Arista EOS SVI Down: Inter-VLAN Routing Troubleshooting

An SVI that will not come up is the most common inter-VLAN routing fault on Arista EOS and the most frequently misdiagnosed, because the configuration usually looks perfect. The rule that explains almost every case is simple: an SVI comes up only when at least one port in that VLAN is up and forwarding in spanning tree, and routing must be enabled globally before any SVI routes anything.

Start with the VLAN, not the SVI

switch# show vlan
switch# show vlan id 20
switch# show interfaces Ethernet1 switchport

Confirm three things: the VLAN exists, it is active (not suspended), and a port is actually a member. On EOS there is no separate VLAN database file — VLANs live in running-config, so a VLAN created but never saved disappears after a reload, which is exactly the kind of "it worked yesterday" fault this step catches.

Then check that a member port is forwarding

switch# show mac address-table vlan 20
switch# show spanning-tree vlan 20
switch# show interfaces Ethernet1 counters errors

If no MAC is learned in the VLAN, either no port is in it or the physical link is down. An access port whose operational access VLAN is 1 (the default) while the design expects VLAN 20 is the single most common cause of "the host cannot reach the gateway", and it is invisible unless you read show interfaces switchport rather than the config.

Now the SVI itself

switch# show interfaces Vlan20
switch# show ip interface brief
switch# show ip route
switch# show running-config interface Vlan20

Look for Vlan20 is up, line protocol is up. If it reports down/down, go back one step — the VLAN has no forwarding port. If it is down but the VLAN is fine, check no shutdown on the SVI and that the IP address is not overlapping another interface's subnet.

Inter-VLAN traffic still failing?

switch# show ip route
switch# show running-config | grep "ip routing"
switch# ping 10.10.20.10 source Vlan10
switch# show ip interface brief

Two checks decide it: ip routing must be enabled globally (EOS switches can forward without routing), and a connected route for each SVI subnet must be present in the routing table. Testing with ping ... source Vlan10 from the switch itself separates a routing problem from an end-host problem in one command. Only after both SVIs ping successfully from the switch is it worth looking at host gateways, VLAN tags on the server NIC, or a firewall policy.

Related reading: Arista EOS VLAN and SVI configuration, Arista EOS troubleshooting cookbook, Arista EOS native VLAN and trunk troubleshooting.

原文链接：https://infrarunbook.com/article/arista-eos-vlan-trunk-configuration-access-trunk-inter-vlan-routing