DF (Designated forwarder) election is used for picking a single
BUM-traffic forwarded per-ES. RFC7432 specifies a mechanism called
service carving for DF election. However that mechanism has many
disadvantages -
1. LBs poorly.
2. Doesn't allow for a controlled failover needed in upgrade
scenarios.
3. Not easy to hw accelerate.
To fix the poor performance of service carving alternate DF mechanisms
have been proposed via the following drafts -
draft-ietf-bess-evpn-df-election-framework
draft-ietf-bess-evpn-pref-df
This commit adds support for the pref-df election mechanism which
is used as the default. Other mechanisms including service-carving
may be added later.
In this mechanism one switch on an ES is elected as DF based on the
preference value; higher preference wins with IP address acting
as the tie-breaker (lower-IP wins if pref value is the same).
Sample output
=============
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torm-11# sh bgp l2vpn evpn es 03:00:00:00:00:01:11:00:00:01
ESI: 03:00:00:00:00:01:11:00:00:01
Type: LR
RD: 27.0.0.15:6
Originator-IP: 27.0.0.15
Local ES DF preference: 100
VNI Count: 10
Remote VNI Count: 10
Inconsistent VNI VTEP Count: 0
Inconsistencies: -
VTEPs:
27.0.0.16 flags: EA df_alg: preference df_pref: 32767
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torm-11# sh bgp l2vpn evpn route esi 03:00:00:00:00:01:11:00:00:01
*> [4]:[03:00:00:00:00:01:11:00:00:01]:[32]:[27.0.0.15]
27.0.0.15 32768 i
ET:8 ES-Import-Rt:00:00:00:00:01:11 DF: (alg: 2, pref: 100)
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