topic Re: Cisco SD Access Questions in Software-Defined Access (SD-Access)

Cisco SD Access Questions

mahmoud zyada — Wed, 12 Mar 2025 20:21:56 GMT

Sorry for this but I have some questions regarding Cisco DNA as it make me confused

First: when two host in the same layer 2 virtual network with anycast gateway and same ip subnet communicate over the fabric , the vni field in the encapsulated packet is populated with the layer 2 vnid value for this layer 2 virtual network but what is case when two hosts in the same layer 3 virtual network but different ip subnets (i.e each host is in different layer 2 virtual network with anycast gateway but both are in same layer 3 virtual network/vrf) communicate over the fabric, what is the vni value of the encapsulated packet in this case ?

Second : regarding Lisp protocol that used as control plane protocol in the fabric , what is the difference between normal ITR and PTR (i.e fabric edge nodes ) and the proxy ptr (i.e borer nodes ) in the fabric as the difference is not clear to me ( for border nodes when forward packet to non lisp site it simply de-encapsulate packets and forward it like any normal etr lisp node so what is the difference of it is role as a proxy) ?

Very Thanks for your help

Re: Cisco SD Access Questions

Andrii Oliinyk — Thu, 13 Mar 2025 06:31:26 GMT

1. When hosts in different Layer 2 VNs but the same Layer 3 VN (VRF) communicate, the Layer 3 VNI is used. This VNI identifies the routing domain.
2. Yes, key difference is that border nodes act as gateways between the LISP fabric and non-LISP networks.

Re: Cisco SD Access Questions

mahmoud zyada — Fri, 14 Mar 2025 12:42:00 GMT

Very thanks for your help , a last couple questions : when we create ip pools under certain layer 3 virtual network , does each ip pool map to vlan which map to ip subnet with anycast gateway as svi configured at edge node which is finally mapped to SG ? also when two hosts in same layer 2 VN (and same layer 3 VN ) communicate is this considered vxlan switching but in the case of hosts in same layer 3 virtual network but different layer 2 VNs (different IP subnets) this is considered inter-vxlan routing ?

Re: Cisco SD Access Questions

Andrii Oliinyk — Fri, 14 Mar 2025 12:51:35 GMT

your Qs are hardly difficult to understand :0) but give me a try...
1) IP-pool is defined in the network hierarchy Design/Network settings, then u may or may not use it in the arbitrary Fabric (depends on your intent & target location in hierarchy). U may bind custom VLAN ID to AnycastGW when u create AcGW,
2) VXLAN is not leveraged only in the cases where both correspondents of communication are on the same EN.

Re: Cisco SD Access Questions

mahmoud zyada — Tue, 18 Mar 2025 10:43:41 GMT

Thanks Andrii for your help and explanation and sorry if me questions is not very well understood , after your answers and with some other search the things become more clear now.

Thanks for your help