Exam 300-630 topic 1 question 55 discussion

I think the question here is a little bit tricky. Unlike the IPN, ISN requirement is just a basic IP connectivity among the sites. Which can be a generic IP network without jumbo frame support. To accommodate that kind of networks, they introduced a new policy which helps to reduce the default control plane packet MTU from 9000 to whatever is being supported. So the ACI is not dictating the minimum MTU but ISN is. My understanding is that this question is asking the minimum MTU that must be supported by ISN, and if the ISN is not supporting 9000, we can adjust the ACI fabric to match whatever is supported. I'd go with B.

The answer is A The MTU of the ISN depends on 2 Factors: 1) The maximum MTU of the frames generated by the endpoints connected to the fabric: If the endpoints are instead configured with the default 1500-byte value, then the ISN MTU size can be reduced to 1550 bytes 2) The MTU of MP-BGP control-plane communication between spine nodes in different sites: By default, the spine nodes generate 9000-byte packets for exchanging endpoint routing information. If that default value is not modified, the ISN must support an MTU size of at least 9000 bytes So assuming the Spines control-plane settings are left at default the answer is A : 9000 https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739609.html#IntersiteNetworkISNdeploymentconsiderations

C. 9100 to make sure no fragmentation/drops occurs

A is https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739609.html

B is correct https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739609.html#IntersiteNetworkISNdeploymentconsiderations

The MTU of MP-BGP control-plane communication between spine nodes in different sites: By default, the spine nodes generate 9000-byte packets for exchanging endpoint routing information. If that default value is not modified, the ISN must support an MTU size of at least 9000 bytes It's A for me https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739609.html#CiscoACIMultiSiteunderlaycontrolplane

from: https://www.cisco.com/c/en/us/support/docs/cloud-systems-management/application-policy-infrastructure-controller-apic/214270-configure-aci-multi-site-deployment.html "By default, the spine nodes generate 9000-byte packets to exchange endpoint routing (i.e MP-BGP) information" --> so indeed C.

I think C is correct. Default SPINE MTU is 9000 + VXLAN Header of 50 + Ethernet header if necessary.

correct is B

I think A