Excluding interfaces from IRB State Calculations
As you know, in order you have an IRB up, you need to have at least one interface up on the VLAN for which the IRB is created.
This condition is sometimes forgot by engineers troubleshooting why an IRB or RVI or SVI(in Cisco terms) is down.
By default all interfaces part of the VLAN contribute to the state of the IRB, but this behavior can be changed to exclude interfaces that contribute to the state of the IRB.
More exactly, you can configure an interface not to be taken in consideration when the switch calculate the state of an IRB.
Juniper provides this feature starting with 14.1X53-D40 on QFX5100.
Let’s see an example.
Two interfaces are part of VLAN100 for which irb.100 is defined:
{master:0}[edit] root@QFX5100# show vlans V100 { vlan-id 100; l3-interface irb.100; } {master:0}[edit] root@QFX5100# show interfaces et-0/0/49 { unit 0 { family ethernet-switching { vlan { members V100; } } } } et-0/0/51 { unit 0 { family ethernet-switching { vlan { members V100; } } } } irb { unit 100 { family inet { address 100.100.100.2/24; } } } {master:0}[edit] root@QFX5100#
The two physical interfaces are up and as expected, the irb.100 is up as well
{master:0}[edit] root@QFX5100# run show interfaces terse | match "irb|et-" et-0/0/49 up up et-0/0/49.0 up up eth-switch et-0/0/51 up up et-0/0/51.0 up up eth-switch irb up up irb.100 up up inet 100.100.100.2/24 {master:0}[edit] root@QFX5100#
Now, let’s configure et-0/0/49 with the autostate-exclude feature:
{master:0}[edit] root@QFX5100# show interfaces et-0/0/49 unit 0 { family ethernet-switching { vlan { members V100; } } } autostate-exclude; {master:0}[edit] root@QFX5100#
You can check the interface and notice that is configured with this feature by looking at the “Logical Interface flags”:
{master:0}[edit] root@QFX5100# run show ethernet-switching interface et-0/0/49 Routing Instance Name : default-switch Logical Interface flags (DL - disable learning, AD - packet action drop, LH - MAC limit hit, DN - interface down, SCTL - shutdown by Storm-control, MMAS - Mac-move action shutdown, AS - Autostate-exclude enabled) Logical Vlan TAG MAC STP Logical Tagging interface members limit state interface flags et-0/0/49.0 294912 AS untagged V100 100 294912 Forwarding untagged {master:0}[edit] root@QFX5100#
This feature does not impact in any way the operation of the interface when it’s activated:
{master:0}[edit] root@QFX5100# run show interfaces terse | match "irb|et-" et-0/0/49 up up et-0/0/49.0 up up eth-switch et-0/0/51 up up et-0/0/51.0 up up eth-switch irb up up irb.100 up up inet 100.100.100.2/24 {master:0}[edit] root@QFX5100#
And the interface is still part of the VLAN:
{master:0}[edit] root@QFX5100# run show vlans Routing instance VLAN name Tag Interfaces default-switch V100 100 et-0/0/49.0* et-0/0/51.0* default-switch default 1 {master:0}[edit] root@QFX5100#
Once you disable the interface that doesn’t have autostate-exclude configured, the IRB goes down:
{master:0}[edit] root@QFX5100# run show interfaces terse | match "irb|et-" et-0/0/49 up up et-0/0/49.0 up up eth-switch et-0/0/51 down down et-0/0/51.0 up down eth-switch irb up up irb.100 up down inet 100.100.100.2/24 {master:0}[edit] root@QFX5100#
This feature on Junos is identical to the SVI Autostate Exclude feature from Cisco platforms.
You can see below some relevant output from a Cisco device that support this feature.
Two interfaces are configured in VLAN 100:
C3750#show vlan | i VLAN0100 100 VLAN0100 active Gi1/0/13, Gi1/0/14 C3750#
The SVI is up:
C3750#show ip interface brief vlan100 Interface IP-Address OK? Method Status Protocol Vlan100 100.100.100.2 YES NVRAM up up C3750#
One of the interface is configured with SVI autostate exclude feature:
C3750#show run interface brief GigabitEthernet1/0/13 Building configuration... Current configuration : 123 bytes ! interface GigabitEthernet1/0/13 C3750port access vlan 100 C3750port autostate exclude end C3750#
You can see the feature configured like this:
C3750#show interfaces GigabitEthernet1/0/13 switchport Name: Gi1/0/13 Switchport: Enabled Administrative Mode: dynamic auto Operational Mode: static access Administrative Trunking Encapsulation: negotiate Operational Trunking Encapsulation: native Negotiation of Trunking: On Access Mode VLAN: 100 (VLAN0100) Trunking Native Mode VLAN: 1 (default) Administrative Native VLAN tagging: enabled Voice VLAN: none Administrative private-vlan host-association: none Administrative private-vlan mapping: none Administrative private-vlan trunk native VLAN: none Administrative private-vlan trunk Native VLAN tagging: enabled Administrative private-vlan trunk encapsulation: dot1q Administrative private-vlan trunk normal VLANs: none Administrative private-vlan trunk associations: none Administrative private-vlan trunk mappings: none Operational private-vlan: none Trunking VLANs Enabled: ALL Pruning VLANs Enabled: 2-1001 Capture Mode Disabled Capture VLANs Allowed: ALL Autostate mode exclude Protected: false Unknown unicast blocked: disabled Unknown multicast blocked: disabled Appliance trust: none C3750#
After the other interface is brought down, the SVI interface goes down as well:
C3750#show ip interface brief GigabitEthernet1/0/14 Interface IP-Address OK? Method Status Protocol GigabitEthernet1/0/14 unassigned YES unset administratively down down C3750#show ip interface brief GigabitEthernet1/0/13 Interface IP-Address OK? Method Status Protocol GigabitEthernet1/0/13 unassigned YES unset up up C3750#show ip interface brief vlan100 Interface IP-Address OK? Method Status Protocol Vlan100 100.100.100.2 YES NVRAM up down C3750#
And this is all about this feature, on both Juniper and Cisco devices that support this feature.
I hope you found this information useful.
Paris ARAU
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