A static entry in a route table that takes precedence over Azure system routes, for instance sending traffic to a virtual appliance or virtual network gateway as next hop. BGP routes are learned dynamically; these are not.
Also called user-defined route.
Read more: Microsoft Learn
In the Ultra Transcenders books
AZ-305AZ-104AZ-700SC-500AI-200AZ-802ALZ
Each book explains UDR in context, with comparison tables and the common traps.
Terms in this definition
- Route table
Resource containing user-defined routes and attached to subnets, shaping traffic that leaves them. Attaching one to GatewaySubnet steers traffic coming in over VPN.
- OVER
Gives a T-SQL window function its window: PARTITION BY, ORDER BY and, if wanted, a ROWS or RANGE frame. Rankings and running totals can then be worked out while every row is kept.
- Chat message roles
Labels on chat messages: instructions go under system, the person's input under user, the model's previous answers under assistant, and results returned by a called tool under tool (or function).
- Virtual network gateway
Lives in GatewaySubnet and comes in two types, ExpressRoute or VPN. Setting it as the next hop in a UDR routes traffic on-premises.
- Next hop
For a destination you specify, returns the route table in use along with the next hop's type and IP. Only routing is checked.
- BGP
Dynamic routing protocol used with both ExpressRoute and VPN connections. On ExpressRoute private peering it is the only way to exchange routes, including a 0.0.0.0/0 default route for forced tunnelling.
Related terms
- Indirect spoke
VNet that hangs off an NVA's VNet through peering instead of attaching to the virtual hub. Reaching it takes a static route on the hub towards the NVA VNet connection, a static route on that connection towards the NVA's IP, and a UDR so replies return through the NVA.
- Longest prefix match
How Azure chooses between routes: if more than one matches a destination, the most specific prefix is used. That is why a 0.0.0.0/0 UDR leaves traffic inside the VNet untouched.
- Network Watcher next hop
Use it to troubleshoot routing for a destination: it returns the route table in effect (System Route or a UDR's table) with the next hop's type and IP. NSG filtering is not examined.