Describes route-tag, route-control, hardware, MTU, and subnet-advertisement requirements for configuring stable transit routing connections across external networks in a Cisco ACI fabric.
Transit routing guidelines are configuration requirements that
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prevent routing loops through consistent route-tag policies,
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control prefix redistribution between L3Outs and VRFs, and
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define hardware, MTU, and VRF enforcement requirements.
Configuration and operational guidelines
The following guidelines apply to transit routing:
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OSPF and EIGRP redistribution: Use the same Transit Route Tag Policy value in all VRFs so that the default routing-loop prevention mechanism operates correctly.
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EIGRP L3Outs: When you enable EIGRP on an L3Out, change the VRF transit-route tag from its default value to a value from 1 through 255.
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Single L3Out profile: Release 2.3(1f) and later supports transit routing within one L3Out profile. Prefix-matching limitations apply to enforced VRFs.
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Hardware support: Routes that are shared between VRFs operate correctly on generation 2 switches. Generation 1 switches can drop packets because of TCAM capacity limitations.
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MTU configuration: Cisco ACI does not support IP fragmentation. Configure consistent MTU values on all platforms, and account for differences in whether platforms include packet headers in their MTU calculations.
To advertise tenant subnets outside the fabric, configure the following settings:
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In the subnet properties, set the tenant subnet scope to Public Subnet.
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Optional: Set Subnet Control to ND RA Prefix.
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Associate the tenant bridge domain with the external L3Out.
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Create a contract association between the tenant EPG and the external EPG.
To configure the route-tag policy, on the VRF/Policy page, use the Transit Route Tag Policy field to open the Create Route Tag Policy page.