1 routes (1 active, 0 holddown, 0 hidden)
inet6.0: 7 destinations, 7 routes (7 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
2001:2222::2/128 *[IS-IS/18] 00:27:18, metric 10
> to fe80::250:56ff:feaa:4b5b via ge-0/0/0.0
2001:9999:8888:7777::/64
*[IS-IS/165] 00:27:18, metric 10, tag 200
> to fe80::250:56ff:feaa:4b5b via ge-0/0/0.0
However, when traffic-engineering is disabled, route tag for IPv4 route is lost, but route tag for IPv6 route is still present:
root@SRX-1# run show route protocol isis
inet.0: 8 destinations, 8 routes (8 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
2.2.2.2/32 *[IS-IS/18] 00:30:14, metric 10
> to 10.10.10.2 via ge-0/0/0.0
192.168.0.0/24 *[IS-IS/165] 00:00:05, metric 10
> to 10.10.10.2 via ge-0/0/0.0
iso.0: 1 destinations, 1 routes (1 active, 0 holddown, 0 hidden)
inet6.0: 7 destinations, 7 routes (7 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
2001:2222::2/128 *[IS-IS/18] 00:28:40, metric 10
> to fe80::250:56ff:feaa:4b5b via ge-0/0/0.0
2001:9999:8888:7777::/64
*[IS-IS/165] 00:28:40, metric 10, tag 200
> to fe80::250:56ff:feaa:4b5b via ge-0/0/0.0
This is an expected behavior. When ISIS traffic-engineering is disabled, TLV 22,134 and 135 are suppressed from being sent. Tags for IPv4 routes are in TLV135 (sub-TLV1). For IPv6, routes tags are in TLV236 which are still present when traffic engineering is disabled.
root@SRX-1# run show isis database SRX-2.00-00 extensive | find tlv
TLVs:
Area address: 49.0001 (3) <<<TLV 1
LSP Buffer Size: 1492
Speaks: IP <<<TLV 129
Speaks: IPV6 <<<TLV 129
IP router id: 2.2.2.2 <<<TLV 134
IP address: 2.2.2.2 <<<TLV 132
Hostname: SRX-2 <<<TLV 137
IS neighbor: SRX-1.02, Internal, Metric: default 10 <<<TLV 2
IS extended neighbor: SRX-1.02, Metric: default 10 <<<TLV 22
IP address: 10.10.10.2
Local interface index: 72, Remote interface index: 0
IP external prefix: 192.168.0.0/24, Internal, Metric: default 0, Up <<<TLV 130
IP extended prefix: 192.168.0.0/24 metric 0 up <<<TLV 135
6 bytes of subtlvs
Administrative tag 1: 100
IP prefix: 10.10.10.0/30, Internal, Metric: default 10, Up <<<TLV 128
IP prefix: 2.2.2.2/32, Internal, Metric: default 0, Up <<<TLV 128
IP extended prefix: 10.10.10.0/30 metric 10 up <<<TLV 135
IP extended prefix: 2.2.2.2/32 metric 0 up <<<TLV 135
IPv6 prefix: 2001:2222::2/128 Metric 0 Up <<<TLV 236
IPv6 prefix: 2001:abdc:1::/64 Metric 10 Up <<<TLV 236
IPv6 prefix: 2001:9999:8888:7777::/64 Metric 0 External Up <<<TLV 236
6 bytes of subtlvs
Administrative tag 1: 200
No queued transmissions