SRv6 locator and SID resolution is performed in the RTM and forwarding of all SRv6 packets is performed in the FIB.
The TTM is used to save details of the SRv6 tunnel but is not used directly to forward user or CPM originated packets.
The RTM and FIB are programmed with the routes of the local and remote locators, the local End.X SIDs, and the local End SIDs.
When a policy is applied to export SRv6 routes from RTM to another IS-IS instance, only the IP Reach TLV and the locator TLV, along with the End SID sub-TLVs, are advertised by the receiving ISIS instance. Local End, End.X, and LAN End.X routes are not exported nor advertised as separate routes.
remote locator (route owner = IS-IS)
All routers in the SRv6 domain populate a resolved remote locator prefix received in the SRv6 Locator TLV in the RTM and FIB.
A SRv6 packet is always forwarded out in the datapath using the FIB.
For algorithm 0, the same prefix is advertised with the IP reach prefix TLV and the SRv6 Locator TLV. A single route entry is however programmed in RTM and FIB.
The prefix of an IGP flexible algorithm locator TLV is never advertised with an IP reach prefix TLV. Therefore, the route of the locator TLV is programmed in RTM and FIB.
remote locator with up to 64 ECMP next hops
IS-IS models a remote locator prefix with two or more ECMP next hops as an IGP route with tunneled next hops using a protected NHLFE with hardware PG-ID per tunneled next hop.
This implementation provides uniform failover in ECMP. IS-IS allocates a hardware PG-ID to each next hop it establishes an adjacency with. That PG-ID is then used when programming SRv6 routes of a remote locator and of a local adjacency that resolve to this next hop.
RTM programs the route into the FIB. IS-IS creates a SRv6 tunnel for the locator prefix. The tunnel is added to the TTM. The IS-IS route entries in RTM and FIB point to the tunnel ID of this tunnel in TTM.
Weighted ECMP, when enabled on the interfaces of this IS-IS instance, is supported when forwarding packets over the locator next hops.
remote locator with primary or backup next hops
IS-IS models a remote locator prefix with a primary next hop or a primary and LFA backup next hop pair as an IGP route with a tunneled next hop using a protected NHLFE with a hardware PG-ID. This provides uniform failover.
RTM programs the route into the FIB. IS-IS creates a SRv6 tunnel for the locator prefix. The tunnel is added to the TTM. The IS-IS route entries in RTM and FIB point to the tunnel ID of this tunnel in TTM.
local locator (route owner = SRv6)
All routers in the SRv6 domain populate a route entry in the RTM and FIB to terminate packets destined for the local locator. This is modeled like any other local route but with the SRv6-specific route owner.
local adjacency SID (route owner = IS-IS)
All routers in the SRv6 domain populate a route entry in the RTM and regular FIB for each local End.X and LAN End.X adjacency SID with a primary and backup next hops.
The RTM, FIB, and SR module entries are modeled exactly like a remote locator prefix with primary and backup next hops.
local End SID (route owner = SRv6)
All routers in the SRv6 domain populate a route entry in the RTM and FIB to terminate packets destined for each local End SID. This is modeled like any other local route but with the SRv6-specific route owner.