We are looking at reworking our layout to start growing to have full redundancy.
MLAG between 2x aggregation x670's Feeding each remote site with 1x 10gigabit uplink. We're good on that simple.
MLAG between our L3 Extremes we plan to use for L3 Routing. Those will connect via standard lag to both of the above aggregation switches. Still good here simple LAG+MLAG's.
Now we reach the L3 portion. Hanging off of those L3 Extremes we have our BRAS/PPPoE Boxes, that are connected on their backend via a LAG to both of the aggregation 670's.
We bring up a VLAN to each of the L3 Extremes with a /30(or/31 whatever), But we want to make sure if one of our L3 x670's die that we have complete redundancy.
Simplest idea is just Enable VRRP, but i REALLY hate the idea of waisted tech resources, and the idea that 1 box is just sitting their idle urks me. So I thought Hey Why not just use OSPF ECMP to solve the issue.
And that led me to the question why ever use VRRP if ECMP exists? Where does the drawback exist that i'm missing to using OSPF ECMP? I get connection based load balancing between the main 2 routers, and failover protection if one fails.
We already plan to use OSPF on the BRAS's to deliver customer /32's based on radius so that we have no waisted IPv4 (as we won't be dedicating subnets to specific servers that might not use them all)
So the comparison
BRAS -> LAG to 2-x670's -> VRRP
BRAS -> VLAN to 2 ports of the BRAS to 2-x670 on a /30 each - > OSPF ECMP