EVPN ELAN FRR Loop Prevent labelHuawei TechnologiesHuawei Campus, No. 156 Beiqing RoadBeijing100095Chinarainsword.wang@huawei.comFuturewei Technologies2386 Panoramic CircleApopkaFL 32703USA+1-508-333-2270d3e3e3@gmail.comHuawei Technologies101 software Avenue, Yuhua DistrictNanjing210012Chinazhu.tong@huawei.com
Routing Area
BESS Working GroupFRRDraftThis document describes how to use Fast Re-Route (FRR) labels avoid
traffic loop in CE failures when deploying FRR protection in EVPN
scenarios.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.In the EVPN active-active scenario, to solve the failure of a CE
access channel to one PE, we can deploy Fast Re-Route (FRR) protection
mode to achieve fast convergence. All active PEs can be deployed with
FRR. When a link failure occurs on the CE connection to the PE, traffic
can be rapidly FRR to another PE to improve the switching performance.
However, if the CE device fails, both the two PEs sense that their CE
link is faulty at the same time. They will each perform fast switching
according to the FRR. Then the traffic will loop between the dual PEs.
If one PE detects a failure and withdraw the ES-AD route, the other
PE, after receiving the withdrawal of the ES-AD route, deletes the FRR
path to the PE, and the loop is eliminated. The time until the loop is
eliminated may be short, but during this time, the loop will cause
traffic congestion between the dual-homing PEs. The FRR Label Extended Community is a new transitive Extended
Community having a Type field value of 0x06 and the Sub-Type TBD. It may
be advertised along with MAC/IP Advertisement routes and Ethernet A-D
per EVI routes. The FRR Label Extended Community is encoded as an 8-octet value, as
follows: If we enable the FRR LABEL function for an instance, then when the
PE advertises the MAC-IP route or Ethernet A-D per EVI route of the
instance, it also carries an FRR Label Extended Community attribute. When another PE on the dual-homed side receives the MAC-IP route or
the EVI-AD route, and uses the Label in the FRR Label Extended Community
attribute as the label for the Edge FRR path. The single- homing-side PE
receives the MAC-IP route or Ethernet A-D per EVI route advertised by
the PE will ignores the FRR Label Extended Community attribute. Because the FRR Label Extended Community attribute is an optional
transitve attribute, if there are RR devices or ASBR devices in the
network, the attributes can be transparently transmitted and processed
by the final PE device. Taking Figure 1 as an example, the EVI1 of PE2 enables the FRR LABEL
function, and PE2 applies for a new label. PE2 advertises the MAC-IP
route and the Ethernet A-D per EVI route carries the label through the
FRR Label Extended Community attribute. Because CE1 is dual- homed to
PE1 and PE2, PE1 learns the MAC address of CE1 from the data plane.
Therefore, when PE1 receives the MAC-IP route or Ethernet A-D per EVI
route from PE2, it can generate the MAC address learned from CE1 to form
an edge FRR entry and the label filled in the FRR entry is the FRR
label. For PE3, even if CE1 is dual-homed to PE1 and PE2 in single-active
mode, PE3 form FRR does not use the FRR label. The feature is available for EVPN ELAN service , EVPN VPWS and EVPN
L3VPN service. The PE receives the traffic from the network side and finds the
corresponding bridge-domain according to the Label. If the Label is a
normal EVI label, the MAC address is normally queried. If the local
outbound interface of the MAC fails, the FRR of the MAC is further
protected. If the Label is an FRR label, the MAC address continues to be
queried normally. If the local outbound interface of the MAC fails, the
FRR of the MAC is no longer protected.Taking Figure 1 as an example. CE2 send traffic to CE1, traffic
arrived PE3 will encapsulate PE2 's EVI label and send to PE1. Traffic
arrived at PE1 and use the EVI label to lookup MAC table, but find the
out-interface is failed. PE1 will do MAC FRR for that and encapsulate
the FRR label, which is advertised by PE2. Traffic arrived at PE2 and
use the FRR label to lookup MAC table. The traffic will send to CE1
according to the MAC infomation. When the MAC's out-interface is failed,
the traffic will dropped to avoid traffic loop. The solution of this document is not only applicable to the EVPN
scenario. The traditional L3VPN can also use this solution to achieve
rapid loop breaking. IANA is requested to assign a new type of FRR label extended
community with value TBD.TBD