Solved: How are EVPN VXLAN Route type 5 generated ?

jeanprochette · ‎08-30-2023

My understanding is that route type 5 is used when routing from two different VNIs but on the same subnet for example.

How or when are those type 5 routes are generated. Is there a type 5 generated whenever a type 2 mac advertisement is generated ?

When a host on a certain vni wants to reach a host in the same subnet but a different vni, i suppose it doesnt send the packets to its default gateway and the VTEP lookup for the L3 VNI in the type 5 database ?

M02@rt37 · ‎08-30-2023

Hello @jeanprochette,

In VXLAN, route type 5 is used to advertise Layer 3 VNI reachability information. It's not specifically used for routing traffic between different VNIs on the same subnet. Instead, it's used to provide information about how to reach Layer 3 subnets across the VXLAN overlay. Route type 5 is used to announce IP prefixes along with their corresponding VTEPs.

Type 2 MAC advertisements are used for MAC address learning and distribution within the same VNI. These advertisements are used to build the MAC address table on the VTEPs and enable communication between hosts within the same VNI.

When a host in one VNI wants to communicate with a host in another VNI on a different subnet, the traffic goes through routing. The host sends the traffic to its default gateway (VTEP) in its own VNI. The VTEP performs a routing lookup to determine if the destination IP address is in a different subnet and, if so, forwards the traffic to the appropriate egress VTEP for the target VNI. This egress VTEP then encapsulates and routes the traffic within its VNI.

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M02@rt37 · ‎08-30-2023

Hello @jeanprochette,

In VXLAN, route type 5 is used to advertise Layer 3 VNI reachability information. It's not specifically used for routing traffic between different VNIs on the same subnet. Instead, it's used to provide information about how to reach Layer 3 subnets across the VXLAN overlay. Route type 5 is used to announce IP prefixes along with their corresponding VTEPs.

Type 2 MAC advertisements are used for MAC address learning and distribution within the same VNI. These advertisements are used to build the MAC address table on the VTEPs and enable communication between hosts within the same VNI.

When a host in one VNI wants to communicate with a host in another VNI on a different subnet, the traffic goes through routing. The host sends the traffic to its default gateway (VTEP) in its own VNI. The VTEP performs a routing lookup to determine if the destination IP address is in a different subnet and, if so, forwards the traffic to the appropriate egress VTEP for the target VNI. This egress VTEP then encapsulates and routes the traffic within its VNI.

Best regards
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jeanprochette · ‎08-31-2023

Hello, thank you for your response.

When you say : '' ...The VTEP performs a routing lookup to determine if the destination IP address is in a different subnet and, if so, forwards the traffic to the appropriate egress VTEP for the target VNI" . By Target VNI do you mean the L3 VNI ?

If the host wants to communicate with a host in another vni but on the same subnet, does the host send it to its default gateway? i would assume no.

Is a L3VNI mandatory for inter vni routing ? cant a type 2 Mac-IP route be enough for that ?