IRB interfaces

Integrated routing and bridging (IRB) interfaces enable inter-subnet forwarding. Network-instances of type mac-vrf are associated with a Layer 3 network-instance of type ip-vrf or type default via an IRB interface.

On SR Linux, IRB interfaces are named irbN, where N is 0 to 255. Up to 4095 subinterfaces can be defined under an IRB interface. An ip-vrf network instance can have multiple IRB subinterfaces, while a mac-vrf network instance can refer to only one IRB subinterface.

IRB subinterfaces are type routed and cannot be configured as any other type.

IRB subinterfaces operate in the same way as other routed subinterfaces, including support for the following:

• IPv4 and IPv6 ACLs

• DSCP based QoS (input and output classifiers and rewrite rules)

• Static routes and BGP (IPv4 and IPv6 families)

• IP MTU (with the same range of valid values as Ethernet subinterfaces)

• All settings in the subinterface/ipv4 and subinterface/ipv6 containers. For IPv6, the IRB subinterface also gets an IPv6 link local address

• BFD

• Subinterface statistics

IRB interfaces do not support sFlow or VLAN tagging.

When frames are coming into a bridged subinterface with the destination MAC matching the IRB MAC address, all VLAN tags are expected to be stripped off as a result of the ingress processing so that the packet can be routed correctly.

As an example, for a frame coming with one Dot1q VLAN tag with ID 10 and destination MAC matching the IRB MAC, the ingress processing strips off that VLAN tag if the subinterface is configured as single-tagged vlan-id 10. Then a routing lookup is done for the inner packet. In the same example, incoming frames are not expected with more than one VLAN tag with VLAN ID 10; however, depending on the platform, frames with additional payload VLAN tags may still be routed correctly, as follows:

• On 7220 IXR-Dx and 7730 SXR systems, frames with payload VLAN tags below the service-delimiting VLAN tags are discarded if their destination MAC address matches the IRB MAC.
• On 7250 IXR-6/10/6e/10e and 7250 IXR-X1b/X3b systems, frames with more than two payload VLAN tags below the service-delimiting VLAN tags are discarded if their destination MAC address matches the IRB MAC. Frames with fewer tags are accepted and routed.
• On 7215 IXS-A1 systems, frames with payload VLAN tags below the service-delimiting VLAN tags are discarded if their destination MAC address matches the IRB MAC. There is an exception to this rule: on a vlan-id optional subinterface, packets with one payload VLAN tag can still be routed. Routed packets are dropped if they contain more that one tag in these subinterfaces configured with vlan-id optional.

--{ candidate shared default }--[  ]--
# info interface irb1
    interface irb1 {
        description IRB_Interface
        admin-state enable
        subinterface 1 {
            admin-state enable
            ipv4 {
                admin-state enable
                address 192.168.1.1/24 {
                }
            }
        }
    }