iBGP configuration between borders

[aleopoldie]

Hello guys,

I have a concern regarding the iBGP configuration between the 2 borders in SDA fabric.

When I look this officiel guide : https://www.cisco.com/c/en/us/support/docs/cloud-systems-management/dna-center/213525-sda-steps-to-configure-fusion-router.html#anc18

They use SVIs to configure the iBGP for BGP redundancy between borders.

Is it a problem if we want to use loopbacks instead of SVIs or sub-interfaces ? what would you advise ? I've used SVIs and sub-interfaces so far but I was wondering why it is not recommended to use loopbacks.

Thanks,

Alex.

[M02@rt37]

Hello @aleopoldie,

Using SVIs or sub-interfaces for iBGP configuration is a common practice. However, using loopback interfaces is also a valid approach, and it has its advantages.

Using SVIs or Sub-Interfaces simplifies configuration. SVIs are easy to configure, especially if you have a limited number of VLANs. If your SDA fabric is VLAN segmented, using SVIs aligns with the VLAN structure.

Using Loopback Interfaces ? You have independence from VLANs! Meaning that Loopback interfaces are not tied to VLANs, providing more flexibility. It also simplifies IP Address Management.

-- If your network design is VLAN-centric, and you find that SVIs align well with your segmentation requirements, using SVIs for iBGP is a straightforward choice.

-- If you prefer a more independent and flexible approach, especially if you foresee changes in the VLAN structure, loopback interfaces might be a good choice.

[jalejand · Accepted solution]

To use loopbacks you would need to recurse to a route to the loopbacks to form the neighbors, that alone has its disadvantages.

1) The route will need an underlying interface to reach the loopback, in SDA, that interface would be LISP interface, which you cannot use for this purpose (would require prefixes to be injected into LISP, which we do not recommend on doing without propper filtering, or recommend on doing at all ).

2) If you create the route between loopbacks using static routing or BGP, you still need to create SVIs or subinterface as next hops nonetheless.