rfc9744v2.txt   rfc9744.txt 
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AC to a VPWS service tunnel (e.g., a VPWS service instance) and then AC to a VPWS service tunnel (e.g., a VPWS service instance) and then
signaling the VPWS service tunnel via an Ethernet A-D per EVI route signaling the VPWS service tunnel via an Ethernet A-D per EVI route
with the Ethernet Tag field set to a 24-bit VPWS service instance with the Ethernet Tag field set to a 24-bit VPWS service instance
identifier (which is unique within the EVI) and the ESI field set to identifier (which is unique within the EVI) and the ESI field set to
a 10-octet identifier of the ES corresponding to that AC. a 10-octet identifier of the ES corresponding to that AC.
Therefore, a PE device that receives such EVPN routes can associate Therefore, a PE device that receives such EVPN routes can associate
the VPWS service tunnel to the remote ES using the ESI field. the VPWS service tunnel to the remote ES using the ESI field.
Additionally, when the remote ES fails and the PE receives the "mass Additionally, when the remote ES fails and the PE receives the "mass
withdrawal" message associated with the failed ES per [RFC7432], a PE withdrawal" message associated with the failed ES per [RFC7432], a PE
device can quickly update its BGP list of available remote entries to device can quickly update its next-hop adjacency list (adjacency
invalidate all VPWS service tunnels sharing the ESI field and achieve list) for all VPWS service tunnels sharing the ESI field and achieve
fast convergence for multi-homing scenarios. Even if fast fast convergence for multi-homing scenarios. Even if fast
convergence was not needed, there would still be a need for signaling convergence were not needed, there would still be a need for
each AC failure (via its corresponding VPWS service tunnel) signaling each AC failure (via its corresponding VPWS service tunnel)
associated with the failed ES so that the BGP path list for each of associated with the failed ES so that the adjacency list gets updated
them gets updated accordingly and the packets are sent to a backup PE and the packets are sent to a backup PE (in case of Single-Active
(in case of Single-Active multi-homing) or to other PEs in the multi-homing) or to other PEs in the redundancy group (in case of
redundancy group (in case of All-Active multi-homing). In the All-Active multi-homing). In the absence of updating the adjacency
absence of updating the BGP path list, the traffic for that VPWS list properly, the traffic for that VPWS service tunnel will be
service tunnel will be black-holed. dropped by the egress PE with a failed ES/AC.
When a single VPWS service tunnel carries multiple ACs across various When a single VPWS service tunnel carries multiple ACs across various
ESs (physical interfaces) without signaling the ACs via EVPN BGP to ESs (physical interfaces) without signaling the ACs via EVPN BGP to
remote PE devices, those remote PE devices lack the information to remote PE devices, those remote PE devices lack the information to
associate the received ES with these ACs or with their local ACs. associate the received ES with these ACs or with their local ACs.
They also lack the association between the VPWS service tunnel (e.g., They also lack the association between the VPWS service tunnel (e.g.,
EVPN service label) and the far-end ACs. This means that, while the EVPN service label) and the far-end ACs. This means that, while the
remote PEs can associate their local ACs with the VPWS service remote PEs can associate their local ACs with the VPWS service
tunnel, they cannot make similar associations for the far-end ACs. tunnel, they cannot make similar associations for the far-end ACs.
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destination PE, thereby potentially wasting network resources. destination PE, thereby potentially wasting network resources.
This waste of network resources during a connection failure may be This waste of network resources during a connection failure may be
transient, as it can be detected and prevented at the application transient, as it can be detected and prevented at the application
layer in certain cases. Section 3.2 outlines a solution for such layer in certain cases. Section 3.2 outlines a solution for such
single-homing VPWS services. single-homing VPWS services.
For VPWS services where one of the endpoints is multi-homed, there For VPWS services where one of the endpoints is multi-homed, there
are two options: are two options:
1. Signal each AC via BGP, allowing the path list to be updated upon 1. Signal each AC via BGP, allowing the adjacency list to be updated
a failure affecting those ACs. This solution is described in upon a failure affecting those ACs. This solution is described
Section 3.3 and is referred to as the "VLAN-signaled FXC in Section 3.3 and is referred to as the "VLAN-signaled FXC
service". service".
