Dual ISP with default route setup

[fahadadi]

This is how my tipo will look end of the day.

eBGP peer Edge <---> ISP

eBGP peer between Edge < --- > Border-Leaf (I am using 65355 to peer eBGP with Edge)

Inside EVPN/VXLAN fabric I have BGP 65001.

I am Planning to do following config for stumble guys mod:

[Edge]

router bgp 3500
  log-neighbor-changes
  neighbor 1.1.1.1
    remote-as 1500
    description ** eBGP peer with ISP-1 **
    address-family ipv4 unicast
      send-community
      send-community extended
  neighbor 192.168.1.1
    remote-as 65535
    address-family ipv4 unicast
      send-community
      send-community extended

[Border-Leaf]

router bgp 65001
  router-id 10.254.1.2
  log-neighbor-changes
  template peer VXLAN_SPINE
    remote-as 65001
    update-source loopback0
    address-family ipv4 unicast
    address-family l2vpn evpn
      send-community
      send-community extended
  neighbor 10.254.0.1
    inherit peer VXLAN_SPINE
    description ** iBGP Peer to Spine-1 **
    no shutdown
  neighbor 10.254.0.2
    inherit peer VXLAN_SPINE
    description ** iBGP Peer to Spine-2 **
    no shutdown
  vrf CUST
    log-neighbor-changes
    address-family ipv4 unicast
      redistribute static route-map RTBH
      aggregate-address XX.XX.XX.0/23 summary-only
      aggregate-address XX.XX.XX.0/24 summary-only
    neighbor 192.168.1.2
      description ** eBGP Peer to Edge1 **
      remote-as 3500
      local-as 65535
      address-family ipv4 unicast
        send-community
        send-community extended

Question:

Q1. Both ISP-1 and ISP-2 sending BGP default routes (instead of full BGP). Assuming Edge will forward that default route to my EVPN fabric, right?

Q2.Are there any issue using 65535 AS between br-leaf and edge router?

Q3. Where do I apply local-preference or AS_PATH prepend to do IP shift to ISP-1 to ISP-2 or ISP-2 to ISP-1?

[M02@rt37]

Hello @fahadadi 

Q1: Yes, the Edge redistributes or advertises that default route to its eBGP peer — in this case, the boder leaf (AS 65535). The border Leaf accept and install that route in the VRF routing table and can then redistribute it into iBGP if needed (to the evpn fabric...).

Q2: you could not use a private ASN from the range 64512–65534 instead ?

Q3: if you want to prefer one ISP over another use local-preference in inbound on the Edge. 

If you want to influence how traffic from outside comes back to you, so use AS_path prepend outbound from Edge to ISP.