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SETUP
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FreeBSD 15.1 with four VNET jails on the same L2 segment:
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172.18.10.0/24
VLAN 1010
VXLAN VNI 10010
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Jails:
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• 172.18.10.10 — PostgreSQL (dns_pg_001)
• 172.18.10.11 — PowerDNS Authoritative
• 172.18.10.12 — PowerDNS Recursor
• 172.18.10.13 — Kea DHCP
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The jails are connected locally through a FreeBSD ng_bridge.
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The VXLAN VTEP extends this L2 segment to an Arista DCS-7150S-24-F running EOS 4.23.15M-2GB.
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Arista SVI:
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172.18.10.1/24
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CONFIRMED OBSERVATIONS
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The intermittent problem mainly affects 172.18.10.10.
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After a period of inactivity, 172.18.10.10 has sometimes become unreachable from the Arista:
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ping 172.18.10.10
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Result:
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100% packet loss
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During such a failure, the Arista VXLAN MAC table contained:
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589c.fc10.cfbe -> Vxlan1 -> 172.17.1.10
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while the Arista ARP table did not contain a usable entry for:
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172.18.10.10 -> 589c.fc10.cfbe
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Packet captures showed that:
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• the Arista ARP request reached the jail
• the jail generated an ARP reply
• FreeBSD encapsulated the reply into VXLAN with VNI 10010
• the encapsulated packet reached the Arista side
• no dynamic ARP entry for 172.18.10.10 appeared on the Arista
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Similar behavior was also observed with 172.18.10.11, so the symptom is not unique to the PostgreSQL jail.
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The jail MAC addresses are fixed.
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WORKAROUND TESTED
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I configured static ARP entries on the Arista.
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For example:
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arp 172.18.10.10 589c.fc10.cfbe arpa
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After the VXLAN MAC entry for .10 was absent, Arista showed:
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172.18.10.10 589c.fc10.cfbe Vlan1010, not learned
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In that state:
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• .10 was reachable from the T640 after more than 15 minutes of inactivity
• a subsequent ping from the Arista succeeded
• after that ping, Arista again showed 589c.fc10.cfbe dynamically learned on Vxlan1
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The same recovery from “not learned” was also reproduced with .11.
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INTERPRETATION / QUESTION
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My current interpretation is that static ARP avoids dependence on the dynamic ARP learning/relearning behavior that previously caused loss of reachability, while VXLAN MAC learning remains dynamic.
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I do not know whether static ARP is the usual workaround for DCS-7150 / EOS 4.23 with static VXLAN, or whether there is a standard configuration or known platform-specific fix for reliable dynamic ARP learning in this setup.
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Has anyone seen this behavior on DCS-7150/FM6000 or EOS 4.23?
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What is the usual solution?
Source: r/Arista · by /u/dmitry-n-medvedev