"Depref" ing vs. "Prepending" a route in BGP

[KMNRuser]

Community,

We have subcontracted Comcast to perform what they label as "SD-WAN", but to me it is simply dual homing. 

We have received an email from a Comcast Account manager wherein he is asking us as the customer about whether or not we want to "depref" or "Prepend" our existing Verizon AS route.   We currently and for years have used Verizon for our Internet access and MPLS, and now that Comcast is implementing this dual homing, they will be advertising out of their router the existing Verizon public IP address space/route.  They have indicated that they can either "depref" or prepend the Verizon route, in order that it is preferred if we want to.

What would the benefits of "deprefing" or "prepending" be for us?  I know that "deprefing" would only affect traffic in our own AS, while it seems to me that "prepending" extra AS numbers would affect how other AS's view the route.  Would we perhaps do both?

Thank you,

KMNRuser

[M02@rt37]

Hello @KMNRuser 

You could consider a combination of both strategies. Prepend the AS_Path on the Comcast-advertised route if you want external networks to prefer sending traffic through Verizon. This approach influences how other ASes view your path. And Depref the Comcast route within your network to ensure that your internal traffic prefers the Verizon path. This way, both outbound and inbound traffic will prefer Verizon, while Comcast serves as a backup.

[paul driver]

Hello
TBH - i wouldn't let them do either 
I would make sure you do not become a transit path for either isp by just advertising your local subnets to both of them
secondarily i would if applicable consider conditionally advertising your networks between either isp that way you the control on how traffic is routed back towards your site and have less chance of  any path attribute you set from being over wrote