2. Bundle several ACs on an ES together per destination endpoint 2. Bundle several ACs on an ES together per destination endpoint
(e.g., ES, MAC-VRF, etc.) and associate such a bundle with a (e.g., ES, MAC-VRF, etc.) and associate such a bundle with a
single VPWS service tunnel. This approach is similar to the VLAN single VPWS service tunnel. This approach is similar to the VLAN
bundle service interface described in [RFC8214]. This solution bundle service interface described in [RFC8214]. This solution
is described in Section 3.2.1. is described in Section 3.2.1.
3. Solution 3. Solution
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to the backup PE is the same as the one described above. to the backup PE is the same as the one described above.
5.2. Attachment Circuit Failure 5.2. Attachment Circuit Failure
In the event of an AC failure, the VLAN-Signaled and default FXC In the event of an AC failure, the VLAN-Signaled and default FXC
modes exhibit distinct behaviors: modes exhibit distinct behaviors:
* Default FXC (Figure 1): In the default mode, a VLAN or AC failure * Default FXC (Figure 1): In the default mode, a VLAN or AC failure
is not signaled. Consequently, in case of an AC failure, such as is not signaled. Consequently, in case of an AC failure, such as
VID1 on CE2, there is nothing to prevent PE3 from directing VID1 on CE2, there is nothing to prevent PE3 from directing
traffic from CE4 to PE1, leading to a potential black hole. traffic from CE4 to PE1, leading to a potential packet loss at the
Application layer OAM may be utilized if per-VLAN fault egress PE with a failed AC. Application layer OAM may be utilized
propagation is necessary in this scenario. if per-VLAN fault propagation is necessary in this scenario.
* VLAN-Signaled FXC (Figure 2): In the case of a VLAN or AC failure, * VLAN-Signaled FXC (Figure 2): In the case of a VLAN or AC failure,
such as VID1 on CE2, this triggers the withdrawal of the Ethernet such as VID1 on CE2, this triggers the withdrawal of the Ethernet
A-D per-EVI route for the corresponding Normalized VID, A-D per-EVI route for the corresponding Normalized VID,
specifically Ethernet-Tag 2. Upon receiving the route withdrawal, specifically Ethernet-Tag 2. Upon receiving the route withdrawal,
PE3 will remove PE1 from its outgoing path list for traffic PE3 will remove PE1 from its outgoing adjacency list for traffic
originating from CE4. originating from CE4.
5.3. PE Port Failure 5.3. PE Port Failure
In the event of a PE port failure, the failure will be signaled, and In the event of a PE port failure, the failure will be signaled, and
the other PE will assume forwarding in both scenarios: the other PE will assume forwarding in both scenarios:
* Default FXC (Figure 1): In the case of a port failure, such as p2, * Default FXC (Figure 1): In the case of a port failure, such as p2,
the route for Service Tunnel 2 (sv.T2) will be withdrawn. Upon the route for Service Tunnel 2 (sv.T2) will be withdrawn. Upon
receiving the fault notification, PE3 will remove PE1 from its receiving the fault notification, PE3 will remove PE1 from its
path list for traffic originating from CE4 and CE5. adjacency list for traffic originating from CE4 and CE5.
* VLAN-Signaled FXC (Figure 2): A port failure, such as p2, triggers * VLAN-Signaled FXC (Figure 2): A port failure, such as p2, triggers
the withdrawal of the Ethernet A-D per EVI routes for normalized the withdrawal of the Ethernet A-D per EVI routes for normalized
VIDs 2 and 3, along with the withdrawal of the Ethernet A-D per-ES VIDs 2 and 3, along with the withdrawal of the Ethernet A-D per-ES
route for p2's ES. Upon receiving the fault notification, PE3 route for p2's ES. Upon receiving the fault notification, PE3
will remove PE1 from its path list for the traffic originating will remove PE1 from its adjacency list for the traffic
from CE4 and CE5. originating from CE4 and CE5.
5.4. PE Node Failure 5.4. PE Node Failure
In the case of PE node failure, the operation is similar to the steps In the case of PE node failure, the operation is similar to the steps
described above, albeit that EVPN route withdrawals are performed by described above, albeit that EVPN route withdrawals are performed by
the route reflector instead of the PE. the route reflector instead of the PE.
6. Security Considerations 6. Security Considerations
Since this document describes a muxing capability that leverages Since this document describes a muxing capability that leverages
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